Tumors of muscle include desmoid tumor (a benign massive growth of fibrous tissue observed most often in parturient women and after surgery), rhabdomyosarcoma (a highly malignant tumor with strong liability to local recurrence and metastasis), liposarcoma, and angioma. Large neurofibromas or neurofibrosarcomas beneath large muscles such as the hamstring may be difficult to differentiate by physical examination or MRI from masses within the muscle. Pseudotumorous growths, sometimes massive, may follow injury to a muscle. Interlacing regenerating muscle fibers and fibroblasts compose the mass. Excision of the entire muscle had been undertaken in several cases in the belief that the growth was a rhabdomyosarcoma, whereas it is actually a benign reaction to trauma (Kakulas and Adams). Metastasis to muscle occurs, most often lymphomatous in our experience.
Thrombosis of arteries or, more often, of veins causes congestion and infarction of muscle. A special type of muscle infarction occurs in patients with complicated and poorly controlled diabetes mellitus (Banker and Chester). Usually it involves the anterior thigh, and occasionally other muscles of the lower limb. The symptoms are the sudden onset of pain and swelling of the thigh, with or without the formation of a tender, palpable mass. Recurrent infarction of the same or opposite thigh is characteristic. The stereotypical clinical picture and the striking MRI appearance obviate the need for diagnostic muscle biopsy. Extensive infarction of muscle is due to the occlusion of many medium-sized muscular arteries and arterioles, most likely the result of embolization of atheromatous material from eroded plaques in the aorta or iliac arteries. Recognition of this complication and immobilization of the limb are of prime practical importance, as muscle biopsy and early ambulation may cause serious hemorrhage into the infarcted tissue.
The pretibial, or compartment syndrome, also well recognized, follows direct trauma or excessive activity (marching, exercising of unconditioned muscles) or ischemic infarction due to arterial occlusion. There is swelling of the extensor hallucis longus, extensor digitorum longus, and anterior tibial muscles. Being tightly enclosed by the bones and pretibial fascia, the swelling leads to ischemic necrosis and myoglobinuria. Permanent weakness of this group of muscles can be prevented by incising the pretibial fascia and thereby decompressing the affected muscles. A similar compartment syndrome can occur in the forearm.
This condition involves the deposition of bone within the substance of a muscle. Two types are recognized. One is a localized form that appears in a single muscle or group of muscles after trauma, and the other is a progressive, widespread ossifying process, entirely unrelated to trauma, in many muscles of the body.
Localized (traumatic) myositis ossificans After a muscle tear, a single blow to the muscle, or repeated minor trauma, a painful area develops in the muscle. It is gradually replaced by a mass of cartilaginous consistency, and within 4 to 7 weeks a solid mass of bone can be felt and seen in CT or radiographs. This most frequently happens in vigorous adult men. The inner thigh muscles (in those who ride horses) and to a lesser extent the pectoralis major and biceps brachii are the most frequent locations. The mass tends to subside after several months if the patient desists from the activity that produced the trauma.