Detecting bone marrow metastasis in cerebellar medulloblastoma: value of disease surveillance with FDG-PET in this setting.

Sir, In this communication, the role of fluorodeoxyglucose positron emission tomography FDG-PET imaging in the detection of bone marrow metastasis in medulloblastoma is underscored. Skeletal involvement is relatively rare in the natural history of medulloblastoma. [1] However, this tumor shows the highest incidence of bone marrow metastasis among the other central nervous system malignancies. [2] We herein illustrate a 27-year-old male, who was diagnosed to have left cerebellar medulloblastoma who had disease recurrence in the form of extensive bone marrow metastasis detected by FDG-PET imaging and subsequently proven by bone marrow biopsy. He had undergone surgery for excision of the tumor one and a half year before. Postoperatively, he had undergone treatment with tomotherapy-based intensity modulated radiation therapy IMRT followed by six cycles of adjuvant chemotherapy one year back and was overall disease-free in the follow-up one-year period. Magnetic resonance imaging (MRI) of brain and spine done three months before did not reveal any disease at either of the sites. There was only cerebrospinal fluid CSF signal intensity area in the left cerebellar hemisphere. It appeared hypointense on T1W images and hyperintense on T2W images and did not show any post-contrast enhancement. The recent whole-body FDG-PET demonstrated diffuse and patchy FDG uptake in the entire axial skeleton and bilateral humerii and femora-consistent bone marrow involvement [Figure 1]. The bone marrow biopsy revealed diffuse replacement of marrow with hyperchromatic small round cells with moderate pleomorphism. On immunohistochemistry these cells were strongly positive for synaptophysin and negative for cytokeratin, epithelial membrane antigen and desmin, ruling out other tumors. Delicate bands of fibrosis were seen around tumor cells [Figure 2].