Brain herniation imaging

BRAIN HERNIATION SYNDROME A Pictorial Review

Thorsang Chayovan R1/Aj.Nuttha 22.11.2014

BRAIN HERNIATION • most common types

– Subfalcine herniation

– descending transtentorial herniation

• Others – Posterior fossa herniations

• ascending transtentorial herniation

• tonsillar herniation

– Transalar herniation

• Rare but important types – transdural/transcranial herniations

– brain displacements across the sphenoid wing

SUBFALCINE HERNIATION

Subfalcine herniation

• most common

• supratentorial mass in one hemicranium

• affected hemisphere pushes across the midline under the inferior "free" margin of the falx, extending into the contralateral hemicranium

Subfalcine herniation: imaging

Axial and coronal images show that

• cingulate gyrus

• anterior cerebral artery (ACA)

• internal cerebral vein (ICV)

are pushed from one side to the other under the falx cerebri.

The ipsilateral ventricle appears compressed and displaced across the midline

Complications

• unilateral obstructive hydrocephalus

– foramen of Monro occlusion

• Periventricular hypodensity with "blurred" margins of the lateral ventricle

– Fluid accumulates in the periventricular white matter

Complications

• When severe, the herniating ACA can be pinned against the inferior "free" margin of the falx cerebri

secondary infarction of the cingulate gyrus

TRANSTENTORIAL HERNIATION

Transtentorial herniations

descending herniations

ascending herniations

Descending transtentorial herniations

• the second most common • a hemispheric mass • initially produces subfalcine herniation • As the mass effect increases,

the uncus of the temporal lobe is pushed medially begins to encroach on the suprasellar cistern hippocampus follows hippocampus effaces the ipsilateral quadrigeminal cistern

both the uncus and hippocampus herniate inferiorly through the tentorial incisura

"Dysautonomia, Multisystem Atrophy and Parkinson's." Dysautonomia, Multisystem Atrophy and Parkinson's. N.p., n.d. Web. 18 Nov. 2014

Descending transtentorial herniation

• Unilateral

• Bilateral ("central“)

– Severe

unilateral DTH: imaging

early

uncus is displaced medially

Ipsilateral aspect of the suprasellar cistern effaced

Ipsilateral prepontine + cerebellopontine angle cistern enlarged

Descending transtentorial herniation

As DTH increases

hippocampus also herniates medially

quadrigeminal cistern compression

midbrain pushed toward the opposite side of the incisura

Descending transtentorial herniation

severe cases

entire suprasellar and quadrigeminal cisterns are effaced.

The temporal horn can even be displaced almost into the midline

bilateral DTH

both hemispheres become swollen

the whole central brain is flattened against the skull base

All the basal cisterns are obliterated

hypothalamus and optic chiasm are crushed against the sella turcica

Complete bilateral DTH

both temporal lobes herniate medially into the tentorial hiatus

midbrain and pons displaced inferiorly through the tentorial incisura

The angle between the midbrain and pons

is progressively reduced from 90° to almost 0°

Complications

• CN III (oculomotor) nerve compression – CN III palsy

• PCA occlusion as it passes back up over the medial edge of the tentorium

– secondary PCA (occipital) infarct

Kernohan notch

• As the herniating temporal lobe pushes the midbrain toward the opposite side of the incisura

– contralateral cerebral peduncle is forced against the hard edge of the tentorium

• Pressure ischemia ipsilateral hemiplegia

– the "false localizing" sign

Duret hemorrhage

"Top-down" mass effect displaces the midbrain inferiorly

closes the midbrain-pontine angle

Perforating arteries from basilar artery

are compressed and buckled

secondary hemorrhagic midbrain infarct

Brainstem hemorrhage

Brainstem hemorrhage

Dorsolateral

Primary injury

Severe DAI

Ventral paramedian

Duret

Hemorrhage in diffuse axonal injury

•Gray-white junction

•Corpus callosum

•Brainstem

hypothalamic and basal ganglia infarcts

complete bilateral DTH

perforating arteries from the circle of Willis compression against the central skull base

hypothalamic and basal ganglia infarcts

POSTERIOR FOSSA MASS: TONSILLAR HERNIATION

ASCENDING TRANSTENTORIAL HERNIATION

Tonsillar herniation

• The cerebellar tonsils are displaced inferiorly and become impacted into the foramen magnum.

• congenital (e.g., Chiari 1 malformation)

– mismatch between size and content of the posterior fossa

• Acquired

– an expanding posterior fossa mass pushing the tonsils downward—more common

– intracranial hypotension: abnormally low intraspinal CSF pressure

• tonsils are pulled downward

Tonsillar herniation: imaging

• Diagnosing tonsillar herniation on NECT scans may be problematic.

Cisterna magna obliteration

Tonsillar herniation: imaging

• MR: much more easily diagnosed

• In the sagittal plane

– the tonsillar folia become vertically oriented

– the inferior aspect of the tonsils becomes pointed

– Tonsils > 5 mm (or 7 mm in children) below the foramen magnum are generally abnormal

• especially if they are peg-like or pointed (rather than rounded)

Tonsillar herniation: imaging

• In the axial plane, T2 scans show that the tonsils are impacted into the foramen magnum

– obliterating CSF in the cisterna magna

– displacing the medulla anteriorly

Complications

• obstructive hydrocephalus

• tonsillar necrosis

ASCENDING TRANSTENTORIAL HERNIATION

Ascending transtentorial herniation

• caused by any expanding posterior fossa mass

– Neoplasms > trauma

Complications

• Acute intraventricular obstructive hydrocephalus

– caused by compression of the cerebral aqueduct

OTHER LESS COMMON HERNIATION: TRANSALAR TRANSDURAL/TRANSCRANIAL HERNIATIONS

Transalar Herniation

• brain herniates across the greater sphenoid wing (GSW) or "ala"

• ascending > descending

Ascending transalar herniation

• caused by a large middle cranial fossa mass

• An intratemporal or large extraaxial mass

Temporal lobe + sylvian fissure + MCA

up and over the greater sphenoid wing

Descending transalar herniation

• caused by a large anterior cranial fossa mass

Gyrus rectus is forced posteroinferiorly over the GSW

displacing the sylvian fissure and shifting the MCA backward

Transdural/Transcranial Herniation

• Rare

• Sometimes called a "brain fungus"

• can be life-threatening

Lacerated dura + a skull defect + increased ICP

Transdural/Transcranial Herniation

• Traumatic

– infants or young children with a comminuted inward skull fracture

• Iatrogenic

– a burr hole, craniotomy, or craniectomy

Transdural/Transcranial Herniation

• MR best depicts these unusual herniations.

• The disrupted dura

– discontinuous black line on T2WI

– Brain tissue, blood vessels, and CSF, are extruded through the defects into the subgaleal space

Kaewlai, R. Imaging of Traumatic Brain Injury. 2013.

Wikipedia

References

• Osborn, Anne G. "Secondary Effects and Sequellae of CNS Trauma."Osborn's Brain: Imaging, Pathology, and Anatomy. Salt Lake City, UT: Amirsys Pub., 2013. N. pag. Print.

• Osborn, Anne G. "Cerebral Vasculature: Normal Anatomy and Pathology."Diagnostic Neuroradiology. St. Louis: Mosby, 1994. N. pag. Print.

• Kaewlai, R. Imaging of Traumatic Brain Injury. 2013. Web.