brain herniation

Cerebral Herniation SyndromesImaging findings and clinical correlation

Cerebral Herniation SyndromesImaging findings and clinical correlation

Thomas E.F. Jongsma1, Esther Sanchez2, Paul R.. Algra1

From the departments of Radiology at

Medical Center Alkmaar, Alkmaar, The Netherlands 1

Free University Medical Center, Amsterdam, The Netherlands 2

Definition of Cerebral Herniation:

Definition of Cerebral Herniation:

Herniation of brain tissue from one compartment (separated by calvarial and /or dural boudaries) to another

CompartmentsCompartments

• Supratentorial• Right

• Left

• Infratentorial

• Spinal

Intracranial compartmentsIntracranial compartments

• Brain tissue in each compartment is contained by (relative) intracranial boundaries:• Falx cerebri

• Tentorium cerebelli

• Skull base (foramen magnum)

Falx cerebri

TentoriumCerebelli

Skull Base(Foramen Magnum)

Neurocranium

Intracranial compartmentsIntracranial compartments

Intracranial CompartmentsIntracranial Compartments

• For each compartment there are laws of Intracranial volume en pressure

• Each compartment abides these laws as good as possible

Intracranial volume Intracranial volume

• Intracranial volume is constant and described by “Monro-Kelly Doctrine”:

• Intracranial components are (almost) non-compressible

• Increase in one volume leads to decrease in another

Vol. Intracranial = V. Brain + V. CSF + V. Blood

Intracranial PressureIntracranial Pressure

http://www.trauma.org/archive/neuro/icp.html

Normal intracranial pressure: 5-15 mmHg


• Pressure components: • Cerebral Perfusion Pressure (CPP)

• Mean Arterial Pressure (MAP)

• Intracranial Pressure (ICP)

• CPP = MAP - ICP

• To maintain CPP: If ICP increases, MAP must increase (autoregulation)


• When MAP cannot increase:• Increased ICP decreases CPP

• Decreased CPP leads to tissue ischemia

• Tissue ischemia leads to edema

• Edema leads to increased ICP

• Further increased ICP leads to:

• Tissue death

When compartmental volume increases and

pressure increases, brain tissue moves from one

compartment to another

When compartmental volume increases and

pressure increases, brain tissue moves from one

compartment to another

Causes of volume increaseCauses of volume increase

• Tumour

• Blood• Subdural • Epidural • Parenchymous

• Ischemia

• Infection

Types of herniation :Types of herniation :• Subfalcine

• Transtentorial• Descending• Ascending

• Tonsillar / Foramen Magnum

• Transcranial / “Fungus Cerebri”

• Miscellaneous• Transalar/ Transsphenoidal • Middle ear encephalocele

Subfalcine HerniationSubfalcine Herniation

Mass effect in cerebral hemisphere forces brain tissue under the falx to

opposite side

Subfalcine Herniation:Structures involved

Subfalcine Herniation:Structures involved

• Falx

• Cingulate Gyrus

• Pericallosal Artery

• Anterior Cerebral Artery

• Corpus Callosum

Subfalcine Herniation: Imaging findings

Subfalcine Herniation: Imaging findings

• Ipsilateral cingulate gyrus is pushed down and under midline falx

• Contralateral cingulate gyrus is compressed

• Depression of ipsilateral corpus callosum and elevation / compression of contralateral corpus callosum

Acquired intracranail Herniation: MR Findings, Laine et al. AJR 1995;165: 967-973


• Falx meningioma with extensive surrounding edema


• Displaced pericallosal artery

• Contralateral cingulate gyrus compressed

• Compression of frontal horns of lateral ventricles

•Ipsilateral cingulate gyrus herniates under falx

•Depression / displacement of corpus callosum

Subfalcine Herniation: Complications and Clinical Signs

Subfalcine Herniation: Complications and Clinical Signs

• Compression of the parafalcine cortex may lead to contralateral leg paresis

• Anterior cerebral artery infarction may lead to ipsilateral frontal infarcts

• Increased ICP leads to somnolence

http://missinglink.ucsf.edu/lm/ids_104_cerebrovasc_neuropath/Case4/CerebralArteryDistribution.htm

Subfalcine Herniation:Complications


• CT Angiogram of patient with subdural hematoma on the right shows displacement of anterior cerebral artery without evidence of infarction



• Right sided mass effect was treated by craniotomy. Hypodensity in the right frontal lobe exemplifies anterior cerebral artery infarct after prolonged subfalcine herniation

Transtentorial HerniationTranstentorial Herniation

Descending

Ascending

Descending Transtentorial Herniation

Descending Transtentorial Herniation

Supratentorial mass effect forces cerebral structures downward through

the opening (incisura) of the tentorium

Descending Transtentorial Herniation:Structures Involved

Descending Transtentorial Herniation:Structures Involved

• Tentorium• Uncus• Parahippocampal gyrus• Perimesencephalic cistern• Mesencephalon • Posterior cerebral artery

