This document discusses different types of brain herniation seen on imaging. The most common types are subfalcine herniation and descending transtentorial herniation. Subfalcine herniation occurs when one hemisphere pushes across the midline under the falx cerebri. Descending transtentorial herniation occurs when the temporal lobe and hippocampus herniate through the tentorial incisura. Other types discussed include tonsillar herniation, ascending transtentorial herniation, and rare transdural herniations. Complications of herniations include hydrocephalus, nerve compression, and infarcts.

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.