Recurrent anaplastic medulloblastoma in cerebrospinal fluid after autologous hematopoietic stem cell transplant

Cerebrospinal fluid (CSF) dissemination can be seen relatively frequently in medulloblastomas and its presence at diagnosis is important for determining both treatment and prognosis. The anaplastic variant is an aggressive variant of medulloblastoma with characteristic histopathologic features and unfavorable prognosis that was included in the latest WHO classification. Herein, we report the CSF cytologic features of a case of recurrent anaplastic medulloblastoma in a 17-year-old male patient who had undergone autologous hematopoietic stem cell transplant as a part of the treatment protocol. The malignant cells were large, had high nucleocytoplasmic ratios, and highly pleomorphic, frequently polylobated nuclei with coarse chromatin and 1-3 visible nucleoli. These CSF cytologic features differed significantly from those of classic medulloblastoma, which usually shows small cells with rounded, rather uniform nuclei with fine ("blastic") chromatin. The differential diagnosis of anaplastic medulloblastoma is broader than that of classic medulloblastoma, as it includes metastatic carcinomas and large cell lymphoma, a differential diagnosis especially pertinent in this patient with a history of autologous hematopoietic stem cell transplant. Awareness of these unusual but distinctive cytologic features is important for the accurate diagnosis of anaplastic medulloblastomas in CSF specimens and to avoid possible diagnostic pitfalls.