Radiology in the diagnosis of colloid cysts of the third ventricle.

A series of 38 cases of colloid cyst of the 3rd ventricle is described in most of whom the diagnosis, important for curative surgery, was made radiologically. The most useful investigative technique was pneumography, by which the tumour was outlined in almost all cases. The lateral "hanging head" projection generally demonstrated the lesion most satisfactorily. Care in manipulating air introduced at ventriculography through the foramina of Monro into the 3rd ventricle was frequently rewarded by clear definition of the tumour. In more than one-third of the cases, the lateral plain skull radiograph showed truncation of the dorsum sellae indicative of chronic obstructive hydrocephalus, and, in the large majority of these, pneumography confirmed that the 3rd ventricle, rather than the interventricular foramen, was the site of obstruction to the drainage of cerebrospinal fluid. Carotid angiography, showing hydrocephalus, and in the same cases elevation and lateral displacement of the anterior portion of the internal cerebral veins yielded strong supportive evidence. Vertebral angiography was less specific, and isotope scanning was quite unhelpful.