Age / Sex : 38 / M

Chief complaint: Lateral ankle pain

What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(답안은 한 개만 보내주시기 바랍니다)

Courtesy: 이선주 (Sun Joo Lee), 인제의대 부산백병원 (Inje University Busan Paik Hospital)

Peroneus Quartus Muscle

Discussion

Findings:

US image obtained transversely to the peroneus tendon just inferior to the lateral malleolus shows the peroneus brevis and peroneus longus tendons, and peroneus quartus muscle posterior to lateral malleolus.

Axial T1-weighted MR image shows normal peroneus brevis and peroneus longus tendons descending posterior to the lateral malleolus. Note the peroneus quartus muscle located in a more posterior position.

Differential Diagnosis: Low-lying Peroneus Brevis Muscle Belly

Diagnosis: Peroneus Quartus Muscle

Discussion:

The peroneus quartus is the most frequent accessory muscle of the ankle with a prevalence that varies approximately from 12 to 22%. The peroneus quartus commonly originates from the muscular portion of the peroneus brevis muscle in the distal one-third of the leg and descends posteromedial to the peroneal tendons, whereas its site of insertion is very variable and includes the retrotrochlear eminence of the calcaneus, the base of the fifth metatarsal bone, the peroneus brevis or longus tendon, the lateral retinaculum of the ankle, and the cuboid bone. The appearance of the distal peroneus quartus musculotendinous junction is also variable. Most subjects presenting the peroneus quartus are usually asymptomatic, but some present tenosynovitis, dislocation and tear of the peroneus brevis tendon due to crowding of the retromalleolar groove. On both US and MRI, the peroneus quartus appears as a discrete muscle or tendon structure, separated from the adjacent peroneus muscles by a fat plane and distal insertion typically onto the retrotrochlear eminence of the calcaneus.

References:

 1.        Wang XT, Rosenberg ZS, Mechlin MB, Schweitzer ME. Normal variants and diseases of the peroneal tendons and superior peroneal retinaculum: MR imaging features. Radiographics 2005; 25:587-602

2.         Sobel M, Levy ME, Bohne WH. Congenital variations of the peroneus quartus muscle: an anatomic study. Foot Ankle 1990; 11:81-89