fetal neurosonogram jucog feb 2013

Professor Hassan Nasrat FRCS, FRCOG

The Fetal Medicine Clinic The First Clinic

JUCOG January 2013

Fetal Nuerosonogram

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Microcephaly

Anencephaly

Chiari Malforma,on

Chiari MalformationChiari MalformationClinical IssuesClinical Issues AFP,AFP, High morbidity &mortalityHigh morbidity &mortality 4%aneuploidy rate4%aneuploidy rate CS at delivery termCS at delivery term 80% need ventriculoperitoneal 80% need ventriculoperitoneal

shuntshunt Can reverse with in utero surgeryCan reverse with in utero surgery Preventive threatment with folic Preventive threatment with folic

acidacid

Imaging FindingsImaging Findings Posterior fossa Posterior fossa „„banana banana

signsign““ Calvarial lemon signCalvarial lemon sign VentruculomegalyVentruculomegaly CM obliterationCM obliteration Head normal or smallHead normal or small

Diagnostic ChecklistDiagnostic Checklist AmniocentesisAmniocentesis Cranial findings easier to Cranial findings easier to

see than ONTDsee than ONTD Compressed CM may be Compressed CM may be

only finding!!only finding!!

14 +4 weeks

Hydrocephalus , T 21Hydrocephalus , T 21Ventriculomegaly

HydrancephalyHydrancephaly

Hydranecphaly

Encephalocele

Occipital EncephaloceleOccipital EncephaloceleImaging FindingsImaging Findings Herniated brain tissueHerniated brain tissue „„cyst within the cystcyst within the cyst““ Ventriculomegaly 70Ventriculomegaly 70--

80%80% Microcephaly 25%Microcephaly 25% PolyhydramniosPolyhydramnios OligohydramniosOligohydramnios

CAVE:CAVE: Associated with multiple Associated with multiple

syndroms ( Meckelsyndroms ( Meckel-- Gruber )Gruber )

HoloprosencephalyHoloprosencephaly

Pilu

Holoprosencephaly

Hemimegalencephaly Arachnoid cyst

ACC

SOP

SchizencephalySchizencephalySchizencephaly

PF-‐Fluid-‐Cyst

Yong seok et al.

Vascular Malforma,ons

Circle of Willis MallformationCircle of Willis Mallformation

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Congenital CNS Anomalies

o Incidence in longtem studies about 1 %

o Only minimal identified at birth

o Screening Increases The Number Of Referred Cases For Evaluation Of Suspected CNS Anomalies.

o The CNS sonographic appearance changes throughout pregnancy

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✤Embryonic development of the CNS in relation to sonographic findings

✤Standard Sonographic Examination of the CNS

✤Fetal Neurosonography and the Role of 3 D (systemic approach to examination of the Posterior Fossa)

Learning Objec,ves

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Embryology of the CNS

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At 5th Week The Cells Destined To Form The Notochord Infiltrate Into The Embryonic Disc.

I t I n d u c e s T h e Overlying Embryonic Tissue To Thicken And Ultimately Fold Over And Fuse As The Neural Tube.

The Fusion Starts In The Midtrunk Of The E m b r y o A n d Subsequently Extends To The Cranial And Caudal Ends

Neural CrestNeural TubeNeural Groove

Neural Plate Ectoderm

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Prosencephalon Mesencephalon

Rhombencephalon

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Three orthogonal images and thick slice of three-dimensional reconstructed image (lower right) of normal brain at the end of 8 weeks of gestation. The development of premature ventricular system is seen. 8

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Three orthogonal images and thick slice of three-dimensional reconstructed image (lower right) of normal brain at the end of 8 weeks of gestation. The development of premature ventricular system is seen. 8

Prosencephalon Mesencephalon

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Normal brain development on the mid-sagittal section between 8 and 12 weeks of gestation). Note the remarkable changing of premature brain appearance.

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Changing Ultrasound appearance of the The Posterior Fossa throughout gesta,on

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AJR:166, February 1996 SONOGRAPHIC ANATOMY OF DEVELOPING CEREBELLUM 433

Fig. 13.-Drawings depicting some relevant features of fetal cerebellar development.A, Axial drawing of developing cerebellum at 5 weeks’ gestational age shows that developing cerebellar hemispheres have not yet grown

toward midline and thatfourth ventricle is covered only byfourth ventricular roof,which is onlytwo cell layers thickatthis stage of development.B, Sagittal drawing of developing cerebellum at 10 weeks’ gestational age shows small cerebellum located rostrally over fourth ventricle,

with caudal fourth ventricle being covered only by thin fourth ventricular roof.C, Sagittal drawing at 16 weeks’ gestational age shows further caudal growth of cerebellum and vermis over fourth ventrIcle, with thick-

ening of caudal fourth ventricular roof.0, Sagfttal drawing at 17 weeks’ gestational age shows cerebellum and vermis covering entire fourth ventricle.

We have shown that the sonognaphic appearance of nor-mal cemebellar development can resemble pathology early inthe second trimester. Our findings indicate that the maturerelationships of the posterior fossa structures are not estab-lished until at least 18 weeks’ gestational age; therefore, theprenatal sonographic diagnosis of Dandy-Walker complexshould not be made before this time.

ACKNOWLEDGMENTS

We thank Professor Ronan O’Rahilly and the Carnegie Laborato-nies of Embryology for supplying the normal fetal specimens, withoutwhich this work could not have been undertaken, and Dr. Stephen T.Hecht for facilitating access to the fetal specimens. Brian W. Chongsupplied the artwork for Fig. 13.

REFERENCES1 . Benacennaf BR, Lister JE, DuPonte BL. First-trimester diagnosis of fetal

abnormalities. A report ofthree cases. J Reprod Med 1988:33:777-7802. Rottem S. Bronshtein M. Transvaginal sonographic diagnosis of congenital

anomalies between 9 weeks and 16 weeks menstrual age. J Clin Ultra-soundl99o;18:307-314

3. Cullen MT, Green J, Whetham J, Salafia C, Gabnielli 5, Hobbins JC.Transvaginal ultrasonographic detection of congenital anomalies in thefirst trimester. Am J Obstet Gynecol 1990:163:466-476

4. Achinon R, Tadmor 0. Screening for fetal anomalies during the first tnimes-ten of pregnancy: tnansvaginal versus transabdominal sonography. Ultra-sound Obstet Gynecol 1991 1:186-191

5. Nicolaides KH, Azan G, Byrne D, Mansur C, Marks K. Fetal nuchal translu-cency: ultrasound screening for chromosomal defects in first trimester ofpregnancy. BMJ 1992:304:867-869

6. Bronshtein M, Blumenfeld I, Kohn J, Blumenfeld Z. Detection ofcleft lip by earlysecond-tnimestertransvaginal sonography. Obstet GynecoIl9S4:84:73-76

7. Achiron A, Rotstein Z, Lipitz 5, Mashiach 5, Hegesh J. First-trimesterdiagnosis of fetal congenital heart disease by transvaginal ultrasonogra-phy. Obstet Gynecol 1994:84:69-72

8. Feess-Higgins A, Larroche J-C. Le d#{233}veloppement du cerveau fcetalhumain. Atlas anatomique. Paris: Masson Editeur, 1987:128-188

9. Lemire RJ, Looser JD, Leech R , Albord EC, eds. Normaland abnormaldevelopment of the human nervous system. Hagerstown, MD: Harper &Row, 1975:144-165

10. MUller F, O’Rahilly R. The human brain at stages 21-23, with particularreference to the cerebral cortical plate and to the development of the cer-ebellum. Anat Embryol 1990:182:375-400

1 1 . Corliss CE. Patton’s human embryology: elements of clinical development.NewYonk: McGraw-Hill, 1976:208-211

12. Bromley B, Nadel AS, Pauker 5, Estroff JA, Benacerraf BR. Closure of thecerebeilan vermis: evaluation with second trimester US. Radiology1994:193:761-763

13. Robinson HP, Fleming JEE. A critical evaluation of sonar “crown-rumpIength measurements. Br J Obstet Gynaecol 1975:82:702-710

14. Hadlock FR Harrist RB, Mantinez-Poyer J. How accurate is second tnimes-ten fetal dating? J Ultrasound Med 1991:10:557-561

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The vermis develops superiorly to inferiorly.

