MB-21: CASE REPORT OF THE NATURAL HISTORY OF INCIDENTALLY FOUND MEDULLOBLASTOMA FOLLOWED RADIOGRAPHICALLY IN A YOUNG ADULT WITH CHRONIC HEADACHES

Medulloblastoma is a malignant tumor diagnosed in 12-25% of pediatric brain tumors, 77% before age 19. The rate sharply declines with increasing age being only diagnosed in 0.4-1% of adult brain tumors. These tumors are diagnosed typically after symptoms noted consistent with increased intracranial pressure. We present a case of a young adult who was followed with serial MRI scans due to history of headaches and developed a cerebellar lesion later diagnosed as medulloblastoma. Patient AG had the original MRI scan for chronic headaches yielding only a right posterior fossa arachnoid cyst. Four years later, persistent headaches warranted another scan showing a new lesion with T2 FLAIR hyperintensity in the left cerebellar hemisphere. Serial scans over two years showed progression in size and complexity of this lesion originally thought benign. AG underwent craniotomy with mass resection resulting in cytoplasmic beta-catenin positive medulloblastoma without anaplasia, metastasis, or CSF involvement. Post-operative imaging showed a small suspicious area near the resection cavity positive for residual medulloblastoma greater than 1.5 cm, thus placing this patient in high-risk treatment category. AG elected proton therapy (36 in the craniospinal region with posterior fossa boost) with vincristine following protocol ACNS0331 and maintenance therapy. Serial MRI scans since are without evidence of residual disease. Literature review found low occurrences of incidental CNS tumors in mainly trauma and research cases. It is rare to have radiographic evidence of the onset of a malignant brain tumor. We present our case as a natural history of medulloblastoma with literature review.