Case 16
History:
64 year old female with bilateral chronic ankle pain
Findings:
Ankle MRI shows a soft tissue lesion just anterior to the Achilles tendon with signal intensity similar to muscle extending inferiorly to about 1 cm before its calcanear attachment with intrinseque edema within its inferior aspect.
Diagnosis:
Discussion:
Accessory soleus muscle is a rare anatomical variant with an 0.7–5.5% incidence manifested by presence of a supernumerary musculature. The anomaly may be unilateral, bilateral, symmetrical or asymmetrical. The proximal origin is typically on the distal posterior aspect of the tibia. Its distal attachment is via a separate tendon on the calcaneus. Patients typically report aching pain after strenuous activity, which has been attributed to close compartment ischemic mechanism since the accessory muscle is invested in a separate fascial sheath with a tenuous blood supply from the posterior tibial artery.
MRI shows soft tissue mass in the posteromedial aspect of the ankle with signal intensity similar to muscle. MRI can show intramuscular edema in cases of muscular strains.
Treatment usually depends on the presence or severity of the symptoms. Asymptomatic patients can be reassured with no active treatment being required. For symptomatic patients, conservative treatment such as orthoses, physical therapy and activity modification may be tried. Surgical approaches include fasciotomy or excision of the muscle.
References:
- Dunn AW. Anomalous muscles simulating soft tissue tumors in the lower extremities. Report of three cases. J Bone Joint Surg 1965;47-A: 1397-400.
- Percy EC, Telep GN. Anomalous muscle in the leg: soleus accessorium. Am J Sports Med 1984; 12: 447-50.
- Leswick DA, Chow V, Stoneham GW. Resident's corner. Answer to case of the month #94. Accessory soleus muscle.Can Assoc Radiol J 2003;54:313–5.
- Palaniappan M, Rajesh A, Rickett A, Kershaw CJ. Accessory soleus muscle: a case report and review of the literature. Pediatr Radiol 1999;29:610–2.
