Clinical interpretation of residual uptake in 11C-methionine positron emission tomography after treatment of basal ganglia germ cell tumors: report of 3 cases.

Although (11)C-methionine (MET)-PET has been used to diagnose intracranial germ cell tumors (GCTs) arising in the basal ganglia, whether this imaging technique is useful in assessing treatment response and residual tumor is still unclear. The authors report 3 cases of basal ganglia GCTs in which the residual MET uptake at the end of treatment did not develop into a relapse, even without additional treatment. Case 1 is a 22-year-old man who had a second relapse of a left basal ganglia germinoma with diffuse dissemination on the walls of both of his lateral ventricles. MET-PET revealed high MET accumulation around tumors and their surroundings (maximum standardized uptake value [SUVmax] 3.3). After all treatments, MET-PET demonstrated mild tracer accumulation in both basal ganglia (SUVmax 2.2). Progression-free survival was 56 months from the second relapse without any further treatment. Case 2 is a 17-year-old boy with a left basal ganglia germinoma that showed increased MET uptake (SUVmax 4.2). After treatment, MET-PET revealed residual MET uptake (SUVmax 2.4) along the left posterior limb of the internal capsule. Progression-free survival was 52 months from the start of treatment. Case 3 is a 7-year-old boy with a left basal ganglia choriocarcinoma with increased tumor MET uptake (SUVmax 2.5). A minor enhanced mass remained on MRI after treatment with residual MET accumulation (SUVmax 1.4). Progression-free survival was 44 months. Treatment strategies based on MET uptake on PET should be carefully designed in patients with basal ganglia GCTs to avoid overtreatment and complications.