CASE 18595 Published on 28.06.2024

Tibialis anterior muscle herniation – Dynamic ultrasound and magnetic resonance imaging

Section

Musculoskeletal system

Case Type

Clinical Case

Authors

Shrishail Adke, Ajith Varrior

Department of Radiology, Seth GS Medical College and KEM Hospital, Mumbai, Maharashtra, India

Patient

24 years, male

Categories
No Area of Interest ; Imaging Technique MR, Ultrasound
Clinical History

A 24-year-old man had a history of blunt trauma to his left leg while playing cricket one year back. He complained of a painless swelling over the anterior aspect of the leg after a few months. It increased in size on standing and during muscle contraction.

Imaging Findings

Ultrasound of the left leg showed a 6mm defect in the echogenic fascia overlying the tibialis anterior muscle (Figure 1). On dynamic examination (Figures 2 and 4/video), there was herniation of the muscle fibres through the myofascial defect on standing and forced dorsiflexion of the foot. It is reduced in the supine position with muscle relaxation and on graded compression. An MRI (magnetic resonance imaging) of the left leg showed a defect in the fascia with bulging of the fibres of the tibialis anterior (Figure 3). There was no abnormal signal intensity in the muscle.

Discussion

Muscle herniation is an entity where there is a defect in the overlying fascia with resultant herniation of muscle fibres through it. It is commonly seen in young individuals such as athletes, military soldiers, and mountain climbers [1]. The aetiology could be either congenital or acquired. A congenital defect in the fascia or perforation by a vessel or nerve serve as potential sites for muscle herniation [2,3]. Acquired causes are usually traumatic, which might be due to direct trauma or due to excess use of the muscle. Iatrogenic muscle hernia is seen after harvesting flaps for reconstruction surgeries [1]. Regular physical activity with muscle hypertrophy is a risk factor. Muscle herniation is commonly seen in the leg and rarely in the thigh and the upper extremities. The most commonly involved muscle is the tibialis anterior. It is also seen in the peroneus longus and brevis, the extensor and flexor digitorum longus, the gastrocnemius and in the rectus femoris [1,3].

The diagnosis of muscle hernia requires a high index of clinical suspicion. The swelling is usually painless and is prominent on muscle contraction and standing. Pain might be due to muscle oedema. Ultrasonography is the initial mode of investigation, which clinches the diagnosis and also rules out common mimics. The additional benefit is the use of dynamic examination with muscle contraction and in standing position. The fascia appears as a thin echogenic line over the muscle. The defect is appreciated on muscle contraction. On relaxation, there might be focal thinning of the fascia with slight elevation, which can be missed easily [4]. A defect is not necessarily seen in every case [5]. The clue to the diagnosis is a focal bulge with thinning of the fascia at the site of the swelling. The mushroom-like (convex superficial contour of the muscle with a narrow defect) and the spoke-like appearance (pinching effect on the echogenic adipose septae at the site of the fascial defect) have been described on ultrasound. The herniated muscle is usually hypoechoic to the normal adjacent muscle [1]. An MRI confirms the diagnosis by depicting the fascial defect. T2/PDFS hyperintensity within the herniated muscle suggests muscle oedema. Dynamic examination with fast imaging makes the defect more conspicuous [5].

Muscle hernias are usually managed conservatively with rest and stocking support [3]. Surgical management is done through fasciotomy [1]. Defect repair is not preferred due to the risk of compartment syndrome [1].

Differential Diagnosis List
Tibialis anterior muscle hernia
Muscle rupture
Haematoma
Muscle hernia
Final Diagnosis
Tibialis anterior muscle hernia
Case information
URL: https://eurorad.org/case/18595
DOI: 10.35100/eurorad/case.18595
ISSN: 1563-4086
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