Appendiceal mucocoele

Appendiceal mucocoeles occurs when there is abnormal accumulation of muocus within the appendix.  The tenacious and viscous mucous causes obstruction of the appendiceal neck and results in dilatation of the lumen.

Epidemiology

The reported prevalence is at appendectomy is 0.2 - 0.3%.

Pathology

Results from chronic appendiceal obstruction that may be caused by either benign or malignant lesions:

• mucosal hyperplasia
• mucinous neoplasms 
  • mucinous cystadenoma of appendix 
  • mucinous cystadenocarcinoma of appendix
• appendiceal carcinoid
• adjacent caecal tumour

Radiographic features

Fluoroscopy - Barium enema

If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocoele, the associated mass effect can cause indentation or lateral displacement of the caecum.

Ultrasound

The presence of an "onion sign" (sonographic layering within a cystic mass) is considered a highly suggestive feature ^2,6.

CT

• typically seen as a well-circumscribed, low-attenuation, spheric or tubular mass contiguous with the base of the caecum
• the finding of curvilinear mural calcification suggests the diagnosis, but is seen in less than 50% of cases 
• intra-luminal bubbles of gas, or an air-fluid level within a mucocele suggest the presence of superinfection, which can occur in both benign and malignant mucocoeles

Treatment and prognosis

Treatment is usually surgical.

Complications

Rupture of an appendiceal mucocoele may lead to pseudomyxoma peritonei