Microscopical synopsis

 blood-filled spaces: artefact-like clefts to cystic areas mimicking cavernous vascular channels but devoid of an endothelial lining
 prominent haemosiderin deposition with numerous siderophages
 giant cells
 storiform proliferation of histiocyte-like and fibroblast-like cells in a capillary-rich stroma
 cellular polymorphism
 hyalinized collagen bundles surrounded by tumour cells in the periphery of the lesion
 epidermal hyperplasia (88%) (#7607620#)
 moderate mitotic rate

Immunochemistry

 factor XIIIa-positive histiocytic cells (#8600785#, #12484439#)

Prognosis

 recurrence rate: 19% (#7607620#), mean duration 2.5 years (#7607620#)
 possible involvement of a regional lymph node (#7607620#, #10874670#)

References

 Calonje E, Fletcher CD. Aneurysmal benign fibrous histiocytoma: clinicopathological analysis of 40 cases of a tumour frequently misdiagnosed as a vascular neoplasm. Histopathology. 1995 Apr;26(4):323-31. PMID: #7607620#