(-branches)• Anterior Choroidal Artery• Oculomotor Nerve (NIII)

Descending Transtentorial Herniation:Imaging Findings

Descending Transtentorial Herniation:Imaging Findings

• Asymmetry of ambient cistern (ipsilateral widening / contralateral effacement)

• Widening of contralateral temporal horn of lateral ventricle

• Herniated brain is forced medially and inferiorly beneath tentorium, into perimesencephalic cistern

• Compression of ipsilateral cerebral peduncle by uncus

• Compression of contralateral cerebral peduncle against tentorial edge (Kernohan’s Notch)

Acquired intracranail Herniation: MR Findings, Laine et al. AJR 1995;165: 967-973

Descending Transtentorial HerniationDescending Transtentorial Herniation

Chronic (hypodens) rightsided subdural hematoma with unilateral descending transtentorial herniation

Descending transtentorial herniationDescending transtentorial herniation

• Shift of midline structures

• Blood

• Compression of lateral ventricles

• Widened temporal horn

• Medial, downward displacement of uncus over right tentorial edge


• Herniated uncus in perimesencephalic cistern

• Ipsilateral midbrain compression

• Asymmetric ambient cistern


• Subdural collection on the left with massive descending transtentorial herniation

Descending transtentorial herniationClinical Findings


• Oculomotor (NIII) nerve palsy by compression of third cranial nerve against tentorial edge:

• Exotropic, hypotropic eye position (down and outward)

• Ipsilateral ptosis

• Ipsilateral fixed, dilated pupil

http://scalpelorsword.blogspot.com/2007/01/droopy-eye.html http://www.bartleby.com



• Classic localizing sign: Damage to the pyramidal tracts causes contralateral hemiparesis

• Kernohan’s (Notch) phenomenon: compression of contralateral cerebral peduncle against tentorial edge may result in ipsilateralhemiparesis: “False localizing sign”

Kernohan, J.W., & Woltman, H.W. (1929). Incisura of the crus due to contralateral brain tumor. Archives of Neurology and Psychiatry, 21, 274-287

Descending Transtentorial HerniationComplications

Descending Transtentorial HerniationComplications

• Focal infarction of uncus / parahippocampal gyrus

• Infarction by compression of posterior cerebral artery (-branches) against the tentorial edge

• Infarction by direct compression of the anterior choroidal artery by the uncus

• Brainstem (Duret) hemorrhage

Complications:Vascular structures at risk


• MRI images of the vascular structures around the uncus(posterior cerebral artery and anterior choroidal artery). The latter

originates from the anterior cerebral artery and traverses alongthe uncus dorsally (arrows)

Wiesmann et al. Identification and Anatomic Description of the Anterior Choroidal Artery by Use of 3D-TOF Source and 3D-CISS MR Imaging AJNR Am J Neuroradiol 2001; 22: 305-310



• Anterior choroidal artery compression may lead to infarcts in the posterior limb of the internal capsule and the lateral aspect of the thalamus

• Posterior cerebral artery compression leads to cerebellar and occipital lobe infarction but may also cause thalamic infarcts

http://rad.usuhs.mil/rad/herniation/herniation.html#intro

Complications:Duret Hemorrhage


• Prolonged and progressive transtentorial herniation leads to stretching and eventually rupture of perforating arteries and venules in the brainstem causing punctate hemorrhage



• Extensive descending transtentorial herniation resulting from gunshot wound to the head; Initial CT scan shows Duret

hemorrhage

Ascending Transtentorial Herniation

Ascending Transtentorial Herniation

Posterior fossa mass forces cerebellar structures upwards

through tentorial incisura

Ascending Transtentorial HerniationStructures involved

Ascending Transtentorial HerniationStructures involved

• As in descending transtentorial herniation

• Quadrigeminal plate cistern can be involved

Ascending Transtentorial HerniationImaging findings

Ascending Transtentorial HerniationImaging findings

• Upward displacement of upper cerebellar surface

• Asymmetry/ effacement of ambient cisterns

• Compression of mesencephalon

• Asymmetry/ effacement of quadrigeminal plate cistern

• Often bilateral changes

Ascending Transtentorial HerniationAscending Transtentorial Herniation

Hemorrhagic arteriovenous malformation in the left cerebellar hemisphere with bilateral ascending transtentorial herniation


