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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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IntracranialPressure
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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IntracranialPressure
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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SubfalcineHerniation
Falx meningioma with extensive surrounding edema
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SubfalcineHerniation
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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Descendingtranstentorialherniation
Herniated uncus in
perimesencephalic
cistern
Ipsilateral midbrain
compression
Asymmetric ambientcistern
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Descendingtranstentorialherniation
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
Ascending Transtentorial Herniation
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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
Ascending Transtentorial Herniation
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AscendingTranstentorialHerniation
Hemorrhagic arteriovenous malformation in the left cerebellar
hemisphere with bilateral ascending transtentorial herniation
Ascending Transtentorial Herniation
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AscendingTranstentorialHerniation
Effacement ofperimesencephaliccistern
Upper surface ofcerebellar hemisphereascends throughtentorial incisura
Hemorrhagic lesion
Ascending Transtentorial Herniation
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AscendingTranstentorialHerniation
Effacement ofquadrigeminal plate
cisterns
Herniation of
cerebellum through
tentorial incisura
Ascending Transtentorial Herniation
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AscendingTranstentorialHerniation
Right sided hemorrhagic contusions with mass effect in theright cerebellum causing unilateral ascending
transtentorial herniation
Ascending Transtentorial Herniation
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AscendingTranstentorialHerniation
Unilateral ascendingtranstentorialherniation on theright side with
compression of theright cerebralpeduncle
Dilated temporalhorn of left ventricleindicating onset ofhydrocephalus
Ascending Transtentorial Herniation
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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
Ascending Transtentorial Herniation
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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
Tonsillar Herniation
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TonsillarHerniation
Right sided tonsillar herniation
Tonsillar Herniation
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TonsillarHerniation
Anteriorly displaced
cervical myelum
Inferiorly displaced
right cerebellar tonsil
Tonsillar Herniation
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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
Tonsillar Herniation
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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
Tonsillar Herniation
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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
MiddleEarEncephalocele
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Cerebral tissue
protruding in left
temporal bone
MiddleEarEncephalocele
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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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