1. Guide to intracranial cysts: A “Cyst-o-matic” approach
Bryan Foley MD, Jennifer Becker MD, Rihan Khan,MD

2. Control #: 680 Title: Intracranial cystic lesions: A “cyst-o-matic” approach to identification with pathologic correlation eEdE#: eEdE-63

3. Disclosures
None

4. Purpose:
The purpose of this exhibit is to provide an interactive case based review of intracranial cystic lesions with a focus on CT and MR, while discussing the etiologies and differential diagnostic considerations.
Approach/Methods:
We present a spectrum of intracranial cystic lesions and interesting variants from cases collected over the last 3 years from everyday neuroradiology practice at a university medical center.

5. Characterizing an intracranial Cyst
Location +
CT or MR imaging features
= Diagnosis or short Differential Diagnosis

6. Anatomic Location Intra-axial Extra-axial Supra or infratentorial
Midline
Off-Midline

7. Findings/Discussion:
Cases will be presented demonstrating common and uncommon intracranial cysts and cystic lesions. First you will see the images, next an image description locating the cyst, then a summary slide with key facts and differential diagnosis.

8. The most Common extra-axial CYst
Arachnoid Cyst
Extra-axial, supratentorial, off-midline
cyst that follows CSF signal, no restricted diffusion

9. Arachnoid cyst
Benign congenital lesion, lined by arachnoid cell single layer
Extraaxial, conforms around brain parenchyma
Most are supratentorial and off-midline
Contain clear fluid that follows CSF signal
Uniclocular, smooth wall, can remodel the calvarium
No restricted diffusion, No enhancement
Typically supratentorial, middle cranial fossa ~65%
Posterior fossa ~10%
Treatment options: observe, resection, shunting
Hemorrhage into cyst can rarely occur
Classic
Uncommon
DDX
Epidermoid cyst (+DWI)
Porencephalic cyst (communicates with ventricle)
Chronic subdural hematoma (old blood products GRE or SWI)

10. Arachnoid cyst
Rare midline arachnoid cyst assumed in the velum interpositum

11. Epidermoid cyst
Extra-axial, basal cistern, para-midline cystic mass, CT hypodense,
MR restricted diffusion and incomplete FLAIR suppression

12. Epidermoid cyst Congenital
Squamous epithelium wall with internal keratin and cholesterol
Location: Extra-axial, paramidline, basal cisterns
Cerebellopontine angle CPA cistern ~50%
Fill cisterns, surround vessels and cranial nerves
CT: hypodense similar to CSF
MR: + DWI restriction, T1 T2 iso to hyperintense, mild heterogeneity, incomplete FLAIR suppression , minimal–no enhancement
DDX
Arachnoid cyst, (no DWI, CSF signal)
Dermoid cyst, (midline, less common, fat T1 signal)

13. Epidermoid cyst
Incidental finding of an intracranial extra-axial, lesion just above the right foramen ovale that is consistent with an incidental epidermoid cyst.

14. Dermoid cyst Extra-axial, suprasellar, midline cystic mass
T1 hyperintense (fat) , FLAIR intense, +DWI

15. Dermoid cyst Benign, congenital Keratin + cholesterol + hair, fat, oil
Midline, suprasellar cistern location most common
Rare, younger age than epidermoid
Can rupture, chemical meningitis
CT: hypodense
MR: fat T1 signal, +DWI, FLAIR intense
DDX
Epidermoid cyst, (no fat signal)
Lipoma (homogeneous)
Craniopharyngioma (multicystic, enhancement)

16. Enlarged perivascular Space
T2 cyst
Intra-axial, supratentorial, follows CSF signal, no enhancement, No restricted diffusion

17. Enlarged perivascular Space
AKA “Virchow-Robin space
Most common intra-axial cyst
Anatomic variant, nonneoplastic
Dilated pia lined spaces along arterioles into brain parenchyma (intra-axial)
Follow CSF signal
Classic located near the anterior commisure in basal ganglia
Also common in white matter, midbrain, and cerebellum dentate nuclei (*infratentorial)
Incidental, usually asymptomatic
DDX
Lacunar infarct
Neurocysticercosis

18. Neuroglial cyst
Intra-axial, supratentorial, follows CSF signal, no enhancement,
No restricted diffusion
There is no restricted diffusion, internal or peripheral enhancement, solid components, or surrounding vasogenic edema.
The cyst does not communicate with the adjacent right lateral ventricle or extend to the right frontal cortex.
Imaging findings are consistent with a Neuroglial cyst

19. Neuroglial cyst Benign congenital lesion Uncommon Intra-axial
Clear CSF like cyst lined by epithelium
Typically intraparenchymal in the frontal lobe
Round, smooth, no enhancement,
Does not communicate with the ventricle
DDX
Enlarged perivascular space
Infectious cyst
Arachnoid cyst
Cystic neoplasm
Companion case of a left temporal lobe Neuroglial cyst

20. Choroid plexus cyst
Intra-axial, intra-ventricular subtle CSF density and T2 hyperintense cystic masses with peripheral enhancement in the choroid plexus glomi in the lateral ventricle atria.
Imaging findings consistent with Choroid Plexus Cysts.

