Myonecrosis

Myonecrosis is a myopathy involving infarction of skeletal muscle and can have the appearances of an intramuscular mass.

Pathology

Myonecrosis represents an infarction of the skeletal muscles. It has a variety of causes :

• post-traumatic (see: calcific myonecrosis) - most common
• compartment syndrome
• prolonged immobilization
• idiopathic
• sickle cell crisis
• diabetic myonecrosis
• crush injury
• severe ischemia
• intra-arterial chemotherapy
• radiotherapy
• rhabdomyolysis
• toxin (e.g. snake bite)

Calcific myonecrosis is a specific form, most commonly observed as a complication of posttraumatic compartment syndrome in the anterior compartment of the leg, and is characterized by dense, dystrophic calcifications.

Radiographic appearance

Plain radiograph

Plain film can usually only demonstrate the late sequelae of myonecrosis characterized by dystrophic soft tissue calcifications .

CT

Also relatively insensitive, it can better assess the exact position and extent of calcifications within the muscles.

MRI

Noncontrast, fluid-sensitive sequences may show aspecific swelling and edema of the muscles.

Absent enhancement of the affected muscle following iv. contrast administration is virtually pathognomonic for myonecrosis. Focal enhancement is suggestive of partial viability of the muscle tissue . Subacute myonecrosis may show rim enhancement, which can be mistaken for an abscess. Administration of iv. contrast is contraindicated in rhabdomyolyis.

In chronic myonecrosis, muscle atrophy, scar tissue formation, or dense calcifications may dominate the picture.

Differential diagnosis

• intramuscular abscess
• intramuscular hematoma