Case 10 :  

A 27-year-old male presents with sudden-onset headache and vomiting. CT scan is performed. 
What is the diagnosis?

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Fig 1 (plain)

Fig 2 (Contrast)

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Imaging Findings
Study 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 Cyst

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.

Imaging Findings

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 lining.


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
Manipal Hospital, Bangalore