Appendiceal Mucocele

An appendiceal mucocele is a dilated appendix filled with mucus. It is a descriptive term for a morphological finding, not a single disease. It is found in 0.2 to 0.3% of appendectomy specimens and accounts for about 8% of appendiceal tumors. Median age at diagnosis is about 55 to 60 years, and women are affected slightly more than men.

Histological types

• Simple retention cyst from luminal obstruction (non-neoplastic)
• Mucosal hyperplasia
• Mucinous adenoma
• Low grade mucinous neoplasm
• Mucinous adenocarcinoma

Neoplastic types make up about 60 to 80%. A diameter over 15 mm on cross-sectional imaging is the usual threshold. Natural history depends on the histology. Retention cysts are inert. Neoplastic mucoceles can rupture, spilling mucus and, if epithelial cells are present, causing pseudomyxoma peritonei. About 15 to 20% of patients have a synchronous colorectal neoplasm, and a smaller number have an ovarian mucinous lesion. Complications: rupture, infection, torsion, intussusception of the cecum, obstruction and gastrointestinal bleeding.

• Incidental finding at endoscopy, imaging or surgery in about half of patients
• Right iliac fossa pain, a palpable smooth mobile mass, weight loss and change in bowel habit
• Presentation as acute appendicitis in a minority, with higher risk of perforation
• Intussusception causing colicky pain and bleeding
• Red flags: peritonitis, increasing abdominal girth (spill and pseudomyxoma), a mass over 6 cm, and a new hernia

1. CT of the abdomen and pelvis with intravenous contrast: a well-encapsulated, thin-walled, cystic, tubular or ovoid mass in the right iliac fossa with fluid or mucin attenuation (0 to 50 HU), a diameter over 15 mm, and mural calcification in about half. Irregular wall thickening, a soft tissue nodule or enhancement suggests malignancy. Free fluid with scalloping of the liver surface suggests spill.
2. Ultrasound: an onion-skin layered cystic mass.
3. Colonoscopy: a submucosal mound at the appendiceal orifice with mucus extruding (volcano sign). Biopsy is avoided because of spill risk. It also excludes synchronous colonic neoplasia.
4. Tumor markers: carcinoembryonic antigen, CA 19-9 and CA 125, which are raised in a minority and are useful for follow-up.
5. MRI when CT is equivocal.

Differentials: appendicitis with abscess, ovarian cyst, mesenteric cyst, Crohn disease, cecal carcinoma, endometrioma.

1. Asymptomatic small lesions on imaging are still resected, because histology cannot be proved without surgery.
2. Operation:
   • Appendectomy with the mucocele removed intact, without grasping, puncture or spill. Open or laparoscopic surgery is acceptable if the specimen is placed in a retrieval bag and the appendix is not handled directly.
   • Right hemicolectomy when the base is involved, the cecum is infiltrated, there is a mass over 2 cm with a suspicious wall, or the margin is positive.
   • Inspect the whole peritoneal cavity and ovaries. Remove any mucin with a sample sent for cytology, and irrigate with warm saline.
   • Avoid converting to cytoreduction unless peritoneal disease is present.
3. Prophylaxis: cefazolin 2 g IV as a single dose within 60 minutes before incision (3 g if over 120 kg), with metronidazole 500 mg IV as a single dose. Enoxaparin 40 mg SC once daily for 7 days after bowel resection (28 days if cancer).
4. Pathology result:
   • Simple cyst, hyperplasia or adenoma with clear margins: no further treatment.
   • Low grade neoplasm without extra-appendiceal mucin: surveillance.
   • Acellular or cellular mucin in the peritoneum: referral for cytoreductive surgery with intraperitoneal chemotherapy.
   • Adenocarcinoma: right hemicolectomy with lymph node dissection, then systemic therapy by stage.
5. Surveillance for neoplastic types: CT and carcinoembryonic antigen at 6 months and then annually for 5 years, and colonoscopy at diagnosis and at 3 to 5 years.

Complications of surgery: wound infection, anastomotic leak (about 3%), ileus and adhesions. Counsel on spill risk and on follow-up.