Clinical History
An 18-year-old male patient was referred to our hospital because of pain in his left knee during flexion. He had had an injury two months before. A meniscal tear was suspected and a MRI of his left knee was requested.
Imaging Findings
No meniscal tears were found. An area appearing as bone oedema was disclosed at the medial-posterior aspect of the tibial epiphysis (Fig. 1, 2). The finding was interpreted as a bone contusion.
There was a mass-like structure that was located between the popliteal vessels, separating them from each other (Fig. 1-3). The signal intensity of this structure equalled that of muscle on all pulse sequences (Fig. 1-4). It originated from the lateral posterior aspect of the femoral metaphysis (Fig. 4) and inserted, by a broad insertion, into the medial head of the gastrocnemius muscle (Fig. 1, 2). No tendon was identified in this mass. The popliteal artery was situated medially to it, with the popliteal vein curving laterally, medially to the lateral head of gastrocnemius (Fig. 1, 2). Although no contrast was given, there were no signs of popliteal artery stenosis or popliteal vein thrombosis. This incidental finding was interpreted as an accessory split of the medial head of the gastrocnemius muscle.
Discussion
Normally the popliteal vessels course between the heads of gastrocnemius muscle [fig.5a]. The anatomic variations of popliteal artery's course in the popliteal fossa are categorized in five types (I, II, III, IV, V)[1]. In type I the popliteal artery courses medially to the normally originated medial head of gastrocnemius muscle [fig.5b]. In type II the medial head of gastrocnemius muscle originates from the intercondylar notch causing displacement of the popliteal artery medially [fig.5c]. In type III there is an accessory split of medial head of gastrocnemius muscle that originates from the lateral-posterior aspect of the femoral metaphysis and courses obliquely to insert into the medial head of gastrocnemius muscle. The popliteal artery lies between this accessory split and the medial head of gastrocnemius muscle [fig.5d]. In type IV the popliteal artery courses in front of the popliteus muscle, or in front of a fibrous band which lies transversely in the popliteal fossa [fig.5e]. In types I-IV the popliteal vein is separated from the artery. The prevalence of these variations in a retrospective study of patients suffering from popliteal artery syndrome were: type I=5.6%, type II=13.6%, type III=37.5%, type IV=9% [2]. Type V includes types I-IV where the popliteal vein is not separated from the popliteal artery. In our case a type III variation was disclosed.
Even in normal subjects the popliteal artery may be compressed during passive dorsiflexion or active plantar flexion of the ankle and could cause a fall in distal blood flow[3]. It may occur in about 50% of the general population[1]. Popliteal artery syndrome may be present in persons without anatomic abnormality (functional) and should be distinguished from the cases, where there is an abnormal course of the popliteal artery[2]. In our case the patient was referred for knee joint evaluation because of a recent injury during a fall, and the pain was attributed to a bone oedema-like lesion that was disclosed at the medial-posterior aspect of the tibial epiphysis. There were no symptoms caused by the anatomic abnormality.
Differential Diagnosis List
Type III popliteal artery due to split of medial gastrocnemius muscle.
Accessory muscle
Anomalous popliteal vessels
Final Diagnosis
Type III popliteal artery due to split of medial gastrocnemius muscle.
