Pleomorphic lipoma lacking mature fat component in extensive myxoid stroma: a great diagnostic challenge

Abstract

Pleomorphic lipoma is a relatively uncommon entity, and is considered as a variant of spindle cell lipoma. Histologically, spindle cell lipoma/pleomorphic lipoma consists of varying quantity of mature fat, bland spindle cells and ropey collagen. In addition, pleomorphic lipoma is characterized by multinucleate giant cells, which possess the "floret-like" nuclei and marked pleomorphism. So, in contrast to spindle cell lipoma, pleomorphic lipoma is more easily misdiagnosed as a malignant tumor. Herein, we report a peculiar case of pleomorphic lipoma occurring in axilla with entirely devoid of mature fat in a 71-year-old male. The histopathological findings demonstrated the tumor was made up of bland spindle cells admixed with scattered "floret-like" cells and irregular ropey collagen in an extensive myxoid stroma. Immunostaining showed that the tumor was positive for the Vimentin, Bcl-2 and CD34, and was negative for S-100, desmin, CD68, and α-SMA. Although no fat component was found in the whole section, the tumor was still diagnosed as a pelomprphic lipoma. To our knowledge, this is the third reported case of pelomprphic lipoma which entirely lacked lipomatous component. Because of the existence of atypical multinucleate giant cells and lack of mature fat, this tumor may be easily misdiagnosed nonlipomatous lesions, such as myxoid fibrosarcoma, giant cell fibroblastoma. So, it is necessary to pay careful attention to the histological spectrum of pleomorphic lipoma, including the tumor with devoid of fat, and it should be kept in mind that pelomprphic lipoma still can be diagnosed even if lacking lipomatous component.

Virtual slides: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1967123180611361.

Figure 1

A,The tumor predominantly consists of spindle cells admixed scattered multinucleated cells and abundant ropey collagen. B, Foccally, in striking myxoid stroma, the cells are scarcely diffused, and the vascular pattern varies from plexiform to dilated intermediate-sized vessels. C, The multinucleate cells have hyperchromatic, pelmorphic and florte-like muclei. D, Scattered inflammatory cells, such as lymphocytes and plasma cells could be seen in myxoid stroma.

Figure 2

A,Diffuse and strong CD34 staining highlighted the tumor cells. B, The floret-like cells were positive for CD34. C, The spindle cells and floret-like cells were negative for SMA, while SMA staining highlighted the dilated vessel. D, All tumor cells including floret-like cells were negative for S-100.