Kaposiform Hemangioendothelioma (KHE) is a rare locally aggressive vascular neoplasm, which occurs in childhood and teenage years. KHE is also associated with Kasabach-Merritt syndrome and has features of both capillary hemangioma and Kaposi sarcoma.

The patient underwent multiple biopsies, surgeries and even a fine needle aspiration (FNA) of a right inguinal lymph node prior to excision of the nodes. All specimens yielded KHE. The hematoxylin & eosin (H&E) stained biopsy slides exhibited uniform, spindle-shaped cells forming slit-like channels filled with red blood cells. The spindle-shape of the cells was not observed in the pleural fluid as cells tend to round up and form 3-dimensional clusters in a fluid medium. The H&E slides also demonstrated hematoidin and hemosiderin-laden macrophages which demonstrates the vascular nature of this tumor.

This would be a difficult if not impossible interpretation to make in a pleural fluid based on cytology alone. The clinical history of lump on the right foot could easily be discounted as irrelevant but should make one think outside the box and consider an age appropriate lesion such as a small round blue cell tumor, a vascular lesion or a sarcoma. A thorough review of the patient history when available will help narrow down the diagnostic choices.

Ancillary tests namely immunohistochemistry (IHC) was key in making the interpretation of KHE in the pleural fluid. The pleural fluid cell block stained diffusely positive for Fli-1, CD31 and CD34 and negative for calretinin and pan-cytokeratin, HHV8, EMA, S-100 and desmin. This immunostaining pattern was also demonstrated in the surgical pathology and FNA specimens.