88862534 Brain Herniation

7/29/2019 88862534 Brain Herniation

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Cerebral Herniation Syndromes

Imaging findings and clinical correlation


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Definition of Cerebral

Herniation:

Herniation of brain tissue from one

compartment (separated by calvarial

and /or dural boudaries) to another


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Compartments

Supratentorial

Right

Left

Infratentorial

Spinal


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Intracranialcompartments

Brain tissue in each compartment is

contained by (relative) intracranial

boundaries:

Falx cerebri

Tentorium cerebelli

Skull base (foramen magnum)


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Intracranialcompartments

Neurocranium

Falx cerebri

TentoriumCerebelli

Skull Base

(Foramen Magnum)


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IntracranialCompartments

For each compartment there are laws of

Intracranial volume en pressure

Each compartment abides these laws as

good as possible


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Intracranialvolume

Intracranial volume is constant and describedby Monro-Kelly Doctrine:

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

Intracranial components are (almost) non-

compressible Increase in one volume leads to decrease inanother


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IntracranialPressure

Normal intracranial pressure: 5-15 mmHg

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


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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)


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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


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When compartmental

volume increases and

pressure increases, braintissue moves from one

compartment to another


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Causesofvolumeincrease

Tumour

Blood Subdural

Epidural

Parenchymous

Ischemia

Infection


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Typesofherniation:

Subfalcine

Transtentorial Descending

Ascending

Tonsillar / Foramen Magnum

Transcranial / Fungus Cerebri

Miscellaneous Transalar/ Transsphenoidal

Middle ear encephalocele


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SubfalcineHerniation

Mass effect in cerebral hemisphere

forces brain tissue under the falx to

opposite side


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Subfalcine Herniation:Structures involved

Falx

Cingulate Gyrus

Pericallosal Artery Anterior Cerebral

Artery

Corpus Callosum

S f


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Subfalcine Herniation:Imaging findings

Ipsilateral cingulate gyrus is pushed down andunder midline falx

Contralateral cingulate gyrus is compressed

Depression of ipsilateral corpus callosum andelevation / compression of contralateral corpuscallosum

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


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Falx meningioma with extensive surrounding edema


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Displacedpericallosalartery

Contralateralcingulate gyruscompressed

Compression

of frontal hornsof lateralventricles

Ipsilateralcingulate gyrusherniates underfalx

Depression /displacement ofcorpuscallosum

Subfalcine Herniation:


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Subfalcine Herniation:

Complications and Clinical Signs

Compression of the parafalcine cortex may lead tocontralateral leg paresis

Anterior cerebral artery infarction may lead to ipsilateralfrontal infarcts

Increased ICP leads to somnolence

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

S bf l i H i ti


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Subfalcine Herniation:Complications

CT Angiogram of

patient with subdural

hematoma on the right

shows displacement of

anterior cerebral artery

without evidence of

infarction

S bf l i H i ti


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Subfalcine Herniation:Complications

Right sided mass

effect was treated by

craniotomy.

Hypodensity in theright frontal lobe

exemplifies anterior

cerebral artery

infarct afterprolonged subfalcine

herniation


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TranstentorialHerniation

Descending

Ascending


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Descending

Transtentorial Herniation

Supratentorial mass effect forces

cerebral structures downward through

the opening (incisura) of thetentorium


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Descending Transtentorial Herniation:Structures Involved

Tentorium

Uncus

Parahippocampal gyrus

Perimesencephalic cistern

Mesencephalon

Posterior cerebral artery(-branches)

Anterior Choroidal Artery

Oculomotor Nerve (NIII)


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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 beneathtentorium, into perimesencephalic cistern

Compression of ipsilateral cerebral peduncle by uncus

Compression of contralateral cerebral peduncle against tentorialedge (Kernohans Notch)

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


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DescendingTranstentorialHerniation

Chronic (hypodens) rightsided subdural hematoma with

unilateral descending transtentorial herniation


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Descendingtranstentorialherniation

Shift of midline structures

Blood

Compression of lateralventricles

Widened temporal horn

Medial, downwarddisplacement of uncusover right tentorial edge


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Herniated uncus in

perimesencephalic

cistern

Ipsilateral midbrain

compression

Asymmetric ambientcistern


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Subdural collection on the left with massive descendingtranstentorial herniation

Descending transtentorial herniation


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Descending transtentorial herniationClinical Findings

Oculomotor (NIII) nerve palsy by compression of thirdcranial nerve against tentorial edge:

Exotropic, hypotropic eye position

(down and outward)

Ipsilateral ptosis

Ipsilateral fixed, dilated pupil

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

Descending transtentorial herniation


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Descending transtentorial herniationClinical Findings

Classic localizing sign: Damage tothe pyramidal tracts causes

contralateral hemiparesis

Kernohans (Notch) phenomenon:compression of contralateral

cerebral peduncle against tentorial

edge may result in ipsilateral

hemiparesis: 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 Herniation


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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:


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Complications:Vascular structures at risk

MRI images of the vascular structures around the uncus(posterior cerebral artery and anterior choroidal artery). The latteroriginates from the anterior cerebral artery and traverses along

the 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

Complications:


