Intramuscular benign lipoma of the sternocleidomastoid muscle: a rare cause of neck mass.

Intramuscular benign lipoma commonly is found on the extremities, but is extremely rare in the head and neck region. Intramuscular type lipomas arise between the muscle fibers and pass through the intermuscular septa, infiltrating the surrounding tissue. A 29-year-old male patient presented with the complaint of a painless and slowly growing lateral neck mass on the left side. Physical examination revealed a 4x5-cm mass adjacent to the sternocleidomastoid (SCM) muscle. CT examination revealed a lobulated, well-circumscribed 5.5x2.5-cm diameter mass with adipose tissue signal density inside the SCM muscle. The surgical exploration of the mass was done under general anesthesia, and it was excised totally. Recurrence was not seen in the 3-year follow-up. This rare entity should be considered in the differential diagnosis of intramuscularly located neck masses. Complete removal of the tumor can only succeed if planned and performed after a thorough preoperative clinical and radiological assessment in order to prevent recurrences.