shows a bright hyperdense tiny lesion in the third ventricle showing no
enhancement on contrast administration. No ventriculomegaly or peri-ventricular
ooze is noted. No adjacent neuroparenchymal edema is seen.
Colloid cysts comprise about 1% of all intracranial tumors and are located
in the superior anterior third ventricle. The embryonic origin of the
colloid cyst is neuroepithelium located in the tela choroidea of the roof
of the third ventricle. Obstruction of the foramen of Monro is common.
CT findings show a smooth, round, homogeneous, high-density lesion located
in the anterior portion of the third ventricle. Colloid cysts do not
contain calcium; therefore, the finding of calcification in lesions in
this area excludes the diagnosis of colloid cyst. No or minimal
enhancement is present on CECT. Dense enhancement should raise the
suspicion of a basilar artery aneurysm or meningioma and is a definite
indication for angiography.
The MRI diagnosis of colloid cyst is based mainly on location and
morphology, and although several entities may occur in this region,
including choroid plexus neoplasm, meningioma, glioma, and granuloma,
there is almost never a question about the diagnosis. Colloid cysts are
remarkably varied in their signal intensity on MRI: lesions are reported
as ranging from markedly hypointense to markedly hyperintense on long TR/TE
images. They can also be high or low intensity on T1-weighted
images. This spectrum of intensities presumably relates to differences in
concentration of paramagnetic substances, free water, and mucoid material.
A thin wall is nearly always discernible and represents the epithelial
1. Maeder PP, Holtas SC,Basibuyuk KN , et al. colloid cyst of the
third ventricle, Correlation of MR and CT findings with histology and
chemical analysis. AJNR 1990;11: 575-581.
Dr. Ashok Raghavan, MD