Chiari 2

KEY FACTS

TERMINOLOGY

• Complex hindbrain malformation

• Virtually 100% associated with neural tube closure defect,

usually lumbar myelomeningocele (MMC)

IMAGING

• Crowded posterior fossa, widened tentorial incisura, tectal

beaking, inferior vermian displacement

• Cascade or waterfall of cerebellum/brainstem downward

○ Uvula/nodulus/pyramid of vermis → sclerotic peg

○ Cervicomedullary kink (70%)

○ Towering cerebellum → compresses midbrain,

associated beaked tectum

○ 4th ventricle elongated with no posterior point

(fastigium)

• Lacunar skull: Focal calvarial thinning with scooped-out

appearance

TOP DIFFERENTIAL DIAGNOSES

• Chiari 1 malformation

• Chiari 3 malformation

• Intracranial cerebral spinal fluid (CSF) hypotension

• Severe, chronic shunted hydrocephalus (congenital)

PATHOLOGY

• Secondary to sequelae of CSF leakage through open spinal

dysraphism during gestation (4th fetal week)

• Methylenetetrahydrofolate reductase (MTHFR) mutations

→ abnormal folate metabolism

• Spine- and brain/skull-associated anomalies common

(myelomeningocele ~ 100%)

CLINICAL ISSUES

• Progressive hydrocephalus

○ Most common cause of death in myelomeningocele

patients

(Left) Sagittal graphic of the

posterior fossa and upper

cervical spine demonstrates

characteristic findings of

Chiari 2 malformation,

including callosal dysgenesis

﬊, tectal beaking ſt, small

posterior fossa, vermian

ectopia ﬇, and medullary

kinking st. (Right) Sagittal

T1WI MR reveals

characteristic Chiari 2

malformation findings. Note

the tectal beaking ſt, vermian

displacement ﬇ through the

foramen magnum, large

massa intermedia st, and

dysplastic corpus callosum ﬊.

(Left) Sagittal T2WI MR

confirms characteristic

findings of Chiari 2

malformation, including tectal

beaking ſt, vermian

displacement through the

foramen magnum ﬇,

"towering" cerebellum st,

large massa intermedia ﬈,

and dysplastic corpus callosum

﬊. (Right) Axial T2WI MR

shows characteristic posterior

fossa crowding at the foramen

magnum, reflecting small

dimensions of the posterior

fossa combined with

cerebellar ectopia and

vermian displacement through

the foramen magnum.

Brain: Pathology-Based Diagnoses: Malformations,

Trauma, and Stroke

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