High-grade appendiceal mucinous neoplasms

High-grade appendiceal mucinous neoplasms (HAMN) are rare mucinous tumours of the appendix showing high-grade cytologic atypia, cf. low-grade appendiceal mucinous neoplasms (LAMN). The distinction between both LAMN and HAMN is done on histological grounds and these tumours look the same on imaging. Please, refer to the LAMN article for a detailed conjoined discussion on their imaging findings. 

Terminology 

Considerable controversy still exists on mucinous neoplasms of the appendix pathologic classification and nomenclature ³. According to a panel of specialist review in 2016, a new nomenclature and classification for the appendiceal mucinous neoplasms based on their histologic type and biologic behaviour has been proposed, which now includes the “high-grade appendiceal mucinous neoplasm”. The HAMN was proposed to include the lesions that have high-grade atypia and thus cannot be grouped as a LAMN, but also do not have the infiltrative invasion to be characterised as an appendiceal mucinous adenocarcinoma ^1,2.

Pathology

Histologically these tumours show high-grade cytologic atypia associated with at least one of the following ^1,2: 

• loss of the muscularis mucosae 
• fibrosis of the submucosa
• rupture of the appendix
• mucin and/or tumoural cells outside the appendix