CSF-like Parenchymal Lesion(s)

Anne G. Osborn, MD, FACR

James D. Eastwood, MD

DIFFERENTIAL DIAGNOSIS

Common

Enlarged Perivascular Spaces
Encephalomalacia
Lacunar Infarction
Neurocysticercosis

Less Common

Porencephalic Cyst
Multiple Sclerosis
Normal Variant
- Hippocampal Sulcus Remnants
- Connatal Cysts

Rare but Important

Neuroglial Cyst
Cryptococcosis
Parasites, Miscellaneous
Mucopolysaccharidoses
Germinolytic Cysts
Miscellaneous Congenital Malformations

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Key imaging questions
- Does lesion follow CSF on all modalities/sequences?
- Is there any mass associated effect?
- Does lesion enhance?
Included
- CSF-like cystic mass(es), e.g., enlarged perivascular spaces, neuroglial cysts
Excluded
- Cystic neoplasms, abscess, resolving hematoma (rarely exactly like CSF)
- Developmental cysts that do not behave exactly like CSF (e.g., epidermoid, neurenteric cysts)

Helpful Clues for Common Diagnoses

Enlarged Perivascular Spaces
- Perivascular spaces (PVSs)
- Can be seen at all ages but ↑ with age
- Filled with interstitial fluid but follow CSF on all sequences
- Most have no abnormality in surrounding parenchyma on PD/FLAIR
  - ≈ 25% have thin hyperintense rim
- Bilateral > unilateral
- Multiple > solitary
  - “Clusters” of variably sized CSF-like cysts characteristic
  - Can occur anywhere but most common locations = basal ganglia, hemispheric white matter, midbrain, dentate nuclei
  - Variant (mostly in elderly) = “état criblé” (“cribriform state”) with multiple tiny cysts in basal ganglia (BG)
Encephalomalacia
- Etiology varies (trauma, infarction, etc.)
- Can be solitary, multifocal, multicystic
- CSF-like ± adjacent FLAIR hyperintensity
Lacunar Infarction
- Solitary or multiple
- Typically along single long unpaired penetrating arteries &/or vascular watershed zones
  - BG, thalamus, white matter (WM) common
  - Multifocal BG infarcts + surrounding gliosis = “état lacunaire” or “lacunar state”
Neurocysticercosis
- Most neurocysticercosis (NCC) cysts are actually in sulci
- Cysts in vesicular stage smooth, thin-walled, with scolex generally visible as “dot” within cyst
- Multiple lesions in mixed stages common
  - Some enhance, some do not
  - Ca++ (multiple = “starry sky” pattern)

Helpful Clues for Less Common Diagnoses

Porencephalic Cyst
- Communicates with ventricle &/or pial surface
- Does not enhance
Multiple Sclerosis
- Chronic “burned-out” lesions
- Appear as CSF foci with hyperintense rinds on FLAIR/PD
- Look for faint hyperintensity surrounding lesions on T1WI (“lesion within a lesion”)
- Do sagittal FLAIR or T2WI to look for other lesions along callososeptal interface
Hippocampal Sulcus Remnants
- “String of beads” cysts medial to temporal horns of lateral ventricles
- Developmental variant, incidental
  - Remnants of vestigial primary embryonic hippocampal sulcus
- Imaging
  - Between hippocampus, dentate gyrus
  - Follow CSF on all sequences
  - No surrounding gliosis
Connatal Cysts
- Single or multiple
- Location
  - Intra- or periventricular (may actually be cysts of anterior choroid plexus)
  - Small cyst adjacent to tip of frontal horn may be normal anatomic variant
- Lined with ependyma
- Present at birth
- Usually transient
- Occasionally seen in older patients
- No septations, no hemosiderin
- Generally isolated without associated abnormalities

Helpful Clues for Rare Diagnoses

Neuroglial Cyst
- Nonenhancing CSF-like cyst
- No surrounding signal abnormality
- Does not communicate with ventricle
- Subcortical WM, choroidal fissure common sites
Cryptococcosis
- Nonenhancing gelatinous pseudocysts in perivascular spaces (PVS)
- Multifocal > > solitary lesions
- Most patients have HIV/AIDS
Parasites, Miscellaneous
- Other than NCC, parasitic brain cysts uncommon
- Hydatid cyst = large nonenhancing unilocular cyst
Mucopolysaccharidoses
- Multiple, bilateral
- Dilated PVSs in deep periventricular WM
Germinolytic Cysts
- Periventricular/subependymal cysts
  - Cyst(s) along caudothalamic groove probably result from germinolysis
  - Glial (not ependymal) lined cysts/pseudocysts resulting from germinolysis
  - Distinguish from “connatal” cysts (intraventricular anterior choroid plexus cysts)
  - Many etiologies, including inherited metabolic disorders (e.g., Zellweger, infantile Refsum), congenital infections (CMV)
  - CSF-like; ± septations, hemosiderin; do not enhance
- Look for associated abnormalities
  - Leukoencephalopathy
  - Delayed myelination
  - Polymicrogyria, pachygyria, heterotopias
Miscellaneous Congenital Malformations
- Several have parenchymal CSF-like cysts as part of syndrome
  - Van der Knaap leukoencephalopathies (megaloencephalic leukoencephalopathy with subcortical cysts, anterior temporal lobe cavitations)
  - Congenital muscular dystrophy (cerebellar cysts common, may represent dilated perivascular spaces)

Image Gallery

Coronal T2WI MR shows cluster of variable-sized CSF-like cysts in left parietal subcortical white matter

. Lesions did not enhance. Follow-up scan 5 years later showed no change.

Axial T1WI MR in a patient with old left internal artery occlusion shows multicystic encephalomalacia. FLAIR, T2-weighted scans showed extensive hyperintensity in residual parenchyma secondary to gliosis, spongiosis.