Sonographic appearance of the peroneus quartus muscle: Correlation with MRimaging appearance in seven patients

PURPOSE: To evaluate the sonographic appearance of the peroneus quartus mus cle. MATERIALS AND METHODS: Thirty-two consecutive patients who underwent both s onography and magnetic resonance (MR) imaging of the lateral ankle were ret rospectively identified during 42 months. Seven of these patients demonstra ted a peroneus quartus muscle, with MR imaging as the standard of reference . The peroneus quartus muscle was characterized at retrospective review of sonographic images with regard to origin, insertion, echogenicity, and loca tion. RESULTS: Of the seven peroneus quartus muscles, six originated from the per oneus brevis muscle, and all seven inserted onto the calcaneus. The muscle portion of the peroneus quartus muscle was hypoechoic, while the tendon por tion was hyperechoic and fibrillar. The location of the peroneus quartus mu sculotendinous junction was variable, Hence, the appearance of the peroneus quartus muscle in the region of the distal fibula ranged from 100% muscle to 100% tendon. CONCLUSION: Variability in the appearance of the peroneus quartus muscle is common with sonography due to variation in the location of the musculotend inous junction. Recognition of these variations will allow correct diagnosi s of a peroneus quartus muscle, and more important, it will allow different iation from adjacent tendon abnormality.