Brain scanning has proved a valuable diagnostic aid in intracranial disease (1). Although an early report suggested that an intracranial cyst could be diagnosed by decreased count rate (2), most reports deal with increased activity seen on the scan with neoplasm, inflammatory changes, hematomata, surgery, and vascular abnormalities. We know of only two reported cases demonstrating a negative defect or area of reduced activity on the brain scan secondary to an avascular lesion such as a cyst (3, 4). This communication reports five cases showing a negative defect on the brain scan secondary to a cyst and demonstrates the features on the brain scan suggestive of the diagnosis of a cyst. Case Reports Case I: A one-year-old girl had been developing normally until a few weeks before admission to the hospital when her parents noted increasing head size and irritability. Examination disclosed slight proptosis of the right eye and an enlarged occipital-frontal circumference of 51.1 cm. The right side of the head transilluminated. Skull films demonstrated slight widening of the suture lines and asymmetry of the skull, which was enlarged on the right. The right parietal bone was thinned, the right middle cranial fossa was elongated and depressed, and the sagittal sinus groove was displaced to the left (Fig. 1, A). The brain scan had a large area of decreased activity on the right with displacement of the normal cerebral structures to the left, especially well demonstrated on the vertex view (Fig. 1, B–D). Pneumoencephalography combined with air introduced into a cystic cavity through the cranial sutures showed marked displacement of the ventricles by the right frontoparietal cyst (Fig. 1, E). Surgery revealed a large arachnoid cyst occupying almost the entire right hemisphere. Case II: A 3-year-old boy had been delivered prematurely, weighing 4 lb. 8 oz. at birth. The child did not appear normal at birth and at the age of two months the diagnosis of “brain tumor” had been made by means of cerebral ventriculography. The child never crawled, sat, stood, or talked. He screamed while awake. The head was elongated with bulging of the right frontoparietal area, and there was a palpable defect of the skull in this area. The interorbital distance was increased. The right side of the head transilluminated. An electroencephalogram showed generalized slowing of electrical activity, more marked on the left. The cerebrospinal fluid had a protein content of 109 mg per 100 cc but was otherwise normal. Skull films demonstrated bulging and thinning of the right frontal and parietal bones with septation of the thinned bone and widening of the interorbital distance (Fig. 2, A and B). The brain scan revealed displacement of the sagittal sinus to the left with a large area of decreased activity occupying the right frontoparietal area.
Read full abstract