Musculoskeletal images. Desmoplastic fibroma of the thigh.

with a 2to 3-month history of increasing discomfort in the left anterior hip and pelvic area. She had also noted a decrease in her stride length, as well as a nontender mass in the thigh. There was some dysesthesia in the leg with long periods of sitting. She denied suffering any associated injury. Her medical history included a protein-S deficiency, a recent atypical Papanicolaou smear that precipitated a cone biopsy of the cervix, and a recent intentional 4-kg weight loss. There was a strong family history of malignant disease. On physical examination her gait was normal and she could squat fully. There was a mobile, firm, slightly tender, soft-tissue mass, 9 × 13 cm in dimension, palpable in the anteromedial aspect of the proximal left thigh. Range of motion in her hip was restricted to 115o of flexion versus 140o on the normal right side. Internal and external rotation was possible to 40° and 45o, respectively, both abduction and adduction to 50o. She had tight hamstrings, a negative Lasèque test and a negative bowstring sign. Findings on neurosensory examination were normal. There was a 3.5 × 5.5-cm geographic café-aulait spot on the medial thigh, and similar ones on the right lower abdomen, left arm, posterior right thigh and posterior left thigh. There was no other evidence of neurofibromatosis. Plain radiographs of the pelvis with inlet and outlet views revealed a 3.0-cm radiolucent defect in the left inferior pubic ramus (Fig. 1). There was some disruption of the inferior cortex, where a 2.0to 3.0-cm fragment had been avulsed from the inferior aspect, probably at the adductor insertion. There was increased density in the adjacent soft tissues. There was no calcification within the lesion. The appearance of the pelvis was otherwise normal. The overall appearance was that of a nonaggressive process. Computed tomography (CT) of the pelvis, enhanced with contiguous 10-mm scans, showed evidence of a fairly extensive heterogeneous softtissue mass within the proximal adductor compartment of the left thigh, with resultant loss of definition of intramuscular septal planes and expansion of the corresponding adductor component. The mass also demonstrated discrete, poorly defined punctate ossification and calcification suggestive of chondrocalcification. It abutted on the inferior pubic ramus and appeared to extend from an inferiorly directed pedunculated exostosis. Magnetic resonance imaging (MRI) of the left thigh revealed an expansile, 3.2 × 1.2-cm lesion in the inferior pubic ramus. It had low signal intensity, similar to adjacent muscle on T1-weighted images. The bony cortex was disrupted at the inferior aspect and was associated with a minimal amount of periosteal new bone formation. Immediately adjacent to, and inseparable from, the lesion at its lateral and inferior aspect, was a large associated soft-tissue mass measuring 8.6 × 7.9 × 9.5 cm (Fig. 2). The mass bulged slightly through the obturator foramen and was inseparable from the lateral fibres of this muscle. The pectineus muscle was draped over the superior aspect of the muscle mass, and the epicentre of the mass was in the adductor compartment. The posterior margin of the mass was inseparable from the quadriceps muscle. The mass lay just below the left femoral head and left hip joint with no evidence of extension into the joint or of a joint effusion. The mass was separated from the femoral vessels by adductor muscles and the proximal left femur. There was no definite evidence of a calcified matrix. After gadolinium was administered, there was slight heterogeneous enhancement of the lesion. Surgical Images Imagier chirurgical