Subacromial impingement by a lipoma arborescens.

Subacromial impingement syndrome (SIS) is the leading cause of shoulder pain. A systemic approach for abnormal causes of SIS is recommended to avoid misdiagnosing rare or sinister pathologies. To our knowledge, only nine cases of subacromial lipoma arborescens associated with impingement syndrome have been reported in the literature. In this report, we briefly discuss histopathologic and radiological signs of an unusual case of impingement syndrome caused by subacromial "lipoma arborescens" and describe arthroscopic synovectomy after the failure of conservative management. The patient remains symptom-free five years after surgery.