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Colloid cyst of the third ventricle

Case contributed by Bruno Di Muzio
Diagnosis certain


Collapse at home. Admission CT brain not available, the patient was then scanned after first neurosurgical approach.

Patient Data

Age: 40
Gender: Female

CT Brain


Marked ventriculomegaly affecting the lateral ventricles with mild periventricular hypoattenuation. The third ventricle is effaced by an ill-defined mass with mixed internal density (predominantly hypodense with a hyperdense component posteriorly). Cerebral aqueduct and fourth ventricle are within normal bilateral. Bilateral frontal approach ventricular drains with the tip within each body of the lateral ventricle. A trace amount of extra-axial blood associated with the left drain. 

MRI Brain


There is a thin-walled cystic lesion located within and expanding the third ventricle, measuring approximately 16 x 21 x 17 mm (L x AP x T). The contents are T1 hypointense (slightly hyperintense relative to CSF) and T2 hyperintense (slightly hypointense relative to CSF). In the posterior aspect of the cystic cavity is well-circumscribed focus of different signal, T1 hyperintense and T2 hypointense. No associated enhancement. The lesion causes obstruction of the Monro foramina bilaterally leading to hydrocephalus, which is overall unchanged compared to the CT from yesterday. Bifrontal EVD are in situ. Small rim of transependymal fluid shift is present. Small amount of blood within the posterior horn of the left lateral ventricle and in a subarachnoid distribution in the frontal lobe are likely related to the EVD placement. The remainder of the brain has unremarkable appearances. No cerebral herniation.



Histology confirmed a colloid cyst. 

Case Discussion

Features are those of obstructive hydrocephalus due to a third ventricle cystic lesion, which was favored to represent a large colloid cyst given its imaging appearances and further confirmed after surgical resection. 

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