Rectus femoris muscle tear appearing as a pseudotumor.

Quadriceps muscle strains are common sporting injuries, but occasionally a tear of the rectus femoris muscle can appear as a soft tissue mass of the anterior thigh with or without a significant history of trauma. Between 1992 and 1996, seven patients were referred to the Orthopaedic Oncology Unit at Walter Reed Army Medical Center with an unexplained soft tissue mass of the thigh. Three were active duty soldiers, three were military dependents, and one was a retired serviceman. All patients were men, and the mean age was 32 years (range, 15 to 73). A palpable, mildly tender mass was confirmed on clinical examination. Laboratory studies and plain radiographs were normal. Magnetic resonance imaging showed an obvious, but often ill-defined, lesion at the musculotendinous junction of the rectus femoris muscle. Four patients subsequently underwent a tissue biopsy to rule out a soft tissue sarcoma. Histologic studies showed fibrosis, degeneration of muscle fibers, and chronic inflammatory cells with no evidence of malignancy. A chronic rectus femoris muscle tear can mimic a soft tissue tumor or sarcoma and needs to be excluded in the differential diagnosis. These tears may occur acutely or may represent an overuse injury caused by repeated microtrauma. Careful history taking, physical examination, and selective radiographic studies, specifically magnetic resonance imaging, can confirm the diagnosis of muscle tear and full functional recovery can be anticipated.