Solitary Cystic Parenchymal Mass, General

Anne G. Osborn, MD, FACR

DIFFERENTIAL DIAGNOSIS

Common

Enlarged Perivascular Space
Encephalomalacia
Neurocysticercosis
Porencephalic Cyst
Glioblastoma Multiforme
Metastasis
Pilocytic Astrocytoma
Abscess

Less Common

Intracerebral Hematoma (Resolving)
Multiple Sclerosis
Ganglioglioma
DNET
Pleomorphic Xanthoastrocytoma
Hemangioblastoma
Meningioma (Cystic)
Epidermoid Cyst
Dermoid Cyst
Neuroglial Cyst
Ependymoma, Supratentorial

Rare but Important

Parasites, Miscellaneous
Schwannoma (Cystic)
Neurenteric Cyst
Desmoplastic Infantile Ganglioglioma

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Definition
- Includes all cyst-like parenchymal masses
- Excludes extra-axial cysts
  - Cisternal (e.g., arachnoid cyst), intraventricular (ependymal cyst)
- Includes “pseudoparenchymal” lesions that can invaginate into brain, mimic cystic parenchymal mass
  - Epidermoid, dermoid cysts; cystic meningioma
Key clinical issue: Effect of age on diagnosis
- Most common in child
  - Encephalomalacia, infection (abscess, parasite), neoplasm (primary > > metastatic)
- Most common in adult
  - Enlarged perivascular space, encephalomalacia, neoplasm (GBM, metastasis), infection (abscess, parasite)
Key imaging issues
- Is cystic mass exactly like CSF?
  - Enlarged perivascular space, encephalomalacia, porencephalic or neuroglial cyst
- Is cystic mass hypodense to parenchyma but hyperdense compared to CSF?
  - Cystic neoplasm, abscess, tumefactive demyelination, epidermoid or neurenteric cyst, parasites
- Is density/signal intensity of surrounding brain abnormal?
  - Encephalomalacia, infection, neoplasm
- Does lesion enhance?
  - Yes: Neoplasm, abscess, resolving (subacute) hematoma, tumefactive demyelination
  - No: Enlarged perivascular space (PVS), encephalomalacia, porencephalic or neuroglial cyst
- Does cyst have mural nodule?
  - Neurocysticercosis (NCC), neoplasm

Helpful Clues for Common Diagnoses

Enlarged Perivascular Space
- Multiple lesions, clusters of variable-sized cysts > > solitary enlarged PVS
- Well-delineated round/ovoid
- Basal ganglia > white matter, midbrain, temporal lobe, dentate nucleus
- Follows CSF density/signal intensity
Encephalomalacia
- Trauma, infarct, surgery
- Follows CSF
- Adjacent parenchyma often hyperintense on T2WI, FLAIR
Neurocysticercosis
- Multiple small > solitary small or large cyst ± visible scolex
- Cyst fluid typically proteinaceous, not exactly like CSF
- ± Enhancement, edema
- Look for multiple parenchymal calcifications (“starry sky”)
Porencephalic Cyst
- CSF-containing cyst contiguous with ventricle
Glioblastoma Multiforme
- 95% central necrosis ± hemorrhage
- Thick, irregular rim enhancement
Metastasis
- Rim enhances
Pilocytic Astrocytoma
- Child, young adult
- Cerebellar cyst + mural nodule
Abscess
- Appearance depends on stage
- Rim enhancement typical in late cerebritis, capsule stages

Helpful Clues for Less Common Diagnoses

Intracerebral Hematoma (Resolving)
- Slightly hyperdense to CSF on NECT
- Hyperintense on T1-, T2WI
- Rim enhancement common
Multiple Sclerosis
- “Tumefactive” MS has “horseshoe-shaped” enhancing rim
Ganglioglioma
- Cortically based cyst + enhancing nodule
- ± Ca++; may remodel skull
DNET
- NECT: Cortically based hypodense mass
  - Hyperdense to CSF
- MR: “Bubbly” appearance
Pleomorphic Xanthoastrocytoma
- Cortically based cyst + nodule
- Look for adjacent “dural tail”
Hemangioblastoma
- Middle-aged adult
- Posterior fossa cyst + enhancing nodule that abuts pia
Epidermoid Cyst
- Irregular “cauliflower-like” margins
- Sylvian fissure, quadrigeminal mass can mimic intra-axial mass
- Looks like CSF on NECT
- Does not suppress on FLAIR, restricts on DWI
Dermoid Cyst
- Fat ± Ca++
- Look for fat “droplets” (rupture)
Neuroglial Cyst
- Well-delineated CSF-like parenchymal cyst
- No enhancement
Ependymoma, Supratentorial
- 1/3 of ependymomas
- 80% parenchymal, not necessarily related to ventricular wall
- Usually large, ± cysts, hemorrhage
- Ca++ seen in 50%
- Variable heterogeneous enhancement of cyst wall, solid component

Helpful Clues for Rare Diagnoses

Parasites, Miscellaneous
- Solitary or conglomerate cyst(s)
- Some (e.g., hydatid cyst) very large
Schwannoma (Cystic)
- Only 1-2% of schwannomas are in brain parenchyma
- Peripheral cyst + enhancing nodule
Neurenteric Cyst
- Most are extra-axial, posterior fossa
- Do occur in supratentorial brain (rare)
- Well-delineated cyst hyperintense to CSF
Desmoplastic Infantile Ganglioglioma
- Infant with cystic supratentorial mass
- Dural-based enhancing mural component

Image Gallery

Coronal T2WI MR shows a solitary cystic left temporal lobe lesion

that followed CSF on all sequences. Note the large perivascular space.

Coronal T1WI MR shows a solitary giant midbrain cyst

that compresses aqueduct

, causing obstructive hydrocephalus

. Enlarged pial-lined cyst was found at surgery.

(Left) Axial FLAIR MR in a patient with history of remote right MCA infarct shows cystic encephalomalacia

with spongiosis and gliosis, seen here as FLAIR hyperintensity

surrounding the infarcted brain. (Right) Axial CECT in a patient with history of systemic cysticercosis and seizure shows a large CSF-like right temporal lobe cyst