William P. Shuman 1

James V. Rogers 1

Laurence A. Mack 1. 2

Ellsworth C. Alvord, Jr 3

David P. Christie2

Received October 16, 1980; accepted after revision January 15, 1981

, Department of Radiotogy, University Hospitat, SB-05, Unive rsity of Washington, Seatt te, WA 98185.

2 Department of Radio logy, Harborvi ew Medi­ca l Center , ZA-65, 325 Ninth Ave., Seattl e , WA 98104. Address reprint requests to L . A. Mack.

3 Department of Pathology, Universi ty Hospi tal, RJ-05, Un iversity of Washington, Seatt le, WA 98195 .

This article appears in the July / August 1981 AJNR and October 198 1 AJR.

AJNR 2:349-356, July / AU9ust 1981 0 195-6 108 / 8 1/ 0204-0349 $00 .00 © American Roentgen Ray Soc iety

Real-Time Sonographic Sector Scanning of the Neonatal Cranium: Technique and Normal Anatomy

349

A commercially available wide field of view real -time mechanical sector scanner can be used t o image the neonatal cranium. Because of the small transducer head size , the open anterior fontanelle can function as an acoustic window. By thus avoiding bone, higher f requency transducers may be used to improve image resolution. Infants may be scanned quickly without sedation in their isolettes in the neonatal intensive care unit. Sterility of the infant environment is maintained by placing the transducer in a surgical glove. Using this technique , detailed normal anatomy can be seen such as vascular structures , caudate nucleus, thalamus, third ventricle, cavum septum pelluci­dum, and the thalamocaudate notch. Angled coronal and sagittal sonographic anatomy is correlated with neonatal cadaver brain sect ions sliced in similar planes centered on the anterior fontanelle .

The mechanical sector scanner has advantages over other real-time devices including improved image resolution , a wider field of view, and a smaller area of transd ucer sk in contact. These unique assets are particularly applicable to the evaluati on of the neonatal cranium . The small transducer of a sector scanner can eas il y be held in contact with the open anterior fontanelle using it as an acousti c window. Thi s window avoids bone and makes possible the use of a higher freq uency transducer resulting in improved reso lution . We report our technique for neonatal crani al sonography using a mechanical sector scanner. Norm al intracran ial anatomy seen in angled coron al and sag ittal planes is presented along with correlating neonatal cadaver spec imens.

Materials and Methods

Seventy-two neonates who were c linica lly suspect for intrac ran ial hemorrhage were examined in their incubators in the neonatal intensive care unit (N ICU) using a mechanical secto r scanner (ATL Mark III Imag ing System) . Thi s has three interna lly focused 5 MHz transducers positioned on a rotating element. Each transducer is ac ti vated through the same 90 0 arc produc ing 18 to 45 images / sec. The tran sducer sk in contact area is 1.5 x 1.5 cm. Images are generated in a c ircular sector format produc ing a pie-shaped fie ld of view with the narrow, sli ghtly truncated end representing the small area of skin contact (f ig . 1). Images are processed through a real-time d igital scan converter and projec ted on a video display system. A freeze frame mode is available so that video images may be recorded on 70 mm film .

In the NICU , the real-tim e sonographic unit is posit ioned beside th e infant incubator . It is not necessary to move the incubator or adjacent support eq uipment or to disturb the oxygen and temperature controlled environment. A small amount of aqueous acoustic coupling gel is placed in the thumb of a steril e size 8 latex surgica l glove . The transducer head is inserted into the thumb of the glove whic h then serves as a steril e barri er (fig . 2). A small amount of acoustic gel is applied to the an terior fontanell e. The glove-encased transducer is passed through th e port of the incubator and placed on th e anterior fontanelle in the coronal p lane (fi gs. 3 and 4). By rock ing the tran sd ucer back and forth , the ventricular system as well as peri ven tricular struc tures can be examined (f ig . 5). Freeze-frame images

350 SHUMAN ET AL. AJNR:2, Ju ly / Augusl 1981

Fig. 1.-End-on frontal d iagram of hand-held unit. The three transducers ro tate in a complete c irc le but are ac ti vated through only a 90 ° arc produc ing a sec lor image wh ich widens as it deepens. Area of skin contac t is small.

