The onion skin sign: a specific sonographic marker of appendiceal mucocele.

Objective: To evaluate the association of the onion skin sign as a sonographic marker for appendiceal mucocele.

Methods: The sonographic onion skin sign was considered specific for the preoperative diagnosis of appendiceal mucocele. Therefore, detection of this sign in a mass located in the right lower abdomen, unrelated to the female reproductive organs, indicated surgical intervention with a presumptive diagnosis of appendiceal mucocele.