Muscle hernias, also known as myofascial defects, are most commonly found in the lower extremities, and represent a focal defect in the muscle fascia with protrusion of muscle through the defect. Muscle hernias may be found occasionally in the upper extremities and may be single or multiple. The most commonly involved muscle is the tibialis anterior.
Muscle hernias are typically asymptomatic, although can cause cramping sensations or pain with or after activity. They may also present as a palpable mass, and be referred for imaging to evaluate for neoplasia. The mass may not be palpable when the patient is relaxed, which is a clinical clue to the diagnosis.
Ultrasound is the modality of choice in the evaluation of suspected muscle hernia, although MRI may be ordered if there is suspicion of neoplasia.
Light pressure examination is preferable, so as not to reduce or efface the herniation. Contraction of the involved muscle may reveal or accentuate the lesion.
The hernia is often hypoechoic to the surrounding muscle and may assume a mushroom shape as it protrudes through and over the fascial defect (the defect is of the deep layer of the deep fascia.) It may thin or elevate the superficial layer of the deep fascia that overlies the muscle.
- better visualization of muscle demarcation
- quantification of fascial defect
- quantification of herniated muscle
- confirmation of defect
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