[An accessory musculus soleus (symptomatic and asymptomatic). The CT findings]

The authors have reviewed 90 CT exams of the foot to identify the presence of the accessory soleus muscle, an anatomic variant corresponding to the finding of a medial backtibial tumefaction, often aching, especially of the Achilles-calcaneal-plantar system. In these cases, US is generally required to demonstrate the alteration, which was an occasional finding in the past, and to exclude the presence of inflammatory or expansile processes of the soft tissues. The accessory soleus is characterized by the presence of accessory muscle fibers, which, in variable number, caudally make for the medial aspect of the calcaneus from the antinode of the soleus muscle. The anatomic variant is much better evidenced by CT, more frequently employed than MR imaging, thanks to its easier approach. As a matter of fact, both methods are capable of defining the relationships with the adjacent tendinous-vascular-nervous structures, involved by mechanical friction in the event of muscle hypertrophy due to overload. Indeed, the review of CT examinations has pointed out a relative relationship between volumetric changes in the soleus and nonphysiological functional demands, giving further evidence of its specific role in the efficiency of the Achilles-calcaneal-plantar system. Therefore, the report in asymptomatic cases is an important prognostic factor which allows the correct clinical picture of subsequent painful symptoms.