Hypoplasia or developmental arrest results in varying size deficits of the inferior portion, leaving a relatively square defect that communicates with the fourth ventricle and separates the lower cerebellar hemispheres.

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ACKNOWLEDGMENTS

















430 BABCOOK ET AL. AJR:166, February 1996

Fig. 4.-Sequential axial sonogramsof posterior fossa in 13- to 14-week-oldfetus.

A, At most rostral level, vermis isidentified between cerebellar hemi-spheres (arrow).

B, At most caudal level, fourth yen-tricular roof, which separates fourthventricle and cisterna magna, is diffi-cult to appreciate, giving impression ofcommunication between fourth ventri-cia and cisterna magna.

Fig. 5.-Serial axial spoiled gradient-recalled acquisition in steady state MR images Fig. 6.-Coronal spoiled gradient-re-of posterior fossa in 13- to 14-week-old fetus. called acquisition in steady state MR im-

A, Vermis is identified between cerebellar hemispheres rostrally (arrow). age of posteriorfossa in 13- to 14-week-oldB, Next caudal image identifies fourth ventricular roof joining cerebellar hemispheres fetus. Vermis is identified rostrally (arrow)

(arrow) and separating fourth ventricle and cisterna magna. but not caudally at this stage of gestation.

Fig. 7.-Axial and sagittal sonograms of pos-tenor fossa in 16-week-old fetus.

A and B, Caudally, fourth ventricular roof isthick enough to be visualized in both axial (A)and sagittal (B) planes (arrow).

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sagittal axial sonograms of posterior fossa in 16-week-old fetus

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fourth ventricular roof is visualized in both planes (arrow)

Effect of Gesta=onal age (Posterior Fossa)

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Lower-most Section

The Vermis Appears To Be Open (arrow) And Communicates With The Four th Vent r ic le Through A Wide

Somewhat Higher Higher Still

No ‘vermian Defect’ Is Seen And The Fourth Ventricle (4) Appears As A Discrete Entity.

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peduncular cistern (cisterna magna) and the fourth ventri-cle. Later, after the 16th postmenstrual week, this ‘normal’open space narrows as the growth and development ofthe vermis progress, giving rise to the median aperture(foramen of Magendie) (Figure 2). Again, this normalsonographic finding may be interpreted by those unfamiliarwith this developmental change as a Dandy–Walker mal-formation or a variant of this. Once again, this may lead topatient anxiety and, in extreme cases, to termination of thepregnancy3.

An important structure that is often not specificallytargeted for imaging during the late second-trimester anat-omy scan is the corpus callosum. The corpus callosum and

its closest anatomic structures, namely the cavum septipellucidi and the pericallosal artery, follow a well-knowndevelopmental timetable. They do not reach a developmen-tal stage that allows for sonographic imaging until post-menstrual weeks 18–19. To search for their presence beforethey reach this critical stage in their development wouldlead to the mistaken diagnosis of agenesis of the corpuscallosum. In cases of agenesis of the corpus callosum, thepericallosal artery, which normally parallels the corpuscallosum, will not follow its normal course. At times, anormal corpus callosum and a normal pericallosal arteryare present and readily imaged, but the cavum septi pellu-cidi is absent, as in the case of septo-optic dysplasia4.

Figure 1 Transvaginal scan of a 14-week fetus. (a) Oblique-1 (sagittal) section: the fetus is facing left. The choroid plexus fills the antrumof the lateral ventricle. The anterior horns appear prominent, but are normal; (b) a Frontal-2 (coronal) section through the anterior hornsof the lateral ventricles. The anterior horns are normal for this gestational age; however, this same sonographic picture at 20 weeks ormore is consistent with ventriculomegaly or hydrocephalus

Figure 2 Three serial, almost axial (horizontal) views through the posterior fossa. (a) This is the lower-most section (see insert). Thevermis appears to be open (arrow) and communicates with the fourth ventricle through a wide (at this gestational age, normal) medianaperture (foramen of Magendie); (b) somewhat higher, the right and left sides of the cerebellar hemispheres appear closer to each other(arrow); (c) higher still, no ‘vermian defect’ is seen and the fourth ventricle (4) appears as a discrete entity. C, cerebellum

Editorial Monteagudo

AMA: First Proof

2 Ultrasound in Obstetrics and Gynecology







AMA: First Proof








AMA: First Proof


The Right And Left Sides Of The Cerebellar Hemispheres Appear Closer To Each Other (arrow);

Effect Of Scanning Level (Posterior Fossa)

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Effect of Gesta=onal age (Lateral Ventricles)

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Hypoplasia Or Dysplasia Should Not Be Diagnosed Prior To 18 Weeks, Before Vermian Development Is Complete.

An Abnormally Steep Scanning Angle May Mimic A Prominent Cleft Between The Lower Portions Of The Cerebellar Hemispheres.

The fetal cerebellum Pitfalls in diagnosis

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Conclusion

•TheCNS displays remarkable embryological and developmental changes throughout gestation.

•Standard Approach of examination and evaluation of the CNS Should Be Followed

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Standard Sonographic Examination of the

FEtal CNS

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Sonography of the CNS

Basic Examination “Neurosongram”

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Planes of Basic ExaminaEon

Axial Planes SagiZal Planes

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Axial Planes

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Axial Planesa: Transventricular

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b: Transthalamic

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C: Transcerebeller

b: Transthalamic

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The Transventricular plane

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Frontal hones

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Frontal hones

Atrium

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Frontal hones

Choroid Plexus

Atrium

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Cavum SepE Pellucidi

Frontal hones

Choroid Plexus

Atrium

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The Transthalamic Plane

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Thalami


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Thalami

Hyppocamas Gyrus


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T

T

The Transcerebeller plane

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T

T


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Frontal hones

T

T


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Cerebellum


Frontal hones

T

T


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Cerebellar vermis

Cerebellum


Frontal hones

T

T


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Cerebellar vermis

Cistrerna Magna2-‐10 mm

Cerebellum


Frontal hones

T

T


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SagiZal Planes

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SagiZal Planes

A: The Midsagittal Plan

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SagiZal Planes

b: Parasgittal plane

A: The Midsagittal Plan

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Mid SagiGal Plane

Corpus Callosum Cavum Sep, Pellucidi

Cerebellum

4th V

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Mid SagiGal Plane

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The Corpus Callosum

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Corpus Callosum

Lateral Ventricles

Third Ventricle

midbrainPituitary

Splenium

Thalamus

hypothalamus

Fourth ventricle

The Corpus Callosum

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Para-‐SagiGal Plane

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Basic Examniation ChecklistBasic Examniation Checklist

Head + NeckHead + NeckMidline & FalxMidline & FalxCavum septi pellucidiCavum septi pellucidiLateral cerebral ventriclsLateral cerebral ventriclsChoroid PlexusChoroid PlexusCerebellumCerebellumCisterna magnaCisterna magna

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Main AbnormaliEes can be Suspected on Basic Planes

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Microcephaly

Anencephaly

Chiari Malforma,on



acidacid






14 +4 weeks



Hydranecphaly

Encephalocele






Pilu

Holoprosencephaly


ACC

SOP


PF-‐Fluid-‐Cyst

Yong seok et al.



