Thin Corpus Callosum

Susan I. Blaser, MD, FRCPC

DIFFERENTIAL DIAGNOSIS

Common

Normal Variant
Immature Brain
Encephalomalacia
Multiple Sclerosis
White Matter Injury of Prematurity
Callosal Dysgenesis
Callosectomy/Callosotomy
Obstructive Hydrocephalus

Less Common

Hypomyelination
Injury (Any Cause)

Rare but Important

Susac Syndrome
Holoprosencephaly
Inherited Metabolic Disorders
Hereditary Spastic Paraplegia with Thin
Corpus Callosum (HSP-TCC)

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Diffuse corpus callosum (CC) thinning can be normal
- Newborn (immature brain)
Abnormally thin CC can be inherited or acquired
- Broad spectrum of congenital malformations, inherited metabolic disorders can all result in thin CC
- Check history for trauma, surgery, ischemia-infarction
Thin CC, normal signal hyperintensity
- Normal variant, immature brain
- Secondary to hemispheric white matter (WM) volume loss
- Dysgenesis
Thin CC, abnormal signal intensity
- Hypomyelination or demyelinating disease (chronic MS, Susac syndrome)
- Injury (trauma, ischemia, radiation, toxic-metabolic insult)
- Obstructive hydrocephalus

Helpful Clues for Common Diagnoses

Normal Variant
- Focal thinning of corpus callosum at “isthmus” (junction between posterior body, splenium) is normal
- Sagittal section slightly off-midline can make corpus callosum appear mildly thinned
Immature Brain
- Hemispheric WM in newborn unmyelinated, corpus callosum thin and hypointense on T1WI
- As myelination progresses, corpus callosum thickens, becomes hyperintense on T1WI
  - Corpus callosum splenium at 4 months
  - Corpus callosum genu at 6 months
  - By 8 months, corpus callosum essentially like an adult’s
Encephalomalacia
- Holohemispheric WM volume loss, regardless of etiology, causes diffuse corpus callosum thinning
- Focal WM loss can cause focal corpus callosum thinning
Multiple Sclerosis
- Look for T2/FLAIR hyperintense lesions along callososeptal interface
- Ependymal “dot-dash” sign along callosoventricular border occurs early
- Longstanding MS with decreased hemispheric WM volume results in thinned corpus callosum
White Matter Injury of Prematurity
- Corpus callosum thinning secondary to periventricular white matter infarction
- Posterior corpus callosum disproportionately affected
Callosal Dysgenesis
- Hypoplasia or absence of part or all of corpus callosum
  - Rostrum, splenium most likely deficient
  - Remnants vary in size, shape, and configuration
- Most common abnormality associated with other malformations
  - Chiari 2 malformation
  - Heterotopias
  - Interhemispheric lipoma
  - Cephaloceles
Callosectomy/Callosotomy
- History important!
- Surgical disruption
- Look for surgical changes of craniotomy, ventriculostomy
Obstructive Hydrocephalus
- Causes 2 kinds of corpus callosum abnormalities: Stretching and intrinsic signal abnormality
- As lateral ventricles enlarge, corpus callosum is stretched, appears thinned
  - Look for associated signal abnormality in corpus callosum (sagittal T2WI/FLAIR best)
- Post-shunt decompression may show corpus callosum thinning, signal abnormality
  - Can appear bizarre, causing horizontal hyperintense “streaks” in corpus callosum on axial imaging
  - Can extend into periventricular WM
  - Theories: Impingement of corpus callosum against falx cerebri with resulting ischemia or axonal stretch

Helpful Clues for Less Common Diagnoses

Hypomyelination
- Undermyelination, delayed myelin maturation
- Diminished/absent WM myelination for age
- Can be primary or secondary to other pathology
Injury (Any Cause)
- Trauma (e.g., axonal injury, radiation-induced leukoencephalopathy)
- Ischemia

Helpful Clues for Rare Diagnoses

Susac Syndrome
- M < F
- Classic triad
  - Encephalopathy (headache, confusion, memory loss)
  - Vision problems (retinal artery occlusions)
  - Hearing loss
- Always involves corpus callosum
  - Central > callososeptal interface lesions
  - Middle callosal “holes” (subacute/chronic)
Holoprosencephaly
- Many variants; often affect corpus callosum
Inherited Metabolic Disorders
- Focal or diffuse atrophy
  - Focal: X-linked adrenoleukodystrophy
  - Diffuse: Many
Hereditary Spastic Paraplegia with Thin Corpus Callosum (HSP-TCC)
- HSP-TCC is 1 of many hereditary spastic paraplegias
  - Autosomal recessive with SPG11 gene mutations on chromosome 15q13-15
  - Progressive neurodegenerative disorder
- Clinical
  - Slow ↑ spastic paraparesis
  - Adolescent-onset cognitive decline
  - Pseudobulbar dysfunction
- Imaging
  - Thin corpus callosum (especially genu, body) with progressive atrophy
  - Cerebral, cerebellar atrophy often associated

Image Gallery

Sagittal T1WI MR in a term infant imaged at 2 days of age shows a thin corpus callosum

with no discernible myelination. This is the normal appearance of an immature, largely unmyelinated brain.

Axial T1WI MR in 32-week-gestation premature infant shows a very thin corpus callosum genu

, reflecting total lack of hemispheric myelination.

(Left) Axial DWI MR in a newborn shows extensive diffusion restriction of the left hemisphere following perinatal stroke. Acute axonal degeneration of the corpus callosum