Mitotically active deep juvenile xanthogranuloma.

Juvenile xanthogranuloma is a relatively rare cutaneous tumor of histiocytic origin, occurring mainly in neonates, children, and young people in the first 2 decades of life. An occurrence in adults is rare. Very rare is also a "deep" subcutaneous and intramuscular localization of this tumor that is called in such case as "deep juvenile xanthogranuloma." A very uncommon variant of this tumor is the so-called mitotically active xanthogranuloma, which was described in the literature only in a single case. We present an interesting case of the mitotically active intramuscular juvenile xanthogranuloma of the upper arm in a 28-year-old woman. Before surgical excision, the tumor was examined by fine-needle aspiration biopsy. A diagnosis of deep malignant melanoma or alveolar rhabdomyosarcoma was considered. One year after the total excision, the patient is free of disease. In the presented case, we emphasize cytologic-histologic correlation. In the differential diagnosis, we considered especially an atypical diffuse giant cell tumor of tendon sheaths and joints (extra-articular pigmented villonodular synovitis) and some rare types of soft tissue leiomyosarcoma, such as epitheloid leiomyosarcoma and leiomyosarcoma with prominent osteoclast-like giant cells.