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Microcephaly

Anencephaly

Chiari Malforma,on



acidacid






14 +4 weeks



Hydranecphaly

Encephalocele






Pilu

Holoprosencephaly


ACC

SOP


PF-‐Fluid-‐Cyst

Yong seok et al.



Ventriculomegaly

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Microcephaly

Anencephaly

Chiari Malforma,on



acidacid






14 +4 weeks



Hydranecphaly

Encephalocele






Pilu

Holoprosencephaly


ACC

SOP


PF-‐Fluid-‐Cyst

Yong seok et al.



ACC

Ventriculomegaly

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Microcephaly

Anencephaly

Chiari Malforma,on



acidacid






14 +4 weeks



Hydranecphaly

Encephalocele






Pilu

Holoprosencephaly


ACC

SOP


PF-‐Fluid-‐Cyst

Yong seok et al.



ACC

PF-‐Fluid-‐Cyst

Ventriculomegaly

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•Ventriculomegaly (hydrocephalus)

•Absent Cavum Septum Pellucidum

•Agenesis of the Corpus Callosum

•Fluid Collection in the posterior fossa

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(< 10 mm is normal). Independent of gesta7onal age

Mild 10 – 15 mmLow Risk

Severe > 15 mm High Risk

mean = 6-‐8 mm

Ventriculomegaly (hydrocephalus)

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Le] Lateral VentricleRight Lateral Ventricle

3rd Ventricle

4th Ventricle

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Aqueduct of Sylvius

Foramen of Monro

Cisterna Magna

Pathogenesis: Ventriculomegaly

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•Square Shaped, Interrupts and Fills The Space Between The Frontal Horns•The CSP: Becomes Visible At 16 Weeks, Obliterate Near Term

Absent CSP

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•Square Shaped, Interrupts and Fills The Space Between The Frontal Horns•The CSP: Becomes Visible At 16 Weeks, Obliterate Near Term


Absent CSP

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A rare finding usually discovered Postnatally in children evaluated for developmental delay.

Associated with various brain malformations:agenesis of the corpus callosumHoloprosencephaly.Setpo-‐optic dysplasia.

Secondary to disruptive process: Hydrocephalus, Chiari II malformation, hydranecephaly.

Absent CSP

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Agenesis of the Corpus Callosum

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Only The Rostrum (1), Genu (2) And Body (3) Are Visible; The Splenium Is Missing. The Corpus Callosum Is Short Posteriorly And Does Not Seem To Overlay The Quadrigeminal Plate

21-‐week Fetus With Par=al Agenesis Of The Corpus Callosum

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Outcome of fetal ACC

Var ies between complete ly asymptomaEc appearance and severe neurologic problems

50 – 100 % of isolated cases will have normal neurological development at 3-‐11 years but Poor prognosis with associated anomalies

Progressive decline in intellect over the years

Most need special educaEon

Long-‐term follow-‐up of children with prenatally diagnosed agenesis of corpus callosum (ACC) J. H. Stupin et al, USOG, 32, 2008

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Fluid Collec,on in the Posterior Fossa

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Fluid Collec,on in the Posterior Fossa•Megacisterna Magna

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•Blak’s Pouch Cyst

•Megacisterna Magna

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•Megacisterna Magna •D-W Malformation &DW- Variant

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•Arachnoid Cyst

•D-W Malformation &DW- Variant

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•Arachnoid Cyst

•D-W Malformation &DW- Variant

Anomalies Of The Meninges

Anomalies Cerebellum

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Mega–Cisterna Magna

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An Enlargement Of The Cisterna Magna Beyond 10 Mm With Intact Vermis

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Lateral Ventricle

Pathogenesis: Mega Cisterna Magna

Cerebral Aqueduct

Choriod Plexus

Third Ventricle

Fourth Ventricle

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Lateral Ventricle

Pathogenesis: Mega Cisterna Magna

Cerebral Aqueduct

Choriod Plexus

Third Ventricle

The Foramina Of Luschka And Magendie Fenestrate Delayed

Fourth Ventricle

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Prognosis:• Isolated Cases: (97%-100%) Are Normal.

• If Not Isolated: Only 11% Have Normal Outcome.

Nonisolated Cases Have VM, Congenital Infection, Or Karyotype Abnormalities.A Large Cisterna Magna Require Careful Search For Other Abnormalities.

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Blake’s Pouch Cyst

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Lateral Ventricle

Cerebral Aqueduct

Choriod Plexus

Third Ventricle

Nonfenestration of the foramina of Luschka and Magendie leads to dilatation of the fourth ventricle and and elevation of the vermis away from the brain stem.

Fourth Ventricle

Pathogenesis: Blake’s Pouch Cyst

There is no communication between the cyst and the subarachnoid space

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Dandy-Walker Malformation

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A Spectrum Of Anomalies Of The Posterior Fossa.

• Dandy-Walker Malformation:✦Increase Of The Posterior Fossa, ✦Complete Or Partially Agenesis Of The Cerebellar Vermis, ✦A Tentorium Elevation

• Variant Of Dandy-Walker: ✦Hypoplasia Of The Cerebellar Vermis In Different

Degrees With Or Without Increase Of The Posterior Fossa.

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Fetal posterior fossa fluid collections 629

Figure 6 Imaging in a patient referred at 20 weeks’ gestation. The transvaginal fetal sonogram (a) demonstrated moderate elevation of thecerebellar vermis but the cisterna magna was not felt to be enlarged and the downslanting tentorium (arrow) suggested a normal position ofthe torcular. At 25 weeks (b) the cisterna magna had increased in size, the rotation of the vermis was increased and the angle formed by thetentorium (arrow) suggested upward displacement of the torcular. At this time, a diagnosis of Dandy–Walker malformation was made andthis was confirmed by prenatal (c) as well as postnatal (d) magnetic resonance imaging.

Figure 7 Demonstration of the torcular on fetal magnetic resonanceimaging. (a) Fetus with Blake’s pouch cyst with the torcular (whitearrow) implanted close to the insertion of the neck muscles (blackarrow). (b) Fetus with Dandy–Walker malformation with obviousupward displacement of the torcular (white arrow) compared withthe neck muscles (black arrow). Notice also the greater size of thecisterna magna and the increased rotation of the cerebellar vermiscompared with the fetus in (a).

was more common in cases with associated anomalies(46% versus 18% of cases). About 90% of fetuses witheither Blake’s pouch cyst or megacisterna magna and noassociated anomalies had normal neurologic developmentcompared with only 50% of those with Dandy–Walkermalformation and vermian hypoplasia (Table 2).