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Complications:Vascular structures at risk

Anterior choroidal arterycompression may lead toinfarcts in the posteriorlimb of the internalcapsule and the lateralaspect of the thalamus

Posterior cerebral arterycompression leads to

cerebellar and occipitallobe infarction but mayalso cause thalamicinfarcts

Complications:


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Complications:Duret Hemorrhage

Prolonged andprogressive

transtentorial

herniation leads tostretching andeventually rupture ofperforating arteries and

venules in thebrainstem causingpunctate hemorrhage

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

Complications:


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Complications:Duret Hemorrhage

Extensive descending transtentorial herniation resulting from

gunshot wound to the head; Initial CT scan shows Duret

hemorrhage


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Ascending

Transtentorial Herniation

Posterior fossa mass forcescerebellar structures upwards

through tentorial incisura

Ascending Transtentorial Herniation


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sce d g a ste to a e at oStructures involved

As in descending transtentorial herniation

Quadrigeminal plate cistern can be involved



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gImaging findings

Upward displacement of upper cerebellar surface

Asymmetry/ effacement of ambient cisterns

Compression of mesencephalon

Asymmetry/ effacement of quadrigeminal plate cistern

Often bilateral changes



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AscendingTranstentorialHerniation

Hemorrhagic arteriovenous malformation in the left cerebellar

hemisphere with bilateral ascending transtentorial herniation



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Effacement ofperimesencephaliccistern

Upper surface ofcerebellar hemisphereascends throughtentorial incisura

Hemorrhagic lesion



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Effacement ofquadrigeminal plate

cisterns

Herniation of

cerebellum through

tentorial incisura



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Right sided hemorrhagic contusions with mass effect in theright cerebellum causing unilateral ascending

transtentorial herniation



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Unilateral ascendingtranstentorialherniation on theright side with

compression of theright cerebralpeduncle

Dilated temporalhorn of left ventricleindicating onset ofhydrocephalus



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special notes

Subtle imaging changes

Less frequent (-ly noted?) than descendingherniation

Often bilateral (no asymmetry)

Differing appearance of perimesencephaliccisterns with different gantry angles in CT maycomplicate imaging findings



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Clinical findings and Complications

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

Compression of arteries (posterior cerebral, superiorcerebellar) may lead to cerebral / occipital or cerebellarinfarction

Rapidly expanding lesions present with emergency

clinical findings due to compression of brainstem nuclei:respiratory failure, coma and death (often coexistent withforamen magnum herniation)


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Tonsillar / Foramen Magnum

Herniation

Posterior fossa mass effect forces

cerebellar tonsils downward through

the foramen magnum

Tonsillar Herniation


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Structures involved

Skull base / foramen magnum

Cerebellar tonsils

Posterior inferior cerebellar artery



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TonsillarHerniation

Right sided tonsillar herniation



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TonsillarHerniation

Anteriorly displaced

cervical myelum

Inferiorly displaced

right cerebellar tonsil



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Special notes

(Subtle) extension of cerebellar tonsils in thespinal canal may be seen in normal individuals orin Chiari I malformation

Extension of 5 mm or more below the foramenmagnum 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



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TonsillarHerniation

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



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Clinical findings / Complications

Compression of brain stem nuclei causesrespiratory / 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 dysesthesiawith cervical flexion: Lhermitte phenomenon


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Transcranial Herniation

Fungus Cerebri

Intracranial mass effect forces

cerebral structures outward through

(iatrogenic) calvarial defect

TranscranialHerniation


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Decompressive right frontal craniotomy in two patients withsevere right sided mass effect. Cerebral structures herniatethrough calvarial defect. Note that there is no midline shift.

Mass effect is orientated away from contralateral hemisphere.

Transcranial HerniationC li ti


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Complications

Decompression usually improves patientsurvival by lowering intracranial pressureand preventing / undoing intracranialherniations

Herniation may lead to infarction ofherniated tissue

Exposed brain / dura is prone to infection


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Miscellaneous

Transalar / Sphenoidal Herniation

Middle Ear Encephaloceles


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Transalar / Sphenoidal

Herniation

Anterior cranial fossa mass effect forces

cerebral structures over the edge of the

sphenoid bone into the middle cranial fossa

Transalar / SphenoidalHerniation


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Herniation

Coexisting with other forms of herniation

Rarely recognized; Imaging may show

displacement of middle cerebral artery

No specific clinical signs.

Complications include (rarely) middle cerebralartery infarct


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Middle ear (Skull base)

encephalocele

Cerebral structures bulge through

(acquired) skull base defect

NO PRESSURE COMPONENTS

MiddleEarEncephalocele


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Left temporal bone defect with protruding cerebraltissue

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



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Cerebral tissue

protruding in left

temporal bone



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Focal osseous defectin left tegmen

Protrusion of cerebralstructures in

epitympanic spacesurrounding the

ossicles

Skullbaseencephalocele


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May occur anywhere along the skull base

Osseous defects may be iatrogenic or

congenital

No specific clinical findings

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88862534 Brain Herniation