Distinguishing between acute appendicitis and appendiceal mucocele: is this possible preoperatively?

Mucocele of the appendix is an infrequent event, characterized by a cystic dilatation of the lumen. It is often diagnosed clinically from signs and symptoms of acute appendicitis or, if it is asymptomatic, as an incidental finding during ultrasonography, computed tomography, or laparotomy.

We evaluated the histological data of patients who were believed to have mucocele of the appendix. These patients (n = 23) were compared with sex- and age-matched control subjects (n = 79) with appendicitis.

The main reason for emergency surgery was lower right abdominal pain in 15 patients, and intestinal obstruction in three. Univariate analysis using sonography demonstrated that the larger appendiceal outer diameter was positively correlated with the diagnosis of appendiceal mucocele (p = 0.001) and the mean white blood cell count was negatively correlated (p = 0.023). In urine analysis, 41.7 % of the mucocele patients and 10 % of the appendicitis patients had microscopic hematuria, respectively (p = 0.019). An outer diameter of 10 mm or more was predictive of appendiceal mucocele diagnosis, with a sensitivity of 76.5 %, specificity of 81 %, positive predictive value of 76.5 %, and negative predictive value of 94.12 %. The overall diagnostic accuracy was 80.2 %. One point was given for the presence of each of these factors to develop a new score. The resulting area under the receiver operator characteristic curve was 0.855 (95 % CI 0.741–0.969) for the score. The histological examination of the specimens revealed mucocele in 15 cases, mucinous cystadenoma in seven cases and mucinous cystadenocarcinoma in one case. Twenty patients underwent appendectomy, and three patients were treated with right colectomy.

A threshold 10-mm diameter of the appendix under compression is a useful preoperative measurement for differentiating between appendiceal mucocele and acute appendicitis. Microhematuria is simple test that can provide a significant role in supporting the clinical diagnosis of appendiceal mucocele in the emergency department.