Aneurysmal fibrous histiocytoma is a rare variant of cutaneous fibrous histiocytoma that results from blood vessel proliferation and haemorrhage into a fibrous histiocytoma. The resulting lesion has a very different clinical appearance, hence the potential confusion with other skin lesions. This report describes the case of a 48 year old woman with a recurrent fibrous histiocytoma with prominent vasculature, which over a three year period recurred on two occasions, showing more progressive features of the aneurysmal variant. In addition, squamous lined cysts were present within this tumour, a finding that has not been described previously. The histological features of this rare lesion and the importance of the differential diagnosis from other similar appearing malignant lesions will be discussed.

Aneurysmal fibrous histiocytoma showing transition from factor XIIIa-positive to -negative. J Dermatol. 2002 Nov;29(11):744-7.

A 39-year-old woman visited us because of a subcutaneous induration on her forehead of 7 months' duration. The tumor was tender, firm, and colored blue-black. Microscopically, the tumor was composed of fibroblastic and histiocytic cells showing no atypicality. In some part intra- or extracellular haemosiderin was diffusely seen. There were some blood-filled spaces of varying size without endothelial lining. From these findings, this case was diagnosed as aneurysmal fibrous histiocytoma (AFH), a variant form of dermatofibroma. Immunohistochemical analysis showed that factor XIIIa-positive histiocytic cells were distributed in the area without haemosiderin, but such cells were absent in the area with its deposition. Furthermore, the cells near the blood-filled space showed transition from factor XIIIa-positive to -negative, suggesting that the stromal instability induced by the attenuation of factor XIII may lead the formation of the blood-filled spaces in AFH.