DISCUSSION

We believe that the most relevant result of our study is thedemonstration that fetal neurosonography allows us tocategorize accurately from mid gestation fluid collectionsin the fetal posterior fossa and to distinguish entities thathave different clinical implications.

In our hands, prenatal diagnosis with sonography wascorrect in almost 90% of cases. We believe that thereason for this improvement in accuracy over previousstudies1,2 is our use of a multiplanar approach andparticularly upon the documentation of the mid-sagittalplane, which is essential for evaluation of the posteriorfossa contents3,5,11. Caution is warranted in diagnosingcerebellar anomalies early in gestation because of theincomplete development of the cerebellar vermis18–20;

however, with meticulous scanning, we were able todocument Dandy–Walker malformation from 17 weeks.

Categorization of posterior fossa fluid collections hasclinical relevance. Blake’s pouch cyst and megacisternamagna, the most frequent diagnoses in our series, hada similar and much more favorable outcome than didDandy–Walker malformation and vermian hypoplasia.They were less frequently associated with other anomalies,underwent spontaneous resolution during gestation in onethird of cases and, when they were not associated withother anatomic or chromosomal anomalies, demonstratednormal postnatal neurodevelopment in about 90% ofcases. This agrees well with previous studies and suggeststhat, when isolated, these conditions should probably beregarded as normal variants11,21.

The term Blake’s pouch cyst was originally introducedinto infantile neuroradiology to indicate a type of obstruc-tive hydrocephalus secondary to failure of formation ofthe foramen of Magendie and Luschka, resulting in acompressive cyst of the posterior fossa displacing superi-orly the cerebellar vermis22–24. More recently, the termhas become popular in fetal imaging studies to indicatecases with a posterior fossa cyst displacing superiorlyan intact cerebellar vermis, typically in association with anormal ventricular system and normal size of the posteriorfossa3,7,11,13. This finding has been interpreted as failed ordelayed regression of the Blake’s pouch, an embryologicalstructure continuous with the fourth ventricle. The entitydescribed in the original neonatal studies and the onelater described in fetal studies are likely to be different,as the latter typically has a normal outcome and appearsto be associated rarely with ventriculomegaly. Megacis-terna magna may be a variation of Blake’s pouch cyst7.From a clinical perspective, the two conditions have manysimilarities.

Dandy–Walker malformation and vermian hypoplasia(previously referred to as Dandy–Walker variant)4 havebeen the subject of many postnatal and fetal studiesand are probably the best known of the posterior fossacystic lesions1,6,9,16,17,25,26. In agreement with previousstudies, we found a high proportion of multiple anomaliesand abnormal neurodevelopment in these cases. It has

Copyright ! 2012 ISUOG. Published by John Wiley & Sons, Ltd. Ultrasound Obstet Gynecol 2012; 39: 625–631.

Cystic dilation of the f o u r t h v e n t r i c l e communicating with a posterior fossa fluid space

Small, rotated, raised, or absent vermis

Elevated tentorium and high position of the torcula

Dandy-Walker Malformation

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The Prognosis :Better In Isolated DWS. Karyotype Abnormalities In About 15%.

Neonatal Mortality: 12% To 55%.Neonatal Morbidity:•Intelligence Is Normal In About 40%•Borderline In 20%•Subnormal In 40%.

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Dandy–Walker MalformationThe Torcular Is Displaced Higher Than Usual, Indicating That This Is A


Table 2 Sonography in fetuses with posterior fossa fluid collections (PFFC), associations with other anomalies, intrauterine regression,outcome and accuracy of prenatal diagnosis

Abnormal neurologicaldevelopment postnatally‡

Prenatal sonographicdiagnosis

Totalcases(n)

Caseswith

associatedanomalies (n)

Lost tofollow-up

(n)TOP(n)

Regressionin utero

(n)*

Sonographicdiagnosis

confirmed†(n)

IsolatedPFFC

(n)

PFFC withassociatedanomalies

(n)

Blake’s pouch cyst 32 8 3 2 11/27 16/18 1/20 1/5Megacisterna magna 27 9 4 2 6/21 16/17 2/16 1/4Dandy–Walker malformation 26 16§ 7 11 0/8 16/19 3/5 2/2Vermian hypoplasia 17 11§ 9 2 0/6 6/8 1/3 2/2Cerebellar hypoplasia 2 2 0 2 0/0 2/2 0 0Arachnoid cyst 1 0 0 0 0/1 1/1 1/1 0Total (n or n (%)) 105 46 23 19/105 (18) 17/63 (27) 57/65 (88) 8/45 (18) 6/13 (46)

*Denominator excludes cases lost to follow-up and terminations of pregnancy (TOP). †Confirmation postnatally or at autopsy;denominator excludes cases lost to follow-up and those that underwent intrauterine regression. ‡Number of cases with abnormalneurological development/number of cases that underwent neurological examination at 1–5 years. §In one case in each group the presenceof associated anomalies was detected only postnatally.

torcular and evaluation of the integrity of the cerebellarvermis. The torcular Herophili cannot be imaged clearlywith sonography due to acoustic shadowing from theskull bones and we inferred its position by observing theangulation of the tentorium (Figure 2). To evaluate thecerebellar vermis we used a combination of qualitativefindings (visualization of fastigium and fissures)3,6,13,14

as well as biometry8,10. Nevertheless, frequently wewere uncertain about vermian integrity, particularly inthe context of Dandy–Walker malformation, becauseof upward compression by the posterior fossa cyst(Figure 3).

Twenty-three (22%) cases were lost to follow-upbecause the parents declined to provide informationor could not be reached, or autopsy reports werenot available. Intrauterine regression of the abnormalposterior fossa findings was noted in 27% of cases. Ofthe remaining 65 cases, prenatal diagnosis was confirmedpostnatally or at autopsy in 88%.

There was one false-positive diagnosis of vermianhypoplasia and seven incorrect diagnoses (Table 3). Inat least two of these cases, the presence of cortical

Figure 2 The position of the torcular Herophili (arrows) is inferredon ultrasound by the direction of the tentorium cerebelli. In (a) thetorcular is found in a normal position, at about the same level asthe site of insertion of the neck muscles on the posterior skull; thisis a Blake’s pouch cyst. In (b) the torcular is displaced higher thanusual, indicating that this is a Dandy–Walker malformation.

Figure 3 Dandy–Walker malformation in a 21-week fetus. Thetransvaginal sonogram (a) failed to demonstrate the anatomiclandmarks of the cerebellar vermis (arrow), fastigium and fissures,and we were uncertain whether this reflected hypoplasia. Aftertermination of pregnancy, autopsy revealed a normally lobulatedvermis (b).

malformations that had escaped prenatal diagnosisresulted in a worse outcome than had been predictedantenatally.

The earliest diagnosis of a posterior fossa fluidcollection was made with sonography at 17 weeks. At thistime a considerable superior rotation of the vermis wasnoted. At 21 weeks a final diagnosis of Dandy–Walkermalformation was made, with a seemingly intactcerebellar vermis (Figure 4). The fetal karyotype wasnormal, no other anomalies were identified, and theparents elected to continue the pregnancy. After birtha further diagnosis of Opitz syndrome was made.

One fetus was diagnosed in utero with a Dandy–Walkermalformation by both ultrasound and MRI and was foundafter termination of pregnancy to have a severe pos-terior fossa hemorrhage with secondary hydrocephalus(Figure 5).

