CNS Malformations and Herniations

Question 1

Defective closure of the rostral end of the neural tube

Absent cranial vault, brain

Answer 1

Anencephaly

Question 2

Defective closure of the caudal end of the neural tube

Malformed spinal cord and meninges protrude through bony defect in spinal column and overlying skin

Maternal folate deficiency during pregnancy may contribute to neural tube closure defects

Answer 2

Myelomeningocele

Question 3

Deficient posterior fossa volume in the developing skull

Herniation of cerebellar vermis through the foramen magnum into the cervical spinal canal

Downward displacement and malformation of the brainstem

Kinks in the neural axis above and below posterior fossa

Medulla overrides cervical spinal cord

Roof of the midbrain protrudes as a beak-like deformity

Lumbosacral meningomyelocele

Hydrocephalus

Answer 3

Arnold Chiari II Malformation

Question 4

Arrested hindbrain development

Absent of hypoplastic cerebellar vermis, cystically dilated fourth ventricle, enlarged posterior fossa, hydrocephalus

Answer 4

Dandy Walker Malformation

Question 5

Cingulate gyrus is pushed under the falx cerebri by expanding frontal/parietal mass

May compress branches of anterior artery (ACA) with infarction in ACA distribution

Answer 5

Subfalcine (cingulate) brain herniation

Question 6

Medial-most part of the temporal lobe (uncus) is pushed out over the edge of the tentorium and wedged into the cleft between the tentorium and cerebral peduncle of the midbrain

Compresses the oculomotor nerve (CN III) ipsilateral fixed dilated pupil

May push midbrain against contralateral tentorium ipsilateral hemiparesis from peduncular compression

Compresses posterior cerebral artery (PCA) with infarction in PCA distribution

Answer 6

Transtentorial (uncal, hippocampal) brain herniation

Question 7

Inferior-most part of the cerebellar hemispheres (tonsils) are pushed into the foramen magnum compressing respiratory centers of the medulla

Tonsillar herniation may result from spinal tap in a patient with increased intracranial pressure (ICP)

Check for papilledema, obtain CT/MRI before tapping patient with suspected increase in ICP

Answer 7

Tonsillar (cerebellar) brain herniation