21. Choroid plexus cyst Benign, congenital and acquired
Location: intraventricular, choroid glomus in atrium
Usually asymptomatic and incidental, rarely can cause hydrocephalus obstruction with large size
Cyst contains protein; CT and MR signal vary iso to hyper T1 and T2, variable enhancement
~75% bright on DWI
enhancement
DDX
Ependymal cyst
Choroid plexus papilloma (child, avid enhancement)
Acute stroke workup demonstrating incidental choroid plexus cysts on DWI

22. Colloid cyst
Intra-axial, intra-ventricular unilocular hyperdense cyst at the upper 3rd ventricle/foramen of Monroe area. MR demonstrates isointense T2 signal and nonenhancment. No acute hydrocephalus.

23. Colloid cyst
Unilocular 3rd ventricle mucin containing cyst derived from endoderm
Characteristic location: antero-superior aspect of the third ventricle, adjacent to the Foramen on Monro and between the fornices
Symptoms asymptomatic/incidental to headache and obstructive hydrocephalus
CT majority are hyperdense
MR signal variable depending on protein and water content, No restricted diffusion
Size subcentimeter – 3 cm
Treatment: surgical excision
Notify physician about findings b/c risk of hydrocephalus and death
DDX
Characteristic location limited differential
Intraventricular metastasis
Astrocytoma

24. Etra-axial, supratentorial, midline cyst in pineal gland
Pineal cyst
Etra-axial, supratentorial, midline cyst in pineal gland

25. Pineal Cyst Benign, fluid cyst in pineal gland Etiology unknown
Incidental finding, relatively common ~25% of adults
Usually asymptomatic
Large cyst can compress cerebral aqueduct and cause hydrocephalus or compress midbrain tectum (Perinaud syndrome)
Rarely hemorrhage complication
Small <1 cm
Signal intensity variable but usually iso to hyperintense to CSF
DDX
Pineocytoma (solid, enhancement)

26. Extra-axial, supratentorial, midline T2 hyperintese cyst in the sella
Rathke cleft Cyst
Extra-axial, supratentorial, midline T2 hyperintese cyst in the sella

27. Rathke Cleft Cyst Usually incidental and asymptomatic DDX
Congenital lesion of residual Rathke’s pouch between the anterior and intermediate pituitary lobes
Usually incidental and asymptomatic
Hemorrhage complication is rare
Sellar and suprasellar mass effect
Symptoms: asymptomatic or related to mass effect, headache, pituitary dysfunction, visual field deficits
Well circumscribed sellar based cyst usually T2 hyperintense based on protein content
No enhancement, peripheral enhancement represents compressed pituitary
DDX
Craniopharyngioma
Pituitary adenoma
Arachnoid cyst

28. Porencephalic cyst
Intra-axial, supratentorial, off-midline CSF cystic cavity that communicates with the ventricles
Congenital or acquired CSF cystic cavity that communicates with the ventricles
Follow CSF signal and density

29. Porencephalic cyst DDX Arachnoid cyst (extraaxial)
CSF filled cavity in the brain parenchyma
Majority are acquired from prior insult
but can be congenital
Communicate with or adjacent to the ventricle
Follow CSF signal, sharp margins, No restricted diffusion
DDX
Arachnoid cyst (extraaxial)
Cystic encephalomalacia

30. Intracranial abscess
Intra-axial, supratentorial, off-midline frontal lobe low density ring enhancing mass with restricted diffusion, surrounding vasogenic edema ,and mass effect . Findings consistent with …

31. Intracranial abscess Rare Appearance of infection depends on stage
early/late cerebritis stage, early/late capsule stage
Commonly supratentorial at grey-white junction
Restricted diffusion (+DWI) and presentation (headache, fever)
Etiology depends on age and immune status, most are hematogenous and pyogenic
Treatment: surgical excision and drainage + antibiotics
DDX “Ring-enhancing mass”
Cystic neoplasm 1° or metastatic
Subacute hematoma or infarction
Demyelinating process

32. neurocysticercosis
Extra-axial, supratentorial, off-midline temporal lobe T2 hyperintense cyst with central enhancing scolex, thin enhancing wall, and absent surrounding vasogenic edema

33. Neurocysticercosis Most common CNS parasitic infection
Caused by the encysted larva of the tapeworm
Taenia solium
Common worldwide and the Southwest United States
Extraaxial, cyst actually in the subarachnoid space but can appear intraparenchymal
Multiple stages: vesicular, colloid, granular, calcified
Early vesicular stage can present as an intracranial cyst
DDX
Malignancy, cystic metastasis
Enlarged perivascular space
Left temporal lobe vesicular stage cyst with scolex

34. Craniopharyngioma
Extra-axial, suprasellar, midline T2 hyperintense cystic sella/suprasellar mass causing obstructive hydrocephalus

35. craniopharyngioma Benign, WHO 1 epithelial tumor from Rathke pouch
Extra-cranial cystic suprasellar mass
Usually T2 hyperintense
Wall and solid components enhance
Look for a calcification
Bimodal distribution children, adults
2 types
- Adamantinomatous: cystic pediatric type
- Papillary: solid adult type
Treatment: resection, radiation
DDX
Dermoid (T1 fat signal, +DWI, no enhancement)
Rathke cleft cyst

36. Cystic brain metastasis Colon adenocarcinoma

37. Hemangioblastoma

38. Cystic Schwannoma

39. Summary/Conclusion: 
We reviewed common and uncommon intracranial cysts.
Start with anatomic localization of a cyst first (intra/extra axial, midline, intraventricular?)
CT and MR imaging features (CSF signal, diffusion, enhancement)
Combine location and appearance to make diagnosis or form a short differential.

40. references
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Salzman KL, Osborn AG, House P et-al. Giant tumefactive perivascular spaces. AJNR Am J Neuroradiol. 2005:26:
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