Low-grade appendiceal mucinous neoplasm (LAMN)

Low-grade appendiceal mucinous neoplasm (LAMN) is an uncommon tumor of the appendix that is usually diagnosed incidentally after surgery (1):

• although LAMN may be asymptomatic, it can rupture and seed mucin and neoplastic epithelium into the peritoneum, causing pseudomyxoma peritonei (PMP)
  • PMP is a complication of mucinous LAMN that can develop from peritoneal seeding in 20% of patients with a mucinous adenoma (2)
• occurs in approximately 1% of the patients undergoing appendectomy (1)
• characterized by low-grade cytologic features, invasion pattern of appendiceal layers, villous or flat proliferative intestinal-type mucinous epithelium, significant mucin production, and typical limitations of the muscularis propria
• patients with LAMN often show appendicitis-like symptoms such as pain in the right iliac fossa, fever, nausea, and vomiting
• depending on the increase in mucin in the appendix lumen, it may present as a palpable mass or may be diagnosed after appendectomies are performed due to appendiceal abnormalities in surgeries performed for other reasons
  • in more advanced stages, patients can present with intermittent colicky pain, intestinal obstruction due to mass effects, and genitourinary symptoms due to obstruction of the ureter
• elevated CEA, Ca 19-9, and Ca-125 may be detected in 56.1-67.1% of patients with LAMN (2)
• patients with LAMN without perforation have a better prognosis with curative surgery, but the presence of perforation causes the intraperitoneal spread of neoplastic cells and mucinous acid, resulting in PMP
  • patients may not have any acute abdominal pain associated with tumor rupture; however, increased mucus accumulation due to tumor implantation causes abdominal swelling, discomfort, pain, and palpable abdominal masses
• appropriate management of this tumor is controversial. T stage, appendix perforation, presence of acellular mucin on the serosa, and surgical margins are risk factors for the development of PMP (1)
  • appendectomy is considered sufficient when there are no risk factors for Tis (LAMN) and T3 disease
  • right hemicolectomy may be sufficient if there are no risk factors for T4a disease, but cytoreductive surgery and hyperthermic intraperitoneal chemotherapy seem to be the most appropriate treatments in the presence of the stated risk factors for T4b disease
• five-year survival rate for localized LAMN is 95% (2)
  • in one series the mean survival time was 93.3 months in patients without recurrence and 32 months in those with recurrence (1)

Reference:

1. Guner M, Aydın C. Low-Grade Appendiceal Mucinous Neoplasm: What Is the Best Treatment? Cureus. 2023 Oct 6;15(10):e46591
2. Gonzalez HH, Herard K, Mijares MC. A Rare Case of Low-grade Appendiceal Mucinous Neoplasm: A Case Report. Cureus. 2019 Jan 29;11(1):e3980