Appendiceal mucoceles occur when there is an abnormal accumulation of mucin causing abnormal distention of the vermiform appendix due to various neoplastic or non-neoplastic causes.
The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middle-aged individuals, particularly considering the epidemiology of the mucinous neoplasms. Though carcinoid tumor is the most common primary appendiceal neoplasm in surgical pathology series, mucoceles due to neoplasms are the most common appendiceal tumors detected on imaging 7.
The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus 7,12. They may be caused by either benign or malignant lesions, categorized into four histologic types:
- mucus retention cyst (due to obstruction most commonly by a fecolith)
- mucosal hyperplasia (analogous to a hyperplastic colonic polyp)
- mucinous cystadenoma of appendix (most common 11)
- mucinous adenocarcinoma of appendix
- myxoglobulosis: a rare mucocele variant seen with multiple small intraluminal globules which can calcify and produce 1-10 mm mobile calcifications
It can be characterized by a right iliac fossa mass with peripheral calcifications 12.
If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocele, the associated mass effect can cause the indentation or lateral displacement of the cecum.
Typically cystic mass with variable internal echogenicity 8. The presence of an "onion sign" (sonographic layering within a cystic mass) is considered a highly suggestive feature 2,6. Acoustic shadowing may be present due to the mural calcifications 12.
They are typically seen as a well-circumscribed, low-attenuation, spherical, or tubular mass contiguous with the base of the cecum.
- curvilinear mural calcification suggests the diagnosis but is seen in less than 50% of cases
- intraluminal bubbles of gas or a gas-fluid level within a mucocele indicate the presence of superinfection, which can occur in both benign and malignant mucoceles
- mural nodularity and irregular wall thickening are suggestive of a malignant process 12
When identifying a mucocele on CT, a search for extraluminal mucin is mandatory, which are low attenuation deposits commonly seen in certain locations 12:
- periappendiceal space
- peritoneal cavity
- at the surface of abdominal viscera, including ovaries and bowel
Seen as a rounded right iliac fossa mass and the typical signal characteristics include:
- T1: depending on the mucin concentration, the signal may be variable, from hypointense to isointense 9
- T2: hyperintense
Treatment and prognosis
Treatment is usually surgical.
- rupture: may lead to pseudomyxoma peritonei (mucinous ascites) if the underlying cause is neoplastic 11,12
- can act as a lead point and result in an ileocolic intussusception 9
Differentiating benign (non-neoplastic mucocele and mucinous cystadenoma) and malignant (mucinous cystadenocarcinoma) appendiceal lesions can be difficult on imaging. Wang et al. 10 found a statistically significant difference in wall irregularity and soft-tissue thickening between malignant and benign cases.
Appendicitis and appendiceal mucocele may be difficult to differentiate, and may sometimes co-exist 12,13.
- an outer diameter of 15 mm or more was predictive of mucocele of the appendix with a sensitivity of 83% and specificity of 92%13
- cystic dilatation of the appendix, mural calcification, and a luminal diameter greater than 13-15 mm are considered features suggestive of coexisting mucocele in patients with acute appendicitis 13,14
- 1. Bennett GL, Tanpitukpongse TP, Macari M et-al. CT diagnosis of mucocele of the appendix in patients with acute appendicitis. AJR Am J Roentgenol. 2009;192 (3): W103-10. doi:10.2214/AJR.08.1572 - Pubmed citation
- 2. Caspi B, Cassif E, Auslender R et-al. The onion skin sign: a specific sonographic marker of appendiceal mucocele. J Ultrasound Med. 2004;23 (1): 117-21. J Ultrasound Med (full text) - Pubmed citation
- 3. Bartlett C, Manoharan M, Jackson A. Mucocele of the appendix - a diagnostic dilemma: a case report. J Med Case Rep. 2007;1 : 183. doi:10.1186/1752-1947-1-183 - Free text at pubmed - Pubmed citation
- 4. Madwed D, Mindelzun R, Jeffrey RB. Mucocele of the appendix: imaging findings. AJR Am J Roentgenol. 1992;159 (1): 69-72. AJR Am J Roentgenol (citation) - Pubmed citation
- 5. Attarde V, Patil P, Apte A et-al. Sonographic appearance of a giant appendicular mucocele. J Clin Ultrasound. 2011;39 (5): 290-2. doi:10.1002/jcu.20809 - Pubmed citation
- 6. Francica G, Lapiccirella G, Giardiello C et-al. Giant mucocele of the appendix: clinical and imaging findings in 3 cases. J Ultrasound Med. 2006;25 (5): 643-8. J Ultrasound Med (citation) - Pubmed citation
- 7. Pickhardt PJ, Levy AD, Rohrmann CA et-al. Primary neoplasms of the appendix: radiologic spectrum of disease with pathologic correlation. Radiographics. 2003;23 (3): 645-62. Radiographics (full text) - doi:10.1148/rg.233025134 - Pubmed citation
- 8. Kim SH, Lim HK, Lee WJ et-al. Mucocele of the appendix: ultrasonographic and CT findings. Abdom Imaging. 1998;23 (3): 292-6. Pubmed citation
- 9. Honnef I, Moschopulos M, Roeren T. Appendiceal mucinous cystadenoma. Radiographics. 2008;28 (5): 1524-7. Radiographics (full text) - doi:10.1148/rg.285075160 - Pubmed citation
- 10. Wang H, Chen YQ, Wei R et-al. Appendiceal mucocele: A diagnostic dilemma in differentiating malignant from benign lesions with CT. AJR Am J Roentgenol. 2013;201 (4): W590-5. doi:10.2214/AJR.12.9260 - Pubmed citation
- 11. Spyropoulos C, Rentis A, Alexaki E et-al. Appendiceal mucocele and pseudomyxoma peritonei; the clinical boundaries of a subtle disease. Am J Case Rep. 2014;15: 355-60. doi:10.12659/AJCR.890837 - Free text at pubmed - Pubmed citation
- 12. Leonards LM, Pahwa A, Patel MK, Petersen J, Nguyen MJ, Jude CM. Neoplasms of the Appendix: Pictorial Review with Clinical and Pathologic Correlation. Radiographics : a review publication of the Radiological Society of North America, Inc. 37 (4): 1059-1083. doi:10.1148/rg.2017160150 - Pubmed
- 13. Lien WC, Huang SP, Chi CL, Liu KL, Lin MT, Lai TI, Liu YP, Wang HP. Appendiceal outer diameter as an indicator for differentiating appendiceal mucocele from appendicitis. The American journal of emergency medicine. 2006 Nov 1;24(7):801-5.
- 14. Bennett GL, Tanpitukpongse TP, Macari M, Cho KC, Babb JS. CT diagnosis of mucocele of the appendix in patients with acute appendicitis. American Journal of Roentgenology. 2009 Mar;192(3):W103-10.
Related Radiopaedia articles
The appendix can be affected by numerous inflammatory, infectious and neoplastic conditions:
- appendiceal diverticulitis
- appendiceal mucocele
- appendiceal intussusception
neoplasms of the appendix
- appendiceal epithelial neoplasms
- Goblet cell carcinoid of the appendix
- appendiceal neuroendocrine tumors
- appendiceal lymphoma