Fig . 2 .-Hand-held unit is placed in surgical g love to maintain steri li ty . Transducer head fi ts into thumb o f g love.

are record ed at the level of the anterior part of the frontal horns, the caudate nuc lei in th e pl ane of the midd le cerebral arteries, the th ird ventri c le, the midbody of th e thalamus, and the atria of the latera l ventric les in the region of th e c horoid plexus. The transducer is th en turned 90° into the sagitta l plane and rocked in a simil ar fashion (figs. 4 and 6) . Sagittal freeze-frame images are recorded at the mid line as well as at the level of both caudate nuc lei and the lateral parts of both lateral ventric les.

Anatomic-pathologic correlation with sonograms was obtained by cutting two neonatal brains in pl anes parall el to the pl anes of th e sonog raphic images generated through th e anterior fontanelle. Th e first brain spec imen was from a term infant whose death 1 week after delivery was attributed to sudden infant death syndrome. At autopsy the location of the anterior fontanell e was marked on the superior su rface of th e brain . Tile brain was then removed from the sku ll and scanned in a water bath to insure that it was sonographi ­call y normal. Next, the brain was sliced five t imes in the coronal plan e with the superior part of each slice beginning just below the anterior fontanelle. The slices extended inferiorl y in five different

Fig . 3 .- Transducer head is placed on anterio r fontanelle and rocked back and forth to sweep sonographic beam through cerebral tissue.

angles relative to the canthomeatal li ne as d iag rammed in figure 5 . These cuts were designed to be parallel to th e sonographic beam and show the same anatomy as th e c lini ca l sonog rams in figures 7 A, SA, 9A, 1 OA, and 11 A. A second brain from a simi lar infant was sliced in fi ve sag ittal planes centered on the anterior fontanelle , as seen in figure 6. The placement of th ese cuts was designed to be parall el to the sonog raphic beam and show the same anatomy as figures 1 2A, 13A, and 14A.

Results and Observations

Coronal Sec tions

Figure 7: co ron al image with the transd ucer placed on the anteri o r fontane lle so that the sonog raphic beam is ang led 80 ° relati ve to the can thomeata l line (fig. 5 , plane 1). The plane of section inc ludes the hypoechoic slitlike frontal horns of the lateral ventric les (5) and the fluid-fill ed cavum of the septum pe lluc idum (6), which lies between the frontal horn s and is a normal structure in preterm infants. The relatively echoic heads of the caudate nuclei (7) lie inferi or to the lateral parts of the frontal horns. Also we ll seen are the bony landmarks, wh ich inc lude the an terior c linoids (1 0) and the f loor of the middle cranial fossa (12). The paren­c hyma of the temporal lobes (11) and frontal lobes (3) has a low echogenic ity relative to the caudate nuclei. Specific gyri such as the gyrus rectus (8) and c ingulate gyrus (1) can be identified by the echogen ic subarachnoid c isterns that outline their boundaries . Vascular anatomy demon­strated includes the pericallosal arte ry (2) and the middle cerebral arteries (9) in the sylvian f issure (13). These arterial struc tures are identified by their pulsations as well as their location .

Figure 8: coronal secti on 70 ° to the canthomeatal line (fig. 5 , plane 2) with the transd ucer on the anteri or fontanelle ang led 10° posteri or to fi gure 7 A. This secti on inc ludes the lateral ventr ic les (5), the foram ina of Monro (1 4), the th ird ventricle (15) , and the parahippocampal gyrus (16) . The bony landmarks of the greater w ing of the sphenoid (17)

AJNR:2, July / August 1981 SECTOR SCANNING OF NEONATAL CRANIUM 35 1

4 5 Fig. 4 .- lmag ing is centered on anterior fontanelle in both coronal and

sag ittal planes. Fig . 5.- Transducer is rocked on anteri or fontanelle so that angled coronal

images may be recorded at f ive different levels; neonatal cadaver brain was sliced in these same planes (see figs. 7 -11 ).

