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ESSENTIAL INFORMATION

Key Differential Diagnosis Issues
- Definition - Includes cystic or cyst-like parenchymal masses - Excludes extraaxial cysts - Cisternal (arachnoid cyst), intraventricular (ependymal or choroid plexus cyst), or choroid fissure cysts - Includes "pseudoparenchymal" lesions that invaginate into brain, mimic cystic parenchymal/intraaxial mass - Cystic meningioma, epidermoid/dermoid cyst
- Key clinical issue: Effect of age on diagnosis - More common in children - Porencephaly, encephalomalacia, infection (abscess, parasite), neoplasm (primary > > metastatic) - More common in adults - Enlarged perivascular space (PVS), encephalomalacia, neoplasm (glioblastoma, metastasis), infection (abscess, parasite)
- Key imaging issues - Does cystic mass follow CSFexactly in density/signal intensity? - Enlarged PVS, encephalomalacia, porencephalic or neuroglial cyst, some parasitic cysts - Does cystic mass notfollow CSF exactly? - Cystic neoplasm, abscess, tumefactive demyelination, epidermoid or neurenteric cyst, some parasitic cysts - Is density/signal intensity of surrounding brain abnormal? - Encephalomalacia, infection, neoplasm - Does lesion enhance (focal nodule or ring)? - Yes: Neoplasm, abscess, resolving (subacute) hematoma, tumefactive demyelination - No: Enlarged PVS, encephalomalacia, porencephalic or neuroglial cyst - Does cyst have mural nodule or scolex? - Neoplasm; neurocysticercosis or other parasites
Helpful Clues for Common Diagnoses
- Enlarged Perivascular Space - Usually multiple but can be solitary - Well-delineated, round/ovoid, isodense/isointense to CSF cyst; may see central/traversing vessel - Large/giant PVS may show surrounding FLAIR hyperintensity due to chronic gliosis
- Cystic Encephalomalacia - Prior injury, including trauma, ischemia/infarction - Cystic areas isodense/isointense to CSF - Adjacent parenchyma often hyperintense on FLAIR due to gliosis without cavitation
- Neurocysticercosis - Parenchymal cysts often multiple but may be solitary ± visible scolex, usually ≤ 2 cm - Cyst fluid may be proteinaceous, not exactly follow CSF - Variable enhancement/edema depending on stage - Parenchymal calcifications often present
- Porencephalic Cyst - CSF-containing cyst contiguous with ventricle - Most commonly seen in children: In utero or perinatal periventricular white matter (WM) injury
- Metastasis - 30% are solitary - Ring enhancement is common, but center typically does not restrict diffusion; helps to distinguish from pyogenic abscess, which shows central ↓diffusion
- Glioblastoma, IDH-Wildtype - Most common malignant primary brain tumor - Cyst formation is common; also necrosis, hemorrhage, neovascularity, vasogenic edema - Thick, irregular rim or nodular enhancement - Supratentorial WM most common location
- Abscess - Appearance depends on stage: Rim enhancement typical in late cerebritis, early and late capsular stages - Central restricted diffusion due to pus: Bright on DWI - Dual rim sign may be seen on T2/FLAIR/SWI (hypointense outside, hyperintense inside)
- Pilocytic Astrocytoma - Usually seen in children, young adults - Cyst with mural nodule is most common pattern; often centered on cerebellar vermis or hemisphere - Cyst contents variably isodense/isointense to CSF
Helpful Clues for Less Common Diagnoses
- Intracerebral Hematoma (Resolving) - Center slightly hyperdense to CSF on NECT - Cystic portion usually hyperintense on T1 and T2WI - Low signal intensity rim (hemosiderin) on GRE/SWI - Rim enhancement common
- Demyelinating Lesion - True cyst formation is uncommon - Tissue destruction may → cyst formation with large, tumefactive lesions (> 2 cm) - Incomplete ring of enhancement ± restricted diffusion - Relative lack of edema, mass effect for size
- Ganglioglioma - Cortically based cyst(s) with enhancing nodule - Variable Ca⁺⁺; may remodel skull if large enough
- Dysembryoplastic Neuroepithelial Tumor - Cortically based mass, common in temporal lobe - Solitary cyst or cluster of multiple cysts ± enhancing nodule(s); may be indistinguishable from ganglioglioma - Calcification in ~ 30%; little or no associated edema
- Pleomorphic Xanthoastrocytoma - Cortically based cyst + nodule - Infiltration of dura/dural tail has been described - Typically larger, more aggressive appearing than ganglioglioma or DNET; + vasogenic edema
- Hemangioblastoma - Young to middle-aged adults - May be multiple, familial (von Hippel-Lindau disease) - Typical: Posterior fossa cyst + enhancing nodule that abuts pial surface; may lack cyst, especially if small - Hypervascular; macroscopic vessels seen with larger lesions; hyperperfusion is typical
- Meningioma, Cystic - Most common intracranial extraaxial tumor - May push deeply into parenchyma; rarely 1° intraaxial - Enhancing mass with ≥ 1 peripheral or intralesional cysts
- Epidermoid Cyst - Irregular, cauliflower-like margins - Typically extraaxial, but can insinuate deeply into brain parenchyma; rarely 1° intraaxial - CT: Similar to CSF; not typically calcified - MR: Does not suppress on FLAIR; marked ↓ diffusion - DWI very helpful to detect postoperative residual
- Dermoid Cyst - Congenital ectodermal inclusion cyst, like epidermoid - Variable fat content, fat-fluid level(s), calcification - Ruptured dermoid → fat droplets in subarachnoid space
- Neuroglial Cyst - a.k.a. glioependymal cyst - Frontal lobe most common site - Unilocular, well-delineated cyst with thin wall; usually suppresses on FLAIR; no diffusion restriction, no enhancement, and no edema - Minimal/no surrounding signal abnormality
- Ependymoma, Supratentorial - 1/3 of ependymomas - 80% parenchymal, not arising within or contacting ventricular surface - Often large, heterogeneous with cyst formation, hemorrhage, calcification (50%) - Variable enhancement of cyst wall, solid component
Helpful Clues for Rare Diagnoses
- Parasites, Miscellaneous - Solitary or conglomerate cyst(s) - Some (e.g., hydatid cyst) characteristically very large - Eccentric nodule may suggest toxoplasmosis
- Schwannoma, Cystic - Only 1-2% of schwannomas arise in brain parenchyma - Nonspecific peripheral cyst and enhancing nodule
- Neurenteric Cyst - Most are extraaxial in posterior fossa/spinal canal - Rarely occur in supratentorial brain - Well-delineated cyst with variable density/signal intensity
- Desmoplastic Infantile Ganglioglioma - Cystic tumor of infants variably involving superficial cerebral cortex, leptomeninges, dura - Large cyst and peripheral tumor nodule - Enhancement of adjacent meninges
- Encephaloclastic Cyst - Uncommon complication of catheter-based intraventricular chemotherapy or deep brain stimulating electrode placement - Cystic dilatation of brain parenchyma around catheter or electrode, surrounding edema

