By:Nour-Eldin Mohammed

NeuroradiologyNeuroradiologyCongenital Malformation Congenital Malformation

of CNSof CNS

Callosal DysgenesisCallosal Dysgenesis

Definitions:One or all segments of CC absent (if partial, body remains)

CC segments front to back:• Lamina rostralis (unmyelinated)• Rostrum (myelinated)• Genu• Body• Splenium

Callosal DysgenesisCallosal Dysgenesis

• General Features:• Axial: Parallel lateral ventricles• Coronal: "Trident" anterior horns

resemble "viking helmet" or "moose head“

• Location: Midline anomaly• Size: CC remnants vary in size,

shape , Remnant may be paper thin or bulbous

Callosal DysgenesisCallosal Dysgenesis

Radially arrayed gyri "point to" 3rd ventricle

Absent Cingulate Gyrus

Callosal DysgenesisCallosal Dysgenesis

Lateral ventricles are key to diagnosis:• Parallel (non-converging)• Widely separated

• Occipital horns often dilated (colpocephaly)• Pointed frontal horns

Callosal DysgenesisCallosal Dysgenesis

Coronal T2WI MRshows agenesis of the corpusCallosum

• trident shaped lateral ventricles

•vertical hippocampi (open

arrow),

•enlarged, "keyhole" shaped

temporal horns and Probst

bundles (curved arrow).

Callosal DysgenesisCallosal Dysgenesis

Axial NECT with widened "windows" shows colpocephaly, calcified (arrow) midline lipoma that extends through choroid fissures into lateral ventricles (open arrows).

Axial TlWI MR shows parallel ventricles, colpocephaly, and a midline lipoma. Note lipoma (arrow) protruding into the lateral ventricles.

Callosal DysgenesisCallosal Dysgenesis

Coronal T2WI MR in fetus shows trident shaped lateralventricles, agenesis of Cc

•"Probst bundle" (curved arrow)

• vertical hippocampus (arrow).

Differential Diagnosis of Callosal Dysgenesis Differential Diagnosis of Callosal Dysgenesis

Partial Absence of Callosal DysgenesisPartial Absence of Callosal Dysgenesis

Destruction of CC

Differential Diagnosis of Callosal Dysgenesis Differential Diagnosis of Callosal Dysgenesis

• Surgery (callosotomy),trauma (Acquired interhemispheric disconnection syndrome)• Hypoxic ischemic encephalopathy (HIE), infarcts• Metabolic

Differential Diagnosis of Callosal Dysgenesis Differential Diagnosis of Callosal Dysgenesis

Stretched Corpus Callosum (e.g.: Hydrocephalus)Stretched Corpus Callosum (e.g.: Hydrocephalus)

• Thinned CC but all parts present

• Severe hydrocephalus often present

LipomaLipoma

Definitions• Mass of mature non-neoplastic adipose tissue•CNS lipomas are congenital malformations, not trueneoplasm

LipomaLipomaGeneral Features• Best diagnostic clue: Well-delineated lobulated extra-axial mass with fat attenuation/intensity

• Location : Midline location common

80% supratentorial :

1.40-50% interhemispheric fissure (over corpus callosum; may extend into lateral ventricles, choroid plexus)2.15-20% suprasellar (attached to infundibulum, hypothalamus)3.10-15% pineal region (usually attached to tectum)20% infratentorial• Cerebellopontine angle (may extend into lAC, vestibule)• Uncommon: Jugular foramen, foramen magnum

LipomaLipoma

(a small interhemispheric lipoma (arrows) above the corpus callosum, found incidentally at MR imaging in this patient with headache.

Sagittal Tl WI MR Sagittal Tl WI MR with fat-saturation

LipomaLipoma

Sagittal TlWI MR shows a well-circumscribed high signal lesion in the pineal region (arrow).The patient was asymptomatic.

Axial gross pathology shows

a quadrigeminal lipoma

(arrow)