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Very Late Frontal Relapse of Medulloblastoma Mimicking a Meningioma in an Adult: Usefulness of 1H Magnetic Resonance Spectroscopy and Diffusion-perfusion Magnetic Resonance Imaging for Preoperative Diagnosis: Case Report

OBJECTIVE AND IMPORTANCE:We present a rare case of very long-term medulloblastoma relapse in an adult patient and discuss the pattern of recurrence and metabolic imaging of the tumor. CLINICAL PRESENTATION:A 45-year-old man was referred for evaluation of a frontobasal midline tumor 21 years after treatment of a cerebellar medulloblastoma by surgery followed by chemotherapy and craniospinal radiotherapy. Magnetic resonance images were suggestive of a meningioma. Several hypotheses were discussed, such as other radio-induced tumors, sarcomas, high-grade gliomas, or lymphomas (previous chemotherapy) and even recurrence of medulloblastoma. Preoperative exploration included 1H magnetic resonance single-voxel spectroscopy (35 and 135 ms echo time), diffusion imaging, and perfusion magnetic resonance imaging. INTERVENTION:On magnetic resonance spectroscopy, N-acetyl-aspartate and an elevated choline/creatine ratio were retrieved, with a huge unidentified peak at 1.27 parts per million (ppm). Myoinositol signal was present at both echo times. On diffusion imaging, the tumor appeared hyperintense, with a low apparent diffusion coefficient value of 0.689. In the perfusion study, the maximal relative cerebral blood volume was 2. Metabolic imaging favored the diagnosis of medulloblastoma over the initially suspected diagnosis of meningioma. The patient underwent complete removal of the tumor that was confirmed to be a metastasis of his primary medulloblastoma. The postoperative course was uneventful, and complementary courses of radiotherapy and chemotherapy were planned. CONCLUSION:Late relapse should be considered, even after several decades, on occurrence of a second intracranial tumor in this context. Our observation validates the clinical interest of preoperative metabolic imaging for brain tumors with distinctive pattern.