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

A Review of Effusion Cytomorphology of Small Round Cell Tumors

BACKGROUND

Small round cell tumors (SRCTs) are a broad category of diverse malignant tumors composed of monotonous undifferentiated cells. Involvement of serous fluids by SRCT is rare; however, the identification of exfoliated malignant cells is a crucial component of management and has significant implications for treatment and prognosis. The most common effusion tumors with SRCT morphology include Ewing sarcoma, synovial sarcoma, rhabdomyosarcoma (RMS), small-cell neuroendocrine carcinoma (SCNC), and desmoplastic SRCT, and the cytomorphologic distinction between these tumors is challenging. The purpose of this article is to describe the morphologic features of the most common SRCT in fluids and propose helpful ancillary testing.

SUMMARY

Effusion SRCTs display similar primitive and undifferentiated morphologic features although each has subtle variations. Ewing sarcoma is a mesenchymal neoplasm and harbors characteristic translocations t(11;22) (EWSR1-FLI1) or t(21;22) (EWSR1-ERG). In fluids, Ewing sarcoma shows poorly differentiated cells of variable size with round to oval nuclei, prominent nucleoli, and scant cytoplasm. In contrast, synovial sarcoma typically involves extremities and expresses a fusion transcript in t(X;18) (SS18-SSX). This soft tissue neoplasm demonstrates uniform cells with irregular nuclear contours, characteristic nuclear folding, and scant cytoplasm. RMS is a neoplasm arising from skeletal muscle, and the alveolar subtype demonstrates a translocation in t(2;13) (PAX3-FOXO1). The malignant cells show a spectrum of small round cells and pleomorphic large cells with rhabdoid morphology. RMS cells characteristically express myogenin and MyoD1, markers of skeletal muscle differentiation. Although SCNC is not a classic SRCT, the morphology is similar. SCNC demonstrates tight clusters of malignant cells with nuclear molding and salt-and-pepper chromatin. This tumor classically has neuroendocrine differentiation and is positive for synaptophysin and chromogranin on immunohistochemistry. And last, desmoplastic SRCT typically presents as an intra-abdominal mass in young men and characteristically harbors the translocation t(11;22) (p13;q12) (EWSR1-WT1). Cytomorphologically, the tumor shows small monomorphic cells occasionally arranged as rosette-like structures.

KEY MESSAGE

The diagnosis of SRCT can be made in effusion samples and is best achieved with a combination of morphologic features, clinical history, and ancillary testing.

Cytologic diagnosis of metastatic embryonal rhabdomyosarcoma in cerebrospinal fluid: A case report

Rhabdomyosarcoma (RMS) originates from a differentiation block in muscle progenitors. Leptomeningeal metastasis is a rare but devastating complication of RMS which can be caused by dissemination of cancer cells in cerebrospinal fluid (CSF). Here, we present a 4-year-old female with RMS originating from the upper nasal wall. The following histologic and immunohistochemistry analyses combined with molecular testing analysis supported the diagnosis of embryonal rhabdomyosarcoma (ERMS). Results from CSF routine test, magnetic resonance imaging scans and CSF cytology indicated metastatic meningitis, thus confirming the diagnosis of metastatic ERMS in CSF. This is the first report to describe the clinical features of ERMS in CSF.

Effusion cytology of epithelioid rhabdomyosarcoma

We report a case of epithelioid rhabdomyosarcoma in a pleural effusion. In contrast to most rhabdomyosarcomas in effusions, the cells presented as cohesive clusters of atypical cells with abundant eosinophilic cytoplasm which mimicked an adenocarcinoma. Immunohistochemistry was positive for epithelial membrane antigen and muscle markers and negative for keratins.