CASE 12939 Published on 21.09.2015

Accessory split of lateral head of gastrocnemius muscle


Musculoskeletal system

Case Type

Anatomy and Functional Imaging


Staikidou Ioanna, Mantzikopoulos Georgios, Pikoulas Konstantinos, Giannikouris Georgios, Kokkinis Konstantinos.

KAT Hospital,CT and MRI Department; alfeiou 4 15235 Vrilissia, Greece;

20 years, female

Area of Interest Musculoskeletal soft tissue, Extremities ; Imaging Technique MR, Image manipulation / Reconstruction
Clinical History
A 20 year-old female complained for knee pain and burning sensation of her left leg of a few weeks duration. The clinical examination was normal. An MRI examination of her left knee was requested for possible internal derangement of joint.
Imaging Findings
There is a fusiform mass-like structure located between the lateral head of gastrocnemius muscle and the vessels of the popliteal fossa (fig.1, 2, 3). Rostrally it has a thin attachment to the posterior cortex of the femur. The signal intensity of this structure follows that of muscle on all pulse sequences. Caudally it is fused with the lateral head of gastrocnemius muscle. The popliteal vessels are not compressed, coursing through the lateral head of gastrocnemius and this structure. The findings are suggestive of an accessory split of the lateral head of the gastrocnemius muscle.
There is a small amount of intraarticular fluid (fig.1a, 3) and a small amount of soft tissue oedema in front of the patella (fig.1b, 1c).
There are numerous accessory muscles in the human body. Most of them are asymptomatic and are discovered incidentally during imaging or surgery [1]. In some cases the discovery of these variations in musculature may explain patient’s symptoms and aid in diagnosis and treatment [1]. At the knee region there are variations of skeletal musculature that may provoke anomalous course of the popliteal vessels and may be responsible for symptoms of popliteal artery entrapment syndrome [2][fig.4]. An accessory muscle should be carefully evaluated, during imaging, as it may compress the neurovascular structures of the popliteal fossa and produce symptoms [3]. MR angiography will reveal the vascular compression [4]. The combination of plain MRI and MR angiography is needed to avoid unsuccessful and mainly unnecessary angioplasty procedures [4].
In our case the young woman had knee pain and intermittent claudication of the ipsilateral leg after physical activity. Symptoms subsided with rest and leg elevation. The MRI disclosed an accessory split of the lateral head of gastrocnemius muscle but the popliteal vessels were not compressed. The patient's symptoms could not be attributed to these findings, so conservative treatment and follow-up of the patient were suggested.
Differential Diagnosis List
Accessory split of lateral head of gastrocnemius muscle.
accessory muscle
Final Diagnosis
Accessory split of lateral head of gastrocnemius muscle.
Case information
DOI: 10.1594/EURORAD/CASE.12939
ISSN: 1563-4086