CSF-like Extra-Axial Mass

Yoshimi Anzai, MD, MPH

Judy Tan, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Helpful Clues for Common Diagnoses

Arachnoid Cyst
- Nonenhancing CSF-like mass, bone remodeling
Neurocysticercosis
- Cyst with a scolex is pathognomonic
- Racemose (grape-like) in basal cisterns: No scolex is typical
- Subarachnoid & intraventricular disease often symptomatic from hydrocephalus &/or meningitis (enhancing)

Helpful Clues for Less Common Diagnoses

Pineal Cyst
- Lies dorsal to midbrain at pineal gland
- Usually asymptomatic, less than 2 cm
Schwannoma (Cystic)
- Commonly located in cerebellopontine angle (CPA) cistern
- Enhancement typical
Epidermoid Cyst
- Lobular, insinuating nonenhancing mass
- Restricted diffusion & FLAIR hyperintensity differentiates from arachnoid cyst

Helpful Clues for Rare Diagnoses

Neurenteric Cyst
- Posterior fossa: Anterior to brainstem, CPA
- Nonenhancing midline or paramedian cyst
- MR signal variable (protein content)
Leptomeningeal Cyst
- Underlying brain shows encephalomalacia
- Communicates with subarachnoid space
- Well-marginated skull defect at site of cyst
Callosal Dysgenesis
- Interhemispheric cyst common
- Parallel lateral ventricles, colpocephaly, high riding 3rd ventricle
Holoprosencephaly (Dorsal Cyst)
- Hydrocephalus is almost always present
- Look for fused thalami, absence of interhemispheric fissures, septum pellucidum
- May see corpus callosum agenesis