Modifications of the sonographic findings throughoutgestation were noted in several cases. Most frequentlythis consisted of the resolution of a Blake’s pouch cystor megacisterna magna. In one case, interpretation ofthe sonographic findings was particularly difficult at mid



Table 2 Sonography in fetuses with posterior fossa fluid collections (PFFC), associations with other anomalies, intrauterine regression,outcome and accuracy of prenatal diagnosis

Abnormal neurologicaldevelopment postnatally‡

Prenatal sonographicdiagnosis

Totalcases(n)

Caseswith

associatedanomalies (n)

Lost tofollow-up

(n)TOP(n)

Regressionin utero

(n)*

Sonographicdiagnosis

confirmed†(n)

IsolatedPFFC

(n)

PFFC withassociatedanomalies

(n)

Blake’s pouch cyst 32 8 3 2 11/27 16/18 1/20 1/5Megacisterna magna 27 9 4 2 6/21 16/17 2/16 1/4Dandy–Walker malformation 26 16§ 7 11 0/8 16/19 3/5 2/2Vermian hypoplasia 17 11§ 9 2 0/6 6/8 1/3 2/2Cerebellar hypoplasia 2 2 0 2 0/0 2/2 0 0Arachnoid cyst 1 0 0 0 0/1 1/1 1/1 0Total (n or n (%)) 105 46 23 19/105 (18) 17/63 (27) 57/65 (88) 8/45 (18) 6/13 (46)

*Denominator excludes cases lost to follow-up and terminations of pregnancy (TOP). †Confirmation postnatally or at autopsy;denominator excludes cases lost to follow-up and those that underwent intrauterine regression. ‡Number of cases with abnormalneurological development/number of cases that underwent neurological examination at 1–5 years. §In one case in each group the presenceof associated anomalies was detected only postnatally.

torcular and evaluation of the integrity of the cerebellarvermis. The torcular Herophili cannot be imaged clearlywith sonography due to acoustic shadowing from theskull bones and we inferred its position by observing theangulation of the tentorium (Figure 2). To evaluate thecerebellar vermis we used a combination of qualitativefindings (visualization of fastigium and fissures)3,6,13,14

as well as biometry8,10. Nevertheless, frequently wewere uncertain about vermian integrity, particularly inthe context of Dandy–Walker malformation, becauseof upward compression by the posterior fossa cyst(Figure 3).

Twenty-three (22%) cases were lost to follow-upbecause the parents declined to provide informationor could not be reached, or autopsy reports werenot available. Intrauterine regression of the abnormalposterior fossa findings was noted in 27% of cases. Ofthe remaining 65 cases, prenatal diagnosis was confirmedpostnatally or at autopsy in 88%.

There was one false-positive diagnosis of vermianhypoplasia and seven incorrect diagnoses (Table 3). Inat least two of these cases, the presence of cortical

Figure 2 The position of the torcular Herophili (arrows) is inferredon ultrasound by the direction of the tentorium cerebelli. In (a) thetorcular is found in a normal position, at about the same level asthe site of insertion of the neck muscles on the posterior skull; thisis a Blake’s pouch cyst. In (b) the torcular is displaced higher thanusual, indicating that this is a Dandy–Walker malformation.

Figure 3 Dandy–Walker malformation in a 21-week fetus. Thetransvaginal sonogram (a) failed to demonstrate the anatomiclandmarks of the cerebellar vermis (arrow), fastigium and fissures,and we were uncertain whether this reflected hypoplasia. Aftertermination of pregnancy, autopsy revealed a normally lobulatedvermis (b).

malformations that had escaped prenatal diagnosisresulted in a worse outcome than had been predictedantenatally.

The earliest diagnosis of a posterior fossa fluidcollection was made with sonography at 17 weeks. At thistime a considerable superior rotation of the vermis wasnoted. At 21 weeks a final diagnosis of Dandy–Walkermalformation was made, with a seemingly intactcerebellar vermis (Figure 4). The fetal karyotype wasnormal, no other anomalies were identified, and theparents elected to continue the pregnancy. After birtha further diagnosis of Opitz syndrome was made.

One fetus was diagnosed in utero with a Dandy–Walkermalformation by both ultrasound and MRI and was foundafter termination of pregnancy to have a severe pos-terior fossa hemorrhage with secondary hydrocephalus(Figure 5).

Modifications of the sonographic findings throughoutgestation were noted in several cases. Most frequentlythis consisted of the resolution of a Blake’s pouch cystor megacisterna magna. In one case, interpretation ofthe sonographic findings was particularly difficult at mid


Blake’s Pouch Cyst The Torcular Is Found In A Normal Position, At About The Same Level As The Site Of Insertion Of The Neck Muscles On The Posterior Skull

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• Are Benign, Noncommunicating Fluid Collections Within Arachnoid Membranes.

• Location: Intracranially And In The Spinal Canal.

• Order Of Frequency Are The Sylvian Fissure Or Temporal Fossa, Posterior Fossa, Over The Cerebral Convexity, And Midline Supratentorial,

• Most Appear Stable And Require No Surgical Treatment. Occasionally They Interfere With CSF Circulation And Require Decompression.

Arachnoid Cysts

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The Differential Diagnosis

53

Depends On The Location.In The Posterior Fossa: DandyWalker Malformation, Inferior Vermian Hypoplasia, Mega–cisterna Magna, And Blake’s Pouch Cysts.

Supratentorial Cysts: Cavum Veli Interpositi, Aneurysm Of Vein Of Galen, Hemorrhage, And Cystic Tumors.

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54

Prenatal diagnosis and outcome of fetal posterior fossa fluid collectionsG. GANDOLFI COLLEONI et al, Ultrasound Obstet Gynecol 2012; 39: 625–631

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Blake’s Pouch Cyst N = 32

Megacisterna Magna N = 27

Dandy – Walker Malformation N=26

Vermian Hypoplasia N=17

Cerebellar Hypoplasia N=2

55

105Fetuses

Arachnoid CystN=1

Sonograph ic d i a g n o s e s were accurate in 88%

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56

✦Isolated Cases Of Blake’s Pouch Cyst And Megacisterna Magna Have An Excellent Prognosis, With A High Probability Of Intrauterine Resolution And Normal Intellectual Development In Almost All Cases.

✦Dandy – Walker Malformation And Vermian Hypoplasia, Even When They Appear Isolated Antenatally, Are Associated With An Abnormal Outcome In Half Of Cases.

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57

•Black’s Pouch Cyst, DW Malformation, and Mega-‐Cisterna Magna Can give Similar Sonographic features.

•However the prognosis is greatly varialbe.

•Careful Neurosonographic assessment using 3 D or Fetal MRI is often Needed

Conclusion

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Originally published in Ultrasound Obstet Gynecol 2007; 30: 233–245

Technical GuidelineHow do we do it? Practical advice on imaging-based

techniques and investigations

Three dimensional ultrasound examination of the fetal central

nervous systemGianluigi Pilu, Tullio Ghi, Angela Carletti,

Maria Segata, Antonella Perolo, Nicola RizzoFrom the Department of Obstetrics and Gynecology

University of Bologna, ItalyAddress for correspondence: [email protected]

Sunday, July 28, 13

mailto:[email protected]

mailto:[email protected]

3D ultrasound is a data set that contains a large number o f 2D p l a n e s ( B -‐mode images).

e.g. If the page of a book is one 2D plane, then the book itself is the enEre data set.

