Appendiceal mucocele

Clinical History

A 67-year-old woman presented to emergency room with a one-week history of increasing abdominal pain. Tenderness in the right lower quadrant of the abdomen was noted. There were no inflammation indices like leukocytosis or elevated levels of C-reactive protein.
Abdominal radiography, ultrasound and abdominal computed tomography examinations were consequently performed.

Imaging Findings

The abdominal radiography didn’t show significant alterations.
The ultrasound showed a hypo-anechoic mass, encapsulated, with high posterior shadow for parietal calcifications in the right lower quadrant of the abdomen, which made it necessary to continue the diagnostic process with CT.
The CT, performed with triphasic technique, confirmed the ultrasound findings, describing an 11 x 3.5 cm oblong mass, in continuity with the caecum, with thickened walls, containing fluid, gas bubbles and parietal calcifications. There was no cleavage plane with ileal loops and there was moderate inflammatory reaction of perivisceral fat. No abdominal and pelvic effusion, no extraluminal gas, no nodal enlargements were detected.
Consequently a laparotomic appendectomy with partial caecum resection was performed.

Discussion

Mucocele of the appendix is a dilated appendix with abnormal accumulation of mucus resulting from obstruction of the appendiceal lumen by a neoplastic or non-neoplastic cause. The non-neoplastic causes are represented by coprolites, retention cysts, hyperplasia mucosae and, rarely, endometriosis. More frequent neoplastic lesions are epithelial forms such as cystadenoma, mucinous cystadenocarcinoma and cholic-like forms. [5]
It is more common in women and the average age is over 50 years. Asymptomatic in 25% of cases, in the remaining it presents as a palpable mass in the right iliac fossa with vague abdominal discomfort, and sometimes with peritoneal signs. Occasionally it causes gastro-intestinal bleeding, haematuria for ureteral compression, intussusception and in case of breakage peritoneal pseudomyxoma due to spreading of gelatinous material in the peritoneum [1].
CT shows mucocele as a well-circumscribed, low-attenuation, spheric or tubular mass, identifying anatomical continuity with the base of the caecum, with greater precision than ultrasound. Moreover, it visualizes very well the wall thickening and perivisceral fat stranding [1].
CT findings of acute appendicitis with associated mucocele can overlap with those of acute appendicitis without mucocele, although some authors proposed cystic dilatation of the appendix, mural calcification (present in less than 50% of cases), and a luminal diameter greater than 1.3 cm to be suggestive of mucocele. The detection of gas bubbles into the appendiceal lumen is suggestive of bacterial superinfection in benign and malignant forms too [2].
It is difficult to use CT findings to differentiate malignant from benign mucoceles; in fact, soft-tissue thickening, wall irregularity, and periappendiceal fat stranding are nonspecific findings that can indicate malignancy, secondary inflammation, or both. However, some authors proposed mucocele wall irregularity and soft-tissue thickening as criteria of malignancy. Moreover, a preoperative CT is important to avoid a mucocele's rupture with peritoneal pseudomyxoma [3].
Anyway, intraoperative frozen specimens are currently crucial to plan the different surgical approach, appendectomy in benign cases, when there is no impairment of the base of the appendix, appendectomy with resection of the caecum in cystadenomas broad-based plant and hemicolectomy in the malignant forms. There is still open debate among surgeons regarding the reasonableness of laparoscopy using, because of the risk of mucocele rupture with peritoneal seeding, compared with laparotomy procedures widely considered the safest [4].
Prognosis of benign forms is excellent, contrary to patients with malignant mucocele that have a 5-year survival-rate of only 20-25%. [3] The possibility of a concomitant gastro-intestinal neoplasm, described in the literature, justifies the use of a postoperative endoscopic study of the large intestine to exclude synchronous neoplasms.

Differential Diagnosis List

Final Diagnosis

Mucinous low-grade cystic tumour with acute phlegmonous appendix

URL:	https://www.eurorad.org/case/12256
DOI:	10.1594/EURORAD/CASE.12256
ISSN:	1563-4086