Positron emission tomographic imaging of acoustic neuromas

Positron emission tomography (PET) examination with both [C-11]methyl-1-met hionine (Met) and [F-18]fluoro-2-deoxyglucose (FDG) was performed in the sa me patients with acoustic neuroma wherever possible in order to compare the usefulness of the two methods. The study included six patients who visited the Osaka City University Hospitals, between April 1994 and October 1998, for complaints associated with acoustic neuroma. All patients were examined by magnetic resonance imaging (MRI) and Met-PET. Four patients were examin ed by FDG-PET. The tumor's region of highest accumulation was selected as t he region of interest; the tumor/normal ratio (T/N ratio) was defined as th e ratio of radioisotope counts for tumor and normal gray matter. All tumors in this series were detected by MRI. In the Met-PET images, four tumors we re easily identified, with a high T/N ratio. However, two tumors could not be identified using Met-PET. On FDG-PET, no cases could be identified. The TN ratio for the four patients with positive Met-PET findings averaged 1.69 4 +/- 0.266. PET, especially Met-PET, is a powerful means of examination pr oviding functional information on tumors in acoustic neuroma. Met-PET may t herefore be useful for acoustic neuroma, which is known to proliferate slow ly, as for malignant tumors, in evaluating the proliferating potential of a tumor, in determining patients in whom to perform radiological treatment a nd in monitoring post-treatment progress.