“Bubbly-Appearing” Intraventricular Mass

Bronwyn E. Hamilton, MD

DIFFERENTIAL DIAGNOSIS

Common

Choroid Plexus Cysts

Less Common

Neurocysticercosis
Central Neurocytoma
Ependymoma
Subependymoma
Epidermoid Cyst
Cavernous Malformation
Ependymal Cyst

Rare but Important

Choroid Plexus Papilloma
Choroid Plexus Carcinoma
Parasites, Miscellaneous
Astroblastoma

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Purely cystic intraventricular masses are usually benign
- Xanthogranulomas > > ependymal or inflammatory cysts
Only truly common “bubbly-appearing” intraventricular masses = choroid plexus cysts (xanthogranulomas)

Helpful Clues for Common Diagnoses

Choroid Plexus Cysts
- Benign xanthogranulomas
- Choroid plexus glomi, bilateral
- Increased prevalence with age
- Usually asymptomatic (rarely cause obstruction)
- Histologically most are xanthogranulomas
  - Benign degenerative process
  - Typically FLAIR hyperintense
  - May restrict on DWI
  - Inhomogeneous enhancement common

Helpful Clues for Less Common Diagnoses

Neurocysticercosis
- Often show rim enhancement
- Look for characteristic scolex, parenchymal/cisternal lesions
- Small intraventricular cysts best seen on FLAIR
Central Neurocytoma
- Who grade II neoplasm
- Younger age patients
  - Nearly 1/2 occur in the 3rd decade
  - 75% between 2nd-4th decades
- Location
  - Arises from septum pellucidum or lateral ventricle wall
  - Anterior (near foramen of Monro), mid-body > > atrium, temporal horn
  - Less common: 3rd ventricle
  - Rare: Extraventricular central neurocytoma
  - 13% bilateral
- Imaging
  - Cyst-like areas seen in 2/3 of cases
  - Moderate enhancement is typical
  - Punctate calcifications in up to 1/2
  - Hemorrhage not uncommon
Ependymoma
- WHO grade II neoplasms
- Arises from differentiated ependymal cells lining ventricles, central canal of the spinal cord
- Mean age ˜ 6 years
- Location
  - 58% 4th ventricle
  - 42% lateral, 3rd ventricles
  - Less common: Extraventricular ependymoma
- Imaging
  - Ca++ in 40-80%
  - Occasional intratumoral hemorrhage yields blood-fluid levels
  - Contrast-enhancement varies; usually intense but spares the cyst-like regions
  - Extension beyond ventricular margins (paraventricular) not uncommon
Subependymoma
- Middle-aged, older adults
- Most located within the 4th, frontal horn of lateral ventricles
- Varied enhancement: None to intense, calcification, cyst formation may occur
- Extension of a subependymoma beyond the ventricular margins is rare, unlike for ependymoma
Epidermoid Cyst
- DWI most specific: Restricted diffusion
- FLAIR next most helpful sequence, showing “gray” CSF or incomplete CSF suppression
Cavernous Malformation
- Intraventricular location is uncommon
- Imaging appearance like cavernous malformations elsewhere
- GRE or SWI sequence helpful to assess for susceptibility due to blood products
Ependymal Cyst
- Lacks enhancement
- CSF signal all sequences (FLAIR most specific)

Helpful Clues for Rare Diagnoses

Choroid Plexus Papilloma
- Nearly half present in 1st decade
- WHO grade I (carcinoma is WHO grade III)
- Presentation with hydrocephalus common; can be due to mechanical obstruction and/or overproduction of CSF
- Locations: Lateral ventricle most common site (50% of cases) > 4th ventricle (40%; most common in adults) > 3rd ventricle (5%)
- Imaging
  - Cauliflower-like lobulated tumor, usually with moderate or intense enhancement
  - Hemorrhage, cyst formation may occur
  - Necrosis and/or parenchymal invasion suggest choroid plexus carcinoma
  - Flow voids common
  - Pure “cystic” variant may occur within ventricles, subarachnoid spaces
Astroblastoma
- “Bubbly” appearance common
- Parenchymal > > intraventricular

Other Essential Information

Enhancing intraventricular tumors may require MR neuraxis screening for drop metastasis, particularly when choroid plexus tumors and ependymoma are suspected
Nonenhancing cystic lesions with DWI restriction characteristic for epidermoid cysts
Neurocysticercosis can rarely mimic other intraventricular cysts, such as colloid cyst
- Cryptococcal infection can present in a similar fashion to cysticercosis