C18.1

Billable

Malignant neoplasm of appendix

HCC Category Mapping

V28HCC 22 — Colorectal, Bladder, and Other Cancers

0.000

V24HCC 11 — Colorectal, Bladder, and Other Cancers

0.306

ESRDHCC 11 — Colorectal, Bladder, and Other Cancers

0.000

What This Code Means

Cancer that starts in the appendix, a small tube-shaped organ connected to the large intestine. This is a type of malignant tumor that can spread to other parts of the body if not treated.

Coding Tips

•Verify the histological type (adenocarcinoma, neuroendocrine, mucinous, etc.) as this may require additional coding with laterality or behavior codes
•Ensure you have documented confirmation of malignancy and that this is not a benign neoplasm (C80 series) or carcinoma in situ (D12.3)

Clinical Significance

Malignant neoplasm of the appendix is a relatively uncommon cancer that may be discovered incidentally during appendectomy for presumed appendicitis. Appendiceal cancers include several histological types with very different prognoses, from low-grade mucinous neoplasms to aggressive adenocarcinomas and neuroendocrine tumors. Accurate coding is essential because treatment ranges from appendectomy alone for early-stage disease to cytoreductive surgery with hyperthermic intraperitoneal chemotherapy for mucinous tumors with peritoneal spread.

Documentation Requirements

✓Confirmation of malignancy (not carcinoma in situ or benign neoplasm)
✓Histological type: mucinous adenocarcinoma, goblet cell carcinoid, neuroendocrine, or non-mucinous adenocarcinoma
✓Stage of disease including peritoneal involvement
✓Presence or absence of pseudomyxoma peritonei
✓Whether diagnosis was incidental at appendectomy or clinically suspected

Commonly Confused Codes

D12.1 — Benign neoplasm of appendix: benign tumors do not map to HCCs; confirm malignancy C18.0 — Cecum: the appendix arises from the cecum; ensure primary site is appendix, not cecum C7A.020 — Malignant carcinoid tumor of appendix: carcinoid/neuroendocrine tumors of the appendix have their own specific code D3A.020 — Benign carcinoid tumor of appendix: benign carcinoid is different from malignant

Code Hierarchy

└C18Malignant neoplasm of colon └C18.1Malignant neoplasm of appendix

└C18.1Malignant neoplasm of appendix