Giant mucocele of the appendix: clinical and imaging findings in 3 cases.

Objective: Clinical and imaging (sonographic and computed tomographic [CT]) findings in 3 cases of giant mucocele of the appendix are described.

Methods: Clinical records of 3 cases of giant mucocele of the appendix were reviewed. All patients had a basal B-mode sonographic examination and a contrast-enhanced sonographic examination using a second-generation low-mechanical index contrast medium. In all cases, a dual-phase spiral CT examination was carried out.

Results: In 2 cases, the abdominal masses were discovered in asymptomatic patients; 1 patient had vague abdominal discomfort. A pathologic diagnosis of benign cystoadenoma was found at pathologic examination in all cases, and malignant pseudomyxoma peritonei was disclosed in 1 patient 1 year later. Common sonographic findings were as follows: (1) a huge abdominal mass with a maximum diameter ranging between 20 and 25 cm; (2) a thin hyperechoic border without either solid vegetations or signs of infiltration of surrounding tissues; (3) a complex internal echo structure with anechoic lacunae interspersed between curvilinear, wavy bands of echogenic material (the so-called sonographic onion skin sign); and (4) avascularity of the masses shown on contrast-enhanced sonography with a low-mechanical index medium. At CT, a well-circumscribed cysticlike mass of low attenuation was displayed in all cases. There was lack of enhancement during a dual-phase examination in 2 cases; in the other, a small peripheral area of faint enhancement was appreciated. Only in the latter case could CT reliably assess the origin of the mass.

Conclusions: It is suggested that a combination of sonographic (namely the onion skin sign) and CT findings may aid in the correct preoperative diagnosis of giant mucocele of the appendix.