Abnormal Shape/Configuration of Corpus Callosum

Susan I. Blaser, MD, FRCPC

DIFFERENTIAL DIAGNOSIS

Common

Normal Variant
Callosal Dysgenesis
Callosotomy
Neoplasm
- Lipoma
- Glioblastoma Multiforme
- Lymphoma, Primary CNS
Decreased White Matter Volume
- Hypomyelination
- Periventricular Leukomalacia
- HIE, Term
- Chronic Cerebral Infarction
- Diffuse Axonal Injury (DAI)
- Multiple Sclerosis
- Radiation and Chemotherapy
Obstructive Hydrocephalus

Less Common

Holoprosencephaly
Holoprosencephaly Variants

Rare but Important

Hypertensive Intracranial Hemorrhage

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Normal corpus callosum (CC) varies in thickness, shape
Isolated callosal dysgenesis not common
- Look for 2nd lesion
- Associated CNS anomalies in > 50%
  - Heterotopia
  - Cortical dysplasia
  - Noncallosal midline anomalies
  - Abnormal brainstem or cerebellum
If not congenital, history crucial!

Helpful Clues for Common Diagnoses

Normal Variant
- Size, shape, thickness of normal corpus callosum vary
  - Splenium, genu are largest parts of corpus callosum
  - Narrowing between body, splenium (“isthmus”) is normal
  - Dorsal surface of fully developed, normally myelinated corpus callosum often “wavy”
- Immature corpus callosum is thin
  - Premyelination
  - Gradually thickens with progressive myelination
Callosal Dysgenesis
- One or all segments absent
  - Rostrum, splenium most likely deficient
  - Remnants vary in size, shape, configuration
- “Micro” corpus callosum
  - Small, but well-formed
  - Often syndromic
- “Mega” corpus callosum
  - Isthmus usually absent
  - Megalencephalic (bulky white matter)
  - Or small to normal brain (syndromic)
Callosotomy
- Surgical disruption
  - Focal: Approach to 3rd ventricle or suprasellar tumor
  - Diffuse: Surgery for intractable seizures
- Best seen on sagittal or coronal MR
Neoplasm
- Can be benign/focal or malignant/diffusely infiltrating
- Lipoma
  - 40-50% of interhemispheric fissure
  - Almost always located in subarachnoid space; blood vessels and cranial nerves course through lipoma; high surgical morbidity → surgery rarely indicated
  - Common in callosal dysgenesis
  - Can be bulky, mass-like (“tubonodular” type, usually associated with corpus callosum agenesis; may extend through choroidal fissures into lateral ventricles)
  - Thin mass curving around corpus callosum body/splenium (“curvilinear” type, corpus callosum present but may be dysgenetic)
  - Midline lipomas may be part of more general midline developmental disorder
- Glioblastoma Multiforme
  - Most commonly seen in adults, can occur in adolescents (rare)
  - “Butterfly” glioma
  - Central necrosis + thick irregular rim enhancement
- Lymphoma, Primary CNS
  - Hyperdense on NECT
  - Strong, uniform enhancement
Decreased White Matter Volume
- Many causes (congenital, acquired)
- All may result in focal or diffuse callosal thinning
- Hypomyelination
  - Chromosomal, inborn errors of metabolism
- Periventricular Leukomalacia
  - Premature infant
  - Increased echogenicity ± loss of normal architecture on ultrasound head
  - May see cavitation, periventricular cysts
  - Reduced volume of periventricular white matter
  - Corpus callosal thinning most commonly in posterior body and splenium
  - “Scalloped” lateral ventricles
- HIE, Term
  - Term infant with profound partial asphyxia → WM/cortex damaged
- Chronic Cerebral Infarction
  - Axonal loss → focal/diffuse thinning of corpus callosum
- Diffuse Axonal Injury (DAI)
  - 20% involve corpus callosum (splenium, undersurface of posterior body)
- Multiple Sclerosis
  - Chronic, late
Obstructive Hydrocephalus
- Acute
  - Corpus callosum stretched, bowed upward
  - Forniceal columns bowed downward
- Chronic
  - Post-shunt encephalomalacia
  - Sequela of acute callosal impingement against falx

Helpful Clues for Less Common Diagnoses

Holoprosencephaly
- Corpus callosum absent in alobar holoprosencephaly
  - Large dorsal “cyst” often present
  - Monoventricle
  - “Pancake” anterior cerebral tissue
- Semilobar may have residual splenium
  - Frontal fusion and hypoplasia
  - Caudate head fusion
  - Splenium may be present
- Lobar
  - Genu may or may not be present
  - Absent anterior midline falx and fissure
  - Gray matter often crosses with genu
Holoprosencephaly Variants
- Middle interhemispheric variant
  - a.k.a. syntelencephaly
  - Splenium, genu present, body deficient
  - Middle corpus callosum body “dips”
  - Gray matter crosses at dip
  - If severe, add bilateral perisylvian polymicrogyria

Helpful Clues for Rare Diagnoses

Hypertensive Intracranial Hemorrhage
- Corpus callosum is rare primary site

Image Gallery

Sagittal T1WI FS MR with a close-up view of the corpus callosum shows normal “wavy” dorsal surface. Note the focal thinning along the posterior body

, a common normal finding.

Sagittal T1WI MR shows a normal neonatal corpus callosum

, thin due to age-appropriate lack of myelin maturation. The cingulate gyrus

is normal.

(Left) Sagittal T1WI MR shows callosal agenesis. Note the radial array of paracentral gyri “pointing” to the 3rd ventricle, as well as the absence of identifiable cingulate gyrus. Hippocampal commissure is visualized posteriorly