The T1-weighted precontrast MR (not shown) demonstrated an area of low signal intensity throughout the left parietal-occipital area which was new. A previous study had shown only postoperative changes. Following the administration of contrast material (gadolinium-DTPA), signal intensity was much enhanced, as seen in image 59 and surronding slices, suggesting either tumor recurrence or radiation necrosis. This finding also represented a change when compared to the previous contrast enhanced MR. The PET scan demonstrated high activity in this region, suggestive of tumor recurrence, and effectively ruling out radiation necrosis.

Treatment options included surgical resection of the area of increased metabolic activity consistent with tumor recurrence or stereotactic radiosurgery to that same area, either as a primary treatment or for palliation, if follow-up MR again revealed contrast enhancement.

Like Thallium SPECT, the PET scan has been very useful in differentiating tumor recurrence and radiation necrosis. It also allows specific targeting of the area of recurrence, which may be surrounded by radiation necrosis in those patients who have received radiation.

Case contributed by Drs. C. D. Sturm and R. Bucholz, St. Louis University.