Buttock mass in a 37-year-old woman.

A 37-year-old woman presented with a 6 month history of a gradually enlarging soft tissue mass over the right gluteal region. She described difficulty in lying supine. She did not report having any fever, chills, weight loss, or systemic symptoms. She denied any antecedent trauma, any numbness, weakness, or discomfort in her left lower extremity. Her medical, surgical, and family history was unremarkable. Physical examination of the left buttock region found a 14 × 12 cm soft, nontender mass over the right gluteal region. There were no overlying skin changes. Tinel’s sign was negative. She had full range of motion of the left hip. Examination of the spine did not reveal topical abnormality. The neurovascular status of the involved extremity was without focal deficit and there was no lymphadenopathy. Plain radiographs, computed tomography (CT) and magnetic resonance imaging (MRI) scans were taken (Figs 1–4). Based on the history, physical examination, and imaging studies, what is the differential diagnosis? From the *Department of Orthopedics/Rehabilitation; and the †Department of Pathology University of Miami, Miami, FL. Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution has approved the reporting of this case report that all investigations were conducted in conformity with ethical principles of research, and that informed consent was obtained Correspondence to: Sean P. Scully, MD, PhD, Department of Orthopedics and Rehabilitation (D-27), University of Miami, P.O. Box 016960, Miami, FL 33101. Phone: 305-325-5532; Fax: 305-325-3928; E-mail: sscully@ med.miami.edu. DOI: 10.1097/01.blo.0000195925.74221.6b CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 446, pp. 291–296 © 2005 Lippincott Williams & Wilkins