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Case ReportpISSN 1738-2637 / eISSN 2288-2928J Korean Soc Radiol 2015;73(4):249-251http://dx.doi.org/10.3348/jksr.2015.73.4.249

INTRODUCTION

The tensor fasciae suralis muscle, also known as the ischio-aponeuroticus, is a rare accessory muscle. It may originate from both of the semitendinosus and the long head of the biceps fem-oris, or from either of them, and inserts into the sural fasciae or the Achilles tendon (1). Although it may present as a popliteal mass, it may also be detected incidentally (2, 3).

We encountered this anatomic variation in the popliteal re-gion, as an incidental finding on magnetic resonance imaging (MRI). The following ultrasound (US) correlated well with the MRI findings, confirming the diagnosis.

CASE REPORT

A 30-year-old man visited the hospital for right knee pain fol-lowing an injury after playing basket ball. He denied previous

local injury or surgery.Physical examination revealed tenderness, swelling and range-

of-motion limitation in the right knee joint. X-ray showed joint effusion without bony abnormality.

MRI of right knee was performed using a 1.5-T MR scanner (Signa HDxt 1.5T; GE Medical Systems, Milwaukee, WI, USA). The examination revealed the tensor fasciae suralis muscle aris-ing from the lateral aspect of semitendinosus muscle, running superficial to the gastrocnemius medial head (Fig. 1). The other abnormality was complete tear of the anterior cruciate ligament.

Subsequently, sonography was carried out with the patient prone using a linear 12-5 MHz array transducer (iU22; Philips Medical Systems, Bothell, WA, USA). The sonograms showed the tensor fasciae suralis muscle as an elongated structure with hyperechoic striations on a hypoechoic background, which is typical echotexture of the normal muscle in the right popliteal region. The muscle extended inferiorly and was attached to the

MR Imaging and Ultrasonographic Findings of Tensor Fasciae Suralis Muscle: A Case Report비복근막장근의 자기공명영상과 초음파 소견: 증례 보고

Keun Ho Kim, MD, Jae Chan Shim, MD*, Ghi Jai Lee, MD, Kyoung Eun Lee, MD, Ho Kyun Kim, MD, Jung Ho Suh, MDDepartment of Radiology, Seoul Paik Hospital, Inje University College of Medicine, Seoul, Korea

The tensor fasciae suralis muscle is a very rare anomalous muscle located in the popliteal region. This anatomic variation has been reported often through cadaver studies. However, there are only a few radiologic reports of this entity. We presented a case of tensor fasciae suralis muscle detected as an incidental finding in magnetic resonance imaging and ultrasound.

Index termsAnatomic VariationLegMagnetic Resonance ImagingUltrasonography

Received February 25, 2015Revised June 12, 2015 Accepted August 5, 2015*Corresponding author: Jae Chan Shim, MDDepartment of Radiology, Seoul Paik Hospital, Inje University College of Medicine, 9 Mareunnae-ro, Jung-gu, Seoul 04551, Korea.Tel. 82-2-2270-0139 Fax. 82-2-2266-6799E-mail: jcshim96@unitel.co.kr

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distri-bution, and reproduction in any medium, provided the original work is properly cited.

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gastrocnemius medial head (Fig. 2). The patient underwent anterior cruciate ligament reconstruc-

tion. His pain disappeared after operation and he was followed up periodically as an outpatient.

DISCUSSION

There are several known accessory muscles of the knee. Acces-

sory slips of the medial or lateral gastrocnemius muscle are fre-quently encountered in popliteal area on knee MRI. An anoma-lous relationship between the popliteal artery and the proximal gastrocnemius may manifest clinically with popliteal artery en-trapment syndrome (4). The variant muscle in superficial popli-teal fossa may simulate soft tissue tumors (5). Of these, the tensor fasciae suralis is located superficially in the popliteal fossa, be-tween the semitendinosus and semimembranosus muscles me-

Fig. 1. MR images of the right knee.A. Sagittal proton density-weighted image shows an anomalous muscle (arrows) running superficially along the popliteal region.B, C. Axial T1-weighted images show an anomalous muscle (arrow) originating from the lateral aspect of semitendinosus muscle (arrowhead). Inferiorly, this muscle located posterior to the gastrocnemius medial head (asterisk). MR = magnetic resonance

A B C

A BFig. 2. US of the right popliteal region.A. Longitudinal panoramic US image shows the tensor fasciae suralis muscle (arrows) extending inferiorly and attaching to the gastocnemius medial head (asterisk).B. Transverse US image shows this muscle (arrow) located posterior to the gastrocnemius medial head (asterisk) and lateral to the semitendino-sus tendon (arrowhead). It shows characteristic internal echotexture of the normal muscle.US = ultrasound

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rounding structures. In addition, the awareness of this variant may prevent its misinterpretation as a pathologic entity.

REFERENCES

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2. Chason DP, Schultz SM, Fleckenstein JL. Tensor fasciae

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3. Montet X, Sandoz A, Mauget D, Martinoli C, Bianchi S. So-

nographic and MRI appearance of tensor fasciae suralis

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White LM. Accessory muscles: anatomy, symptoms, and

radiologic evaluation. Radiographics 2008;28:481-499

5. Dunn AW. Anomalous muscles simulating soft-tissue tu-

mors in the lower extremities. Report of three cases. J

Bone Joint Surg Am 1965;47:1397-1400

6. Tubbs RS, Salter EG, Oakes WJ. Dissection of a rare acces-

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dially and the biceps femoris muscle laterally (4). Although it may arise from the distal aspect of any of the hamstring muscles, the majority of reported cases indicated that it originates from the distal semitendinosus muscle. It may insert into the posteri-or fasciae of the leg, into the gastrocnemius medial head, or via a long thin tendon onto the superficial aspect of the Achilles ten-don (6). The incidence of this anomalous muscle-tendon unit is unknown, but the tensor fasciae suralis is very rare (2, 4).

It is an unusual cause of a popliteal soft tissue swelling and may be mistaken for a mass, aberrant vessel, thrombus of superficial vessel such as lesser saphenous vein or pathologic change of su-perficial nerve, when prominent. Furthermore, because the tissue characteristics resemble either normal muscle or tendon, it may be missed altogether on routine imaging studies (2, 3).

In our case, the tensor fasciae suralis muscle was not apparent on physical examination. But it may be more prominent on the skin during muscle contraction, such as during resisted flexion of the knee.

Although it can be suspected on physical findings, it can be accurately identified with US or MRI. The accessory semimem-branosus has been described as a muscle similar in location but arising from the semimembranosus (7). In practice, differentiat-ing between these entities may be difficult, especially if the full extent of the muscle is not imaged (4).

In conclusion, the tensor fasciae suralis muscle can be clini-cally mistaken as a pathologic finding in popliteal region. US or MRI imaging is an excellent means of detecting cases of anoma-lous muscle and determining its anatomic relationship with sur-

비복근막장근의 자기공명영상과 초음파 소견: 증례 보고

김근호 · 심재찬* · 이기재 · 이경은 · 김호균 · 서정호

비복근막장근은 슬와부에 위치하는 매우 드문 비정상 근육이다. 이 해부학적 변이는 카데바 연구를 통해 종종 보고되었

다. 하지만 이것의 영상의학적 보고들은 몇 개 되지 않는다. 이에 저자들은 자기공명영상과 초음파에서 우연히 발견된 비

복근막장근의 소견을 보고하고자 한다.

인제대학교 의과대학 서울백병원 영상의학과