Pleomorphic Lipoma
Definition
- Neoplasm of mature fat containing atypical cells, restricted in location to the dermis or subcutis of the posterior neck, upper back or shoulders
Diagnostic Criteria
- Must be located in subcutis or dermis of posterior neck, upper back and shoulders
- If located in other sites, we consider it to be atypical lipomatous tumor
- Variable amount of adult fat
- 10-90% of lesion
- Rarely fat free, see below
- No lipoblasts
- Atypical cells range from rare to frequent
- Hyperchromatic enlarged nuclei
- May form semicircle of nuclei (floret cells)
- May be in fatty or non-fatty stromal areas
- Bundles of dense ropey collagen
- Stroma may be myxoid
- Vessels may be prominent, arborizing, thick walled
- Mast cells may be numerous
- CD34 positive, usually extensive
- Occasionally may display same variants as seen in spindle cell lipoma
- Vascular pleomorphic lipoma
- Branching dilated or cleft like-spaces
- Papillary projections of tumor cells into the spaces
- Spaces usually cell free
- Spaces lined by endothelial cells with lymphatic phenotype
- D2-40 positive, CD31 focal or negative
- Previously termed pseudovascular
- Based on studies without D2-40
- Recognized based on location, areas of typical pleomorphic or spindle cell lipoma patterns and CD34 positvity
- Branching dilated or cleft like-spaces
- Fibrous pleomorphic lipoma
- Abundant fibrous stroma
- Bundles of collagen
- EVG negative
- Recognized based on location, areas of typical pleomorphic or spindle cell lipoma patterns and CD34 positvity
- Fat free (or almost free)
- May include above variant patterns
- May be predominantly myxoid
- Plexiform or curvilinear vasculature and vascular hyalinization may be prominent
- Recognized by location, CD34 reactivity and presence of areas with typical features of pleomorphic or spindle cell lipoma
- Rare tumors combined with hibernoma have been reported
- No distinct clinical features
- Vascular pleomorphic lipoma
- Frequent histologic overlap with spindle cell lipoma
- Contains small spindle cells with scant cytoplasm
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting : July 29, 2007
Updates: May 25, 2009; July 26, 2009