Muscle herniation: explanation and ultrasound assessment
Muscle herniation is defined as a focal protrusion of muscle through acquired/congenital fascial layer defects which can lead to palpable subcutaneous soft tissue masses, pain, cramp or local tenderness. Ultrasound (US) should be done according to the SonoSkills quality- and pathology checklist. Most muscle herniations have a hypoechoic appearance to surrounding muscles, and may mimic a convex mass due to protrusion through/over the fascial defect. Contracting the muscle helps identifying the site and nature of the herniation. The size/shape of the mass might change following the muscle contraction. Muscle fibers are mostly continuous; fiber defects can happen. The fascial echo defects can be found in most cases. Be aware of any hematomas present. Doppler imaging helps in visualizing neovascularization. According to Zhou et al. (2017) the diagnostic accuracy of ultrasound is similar to MRI. It can be used to observe the location, shape, size, internal echo of the herniation in a dynamical way. It should be used as the first choice of imaging modality.