Specific Imaging Findings

The classic imaging appearance of ganglioglioma (GG) is a cystic mass with a solid tumor nodule which may or may not enhance after contrast administration (about 50% show some enhancement on CT and MRI). This appearance probably occurs in only one-half of the tumors, more commonly in children. Another characteristic feature is the presence of calcifications, which are typically peripheral and shell-like; this is again found in about half of cases. Most GGs occur in the temporal lobes and involve the cortex (and thereby cause seizures). Unfortunately, most GGs have nonspecific imaging features and may be found anywhere in the brain, more likely in the cerebellum, brainstem, spinal cord, optic chiasm, pineal gland, and inside the ventricular system. The lesion size is usually between 3 and 6 cm at the time of discovery. Other imaging appearances include a solid mass (without or with contrast enhancement) and an infiltrating lesion. GGs do show relatively high diffusion, being bright on ADC maps, reflecting their low cellularity. Superficially located tumors tend to expand the overlying cortex and at times MRI may show a discreet cortical dysplasia associated with the tumor. Because they are longstanding, the overlying skull may demonstrate remodeling of its inner table. On nuclear medicine studies with both FDG and thallium, GGs show increased uptake. On MRS they demonstrate nonspecific findings with low n-acetyl aspartate, mildly elevated choline, normal creatine and high myo-inositol on short echo time studies. Lactate may be present, often related to recent seizure activity.