The topography code indicates the site of origin of a neoplasm; in other words, where the tumor arose. No changes or additions were made to the topography codes in the Third Edition of ICD-O. Topography codes or rubrics C00-C80 are based on the malignant neoplasm section of Chapter II of ICD-10, as noted in the unit on differences between ICD-O and ICD-10. All neoplasms, whether malignant, benign, in situ, or uncertain whether benign or malignant, are coded with the same set of topography codes in ICD-O.

Adjectival Forms

The topographic site of neoplasm may be described by using the noun or its related adjective, for example "glioma of pons" or "pontine glioma." In general, noun forms appear in the numerical list and alphabetic index of ICD-O; for example, "pons" is listed but "pontine" is not. Only a few of the commonly encountered adjectives, such as "uterine" and "gastric," have been listed in ICD-O for the convenience of coders. When there is doubt, the coder should consult a medical dictionary to determine the correct noun that the adjective corresponds to.

Special Topography Codes

Divisions of the Esophagus

Because two incompatible systems are widely used to subdivide the esophagus, both are included in ICD-O and ICD-10 (Figure 15). The terms cervical, thoracic, and abdominal are radiographic and intraoperative descriptors; upper, middle, and lower third are endoscopic and clinical descriptors.

Figure 15. Code Structure for Esophagus
Code Site
C15 Esophagus
C15.0 Cervical espophagus
C15.1 Thoracic esophagus
C15.2 Abdominal esophagus
C15.3 Upper third of esophagus
Proximal third of esophagus
C15.4 Middle third of esophagus
C15.5 Lower third of esophagus
Distal third of esophagus
C15.8 Overlapping lesion of esophagus
C15.9 Esophagus, NOS

Branchial Cleft and Meckel Diverticulum as Sites of Neoplasms

Both "branchial cleft" and "Meckel diverticulum" are congenital abnormalities and as such are coded to categories C18.0 and C43.0 respectively in ICD-10. However, these anomalies create tissues in which neoplasms can arise. The codes C10.4, branchial cleft, and C17.3, Meckel diverticulum, are included in the topography section in ICD-O. The phrase "site of neoplasm" appears in parentheses after each term to indicate that they are to be used only when they are the site of origin of a neoplasm. ICD-O topography codes should not be used for these congenital anomalies unless a neoplasm arises in them.