Soleus Accessorius: An Uncommon Anatomic Variant of the Calf Muscle

Anatomical variants like the soleus accessorius underscores the incredible diversity within the human body. It serves as a reminder that healthcare professionals should remain vigilant, especially in cases where unexpected structures or variations are encountered during diagnosis or treatment.

Sagittal T2w and T1w – MRI 0.3 Tesla

The soleus accessorius, also known as accessory soleus, is a relatively rare anatomical variant of the calf muscle, the soleus. The soleus muscle is one of the two major muscles in the calf, with the other being the gastrocnemius. The soleus accessorius, when present, is typically an additional muscle belly or slip located adjacent to the primary soleus muscle.

The presence of a soleus accessorius can have clinical significance in several ways:

1. Misdiagnosis: An accessory soleus can be mistaken for a soft tissue mass or other pathology in medical imaging studies, potentially leading to misdiagnosis and unnecessary medical interventions.

2. Functional Impact: In some cases, the soleus accessorius can be associated with altered biomechanics and may contribute to conditions like posterior compartment syndrome, leading to pain and discomfort in the lower leg.

3. Surgical Considerations: Surgeons and orthopedic specialists need to be aware of a soleus accessorius when performing procedures on the calf muscles to avoid accidental damage or complications.

Common Peroneal Nerve Schwannoma

Palpable mass on the lateral side of the popliteal fossa.

The mass is characteristically eccentric with respect to the affected nerve, and the nerve is displaced to the periphery of the mass. 

The ultrasound picture allows us to distinguish the internal structure of the lesion accurately and study the entire course of the nerve. 

The histologic architecture of the mass is with more myxoid material peripherally and more fibrous tissue centrally. 

The study with elastosonography shows the different structural characteristics of the various components of the mass, distinguishing between the “softer” mixoids and the “harder” fibrous ones.

My suggestion is always to combine MRI and ultrasound examinations to define these kinds of lesions better.