References

Selected References

Images

Selected Images

Enlarged Perivascular Space Axial CECT demonstrates an ovoid, well-circumscribed, CSF-density structure, consistent with an enlarged perivascular space in the posteroinferior aspect of the right putamen. Enlarged perivascular spaces are isodense/isointense to CSF on CT/MR.

Cystic Encephalomalacia Axial FLAIR MR shows a large, thin-walled cyst isointense to CSF in the right temporal pole in a patient previously treated for herpes simplex virus type 1 encephalitis. Areas of gliosis are present posterior to the cyst and in the medial left temporal lobe .

Neurocysticercosis Axial FLAIR MR demonstrates a classic parenchymal neurocysticercal cyst with an eccentric nodule (scolex) in the left parietal lobe. Cyst fluid is isointense to CSF. Note mild perilesional edema .

Porencephalic Cyst Coronal T2 FS MR in a 2-month-old born to a mother using methamphetamine shows a well-circumscribed right frontal porencephalic cyst without surrounding edema or mass effect. The cyst was likely due to intrauterine vascular injury to the periventricular white matter.

Metastasis Axial CECT shows a large, rim-enhancing, cystic mass in the right cerebellar hemisphere with mass effect on the 4th ventricle and only minimal associated edema. At surgery, a metastasis related to HPV-positive oropharyngeal squamous cell carcinoma was found.

Glioblastoma, IDH-Wildtype Axial T1 C+ MR shows a ring-enhancing mass in the left posteroinferior frontal lobe with associated vasogenic edema. The enhancing rim is moderately thick and irregular, and no central diffusion restriction was present on DWI. Biopsy confirmed glioblastoma.

