Brain herniation imaging

CT and MR findings in brain herniation with reasoning

1. BRAIN HERNIATION SYNDROME
A Pictorial Review
Thorsang Chayovan R1/Aj.Nuttha
22.11.2014

4. 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

5. SUBFALCINE HERNIATION

6. 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

9. 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

11. Complications
•unilateral obstructive hydrocephalus
–foramen of Monro occlusion


•Periventricular hypodensity with "blurred"
margins of the lateral ventricle
–Fluid accumulates in the periventricular white
matter

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



 secondary infarction of the cingulate gyrus

14. TRANSTENTORIAL HERNIATION

15. Transtentorial herniations

descending herniations


ascending herniations

16. 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

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

19. Descending transtentorial herniation
•Unilateral
•Bilateral ("central“)
–Severe

20. unilateral DTH: imaging
early

uncus is displaced medially

Ipsilateral aspect of the suprasellar cistern
effaced

Ipsilateral prepontine + cerebellopontine angle
cistern enlarged

22. Descending transtentorial herniation
As DTH increases

hippocampus also herniates medially

quadrigeminal cistern compression

midbrain pushed toward the opposite side of
the incisura

23. Descending transtentorial herniation
severe cases

entire suprasellar and quadrigeminal cisterns
are effaced.

The temporal horn can even be displaced almost
into the midline

25. 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

28. 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°

30. 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

33. 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

37. 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

38. Brainstem hemorrhage
Brainstem hemorrhage
Dorsolateral
Primary
injury
Severe DAI
Ventral
paramedian
Duret

39. Hemorrhage in diffuse axonal injury
•Gray-white junction
•Corpus callosum
•Brainstem

40. 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

44. POSTERIOR FOSSA MASS:
TONSILLAR HERNIATION
ASCENDING TRANSTENTORIAL HERNIATION

46. 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

47. Tonsillar herniation: imaging
•Diagnosing tonsillar herniation on NECT scans
may be problematic.

Cisterna magna obliteration

49. 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)

50. 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

52. Complications
•obstructive hydrocephalus
•tonsillar necrosis

53. ASCENDING TRANSTENTORIAL
HERNIATION

55. Ascending transtentorial herniation
•caused by any expanding posterior fossa mass
–Neoplasms > trauma

58. Complications
•Acute intraventricular obstructive
hydrocephalus
–caused by compression of the cerebral aqueduct

61. OTHER LESS COMMON HERNIATION:
TRANSALAR
TRANSDURAL/TRANSCRANIAL
HERNIATIONS

62. Transalar Herniation
•brain herniates across the greater sphenoid
wing (GSW) or "ala"
•ascending > descending

63. 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

67. 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

68. Transdural/Transcranial Herniation
•Rare
•Sometimes called a "brain fungus"
•can be life-threatening


Lacerated dura + a skull defect + increased ICP

70. Transdural/Transcranial Herniation
•Traumatic
–infants or young children with a comminuted
inward skull fracture
•Iatrogenic
–a burr hole, craniotomy, or craniectomy

71. 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

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

75. Wikipedia

80. 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.