Colloid Cyst

A, Coronal T2-weighted sequence shows a very low-signal colloid cyst of the third ventricle, with obstruction of Monro's foramen.
B, High signal intensity can be seen on the T1-weighted sequence. Aspiration during the endoscopic procedure was difficult. The cyst's contents were evacuated after opening the cyst's wall by using larger aspirating probes.
Baseline CT and CT studies obtained during present admission.
A, Baseline noncontrast axial 5-mm section shows hyperdense colloid cyst (arrow) in the rostral aspect of the third ventricle. There is moderate dilatation of the lateral ventricles and cerebral atrophy secondary to AIDS. In this view, the colloid cyst is round in appearance.
B, CT scan obtained immediately after acute neurologic deterioration shows marked hydrocephalus and hypodensity in the white matter of the frontal lobes. The etiology of the presumed punctate hemorrhage in the right frontal lobe is not known.
C, CT obtained immediately after the initial ventriculostomy shows a right-sided catheter that has decompressed the lateral ventricle. The left lateral ventricle remains enlarged and there is mild midline shift to the right. A small amount of blood is present in the right lateral ventricle secondary to catheter insertion.
D, CT done after insertion of left-side ventriculostomy shows decreased hydrocephalus, compared with B, and no midline shift.

Postmortem MR imaging. A, Coronal T1-weighted image (560/15/1 [TR/TE/excitations]) of the fixed brain shows that the colloid cyst is centrally of higher signal intensity [c] and its rim is relatively hypointense. The lesion is oval-shaped in this projection. The linear hyperintensities in the left basal ganglia are related to a hemorrhagic infarction (see fig 3A).
B, Corresponding proton density–weighted image (4500/15/1) shows the lesion to be homogeneous and of similar signal intensity to white matter.
C, Corresponding T2-weighted image (4500/105/1) shows the central portion of the cyst to be hypointense and its rim to be slightly hyperintense. Cortical sulci dilatation is well seen in this sequence.

In vivo MR imaging of a colloid cyst (different patient).
A, Axial noncontrast T1-weighted image shows oval-shaped, hyperintense colloid cyst [c].
B, Corresponding T2-weighted image shows the cyst to be markedly hypointense. There is no hydrocephalus in this patient.