Desmoplastic Small Round Cell Tumor, a "Floating Island" Pattern in Pleural Fluid Cytology: A Case Report and Review of the Literature

Abstract

Desmoplastic small round cell tumor (DSRCT) is a rare aggressive sarcoma with characteristic clinical and pathologic features. It typically involves pelvic and abdominal organs of young male patients, and patients usually present at advanced stage with poor prognosis. A few reports are available describing the cytopathologic features of DSRCT in serous effusions, with the majority of published cases depicting undifferentiated small blue cells that need to be distinguished from other small blue cell tumors. We report an interesting case of DSRCT involving a pleural effusion with a "floating island" pattern that has been described in hepatocellular carcinoma, renal cell carcinoma, and adrenal cortical carcinoma. In our case, the epithelioid tumor cells form cohesive aggregates surrounded by a single layer of spindle cells, mimicking the "endothelial wrapping" in other tumors with "floating island" patterns. We demonstrate, by ancillary testing, that these peripheral spindle cells are tapered/flattened DSRCT cells, in contrast to endothelial wrapping cells, as seen in other tumors with this unique cytomorphology. To our knowledge, this is the first case report describing DSRCT showing a "floating island" pattern that needs to be differentiated from metastatic hepatocellular carcinoma, renal cell carcinoma, and adrenal cortical carcinoma in effusion cytology.

Figure 1

The excised supraclavicular lymph node showed the characteristic morphology of DSRCT. Cohesive nests of undifferentiated small blue cells with some degree of nuclear atypia were seen embedded within moderately cellular fibrous stroma (histopathology, hematoxylin and eosin stain, 100x).

Figure 2

CT examination confirmed a unilateral right pleural effusion and small lung nodules (transverse computed tomographic image of patient's chest demonstrating posterior right chest effusion).

Figure 3

Liquid-based cytology slides contained rare crowded groups of lesional cells with nuclear overlapping, high nuclear/cytoplasmic ratios, open chromatin, and small but discernible nucleoli. These cells were difficult to differentiate from reactive mesothelial cells by microscopy (ThinPrep, Papanicolaou stain, 600x).

Figure 4

A cohesive and crowded group of metastatic DSRCT cells in pleural fluid with central epithelioid forms having minimal to moderate eosinophilic cytoplasm and open chromatin. Some cells at the tumor group margin have elongated/spindled morphologies with more dense chromatin (cell block, hematoxylin and eosin stain, 400x).

Figure 5

A higher magnification view of DSRCT involving fluid. The image shows a cohesive and crowded group of lesional cells from the pleural fluid with central epithelioid forms. Small arrows mark peripheral elongated/spindled forms. Some of these cells have more dense chromatin, while others have chromatin that is similar to that seen in the epithelioid cells within the body of the island (cell block, hematoxylin and eosin stain, 600x).

Figure 6

The “floating island” pattern of hepatocellular carcinoma. This image is used to illustrate the unique tumoral growth pattern of cohesive sheets of lesional epithelial cells that are intimately invested by a delicate outer layer of flattened endothelial cells. Arrows mark some of the peripheral wrapping endothelial cell nuclei (cell block, hematoxylin and eosin stain, 400x). This photomicrograph comes from a metastatic moderately differentiated hepatocellular carcinoma in a 64-year-old female and is not from the index patient in the current case report. It is presented for comparison as an example of a morphologic differential diagnosis with some overlapping features with the current unique example of metastatic DSRCT.

Figure 7

A cohesive group of metastatic DSRCT cells in pleural fluid with central epithelioid forms and a few flattened/elongated cell forms at the periphery of the island, marked with small arrows. The lesional central epithelioid cells are diffusely immunoreactive with cytokeratin AE1/AE3, and the peripheral spindled forms show the same pattern of reactivity with strong cytoplasmic staining (cell block, AE1/AE3 immunohistochemistry, 400x).

Figure 8

A cohesive group of metastatic DSRCT cells in pleural fluid with central epithelioid forms and a few flattened/elongated cell forms at the periphery of the island, marked by small arrows. The lesional epithelioid cells are nonreactive with smooth muscle actin (SMA), and the peripheral spindled forms show the same pattern of reactivity with no cytoplasmic staining (cell block, SMA immunohistochemistry, 400x).