Abscess Axial T1 C+ MR shows an irregularly ring-enhancing cystic lesion with extensive surrounding vasogenic edema. The rim of the lesion is thinner medially than laterally, as is often seen with large pyogenic abscesses. Central DWI restriction was present (not shown).

Pilocytic Astrocytoma Sagittal T1 C+ MR shows a large, cystic mass with rim enhancement and an eccentric, enhancing nodule . Mass effect on the 4th ventricle → obstructive hydrocephalus. Cyst contents are mildly hyperintense to CSF. Pilocytic astrocytoma was confirmed surgically.

Intracerebral Hematoma (Resolving) Axial CECT shows a rim-enhancing, cystic-appearing lesion of the right temporal lobe with no associated edema and with cyst contents appearing mildly hyperdense to CSF. There was clinical concern for metastasis, abscess, or glioblastoma.

Intracerebral Hematoma (Resolving) Axial NECT in the same patient 3 months earlier shows a right temporal lobe traumatic hematoma with surrounding vasogenic edema. The two studies and the history of severe head trauma are consistent with a diagnosis of resolving hematoma.

Demyelinating Lesion Axial T1 C+ MR in a patient with multiple sclerosis shows a large, centrally hypointense, cystic-appearing lesion with an open ring pattern of enhancement and mild local mass effect, consistent with an active demyelinating plaque.

Ganglioglioma Coronal T2 MR in a young patient with epilepsy shows a cystic mass with an eccentric nodule in the right medial temporal region. Postcontrast study showed intense enhancement of the nodule (not shown). Histopathology revealed ganglioglioma.

Dysembryoplastic Neuroepithelial Tumor Coronal T1 C+ MR shows a peripheral, cortically based dysembryoplastic neuroepithelial tumor in the right frontal parasagittal region with a large cyst, a small enhancing eccentric nodule , and no associated edema.

Pleomorphic Xanthoastrocytoma Axial DWI MR shows a large, cystic frontotemporal mass with a mural nodule . The cyst portion was isointense to CSF on all sequences, and the nodule demonstrated intense enhancement post gadolinium (not shown). Pleomorphic xanthoastrocytoma was confirmed surgically.

Hemangioblastoma Axial T2 MR shows a cystic mass with a mural nodule and vasogenic edema. Flow voids are present with the nodule , consistent with hypervascular tumor. Hemangioblastoma was confirmed surgically in this patient who did not have von Hippel-Lindau disease.

Meningioma, Cystic Axial T2 MR shows a hyperintense, cystic mass and a solid, dural-based nodule . This cystic meningioma pushes deeply into the brain, making differentiation between intraaxial and extraaxial location difficult.

Epidermoid Cyst Coronal FLAIR MR shows a lobulated cystic lesion centered on the left choroid fissure but insinuating into adjacent brain parenchyma. The lesion is not isointense to CSF on FLAIR, and there was marked restricted diffusion on DWI (not shown). An epidermoid tumor arising in the choroidal fissure was found at surgery.

Dermoid Cyst Sagittal T1 MR shows a subfrontal low signal intensity cyst with nondependent T1 hyperintensity . The presence of fat was confirmed with fat suppression in this unruptured dermoid cyst.

Neuroglial Cyst Axial FLAIR MR shows a large, well-marginated neuroglial cyst in the left frontal lobe that was isointense to CSF on all imaging sequences. There is minimal perilesional FLAIR hyperintensity.

Neuroglial Cyst Coronal FLAIR MR in a 4-month-old demonstrates a well-circumscribed cyst that is isointense to CSF. There is mass effect on the adjacent temporal lobe, and mild uncal herniation was present (not shown). The lesion was decompressed surgically and was shown to be consistent with a neuroglial cyst.

Ependymoma, Supratentorial Axial T2 MR shows a supratentorial mass with cystic and solid components . Calcification (on CT) and hemorrhage (on SWI) were present, but no perilesional edema. The thick rim of T2-intermediate solid tissue enhanced post gadolinium (not shown).

Parasites, Miscellaneous Axial CECT shows a large, unilocular, CSF-density parenchymal cyst without edema or enhancement. Echinococcal cysts grow slowly and may attain a very large size. This one exerts mass effect with trapping of the left lateral ventricle.