The 3 D probe acquire the data by moving a B mode transducer within a housing like a hand held Japanese fan .

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Pyramid Of Volume Informa=on

✴ “Walking” through the volume is similar to leafing through the pages of a book i.e. walking through the various 2D planes that make up the entire volume.

✴ The Volume can be dissected in any plane, to get “Multiplanar Imaging”

the acquired volume unlike the defined rectangle shape of a book looks like a pyramid or triangle of volume informaEon with a broad base

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61

3D volumes of the fetal brain obtained from an axial approach: the ‘start’ scan

3D volumes of the fetal brain obtained from an axial approach: the ‘start’ scan

Cavum septi pellucidi midline


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midline

A B

CSunday, July 28, 13


midline

A B

C

A and B rotated on Z plane until midline is aligned with C plane

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A B

C

Corpus callosum + cavum septi pellucidi

Cerebellar vermis

Acoustic shadowSunday, July 28, 13


midline

midline

Corpus callosum

Cavum sep* pellucidi

Corpus callosum + cavum sep* pellucidi

64

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4v

Brain stem Cerebellar vermis

Angled Insona,on of Posterior Fossa to Visualize brain Stem

65

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4vhemisphere

hemisphere

hemisphere

hemisphere

vermis

tentorium

tentorium

4v

vermis

vermian fissures

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body atrium

Occipital horn

Temporal horn

Sylvian fissure

67

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68

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69

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70

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71

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72

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73

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3v

Normal corpus callosum

Absent corpus callosum

3v

3v

Par,al agenesis

74

Agenesis of the corpus callosum

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Normal Posterior Fossa At Midgesta=on

SagiGal viewAxial view

Prenatal diagnosis and outcome of fetal posterior fossa fluid Collec=onsGandolfi Colleoni et al., UOG 2012

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Cavum Sep, Pellucidi


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Cerebellar vermis


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Cisterna Magna

Cerebellar vermis


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Cisterna Magna

Tentorium

Cerebellar vermis


Cisterna Magna

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76

Applica=on of 3 D Imaging in Prenatal diagnosis of Fetal

Posterior Fossa Fluid Collec=on

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77


Brainstem–vermis and brainstem–tentorium angles allow accurate categorization of fetal upward rotation of cerebellar vermisP. VOLPE*, et al Ultrasound Obstet Gynecol 2012; 39: 632–635

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Categoriza,on of posterior fossa fluid collec,ons (1)

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Blake’s pouch cyst Megacisterna magna D-‐W

Findings Upward rotation of an intact vermis with normal torcular

Cisterna magna >10mm with intact and normally positioned cerebellum

Upward rotation of the vermis (normal or hypoplastic) with

elevated torcular

SagiGal

Axial

Categoriza,on of posterior fossa fluid collec,ons (1)

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79

•Transverse Diameter Of The Cerebellum.

•The Intactness And Size Of The Vermis.

•The Depth Of The Cisterna Magna (10 Mm)

Axial View

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80

BT and BV angle in posterior fossa malformations 633

Figure 1 Measurement of brainstem–vermis (BV) and brainstem–tentorium (BT) angles. (a) A median view of the fetal brain is obtained (inthis case after acquisition of an ultrasound volume starting from an axial view) and the main anatomic landmarks are identified. (b) A line isdrawn tangentially to the dorsal aspect of the brain stem and a second line is drawn tangentially to the ventral contour of the cerebellarvermis; the interposed angle (1) is the BV angle; the BT angle (2) is measured between the first line and a third line tangential to the tentorium.

Figure 2 Measurement of brainstem–vermis (BV) angle (1) and brainstem–tentorium (BT) angle (2) in fetuses with: (a) Blake’s pouch cyst;(b) cerebellar vermis hypoplasia; and (c) Dandy–Walker malformation. The BV angles are 26!, 39! and 73!, respectively and the BT anglesare 45!, 50! and 66!. These images were obtained from three-dimensional ultrasound volumes acquired originally by positioning the probealong the posterior fontanelle. Corresponding images from the same cases obtained by acquiring the volumes with a transabdominal axialapproach are also provided (d,e,f), to demonstrate the excellent correlation between the two approaches.

view of the brain were used for measurements in thestudy group, and 3D volumes were used for controls,utilizing 4D View 9.0 (GE Healthcare, Milan, Italy) andAdobe Photoshop 6.0 (Adobe Systems Incorporated, SanJose, CA, USA) software, respectively. All measurementswere performed by two operators (E.C., P.V.). Statis-tical analysis was performed by calculating means andSDs. Groups were compared using the Mann–WhitneyU-test.

RESULTS

The study group included 31 fetuses at 19–28 weeks’gestation with posterior fossa fluid collections (12with Blake’s pouch cyst, 12 with Dandy–Walkermalformation and seven with vermian hypoplasia)(Figure 2). The control group comprised 80 normalfetuses at 20–24 weeks’ gestation. BV and BT anglemeasurements are reported in Table 1. Controls always



The Vermis: Shape, Size, Fissures

The Tentorium: Level

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81





RESULTS



Brainstem-vermis (BV) angle

Brainstem-tentorium (BT) angle


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Blake’s Pouch Cyst

Measurement Of Brainstem–vermis (BV) Angle (1) And Brainstem–tentorium (BT) In Three Conditions

Cerebellar Vermis Hypoplasi

Dandy–Walker Malformation.

The Angles Has The Widest Measurement In DA Malformation

82





RESULTS







RESULTS







RESULTS



Sunday, July 28, 13

634 Volpe et al.

Table 1 Brainstem–vermis (BV) and brainstem–tentorium (BT) angles in fetuses with upward rotation of the cerebellar vermis and incontrols

BV angle (!) BT angle (!)

Ultrasound findings n Mean SD Range Mean SD Range

Controls 80 9.1 3.5 4–17 29.3 5.8 21–44Blake’s pouch cyst 12 23.0 2.8 19–26 42.2 7.1 32–52Vermian hypoplasia 7 34.9 5.4 24–40 52.1 7.0 45–66Dandy–Walker malformation 12 63.5 17.6 45–112 67.2 15.1 51–112

80

60

40

20

0

Brai

nste

m–v

erm

is a

ngle

(°)

Normal Blake’s pouchcyst

Vermianhypoplasia

Dandy–Walkermalformation

Figure 3 Box-and-whisker plot of distribution of brainstem–vermisangle in controls and in fetuses with upward rotation of thecerebellar vermis. Medians are indicated by a line inside each box,25th and 75th percentiles by box limits and 5th and 95th percentilesby lower and upper bars, respectively.

had a BV angle < 18! and a BT angle < 45!. The BVangle was significantly increased in each of the threesubgroups of anomalies (Figure 3, Table 2), the angleincreasing with increasing severity of the condition. TheBT angle demonstrated a similar pattern, but there wasmore overlapping among groups (Figure 4, Table 2).

DISCUSSION

Our results suggest that measurement of the BV anglediscriminates accurately posterior fossa fluid collectionsassociated with upward rotation of the cerebellum.

