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Appendiceal neoplasms are rare tumors of the appendix that may present incidentally, mimic acute appendicitis, or cause complications like pseudomyxoma peritonei (PMP). They represent <1% of all gastrointestinal malignancies.

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Classification

WHO / PSOGI 2016–2020 consensus classification

Type	Pathology
1. Epithelial Neoplasms	Mucinous epithelial tumors:
• Low-grade appendiceal mucinous neoplasm (LAMN).
• High-grade appendiceal mucinous neoplasm (HAMN).
• Mucinous adenocarcinoma.

Non-mucinous adenocarcinoma: • Classical adenocarcinoma (colonic type). • Signet ring cell adenocarcinoma (very aggressive). | | Neuroendocrine Tumors (NETs) | • Most common primary appendiceal neoplasm. • Usually small (<2 cm), located at the tip. • May cause carcinoid syndrome if metastatic. | | Mixed Tumors | • MANEC (mixed adenoneuroendocrine carcinoma). • Goblet cell adenocarcinoma (aggressive, mixed mucinous + endocrine features). | | Mesenchymal Tumors | Leiomyoma, GIST, lipoma (rare). | | Lymphoma | Very rare primary appendiceal lymphoma. |

Clinical Presentation

Mimic acute appendicitis (pain, fever, RLQ tenderness).
Incidental finding in appendectomy specimens.
Mucocele (distended appendix filled with mucin).
Complications: PMP, bowel obstruction, GI bleeding.

Complications

Appendiceal neoplasms can perforate → seeding of peritoneum → PMP (esp. mucinous types).
NETs may metastasize to regional lymph nodes and liver.
Signet ring carcinoma → aggressive peritoneal/serosal spread.

Radiology

Modality	Imaging features
Mucinous neoplasms	Low attenuation cystic lesion, may rupture with peritoneal deposits.
Adenocarcinoma	Irregular wall thickening, periappendiceal invasion
NETs	Small enhancing soft-tissue nodule, often tip of appendix.
PMP	Low attenuation mucinous ascites, scalloping of solid viscera.

Classification

Clinical Presentation

Complications

Radiology

Management