A 19-year-old female dancer was referred to our hospital after being evaluated as having a 1-cm nonpainful mass in her right anterior leg that appeared during the day and disappeared the next morning. The ultrasound result of her leg was negative for any pathology (Figure 1). The patient was asked to exercise her legs by going up and down the stairs of our six-story hospital for 10 min. At the end of this exercise, ultrasound showed a subcutaneous hypoechoic 1 cm mass (Figure 2 and Additional file 1) bulging out from the fascia of the tibialis anterior muscle with a defect in the fascia itself.
Discussion
A muscular hernia through an overlying fascial defect, such as loosening or tearing, is most commonly reported in athletes or individuals with occupations that cause excessive strain on the legs like dancers such like our case. They occur usually in the lower limb, and usually, they affect the tibialis anterior muscle because its fascia is the most vulnerable to trauma, although other muscles in the lower leg, such as muscle of the extensor digitorum longus, peroneus longus, peroneus brevis, and gastrocnemius, have also been reported [1]. This rare entity could be acquired due to trauma or congenital due to fascial defect. Muscle hernia when present protrudes through a defect with the final result of subcutaneous soft tissue mass [2]. It was thought that isomeric muscle contraction in an upright position induces elevated pressure in fascias, and consequently, an elevated pressure causes muscle herniation at the weak points of fascias [3].
Clinical findings include the presence of soft, compressible nodules that vary in size depending on their position. This mass is characterized by herniation during leg dorsiflexion also known as `fencer's lunge position [4].
Although this condition is typically diagnosed by clinical observation, imaging specially ultrasound should confirm the diagnosis to avoid unnecessary biopsy. The clinical differential diagnoses are soft tissue tumors, such as lipoma, leiomyoma, Schwannoma, and dermatofibroma. However, these tumors do not change when a subject's position changes. The dynamic ultrasound study as shown in our case is essential in diagnosing anterior tibialis hernia. Usually, they are asymptomatic, but some person reported vague and fatigued pain aggravated by exercise and by work [1-4].
The treatment is controversial; surgery is an option in symptomatic patients. Dynamic ultrasound should be done in every patient suffering from leg pain or suffering from a strange vanishing behavior of leg masses. Static ultrasound could be negative as in our first ultrasound scan which was done during rest [5]. Ultrasound practitioners should ask the patients to exercise their muscles when muscle hernia is in the differential diagnosis.