• Effacement of perimesencephalic cistern

• Upper surface of cerebellar hemisphere ascends through tentorial incisura

• Hemorrhagic lesion


• Effacement of quadrigeminal plate cisterns

• Herniation of cerebellum through tentorial incisura


• Right sided hemorrhagic contusions with mass effect in the right cerebellum causing unilateral ascending

transtentorial herniation


• Unilateral ascending transtentorial herniation on the right side with compression of the right cerebral peduncle

• Dilated temporal horn of left ventricle indicating onset of hydrocephalus

Ascending Transtentorial Herniationspecial notes

Ascending Transtentorial Herniationspecial notes

• Subtle imaging changes

• Less frequent (-ly noted?) than descending herniation

• Often bilateral (no asymmetry)

• Differing appearance of perimesencephalic cisterns with different gantry angles in CT may complicate imaging findings

Ascending Transtentorial HerniationClinical findings and Complications

Ascending Transtentorial HerniationClinical findings and Complications

• Slowly evolving posterior fossa mass effect will often present with signs of hydrocephalus: Headache, nausea, vomiting etc.

• Compression of arteries (posterior cerebral, superior cerebellar) may lead to cerebral / occipital or cerebellar infarction

• Rapidly expanding lesions present with emergency clinical findings due to compression of brainstem nuclei: respiratory failure, coma and death (often coexistent with foramen magnum herniation)

Tonsillar / Foramen Magnum Herniation

Tonsillar / Foramen Magnum Herniation

Posterior fossa mass effect forces cerebellar tonsils downward through

the foramen magnum

Tonsillar HerniationStructures involved

Tonsillar HerniationStructures involved

• Skull base / foramen magnum

• Cerebellar tonsils

• Posterior inferior cerebellar artery

Tonsillar HerniationTonsillar Herniation

• Right sided tonsillar herniation


• Anteriorly displaced cervical myelum

• Inferiorly displaced right cerebellar tonsil

Tonsillar HerniationSpecial notes

Tonsillar HerniationSpecial notes

• (Subtle) extension of cerebellar tonsils in the spinal canal may be seen in normal individuals or in Chiari I malformation

• Extension of 5 mm or more below the foramen magnum is considered abnormal

• Often coexisting with ascending transtentorial herniation

Aboullez etal. Position of cerebellar tonsils in the normal population and in patients with Chiari I malformation: A quantative approach with MR Imaging. J Comp Assist Tomogr 1985;9: 1033-1036


• Chiari I malformation with extension of the cerebellum in the upper cervical spinal canal in a patient with a frontal mass

Tonsillar HerniationClinical findings / Complications

Tonsillar HerniationClinical findings / Complications

• Compression of brain stem nuclei causes respiratory / cardiac failure, coma, death

• Compression of posterior inferior cerebellar artery (PICA) may cause cerebellar infarcts

• Patients with Chiari I malformation can be symptom free but may experience dysesthesia with cervical flexion: “ Lhermitte phenomenon”

Transcranial Herniation “Fungus Cerebri”

Transcranial Herniation “Fungus Cerebri”

Intracranial mass effect forces cerebral structures outward through

(iatrogenic) calvarial defect

Transcranial HerniationTranscranial Herniation

• Decompressive right frontal craniotomy in two patients with severe right sided mass effect. Cerebral structures herniate through calvarial defect. Note that there is no midline shift.

Mass effect is orientated away from contralateral hemisphere.

Transcranial HerniationComplications

Transcranial HerniationComplications

• Decompression usually improves patient survival by lowering intracranial pressure and preventing / undoing intracranial herniations

• Herniation may lead to infarction of herniated tissue

• Exposed brain / dura is prone to infection

MiscellaneousMiscellaneous

Transalar / Sphenoidal Herniation

Middle Ear Encephaloceles



Anterior cranial fossa mass effect forces cerebral structures over the edge of the

sphenoid bone into the middle cranial fossa



• Coexisting with other forms of herniation

• Rarely recognized; Imaging may show displacement of middle cerebral artery

• No specific clinical signs.

• Complications include (rarely) middle cerebral artery infarct

Middle ear (Skull base) encephalocele

Middle ear (Skull base) encephalocele

Cerebral structures bulge through (acquired) skull base defect

NO PRESSURE COMPONENTS

Middle Ear EncephaloceleMiddle Ear Encephalocele

• Left temporal bone defect with protruding cerebral tissue

Papanikolaou et al. Skull Base. 2007 September; 17(5): 311-316


• Cerebral tissue protruding in left temporal bone


• Focal osseous defect in left tegmen

• Protrusion of cerebral structures in epitympanic space surrounding theossicles

Skull base encephaloceleSkull base encephalocele

• May occur anywhere along the skull base

• Osseous defects may be iatrogenic or congenital

• No specific clinical findings

brain herniation

Documents

anterior choroidal

anterior cerebral

contralateral

posterior

ascending

descending

middle ear

sided mass