Appendiceal Mucinous Neoplasm with High Risk of Recurrence

Definition

Neoplasm of the appendix with features of mucinous adenoma but with evidence of epithelial spread beyond the muscularis propria

Borderline mucinous tumor
Disseminated peritoneal adenomucinosis
Low grade mucinous neoplasm (WHO preferred term, includes low and high risk of recurrence neoplasms, see Controversy)
Mucinous carcinoma (see Controversy)
Mucinous neoplasm of low malignant potential
(Note that ovarian involvement has by some been taken to represent a primary ovarian carcinoma, see Controversy)

Epithelial lesion oexhibiting features of mucinous adenoma (see detailed adenoma criteria)
- Simple mucinous columnar epithelium
- Low grade dysplasia
- Sessile, usually circumferential, lining of appendiceal luminal surface
Extra-appendiceal mucinous implants containing epithelium

Frequent mucin dissection of the wall
- Neoplastic epithelium may be present in intramural mucin
Commonly associated with luminal dilation

Implants largely intraperitoneal
- Implants frequently paucicellular
- Frequently involves surface of liver and spleen
- Frequently involves ovary
  - May produce mucinous cysts that have the appearance of primaries (see Controversy)
- May involve lining of fallopian tubes
No metastases to nodes or parenchyma of organs other than ovary
Mucinous neoplasm with high risk of recurrence is the most frequent cause of pseudomyxoma peritonei
- Extensive mucin secretion producing abdominal distension
Specimen may need to be entirely submitted to make this diagnosis
Occasional cases may have discrepant findings of invasive carcinoma in implants but typical low grade neoplasm in the appendix
- Clinical significance is unclear

Teri A Longacre MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates : 10/7/10, 2/10/12