Ependymal/Subependymal Lesions

Bronwyn E. Hamilton, MD

DIFFERENTIAL DIAGNOSIS

Common

Normal Variant (Mimic)
Tuberous Sclerosis Complex
Subependymal Giant Cell Astrocytoma
Focal Cortical Dysplasia
Heterotopic Gray Matter
Developmental Venous Anomaly
Multiple Sclerosis

Less Common

Metastases
- Glioblastoma Multiforme
- Lymphoma, Primary CNS
- Germinoma
- Medulloblastoma (PNET-MB)
- Ependymoma
- Choroid Plexus Carcinoma
Ventriculitis
Opportunistic Infection, AIDS

Rare but Important

Neurosarcoid
TORCH, General
Vasculitis
Langerhans Cell Histiocytosis
Alexander Disease

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Ependyma is the thin epithelial membrane lining the ventricular system of the brain & spinal cord
Subependymal lesions lie beneath the ependyma
Majority of ependymal/subependymal lesions are infectious or neoplastic

Helpful Clues for Common Diagnoses

Normal Variant (Mimic)
- Normal “indentations” into ventricles: Caudate heads, thalami, pes hippocampus, facial colliculus
- Subependymal veins enhance & may mimic pathology
Tuberous Sclerosis Complex
- Calcified subependymal nodules classic
- Cortical/subcortical tubers at juxtacortical location
- White matter lesions along lines of neuronal migration may extend to ependyma
- Subependymal giant cell astrocytoma (SGCA) in 5-10%
Subependymal Giant Cell Astrocytoma
- Enlarging, enhancing intraventricular mass in patient with tuberous sclerosis complex
- Typically at foramen of Monro
Focal Cortical Dysplasia
- Radially oriented white matter bands
  - Thin linear/wedge-shaped “comet-tail” shaped hyperintensities
  - Extend from ependymal to subcortical white matter
  - Best seen on FLAIR > T2WI
- Associated with overlying cortical thickening
  - Mild mass effect common
  - Non-enhancing, mildly T2 bright
- Imaging & histologic features similar to cortical/subcortical tubers of TSC
Heterotopic Gray Matter
- Nonenhancing nodules along inner ventricle margin
- Gray matter signal on all sequences
- May be associated with seizures or incidental
Developmental Venous Anomaly
- Enhancing “Medusa head” with enlarged draining vein
- May have enlarged subependymal veins
- Often occurs at angle of ventricle
- Focal, unilateral lesion
Multiple Sclerosis
- Demyelinating process characterized by periventricular lesions
- Enhancing lesions often extend to involve ependyma
- Incomplete ring suggests demyelination

Helpful Clues for Less Common Diagnoses

Metastases
- Etiology: CNS > systemic primaries
  - PNET-MB most common (pediatrics)
  - GBM & anaplastic gliomas (adults)
  - Lymphoma/leukemia can seed CSF
- Narrow differential by history & imaging
Ventriculitis
- Ventriculomegaly with debris levels & ependymal enhancement
- Periventricular T2 hyperintensity characteristic
- Usually due to intraventricular rupture of adjacent brain abscess, meningitis or shunt complication
Opportunistic Infection, AIDS
- Toxoplasmosis & lymphoma may extend along ventricular margins
- CMV cause ventriculitis, meningitis or ischemia; ventriculitis common
- TB may cause ventriculitis

Helpful Clues for Rare Diagnoses

Neurosarcoid
- Dural & leptomeningeal disease common
- Ependymal, perivascular space enhancement
- Pial enhancement with underlying white matter T2 hyperintensity characteristic
- May involve choroid plexus & extend to ventricular margin
TORCH, General
- Congenital infections caused by transplacental transmission of pathogens
- White matter volume loss & T2 hyperintensity common to all TORCH infections
- Periventricular calcification may be seen in CMV or Toxoplasmosis
- CMV: Microcephaly, periventricular pseudocysts & hyperintensities; commonly associated with migrational disorders
- Toxoplasmosis: Parenchymal & periventricular calcifications
Vasculitis
- Suggested by linear enhancement along the course of deep white matter penetrating vessels
- Enhancement may extend to ependyma
- Usually associated with confluent surrounding T2 hyperintensity
- DWI restriction is common
Langerhans Cell Histiocytosis
- Rare subependymal involvement
- May involve choroid plexus & mimic subependymal disease
Alexander Disease
- Predilection for frontal lobes
- Intense bands of enhancement in periventricular/subependymal location
- Near complete lack of myelination in infants with large head suggest diagnosis