and the floor of the middle cranial fossa (12) are dense bands of linear echoes defining the inferior extent of the cranium . The homogenous low echogenic brain paren­chyma of the temporal lobe (11) is again defined w ith the cingu late gyrus (1) and parahippocampal gyrus (16) bounded by the hyperechoic subarachnoid cisterns. The peri callosal artery (2) is seen in the midline pulsating supe­rior to the hypoechoic corpus callosum (4) . The corpu s callosum is a homogenous hypoechoic bridge of tissue just superior to the medial parts of the lateral ventric les. The lateral ventricles (5) are arcuate and slit li ke with the foramin a of Monro (14) extending from their inferior medial margins . The fluid-filled hypoechoic cavum of the septum pellucidum (6) lies between the lateral ventricles and must be distin­guished from the more inferiorly placed third ventricle (1 5) . Adjacent to the inferolateral margins of the lateral ventri oles are the bodies of the caudate nuclei (7).

Figure 9: coronal section 60° to the canthomeatal line (fig. 5 , plane 3) with the transducer on the anterior fontanelle ang led 10° posterior to figure SA . This plane includes the lateral ventric les (5) , the body of the caudate nucleus (7), the thalamus (22) , the cerebral peduncles (19) , and the upper extent of the pons (20). The ventricles continue to be arcuate and slitli ke with the perica llosal artery (2) pulsating just superior to the hypoechoic corpus callosum (4) . The body of the caudate nucleus (7) is again noted to be more echogenic than the surrounding white matter. The thalami (22) are large bilateral medium echo level structures inferior, medial , and posterior to the caudate nuclei. The cerebral peduncles (19) extend inferiorly in V-shaped hypoechoic bands that fuse at the pons (20), an equally hypoechoic structure. Bright specular echoes lateral to the pons repre­sent the edges of the tentorium (21) and the c horoidal fissure (34).

Figure 10: coronal section 50 ° to the canthomeatal line (fig . 5 , plane 4) with the transducer centered on the anterior fontanelle and angled 10° posterior to figure 9A . The plane

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Fig. 6 .- Transducer is turned 90° and rocked on the anteri or fontanelle so that angled sag ittal images may be recorded of midline and two lateral levels on each side; neonatal cadaver brain was sli ced in these same planes (see figs. 12-1 4) .

of thi s section inc ludes the lateral ventri c les (5), the thala­mus (22) , the quadrigeminal c istern (23), and the ce rebellar vermi s (24) . The lateral ventricles are again slit like w ith the echoic caudate nuc lei (7) in a simil ar inferolatera l pos ition relati ve to the ventric les. The large hypoechoic thalami (22 ) are inferi or to the ventric les and are separated dorsocau­dall y by the echoic quadrigeminal c istern (23). The parahi p­pocampal gyru s (16) bord ers the infero lateral marg ins of the quadrigeminal c istern . The hi ghl y echogenic ve rmis of the cerebellum (24) is the most inferi or structure. The slop­ing tentorial marg ins (2 1) outline the superi or aspect of the cerebellum , with the pari etal bone identified laterall y (25).

Figure 11 : coronal section 40 ° to the canthomeatal line (fig . 5, plane 5) with the transducer on the anteri or fontanelle angled 10° posterior to fi gure 10A. Thi s pl ane of sec ti on inc ludes the atri a of the lateral ventric les (5), the spl enium of the corpu s callosum (27) , and the vermi s of the ce rebel­lum (24). The pul sating peri ca ll osa l artery (2) continues in the midline between the superi o r marg ins of the ventric les . The pulsatil e highly echogenic c horoid plexus (26) can be seen lying along the inferom edial portion of the atri a of the lateral ventric les. The larg e hypoechoic structure separating the lateral ventric les is the splenium of the corpu s co llosum (27) . The posteri o r part of the sylvian fi ssure (1 3) is seen as a horizontal band of linear echoes lateral to the ventric les.

Sagitta l Sec tions

Figure 12: midline sag ittal plane with the transducer cen­tered on the anterior fontanell e (fi g . 6, plane 1). Thi s sect ion inc ludes the pulsatil e callosa l margin al (2S) and peri callosal arteri es (2) whi c h are immedi ately superi or to the large flui d­filled cavum septum pelluc idum and cavum vergae (35). Inferior to the cava is the fluid-fill ed anechoic third ventric le (15) . Extending from the posteri o r inferi o r marg in of the third ventri c le is the ce rebral aqued uct (29) whi ch traverses inferiorl y over the hypoechoic midbrai n (1 S). The pons (20)

352 SHUMAN ET AL. AJNR:2, July/ August 1981

A 8 Fig . 7.-Coronal sec ti on 80° to canthomeatalline is descri bed in text under Results and Observations.

