Benign tumors
Low grade appendiceal mucinous neoplasm / LAMN

Reviewer: Jaleh Mansouri, M.D. (see Authors page)

Revised: 4 March 2016, last major update August 2012

Copyright: (c) 2003-2017,, Inc.

PubMed Search: Mucinous cystadenoma appendix or Low grade appendiceal mucinous neoplasm
Cite this page: Low grade appendiceal mucinous neoplasm / LAMN. website. Accessed October 17th, 2017.
Definition / general
  • Most common mucinous neoplasm of appendix
  • Previously called mucinous cystadenoma
  • May be associated with ovarian mucinous cystadenoma and colonic neoplasms
  • May present with pain due to distention, symptoms of acute appendicitis, pseudomyxoma peritonei or as abdominal mass
  • May represent a continuum with noncystic adenomas
  • Peaks in 60’s (age)
  • When associated with diverticula (30-40% of time), may cause pseudomyxoma peritonei (Mod Pathol 2000;13:495)
  • Sample thoroughly to rule out malignancy
  • If spreads beyond appendix, survival rates were 100%, 86% and 45% at 3-, 5- and 10- years on one study (Am J Surg Pathol 2003;27:1089)
  • Case reports
  • 54 year old woman with mucinous cystadenoma of pancreas and appendix (JOP J Pancreas 2004;5:97)
  • Treatment
  • Excision
  • Low recurrence rate if low grade features and confined to appendix
  • Gross description
  • Variable cystic luminal dilation, usually filled with viscid mucus
  • 20% perforate appendix
  • Mucin often attached to serosa or free in peritoneal cavity
  • Microscopic (histologic) description
  • Usually intestinal type epithelium (crowded columnar cells with basal, elongated, hyperchromatic nuclei, often with large amounts of apical mucin)
  • Dysplastic changes often minimal but greatest at crypt bases
  • High grade dysplastic changes less common
  • Villous adenomas may completely replace appendiceal mucosa
  • May resemble serrated adenoma (mixed hyperplastic polyp and adenoma) or borderline ovarian mucinous tumor
  • Occasionally see foreign body giant cell reaction, granulation tissue, chronic inflammation, fibrosis, calcification, displaced epithelium or mucin within muscularis propria
  • Muscularis mucosa may be thin/absent and replaced with hyalinization / fibrosis
  • Rarely heterotopic bone formation (Arch Pathol Lab Med 1996;120:666)
  • Microscopic (histologic) images

    Images hosted on other servers:

    Intestinal type epithelial lining

    Lined by pseudostratified columnar cells with low grade dysplastic changes

    Involving diverticulum

    Negative stains
  • CK7 (usually)
  • Differential diagnosis
  • Retention cyst or simple mucocele (usually < 1 cm, no neoplastic epithelium despite extensive sampling), invasive adenocarcinoma (infiltrative pattern, desmoplastic stroma)