Abstract

Fat-free and low-fat variants of spindle cell lipoma are rare subtypes first coined in 2007. Majority of cases have been reported as solitary subcutaneous or deeply seated lesions arising in the posterior neck, upper back or shoulder of middle-aged patients with a male predilection of approximately 10:1. Herein, we report an unusual presentation of two low-fat SCL lesions in a 45-year-old female who presented with 2 sub-centimeter pink-tan papules on her posterior upper leg. Clinically, these appeared to represent neurofibromas or lipofibromas. Microscopic examination of both lesions revealed pauci-cellular superficial dermal proliferations composed of spindle cells with bland fusiform nuclei admixed with myxoid stroma, scant ropey/wiry collagen fibers, few scattered mast cells and rare adipocytes. Nuclear pleomorphism and/or floret-like giant cells of pleomorphic lipoma were not seen. Immunohistochemistry showed strong immunoreactivity of CD34 in the spindle cell component. The spindle cells were otherwise negative for S-100, Sox-10, CD117 and smooth muscle actin.  In summary, the presence of adipocytes may paradoxically be the least helpful feature in diagnosis of low-fat or fat-free SCL. This highlights the importance of assessment of the non-lipogenic components in the diagnosis of adipocytic neoplasms.