A 8 Fig. 8 . -Coronal secti on 70 ° to canthomeatal line is described in text under Results and Observat ions.

AJN R:2. July/ August 1981 SECTOR SCANN ING OF NEONATAL CRANIUM 353

A B Fig . 9. - Coronal sec tion 60° to canthomeatal line is descri bed in tex t under Results and Observation s.

A B Fig. 1 O. - Coronal section 50.0 to cant hom eata I line is descri bed in text under Resu lts and Observations.

3 54 SHUMAN ET AL. AJNR:2, July / August 1981

A B Fig . 11 .- Coronal section 40 0 to canthomeatalline is described in text under Results and Observations.

A B Fig . 12.-Midline sagittal secti on centered on anteri or fontanelle is described in tex t under Results and Observations.

and the medulla (30) are continuous with the midbrain and are of equally low echogenic ity . Posterior to the pons is the very echogenic vermis of the cerebellum (24). The specular occ ipital bone (31) forms the inferior margin of the posterior fossa .

Figure 13 : sagittal plane with the transducer centered on the anteri or fontanelle and angled 10° lateral to the midline (fig . 6, plane 2). The atrium of the lateral ventric le (5) is filled with the pulsatil e , highly echogenic choroid plexus (26) . The la rge hypoechoic thalamus (22) is inferi or to the convex ity of the lateral ventric le , with the more echoic caudate nuc leus (7) lying just anteri or to the thalamus. At the superior part of

the junction line between them, the thalamocaudate notch (32) can be identified . The inferior bony margins are formed by the floor of the anterior fossa (33) and the occipital bone (31 ).

Figure 14: sagittal plane with the transducer on the an­terior fontanelle angled 20° lateral to the midline (fig . 6, plane 3). This plane of section includes the fluid-filled atrium , occipital horn , and temporal horn of the lateral ventricles (5 , 3 6 , 37 , respectively) . The highly echoic choroid plexus (26) can be seen running along the floor of the atrium into the temporal horn . Encased by the sweep of the ventricle is the lateral part of the thalamus (22) .

AJ NR:2. July / Aug ust 1981 SECTOR SCANNING OF NEONATAL CRANIUM 355

A 8 Fig. 13. - Sag ittal section 10 ° lateral to midline is described in tex t under Results and Observations.

A 8 Fig. 14. - Sagittal secti on 20° lateral to midline is described in text under Resu lts and Observations .

Discussion

Sonography of the head was first performed in 1955 and involved the use of A-mode to detect midline structures and obtain a crude estimation of ventricular size [1] . Two dimen­siona l bidirectional echoencephalography appeared in 1963 and was a sign ificant techni cal advance since it prov ided better information about ventri cular size as well as intracra­nial spatial relationships [2, 3]. However, only a relat ively few highly specular structures could be demonstrated. The next technical improvement was the app licat ion of gray scale compound static scan ners to echoencephalography, which markedly improved image information content [4-6].

Numerous cran ial structures, includ ing ventricles, brain stem, basa l ganglia, and brain parenchyma , cou ld be visu­ali zed . The accuracy of compound gray scale echoence­phalog raphic measurements has been we ll establi shed and compares with those obtained from computed tomog raphy (CT) [7 , 8]. Gray scale compound imaging offers several advantages over CT: less time required per study, lack of ion izing radiation , significant ly lower cost, elimination of the need for sedation, and fewer artifacts [8]. However, for both CT and compound gray scale sonography, a newborn pa­tient must be removed from the protective environment of the NICU and the infant incubator.

