Rectus Muscle Strain Akin to a Mass Lesion of the Thigh: Sonography Distinguishes the Nuance

A 16-yr-old boy was seen for a palpable mass in his left thigh for the previous 2–3 wks. He denied having any concomitant pain, and the medical history was otherwise unremarkable. During physical examination, the lower limbs were found to be symmetric. The mass could not be visualized when he was standing or sitting in a relaxed position; but as he contracted the left quadriceps muscle, a 3-cm × 3-cm bulging mass could easily be observed. Results of the neurological examination of the lower limbs were normal. Radiographs of the thigh were noncontributory. Muscle sonography was performed, and it was consistent with a partial tear of the rectus femoris muscle during dynamic examination (Fig. 1). A home-based regimen, including stretching and isometric strengthening exercises for rectus femoris muscle, was prescribed.FIGURE 1: Serial sonographic images of rectus femoris muscle (longitudinal view) demonstrating the partially deteriorated pennate structure in neutral position (A) and slightly bulging mass formation in full contraction (B).A mass lesion found during the musculoskeletal examination of an adolescent patient always poses challenges to the clinician because soft tissue sarcomas or some other malignant disorders need to be excluded. Moreover, the wide spectrum of differential diagnoses also comprises some benign diseases, including infection, hematoma, lipoma, fibroma, hygroma, and some vascular tumors.1–3 However, muscle strain is another benign pathology that can easily be misdiagnosed, unless physicians are familiar with it. There are several reports in the literature that mention patients who were seen by oncologists and who had even undergone muscle biopsies before their correct diagnoses of simple strains were made.4 It is important to get a detailed medical history so that the subset of patients in whom a specific episode of trauma is absent are not overlooked. The authors, by means of this report, emphasize the role of muscle sonography which, in the hands of experienced clinicians, can provide dynamic imaging and comparison with the normal side.