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

Abstract

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.

A Review of Effusion Cytomorphology of Small Round Cell Tumors

“…The incidence of RMS is 5.4 per million total population younger than 15 years, and this tumor arises from various sites, most frequently the head and neck, extremities, and genitourinary tract [35, 38]. RMS is further subclassified as embryonal, alveolar, and pleomorphic types and develops predominately in younger children, older children/adolescents, and older adults, respectively [23, 36, 39-41].…”

“…The cellularity ranges from scattered singly dispersed cells to abundant loosely cohesive tumor cell clusters in a background of occasional karyorrhexis, proteinaceous debris, reactive mesothelial cells, and inflammation [1, 4, 37, 39, 40, 43]. Cytomorphologically, there is a spectrum of small round cells and pleomorphic large cells [1, 39, 40]. The small round cells are discohesive, polymorphous, and approximately 2–5 times the size of mature lymphocytes [7, 42].…”

“…In fluids, sarcoma cells round up due to the lack of surrounding stromal tissue [4]. This results in morphologic overlap, and the elongated cells of embryonal RMS are not readily apparent [39]. Additionally, mucoid substances have not been described in effusion cytology involving RMS [39].…”

Effusion cytology of epithelioid rhabdomyosarcoma

“…Rhabdomyosarcoma presenting in effusion cytology specimens is an uncommon but well described event. [1][2][3][4][5][6][7][8][9][10][11] Typically, the cells of rhabdomyosarcoma present in effusion specimens as dyshesive individual cells with scant cytoplasm which has been described as a small round blue cell tumor. Alveolar rhabdomyosarcoma cases can have more abundant cytoplasm, but typically still resemble a small round blue cell tumor.…”

“…Rhabdomyosarcoma presenting in effusion cytology specimens is an uncommon but well described event . Typically, the cells of rhabdomyosarcoma present in effusion specimens as dyshesive individual cells with scant cytoplasm which has been described as a small round blue cell tumor.…”