Mucinous neoplasms of the appendix

Mucinous neoplasms of the appendix are epithelial tumours of the appendix that produce mucin. They represent a spectrum of malignant potential, and are the most common cause of pseudomyxoma peritonei.

Pathology

Classification

According to a panel of specialists consensus published in 2016 (Peritoneal Surface Oncology Group International), a nomenclature and classification for the appendiceal mucinous neoplasms based on histologic type and biologic behaviour has been proposed ^1-3:

Premalignant

These lesions have no capacity to cause pseudomyxoma peritonei:

• appendiceal adenoma - tubular, tubulovillous, and villous subtypes

• serrated appendiceal polyp

Uncertain malignant potential

• low-grade appendiceal mucinous neoplasm (LAMN)

  • typically do not cause nodal or distant extraperitoneal metastases ³

• high-grade appendiceal mucinous neoplasm (HAMN)

Malignant

• appendiceal mucinous adenocarcinoma

• poorly differentiated (mucinous) adenocarcinoma w signet ring cells - ≤50% signet ring cells

• (mucinous) signet ring cell carcinoma - >50% signet ring cells

It is important to note that in cases of peritoneal spread, the histologic grade of the peritoneal disease may be different than the primary appendiceal tumour. In these case, the peritoneal histology is considered more important for prognostication ³.

Radiographic features

On imaging, they are difficult to be distinguished from each other, particularly when comparing the low- and high-grade appendiceal mucinous neoplasms, and generally are referred to as a "mucinous neoplasm of the appendix". 

Treatment and prognosis

Management varies depending both on the type of appendiceal tumour and (often more importantly) on the histology and extent of peritoneal disease. Surgical approaches, particularly for newer categories of disease (e.g. HAMN) remain under investigation ³.

In general, premalignant mucinous appendiceal tumours are treated by surgical resection. Indeterminate-behaviour lesions such as LAMN are often followed with surveillance imaging after resection. Adenocarcinoma is generally treated with right hemicolectomy and nodal dissection, due to improved survival compared to appendicectomy alone ³.

Patients with peritoneal disease (i.e. pseudomyxoma peritonei) may be treated by cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (HIPEC), particularly if peritoneal disease is low-grade ³.

See also

• appendiceal mucocele