In the late first trimester, the fourth ventricle is largeand a relatively small cerebellum is located on top of it.In the following weeks, the cerebellum grows to enfoldcompletely the fourth ventricle. However, a small finger-like appendage of the fourth ventricle, the Blake’s pouch,is frequently seen protruding into the cisterna magna,caudal to the cerebellum8. It has been suggested thatthere is a continuum of anatomic anomalies involv-ing the fourth ventricle–Blake’s pouch complex8. Theone with least clinical impact among these anomaliesis the Blake’s pouch cyst, a persistence of the Blake’spouch that results in an isolated superior displacementof the cerebellar vermis. At the other end of the spec-trum lies the Dandy–Walker malformation, in which

80

60

40

20

Brai

nste

m–t

ento

rium

ang

le (°

)


Vermianhypoplasia


Figure 4 Box-and-whisker plot of distribution of brainstem–tentorium angle in controls and in fetuses with upward rotation ofthe cerebellar vermis. Medians are indicated by a line inside eachbox, 25th and 75th percentiles by box limits and 5th and 95th

percentiles by lower and upper bars, respectively.

Table 2 Statistical comparison of brainstem–vermis (BV) andbrainstem–tentorium (BT) angles in controls and in fetuses withupward rotation of the cerebellar vermis

P (Mann–Whitney U-test)

Comparison* BV angle BT angle

Controls vs Blake’s pouch cystfetuses

< 0.00000005 < 0.000005

Controls vs Dandy–Walkerfetuses

< 0.00000005 < 0.00000005

Controls vs vermian hypoplasiafetuses

< 0.00005 < 0.00005

Blake’s pouch cyst vsDandy–Walker fetuses

< 0.00005 < 0.00005

Blake’s pouch cyst vs vermianhypoplasia fetuses

< 0.005 0.01

Vermian hypoplasia vsDandy–Walker fetuses

< 0.0005 < 0.005

*Group with smaller angle vs. group with larger angle.

the upward displacement of a normal to hypoplasticvermis is associated with enlargement of the cisternamagna. In vermian hypoplasia (previously referred to asDandy–Walker variant) the cisterna magna is of normalsize and the vermis is small and frequently (although not


634 Volpe et al.

Table 1 Brainstem–vermis (BV) and brainstem–tentorium (BT) angles in fetuses with upward rotation of the cerebellar vermis and incontrols

BV angle (!) BT angle (!)

Ultrasound findings n Mean SD Range Mean SD Range

Controls 80 9.1 3.5 4–17 29.3 5.8 21–44Blake’s pouch cyst 12 23.0 2.8 19–26 42.2 7.1 32–52Vermian hypoplasia 7 34.9 5.4 24–40 52.1 7.0 45–66Dandy–Walker malformation 12 63.5 17.6 45–112 67.2 15.1 51–112

80

60

40

20

0

Brai

nste

m–v

erm

is a

ngle

(°)


Vermianhypoplasia


Figure 3 Box-and-whisker plot of distribution of brainstem–vermisangle in controls and in fetuses with upward rotation of thecerebellar vermis. Medians are indicated by a line inside each box,25th and 75th percentiles by box limits and 5th and 95th percentilesby lower and upper bars, respectively.

had a BV angle < 18! and a BT angle < 45!. The BVangle was significantly increased in each of the threesubgroups of anomalies (Figure 3, Table 2), the angleincreasing with increasing severity of the condition. TheBT angle demonstrated a similar pattern, but there wasmore overlapping among groups (Figure 4, Table 2).

DISCUSSION

Our results suggest that measurement of the BV anglediscriminates accurately posterior fossa fluid collectionsassociated with upward rotation of the cerebellum.

In the late first trimester, the fourth ventricle is largeand a relatively small cerebellum is located on top of it.In the following weeks, the cerebellum grows to enfoldcompletely the fourth ventricle. However, a small finger-like appendage of the fourth ventricle, the Blake’s pouch,is frequently seen protruding into the cisterna magna,caudal to the cerebellum8. It has been suggested thatthere is a continuum of anatomic anomalies involv-ing the fourth ventricle–Blake’s pouch complex8. Theone with least clinical impact among these anomaliesis the Blake’s pouch cyst, a persistence of the Blake’spouch that results in an isolated superior displacementof the cerebellar vermis. At the other end of the spec-trum lies the Dandy–Walker malformation, in which

80

60

40

20

Brai

nste

m–t

ento

rium

ang

le (°

)


Vermianhypoplasia


Figure 4 Box-and-whisker plot of distribution of brainstem–tentorium angle in controls and in fetuses with upward rotation ofthe cerebellar vermis. Medians are indicated by a line inside eachbox, 25th and 75th percentiles by box limits and 5th and 95th

percentiles by lower and upper bars, respectively.

Table 2 Statistical comparison of brainstem–vermis (BV) andbrainstem–tentorium (BT) angles in controls and in fetuses withupward rotation of the cerebellar vermis

P (Mann–Whitney U-test)

Comparison* BV angle BT angle

Controls vs Blake’s pouch cystfetuses

< 0.00000005 < 0.000005

Controls vs Dandy–Walkerfetuses

< 0.00000005 < 0.00000005

Controls vs vermian hypoplasiafetuses

< 0.00005 < 0.00005

Blake’s pouch cyst vsDandy–Walker fetuses

< 0.00005 < 0.00005

Blake’s pouch cyst vs vermianhypoplasia fetuses

< 0.005 0.01

Vermian hypoplasia vsDandy–Walker fetuses

< 0.0005 < 0.005

*Group with smaller angle vs. group with larger angle.

the upward displacement of a normal to hypoplasticvermis is associated with enlargement of the cisternamagna. In vermian hypoplasia (previously referred to asDandy–Walker variant) the cisterna magna is of normalsize and the vermis is small and frequently (although not


Box-and-whisker plot of distribution of brainstem–vermis angle in controls and in fetuses with upward rotation of the cerebellar vermis. Medians are indicated by a line inside each box, 25th and 75th percentiles by box limits and 5th and 95th percentiles by lower and upper bars, respectively.

Box-and-whisker plot of distribution of brainstem– tentorium angle in controls and in fetuses with upward rotation of the cerebellar vermis. Medians are indicated by a line inside each box, 25th and 75th percentiles by box limits and 5th and 95th percentiles by lower and upper bars, respectively.

Brainstem–vermis Angle Brainstem– Tentorium Angle

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84

Fetal posterior fossa fluid collections associated with upward rotation of the cerebellar vermis range from benign asymptomatic conditions to severe abnormalities associated with neurological impairment.

The most frequent of these anomalies, Blake’s pouch cyst, vermian hypoplasia and Dandy–Walker malformation, have a similar sonographic appearance but a very different prognosis

Conclusion

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85

In Summary

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Examination Of The Posterior Fossa And The Cerebellum

Midsagittal ViewsAxial View

86

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PracEcal Approach to the DD of Posterior Fossa Cyst and CysEc like Lesions

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1. Is the Vermis Present?Is the Vermis intact?

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2. Is the Toruclar in a normal posiEon (tentorial Cerebelli)?

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3. What is the shape of the cerebellar cled?

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3. What is the shape of the cerebellar cled?

