Dermal plexiform spindle cell lipoma.

Spindle cell lipoma located in the dermis is uncommon. The plexiform variant of this tumor is rare. In fact, only six cases of this variant have been described previously. We report herein a case of dermal plexiform spindle cell lipoma with prominent myxoid matrix. A 47-year-old male patient presented with a solitary, 2.2 cm-cutaneous mass in the right buttock region that had slowly increased in size for over one year. The dermal lesion was characterized by a mixture of mature adipocytes, spindle shaped cells and inconspicuous ropey collagen bundles in a mucinous background. This lesion showed a fascicular and plexiform pattern with adipocytes irregularly arranged, predominant in the depth of the lesion. Immunohistochemically, the spindle cells were positive for CD34, factor XIIIa, and vimentin, and negative for retinoblastoma protein, claudin-1, GLUT-1, epithelial membrane antigen, neurofilament protein, and Sox-10. S100 protein stained a thinned cytoplasmic rim of mature adipocytes and labeled about 25% of spindle cells in the most superficial areas. A review of the seven cases published, including the present report, revealed that there were five females and two males. Most cases located in the thigh-groin-buttock area. The age of the patients ranged from 32 to 58 years with a mean of 45.7 years. Clinical diagnosis suggested a lipomatous or neural tumor in six cases. The main differential diagnosis includes dermal intraneural plexiform neurofibroma and purely intradermal monophasic plexiform spindle cell nevus.