Schwannoma, Cystic Axial T1 C+ MR shows a right occipital cystic mass with a cortically based, enhancing nodule . Parenchymal schwannoma was found at surgery. Though schwannomas are often mixed cystic and solid, only 1-2% of schwannomas arise in brain parenchyma.

Neurenteric Cyst Coronal T1 C+ FS MR shows a large, somewhat lobulated, CSF-like, nonenhancing, parenchymal cyst . Neurenteric cyst was confirmed surgically. These lesions more commonly occur in the posterior fossa and spinal canal, and they are commonly bright on T1WI.

Desmoplastic Infantile Ganglioglioma Coronal T1 C+ MR in a 22-month-old boy with a large head shows a very large, cystic mass with an enhancing nodule . Cyst contents were isointense to CSF on multiple imaging sequences. Desmoplastic infantile ganglioglioma was confirmed at surgery.

Encephaloclastic Cyst Axial T2 MR s/p deep brain stimulating electrode placement weeks earlier shows a well-circumscribed cyst around the left electrode with vasogenic edema but no ↓ diffusion or enhancement (not shown). Sterile cyst was found surgically.

Additional Images

Enlarged Perivascular Space Coronal T2 MR shows a solitary cystic left temporal lobe lesion that followed CSF on all sequences. Note the large perivascular space.

Enlarged Perivascular Space Coronal T1 MR shows a solitary giant midbrain cyst that compresses aqueduct , causing obstructive hydrocephalus . Enlarged pial-lined cyst was found at surgery.

Cystic Encephalomalacia Axial FLAIR MR in a patient with history of remote right middle cerebral artery infarct shows cystic encephalomalacia with spongiosis and gliosis, seen here as FLAIR hyperintensity surrounding the infarcted brain.

Neurocysticercosis Axial CECT in a patient with a history of systemic cysticercosis and seizure shows a large CSF-like right temporal lobe cyst . No other lesions were identified.

Porencephalic Cyst Coronal T1 C+ MR shows a large left temporal lobe cyst that thins and expands overlying skull . Note compression of the lateral ventricle . Surgery disclosed cyst lined by gliotic brain.

Glioblastoma, IDH-Wildtype Axial NECT in a patient with a 2-day history of increasing headache and left-sided weakness had CT scan to "rule out stroke." NECT shows a low-density right temporal lobe mass . Enhancing rim was seen on T1 C+ MR (not shown). Biopsy disclosed glioblastoma multiforme.

Metastasis Axial CECT shows a cystic-appearing mass with a thin, enhancing rim and edema . Preoperative diagnosis was abscess, but biopsy disclosed adenocarcinoma. Right parahilar mass was found on chest radiograph. A bronchogenic carcinoma primary was diagnosed.

Pilocytic Astrocytoma Axial NECT in a 7-year-old shows a hypodense left cerebellar mass that is hyperdense compared to CSF. Patchy enhancement of solid component was seen on CECT (not shown).

Abscess Axial CECT shows an ill-defined, cystic lesion with surrounding edema in a patient with pyogenic meningitis and enhancement in basilar cisterns . These findings are characteristic of late cerebritis stage of abscess formation.

Intracerebral Hematoma (Resolving) Axial CECT shows a low-density mass that is not quite as hypodense as CSF in adjacent ventricles. Thin rim enhancement is seen together with some adjacent edema . MR disclosed features of late subacute hematoma.

Demyelinating Lesion Axial T1 MR shows a cystic-appearing right posterior parietal lobe mass . Several other subtle, hypointense lesions are present . Faint rim enhancement was seen on T1 C+ MR (not shown).

Demyelinating Lesion Axial NECT shows a hypodense right posterior parietal mass with extensive white matter edema . Partial ("horseshoe") rim enhancement seen on T1 C+ MR (not shown) was characteristic of tumefactive demyelination.

Ganglioglioma Axial T1 C+ MR shows classic ganglioglioma with a cortically based enhancing nodule and nonenhancing cyst .

Ganglioglioma Sagittal T1WI MR shows a solitary cystic mass with nodule that enhanced following contrast administration.

Dysembryoplastic Neuroepithelial Tumor Axial CECT in a 16-year-old with longstanding seizures shows a nonenhancing, cystic-appearing cortical mass . Note subtle remodeling of adjacent skull. Both the patient's history and this CT are classic for DNET.

Pleomorphic Xanthoastrocytoma Axial T1 C+ MR shows a cystic mass in right medial temporal lobe with an enhancing, cortically based nodule .