4. Brainstem–vermis (BV) Angle And Brainstem–tentorium (BT) Angle

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88

Ultrasound Obstet Gynecol 2012; 39: 625–631Published online 14 May 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.11071

Prenatal diagnosis and outcome of fetal posterior fossa fluidcollections

G. GANDOLFI COLLEONI*, E. CONTRO*, A. CARLETTI*, T. GHI*, G. CAMPOBASSO†,G. REMBOUSKOS†, G. VOLPE‡, G. PILU* and P. VOLPE†*Department of Obstetrics and Gynecology, University of Bologna, Bologna, Italy; †Fetal Medicine Unit, Di Venere and Sarcone Hospitals,ASL Bari, Bari, Italy; ‡Department of Obstetrics and Gynecology, University of Bari, Bari, Italy

KEYWORDS: cerebellar anomalies; Dandy–Walker malformation; fetus; megacisterna magna; prenatal diagnosis; ultrasound

ABSTRACT

Objective To evaluate the accuracy of fetal imagingin differentiating between diagnoses involving posteriorfossa fluid collections and to investigate the postnataloutcome of affected infants.

Methods This was a retrospective study of fetuses withposterior fossa fluid collections, carried out between 2001and 2010 in two referral centers for prenatal diagnosis. Allfetuses underwent multiplanar neurosonography. Parentswere also offered fetal magnetic resonance imaging (MRI)and karyotyping. Prenatal diagnosis was compared withautopsy or postnatal MRI findings and detailed follow-upwas attempted by consultation of medical records andinterview with parents and pediatricians.

Results During the study period, 105 fetuses were exam-ined, at a mean gestational age of 24 (range, 17–28)weeks. Sonographic diagnoses (Blake’s pouch cyst, n = 32;megacisterna magna, n = 27; Dandy–Walker malfor-mation, n = 26; vermian hypoplasia, n = 17; cerebellarhypoplasia, n = 2; arachnoid cyst, n = 1) were accuratein 88% of the 65 cases in which confirmation was pos-sible. MRI proved more informative than ultrasound inonly 1/51 cases. Anatomic anomalies and/or chromosomalaberrations were found in 43% of cases. Blake’s pouchcysts and megacisterna magna underwent spontaneousresolution in utero in one third of cases and over 90% ofsurvivors without associated anomalies had normal devel-opmental outcome at 1–5 years. Isolated Dandy–Walkermalformation and vermian hypoplasia were associatedwith normal developmental outcome in only 50% ofcases.

Conclusion Prenatal neurosonography and MRI aresimilarly accurate in the categorization of posterior fossa

fluid collections from mid gestation. Blake’s pouch cystand megacisterna magna are risk factors for associatedanomalies but when isolated have an excellent prognosis,with a high probability of intrauterine resolution andnormal intellectual development in almost all cases.Conversely, Dandy–Walker malformation and vermianhypoplasia, even when they appear isolated antenatally,are associated with an abnormal outcome in half of cases.Copyright ! 2012 ISUOG. Published by John Wiley &Sons, Ltd.

INTRODUCTION

Fluid collections in the fetal posterior fossa encompassa wide spectrum of different entities, ranging fromnormal variants to severe anomalies1. They may havea similar anatomic as well as sonographic appearance,and diagnostic errors with significant implications forcounseling and management have been described2.

More recently, several reports have shed light on thenormal and abnormal development of the posterior fossacontents, leading to a new clinical classification of fluidcollections3–7. In addition, new advances in prenatalimaging have allowed more detailed evaluation of thesecontents from mid gestation3,6–14.

The aim of our study was to evaluate the diagnosticaccuracy of fetal neurosonography15 and magneticresonance imaging (MRI) in cases of posterior fossa fluidcollections and to assess the outcome of affected infants.

PATIENTS AND METHODS

This was a retrospective study conducted between Decem-ber 2001 and January 2010 in two referral centers for pre-natal diagnosis. All fetuses diagnosed with an abnormal

Correspondence to: Prof. G. Pilu, Clinica Ostetrica e Ginecologica, Universita degli Studi de Bologna Via Massarenti 13, 40138 Bologna,Italy (e-mail: [email protected])

Accepted: 14 November 2011

Copyright ! 2012 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

626 Gandolfi Colleoni et al.

fluid collection in the posterior fossa were included. Inall cases a detailed neurosonographic evaluation, includ-ing multiplanar visualization of the posterior fossa, wasperformed as described previously6,8,12,14–16. The cate-gorization of sonographic findings was based on recentstudies3,4,7 and is summarized in Table 1 and Figure 1.In each case we attempted to evaluate the integrity ofthe cerebellar vermis, as this has been reported to have amajor impact on outcome9,17. Whenever possible, serialsonograms and prenatal MRI were also performed andfetal karyotype was obtained. Prenatal diagnosis was com-pared with autopsy or postnatal MRI findings. A detailedfollow-up was attempted in each case by consultation ofmedical records and interview with the parents and withthe pediatricians taking care of the infants.

RESULTS

A total of 105 fetuses were included in the study(Table 2). The mean gestational age at diagnosis was24 (range, 17–28) weeks. There were associatedmalformations in 46 (43%) cases, in two of which theassociated anomalies were only discovered after birth.These associated malformations included other cerebralabnormalities in 23, chromosomal aberrations in nine

Table 1 Categorization of posterior fossa fluid collections

Findings Diagnosis

Upward rotation of an intactvermis with normal torcular

Blake’s pouch cyst

Cisterna magna depth > 10 mmwith intact and normallypositioned cerebellum

Megacisterna magna

Upward rotation of the vermis(normal or hypoplastic) withelevated torcular

Dandy–Walker malformation

Hypoplastic vermis with normaltorcular

Vermian hypoplasia

Large cisterna magna with smallcerebellum

Cerebellar hypoplasia

Cyst with a mass effect resultingin distortion of the cerebellum

Posterior fossa arachnoid cyst

(trisomy 18, n = 3; trisomy 21, n = 2; trisomy 13, n = 1;triploidy, n = 1; unbalanced translocation, n = 1; mosaic45X/46XX, n = 1), genetic syndromes in three (one eachof Opitz, PHACE and oral-facial-digital syndromes) andmiscellaneous conditions in 13.

The greatest difficulties we encountered in thesonographic categorization of posterior fossa fluidcollections included assessment of the position of the

Figure 1 Categorization of posterior fossa fluid collections on ultrasound: (a,b) Blake’s pouch cyst; (c,d) megacisterna magna; (e,f) vermianhypoplasia; (g,h) Dandy–Walker malformation; (i,j) cerebellar hypoplasia; (k,l) arachnoid cyst of the posterior fossa.


Blacke’s Pouch Cyst Cystegacisterna Magna

Vermian Hypoplasia D-‐W Malforma,on

Cerebellar Hypoplasia Arachinoid Cyst-‐Pos Fossa

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Normal Megacisterna magna Blake’s pouch cyst

Vermian hypoplasia Dandy-‐Walker malforma,on

tentorium

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Standard and Fetal Neurosonography

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Take Home Message

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✦ examina,on of the Fetal CNS should be follow a Standard Protocol

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✦ Examina,on should include at least three axial planes.

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✦ In Each plane the defined landmarks should should be reported as normal or suspicious

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✦ In the presence of possible abnormali,es pa,ent should be referred for detailed neuorsonogram which include mutli-‐planner 3 D Sanning.

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✦ In the presence of possible abnormali,es pa,ent should be referred for detailed neuorsonogram which include mutli-‐planner 3 D Sanning.

✦ 3 D scanning with mul,planner analysis offers comparable analysis to fetal MRI

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Thanks

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fetal neurosonogram jucog feb 2013

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