Extensor digitorum brevis manus: A case of fourth-compartment syndrome.

The presence of an extensor digitorum brevis manus represents a variation of the normal anatomy of the fourth extensor compartment of the wrist. It usually presents as a swelling on the dorsum of the wrist and is often inaccurately diagnosed. An awareness of its existence and of its characteristic appearance on diagnostic imaging studies is the basis for diagnosis. Symptomatic cases require division of the extensor retinaculum or excision of the muscle, depending on subtype, while asymptomatic cases require no intervention.