ular cysts are most often found in
the atria of the lateral ventricles and foramen of Monro. CPCs
are the most common of all intracranial neuroepithelial cysts,
occurring in up to 50% of autopsies. Most CPCs are actually
xanthogranulomas. Lipid accumulates in the choroid plexus
from degenerating &/or desquamating choroid epithelium.
CPCs are common incidental imaging findings in middle-aged
and older adults. They are usually bilateral and are often
multicystic. Most CPCs are small, measuring 2-8 mm in
diameter. They typically do not suppress completely on FLAIR
and may show moderately high signal intensity on DWI.
Ependymal cysts (ECs) are rare, benign, ependymal-lined cysts
of the lateral ventricles. Most ECs, even large ones, are
asymptomatic and incidental. EC patients presenting with
headache, seizure, &/or obstructive hydrocephalus have been
reported in the literature. They contain clear serous CSF-like
fluid secreted from ependymal cells. ECs typically follow CSF
on all sequences and suppress completely on FLAIR.
CCs occur almost exclusively in the foramen of Monro,
attached to the anterosuperior portion of the 3rd ventricular
roof. They are wedged into the foramen and are typically
straddled by the fornices. CCs are endodermal in origin and
contain viscous gelatinous material consisting of mostly
mucin. CCs may also contain blood degradation products,
foamy cells, and cholesterol crystals. Even relatively small CCs
may suddenly obstruct the foramen of Monro, causing acute
hydrocephalus. Occasionally brain herniation with rapid clinical
NECT is virtually pathognomonic of a CC.
Infratentorial intraaxial cysts: Parenchymal infratentorial
cysts are rare; most are PVSs. The only common site is in and
around the dentate nuclei. Most are asymptomatic.
Occasionally, large PVSs occur in the pons and can be a rare
Nonneoplastic, nonparasitic cysts in the 4th ventricle are
uncommon. The most common cause is not a true cyst but an
enlarged, "encysted" 4th ventricle. Infection or aneurysmal
subarachnoid hemorrhage may cause outlet foraminal
obstruction. When combined with superior obstruction near
the aqueduct, the 4th ventricle can become completely
encysted. Choroid plexus continues to produce CSF. With
egress blocked, the 4th ventricle enlarges. ECs can arise in the
4th ventricle, a much less common posterior fossa location
than the CPA. Some ECs are so similar to CSF that only FLAIR
and DWI permit distinction of an EC from CSF in an enlarged
but otherwise normal-appearing 4th ventricle.
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