Appendix
Other tumors
Mucinous neoplasms (LAMN and HAMN)

Author: Michael Feely, D.O. (see Authors page)
Editor: Raul S. Gonzalez, M.D.

Revised: 27 October 2017, last major update October 2017

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Mucinous neoplasms appendix[title] free full text[sb]
Cite this page: Feely, M. Mucinous neoplasms (LAMN and HAMN). PathologyOutlines.com website. http://pathologyoutlines.com/topic/appendixmucinousneoplasm.html. Accessed November 23rd, 2017.
Definition / general
  • Evolving nomenclature with considerable controversy, although recent consensus terminology has been established (Am J Surg Pathol 2016;40:14)
  • Variable clinical consequences depending on the location of neoplastic epithelium and associated mucin
  • By definition, must lack infiltrative invasion, which would be termed mucinous adenocarcinoma
Essential features
  • Low grade appendiceal mucinous neoplasm (LAMN) is a low grade noninvasive epithelial proliferation that can cause pseudomyxoma peritonei if the appendix ruptures
  • Similar, rare lesions with high grade nuclear dysplasia are termed high grade appendiceal mucinous neoplasm (HAMN)
Terminology
  • Low grade appendiceal mucinous neoplasm (LAMN): lesion arising in appendix with low grade epithelial features in the absence of infiltrative growth
  • High grade appendiceal mucinous neoplasm (HAMN): lesion arising in appendix with high grade epithelial features in the absence of infiltrative growth
  • Pseudomyxoma peritonei: strictly clinical term for apparent mucinous ascites or peritoneal mucin deposition
  • Mucocele: strictly clinical term for dilated, mucin filled appendix
  • Cystadenoma: outdated diagnostic term that should no longer be used
Epidemiology
Clinical features
  • Typically occurs in patients during their sixth decade of life, although age range is broad; more common in women (Am J Surg Pathol 2009;33:1425)
  • Most patients with disease restricted to the appendix present with acute appendicitis-like symptoms, while those with disseminated disease may present with abdominal or ovarian masses or pseudomyxoma peritonei
Radiology description
  • Appendix with a diameter of more than 15 mm, a soft tissue mass or wall thickening may raise the possibility of a mucinous neoplasm (Cancer Imaging 2013;13:14)
Prognostic factors
  • Mucinous lesions confined to appendix largely considered cured by resection
  • Lesions with extra-appendiceal acellular mucin considered to be low risk for recurrence or progression, occurring in about 4% of cases (Am J Surg Pathol 2009;33:248)
  • If extra-appendiceal mucin contains neoplastic epithelium, patient is at high risk for recurrence or dissemination, which occurs in 33 - 75% of these cases (Am J Surg Pathol 2009;33:248, Am J Surg Pathol 2009;33:1425)
Treatment
  • Simple appendectomy considered sufficient for lesions limited to appendix
  • Close surveillance for patients with localized periappendiceal disease following initial surgery
  • Disseminated peritoneal disease may be treated with hyperthermic intraperitoneal chemotherapy (HIPEC) following cytoreductive surgery
Gross description
  • Typically, appendix appears dilated with luminal mucin, although diameter may appear unremarkable
  • Serosa appears smooth when appendiceal wall is intact
  • Adhesions or extra-appendiceal mucin are concerning for underlying rupture
Gross images

Images hosted on other servers:

Mucocele: dilated appendix

LAMN

Microscopic (histologic) description
  • Villous or occasionally flat proliferation of mucinous epithelial cells originating from appendiceal lumen
  • Lesional cells typically demonstrate abundant apical mucin with elongated nuclei and low grade nuclear atypia (LAMN); however, nuclei may appear compressed or rarely high grade (HAMN)
  • Often associated with atrophy of underlying lymphoid tissue, crypt loss and effacement of muscularis mucosae
  • Broad dissection of mucin, epithelium or both may occur with potential involvement of extra-appendiceal surface, an important finding affecting prognosis
  • Extra-appendiceal mucin incites a serosal reaction and may contain neovascularization, assisting in differentiation from benign transfer of mucin during gross examination
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Dr. Michael Feely:

LAMN in cross section

Villous architecture in LAMN

Low grade epithelium in LAMN

LAMN with extra-appendiceal mucin

Extra-appendiceal mucin with serosal reaction

Cellular extra-appendiceal mucin



Images hosted on other servers:

Intestinal type epithelial lining

Involving diverticulum

Lined by pseudostratified
columnar cells with low
grade dysplastic changes

Negative stains
Molecular / cytogenetics description
  • Frequently harbor KRAS mutations and loss of chromosome 5q has been reported (Am J Pathol 1999;154:1849)
  • GNAS alterations have been reported to occur in 50% of cases (Br J Cancer 2013;108:951)
  • Microsatellite instability and BRAF mutations have not been demonstrated
Differential diagnosis
Board review question #1
Which finding associated with a mucinous neoplasm has the greatest risk of progression?

  1. Acellular mucin outside the right lower quadrant of abdomen
  2. Acellular mucin restricted to right lower quadrant of abdomen
  3. Extra-appendiceal mucin containing low grade epithelium
  4. High grade epithelium confined to appendix
  5. Low grade epithelium confined to appendix
Board review answer #1
C. Extra-appendiceal mucin containing low grade epithelium.