356 SHUMAN ET AL. AJNR :2. July / August 198 1

Thi s problem is so lved by using a compact high resoluti on real-time sonog raphic scanner that may be easil y trans­ported to the NICU . The infant can be scanned in the inc ubator without sedation and w ithout disturbing support equipment. Rapid identificati on of intracranial anatomy is made possible by the freedom of movement of the hand­held transducer and the rea l-time display. Such a technique has been reported using linear array rea l-time eq uipment [9. 10]. However . several authors recog nize problems with the use of linear array real-time related to the size to the trans­ducer head. which is 8- 16 cm long [7. 12]. Since only a small part of the large fl at transducer face is in contact with the sk in of the c urved in fant skull . onl y a narrow rectangular fi eld of vi ew is obtained. The mechnica l sector scanner produces a 90 ° sector arc image using a small area of sk in contac t to generate a fi eld of view that broadens as it extends away from the transducer. Thi s is a significant improvement in fi eld size compared with linear array rea l­

time scanners. Several authors have reported the use of the anteri or

fontanell e as an acousti c window into the neonatal c ranium [10- 11 . 12. 15 . 16]. The small area of skin contact required fo r a sector scanner makes it parti c ularl y suited to thi s technique. By imag ing through the anteri o r fontanelle and thus avoiding bone. higher frequency transducers may be used whic h result in improved image reso lution. Pl ac ing the transd ucer inside a new steril e surg ical glove for each neonate helps control c ross-contaminati on yet does not deg rade the image or inc rease acousti c gai n requirements.

The advent of improved neonatal care in high ri sk nurser­ies has meant the survival of more premature infants. in­creas ing the c linical demand for safe. detailed intrac ranial imag ing . Our experi ence demonstrates that a considerable amount of informati on about norm al neonatal intracranial anatomy can be obtained usi ng real-time sector scanning th rough the ante ri or fontanelle.

REFEREN CES

1. Leksell L . Echo-encephalog raphy. I. Detection of intrac ranial com plications fo llowing head injury. Acta Chir Scand 1956;1 10 :301 -315

2 . deVlieger M. Evaluation of echoencephalog raphy. JCU 1980;8: 39- 47

3 . Kassoff G . Garrett WJ . Radavanovich G. Ult rasoni c atlas of normal brai n of infant. Ultrasound Med Bioi 1974; 1 : 259- 266

4 . Babcock OS. Han BK . LeQuesne GW. B-Mode gray scale ultrasound of th e head in th e newborn and young infant. AJR 1980; 13 4 : 4 57 -468

5. Johnson ML. Mack LA. Rumack CM. Frost M . Rashbaum C. B­mode encephalog raphy in th e norm al and high ri sk infant. AJR 1979; 133: 375- 381

6. Denkhaus H. Winsberg F. Ultrason ic measurement of the fetal ventricular system. Radiology 1979; 13 1 : 781 - 787

7 . Skolnick ML. Rosenbaum AE. Matzuk T. Guthkelch AN. Heinz ER . Detection of d ilated cerebral ventric les in infants: a co rrel­ati ve stud y between ultrasound and co mputed tomography. Radiology 1979;13 1 :447-45 1

8 . Morgan CL . Trought WS. Rothman SJ. Jimenez JP. Compari­son of gray-scale ultrasonog raphy and computed tomography in th e evaluation of macrocrania in infants. Radiology 1979;132 : 1 19 -1 23

9 . Pape KE . Blackwell RJ . Cusick G. et a!. Ultrasound detection of brain damage in preterm infants. Lancet 1979;1 : 1261-1264

10. London DA. Carroll BA. En zmann DR. Sonog raphy of ventric­ular size and germin al matri x hemorrh age in premature infants. AJNR 1980; 1 : 295- 300

1 1. Ben-Ora A. Eddy L. Hatch G. Solida B. The ante rior fontanelle as an acoustic window to the neonatal ventri cular sys tem. JCU 1980;8: 65- 67

12. Cooke RW. Ultrasound examination of neonatal heads (letter) . Lancet 1979;2 : 38

13. Grant EG . Schellinger D. Borts FT. et a!. Real-time sonog raphy of th e neonatal and in fant head. AJNR 1980;1 :487- 492

14. Edwards MK . Brown DL. Muller J . Grossman CB. Chua GT. Cri bside neurosonog raph y: real-time sonography for intracra­nial in vestigation of the neonate. AJNR 1980; 1 : 501 -505