Squash cytology of a case of medulloblastoma with myogenic differentiation.

Medulloblastoma with myogenic differentiation is not a distinct entity but a pattern of differentiation seen in <1% of medulloblastomas. Although squash cytology of medulloblastoma is well described, there are no reports available describing squash cytomorphology of this unusual variant of medulloblastoma. Intraoperative squash smears on a 2-year-old girl with a midline posterior fossa space occupying lesion revealed features of an embryonal tumor composed of small, round, and blue cells. In addition, it had several large, round, eosinophilic rhabomyoblasts, and a few strap cells scattered among the sea of small blue cells. Subsequent histology showed features of a medulloblastoma, classic type with myogenic differentiation. Molecular subtyping, based on immunohistochemistry alone, was in keeping with a non-Wnt/non-SHH activated type. Here we describe the squash cytomorphological details of a case of medulloblastoma with myogenic differentiation, along with its cytological differentials.