Cytologic Diagnosis of Metastatic Alveolar Rhabdomyosarcoma in Cerebrospinal Fluid: A Case Report

Rhabdomyosarcoma is a malignant soft tissue tumor which shows skeletal muscle differentiation. Leptomeningeal metastasis can occur as a late complication, but currently there are no reports that have documented the cytologic features in cerebrospinal fluid (CSF). We report a case of metastatic alveolar rhabdomyosarcoma diagnosed in the CSF of a 28-year-old male who was originally diagnosed with rhabdomyosarcoma on the neck, and that went through systemic therapy. The tumor was positive for anaplastic lymphoma kinase, but progressed despite additional therapy with crizotinib. The CSF specimen revealed small round cells, large atypical cells with abundant cytoplasm and eccentric nuclei, and cells with horseshoe-shaped nuclei. These cytologic findings were in agreement with previous literature and well-correlated with histopathology. This is the first report to document the cytologic feature of rhabdomyosarcoma in CSF. In many cases it is difficult to perform ancillary tests in a CSF specimen and cytopathologists should be aware of the cytomorphologic characteristics to avoid misdiagnosis.