Diagnosis of alveolar rhabdomyosarcoma in effusion cytology: a diagnostic pitfall

Serous fluid: Metastatic sarcomas, melanoma, and other non-epithelial neoplasms

While most tumors metastatic to the serous membranes are of epithelial origin, cytologists should be aware that non-epithelial neoplasms can also cause malignant effusions including sarcomas, melanomas, germ cell tumors, and, more rarely, brain tumors. The differential diagnosis of a malignant effusion is accordingly broad, especially for the small round blue cell tumors that includes not only mesenchymal tumors, but also non-mesenchymal tumors, such as neuroblastoma and Wilms tumor. Diagnosing non-epithelial malignancies in effusion specimens based entirely upon their cytomorphologic features is difficult because these neoplasms often exhibit considerable morphological overlap and their cytomorphology can differ from the original tumor. As malignant cells have a tendency to round up in body fluids these non-epithelial neoplasms can therefore mimic reactive mesothelial cells and metastatic adenocarcinoma. The use of ancillary studies including immunostaining, FISH, and molecular studies is thus often critical to reach a definitive diagnosis. This review article will be incorporated finally as one of the chapters in CMAS (CytoJournal Monograph/Atlas Series) #2. It is modified slightly from the chapter by the initial authors in the first edition of Diagnostic Cytopathology of Serous Fluids.

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.

Pericardial metastasis from alveolar rhabdomyosarcoma: A case report

Alveolar rhabdomyosarcoma (ARMS) commonly occurring in children and adolescents, is a rare and aggressive soft tissue malignancy demonstrating rapid growth and dissemination. Although their histopathologic and immunohistochemical findings are well known, cytomorphological features on serous effusions have not been well documented. A case of metastatic rhabdomyosarcoma diagnosed on cytological examination of the pericardial fluid cytology and discuss the diagnostic difficulties that were encountered in this case has been presented.

Alveolar rhabdomyosarcomas involving serous cavity fluid specimens exhibit diverse cytomorphologies: A case report and review of the literature

Involvement of serous cavity specimens by alveolar rhabdomyosarcoma (ARMS) is a rare event and only a few case reports have been reported in the literature, with conflicting cytomorphologic patterns. Herein, we report on a 41-year-old man with no significant past medical history who presented with pancytopenia and shortness of breath and was found to have widely metastatic sinonasal alveolar rhabdomyosarcoma, including involvement of the pleura. The pleural fluid specimen was cellular and contained ARMS cells in small-to-medium sized three-dimensional fragments that resembled an adenocarcinoma or mesothelioma, and numerous single cells were seen in the background. The individual tumor cells demonstrated variable morphology; all were large, with varying degree of cytoplasm, and multinucleated cells were commonly seen in the background. The cells were negative for calretinin and claudin-4 and were positive for myogenin, confirming the diagnosis. Given the cytomorphologic diversity of ARMS seen in serous fluid specimens, patient history and the use of confirmatory immunostains are essential.

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.

Effusion cytomorphology of small round cell tumors

Background:

Small round cell tumors (SRCTs) are a group of tumors composed of small, round, and uniform cells with high nuclear/cytoplasmic (N/C) ratios. The appearance of SRCT neoplastic cells in the effusion fluid is very rare. We reported the cytomorphological findings of SRCTs in effusion cytology, and performed statistical and mathematical analyses for a purpose to distinguish SRCTs.

Materials and Methods:

We analyzed the cytologic findings of effusion samples from 40 SRCT cases and measured the lengths of the nuclei, cytoplasms, and the cell cluster areas. The SRCT cases included 14 Ewing sarcoma (EWS)/primitive neuroectodermal tumor cases, 5 synovial sarcoma cases, 6 rhabdomyosarcoma cases, 9 small cell lung carcinoma (SCLC) cases, and 6 diffuse large B-cell lymphoma (DLBL) cases.

Results:

Morphologically, there were no significant differences in the nuclear and cytoplasmic lengths in cases of EWS, synovial sarcoma, and rhabdomyosarcoma. The cytoplasmic lengths in cases of SCLC and DLBL were smaller than those of EWS, synovial sarcoma, and rhabdomyosarcoma. The nuclear density of the cluster in SCLC was higher than that in other SRCTs, and cases of DLBL showed a lack of anisokaryosis and anisocytosis.

Conclusion:

We believe that it might be possible to diagnose DLBL and SCLC from cytologic analysis of effusion samples but it is very difficult to use this method to distinguish EWS, synovial sarcoma, and rhabdomyosarcoma. Statistical and mathematical analyses indicated that nuclear density and dispersion of nuclear and cytoplasmic sizes are useful adjuncts to conventional cytologic diagnostic criteria, which are acquired from experience.

Cytological diagnosis of metastatic alveolar rhabdomyosarcoma in the ascitic fluid: Report of a case highlighting the diagnostic difficulties

Alveolar rhabdomyosarcoma is an uncommon tumor affecting adolescents and young adults that is only rarely encountered in body fluid cytology. We report the cytological features of metastatic alveolar rhabdomyosarcoma in the ascitic fluid of a 17-year-old female patient, who had presented with abdominal distention, 21 months after being diagnosed with perirectal alveolar rhabdomyosarcoma. The rare single neoplastic cells that were admixed with abundant reactive mesothelial cells were initially misinterpreted as reactive mesothelial cells. However, their neoplastic nature was established after a careful review of their cytological features and the performance of immunoperoxidase stains. Compared to the reactive mesothelial cells that were present in the sample, the malignant cells were smaller, with less ample and more homogenous cytoplasm. They had slightly larger, more hyperchromatic, and more frequently eccentric nuclei, with larger nucleoli. This case highlights the potential pitfall of the misinterpretation of metastatic alveolar rhabdomyosarcoma cells for reactive mesothelial cells. Awareness of this potential diagnostic problem and recognition of the cytomorphological features of this neoplasm in the body fluids allows the identification of malignant cells, even when they are rare and intimately associated with mesothelial cells.