Hemangioblastoma Axial T1 C+ FS MR in a 42-year-old shows a posterior fossa parenchymal cystic mass with an enhancing nodule that abuts pia.

Epidermoid Cyst Axial NECT shows a left temporal lobe CSF-like mass. Note that the margins are irregular and slightly lobulated . Mass did not suppress on FLAIR and showed strong restriction on DWI. Sylvian fissure epidermoid was found at surgery.

Dermoid Cyst Axial NECT shows a calcified, hypodense frontal mass that is like fat (not CSF). Note fat droplets in subarachnoid space . This was diagnosed as a ruptured dermoid.

Neuroglial Cyst Axial FLAIR MR shows a cyst of CSF intensity in the right medial temporal lobe that is difficult to distinguish in one plane only from a cyst of the choroid fissure.

Neuroglial Cyst Sagittal T2 MR shows huge CSF-like tectal cyst with a thin rim of parenchyma stretched around the lesion.

Ependymoma, Supratentorial Axial NECT in a young child shows a cystic mass in right hemisphere that has a solid component , Ca⁺⁺ , and severe white matter edema. WHO grade III cellular ependymoma was the diagnosis.

Enlarged Perivascular Space Axial FLAIR MR shows a well-defined, CSF signal intensity cyst in the subcortical white matter of the left anterior temporal lobe, a newly recognized characteristic location for an enlarged perivascular space. Note mild surrounding perilesional FLAIR hyperintensity.

Cystic Encephalomalacia Axial NECT shows cystic encephalomalacia in the left frontal lobe with associated volume loss after a gun shot injury. Note the bullet fragments in the region of encephalomalacia.

Porencephalic Cyst Axial FLAIR MR shows a large left frontal porencephalic cyst communicating with the left frontal horn. There is mild surrounding FLAIR hyperintensity due to gliosis. The etiology of this porencephalic cyst was thought due to a remote infarct.

Metastasis Axial FLAIR MR shows a large, cystic mass with fluid-fluid level due to hemorrhage. Note the small eccentric nodule , perilesional edema , and mass effect. At resection, this was a metastatic melanoma.

Glioblastoma, IDH-Wildtype Axial FLAIR MR shows a large, cystic mass in the right parietal lobe with the cyst contents hyperintense to CSF. There is moderate perilesional edema and mass effect. Biopsy revealed glioblastoma.

Abscess Axial DWI MR shows a cystic lesion with marked restricted diffusion typical of a pyogenic abscess.

Intracerebral Hematoma (Resolving) Axial T2 MR shows a resolving late subacute hemorrhage in the right occipital lobe. T1 MR showed hyperintensity and SWI susceptibility changes (not shown). Note prominent flow voids in the occipital region due to an arteriovenous malformation, which was the etiology of the intracerebral hemorrhage.

Pleomorphic Xanthoastrocytoma Axial FLAIR MR demonstrates a large, cystic, solid, cortically based mass in the left frontal lobe. On postcontrast images, there was rim and eccentric nodular enhancement (not shown). Histopathology showed a pleomorphic xanthoastrocytoma.

Hemangioblastoma Axial T2 MR shows a hemangioblastoma with lobulated cystic and nodular solid components . There is surrounding edema with mass effect on the 4th ventricle. Note prominent flow voids along its posterior aspect due to the highly vascular nature of this tumor.

Neuroglial Cyst Axial T2 MR shows a well-defined cyst in the right choroidal fissure, a typical location for a neuroglial cyst.

Desmoplastic Infantile Ganglioglioma Coronal T1 C+ MR in an infant with a large head shows cystic desmoplastic infantile ganglioglioma with an enhancing, dural-based nodule . (Courtesy M. Sage, MD.)

Encephaloclastic Cyst Axial T1 MR in a patient with acute leukemia receiving methotrexate via a ventricular catheter shows a cystic lesion along the catheter with extensive edema in the adjacent brain parenchyma. Encephaloclastic cyst is a rare complication of intraventricular chemotherapy.

Neuroglial Cyst Axial FLAIR MR shows a left temporal lobe cyst that suppresses completely. This could be a solitary enlarged perivascular space or neuroglial cyst.

50 KiB Raw Blame History

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Helpful Clues for Common Diagnoses

Helpful Clues for Less Common Diagnoses

Helpful Clues for Rare Diagnoses