Low-grade appendiceal mucinous neoplasm (LAMN)

Introduction

a rare adenoma malignancies of the appendix (0.4-1% of GIT neoplasms but prevalence rising in Western countries by 3% per annum) with symptoms varying depending on the clinical manifestations
found in 0.3% of appendectomy specimens
most commonly found in men, aged in 60's
LAMNs less than 2cm are rarely malignant and are classified as benign simple or retention mucoceles
masses larger than 6 cm present with a higher risk of malignant cells, a higher risk of appendiceal perforation, and development of PMP
elevated CEA, Ca 19-9, and Ca-125 may be detected in 56-67% of patients with LAMN
molecular genetics demonstrate CDX2, MUC-2, CK 20, β- catenin, CEA, CA 19-9, and KRAS mutations identified
usually a relatively indolent disease and rarely develop metastases outside the peritoneal cavity
the most worrisome complication of this particular neoplasm is seeding of mucin into the adjacent peritoneum leading to pseudomyxoma peritonei (PMP)¹⁾
there is a 35% risk of a concurrent GI malignancy in patients with LAMN

most are incidental findings after appendicectomy
- may cause RIF pain secondary to distention of the appendix by mucin which is the most common clinical presentation in early stage disease
others tend to be diagnosed late and may result in:
- diverticula
- herniations
- dissections
- rupture
- seeding of mucin into the adjacent peritoneum, leading to pseudomyxoma peritonei (PMP)
  - this has a high mortality rate (25% 5 year survival compared to 95% in those with localised LAMN)
  - occurs in 20% of cases with a mucinous adenoma

Surveillance radiographic imaging every six months post appendectomy for two years for adequate monitoring of tumor recurrence and complications associated with PMP
those with a high risk of disease progression, follow-up should continue for the first five years after diagnosis of LAMN (ie. those with evidence of infiltration of malignancy into submucosa or with the presence of lymph node metastasis)

¹⁾