ANAL CANAL (ICD‐O‐3 C21, ICD‐O‐3 C44.5)

The anal canal (Fig. 189) extends from rectum to perianal skin (to the junction with hair‐bearing skin). It is lined by the mucous membrane overlying the internal sphincter, including the transitional epithelium and dentate line. Tumours of anal margin and perianal skin defined as within 5 cm of the anal margin (ICD‐O‐3 C44.5) are now classified with carcinomas of the anal canal (Fig. 190).

Rules for Classification

The classification applies only to carcinomas. There should be histological confirmation of the disease and division of cases by histological type.

Regional Lymph Nodes (Fig. 191)

The regional lymph nodes are the perirectal (1), internal iliac (2), external iliac (3) and inguinal lymph nodes (4).

Schematic illustration of the anal canal. — **Fig. 189**

Schematic illustration of carcinomas of the anal canal. — **Fig. 190**

Source: From Zinner MI, Ashley SW (2012) *Maingot’s Abdominal Operations*, 12th edition, McGraw Hill Education. © 2012 McGraw Hill Education.

Schematic illustration of Regional Lymph Nodes. — **Fig. 191**

TNM3 Clinical Classification

T0	No evidence of primary tumour
Tis	Carcinoma in situ, Bowen disease, high‐grade squamous intraepithelial neoplasia (HSIL), anal intraepithelial neoplasia (AIN II–III)
T1	Tumour 2 cm or less in greatest dimension (Fig. 192)
T2	Tumour more than 2 but not more than 5 cm in greatest dimension (Fig. 193)
T3	Tumour of more than 5 cm in greatest dimension (Fig. 194)
T4	Tumour of any size invades adjacent organ(s), e.g., vagina, urethra, bladder^* (Fig. 195)

Schematic illustration of tumour 2 cm or less in greatest dimension. — **Fig. 192**

Schematic illustration of tumour more than 2 but not more than 5 cm in greatest dimension. — **Fig. 193**

Schematic illustration of tumour of more than 5 cm in greatest dimension. — **Fig. 194**

Schematic illustration of tumour of any size invades adjacent organ(s), e.g., vagina, urethra, bladder. — **Fig. 195**

Note

^* Direct invasion of the rectal wall, perianal skin, subcutaneous tissue or the sphincter muscle(s) alone is not classified as T4.

N – Regional Lymph Nodes

NX	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1a	Metastases in inguinal, mesorectal and/or internal iliac nodes (Fig. 196)
N1b N1c	Metastases in external iliac nodes (Fig. 197) Metastases in external iliac and in inguinal, mesorectal and/or internal iliac nodes (Fig. 198)

Schematic illustration of Metastases in inguinal, mesorectal and internal iliac nodes. — **Fig. 196**

Schematic illustration of Metastases in external iliac nodes. — **Fig. 197**

Schematic illustration of Metastases in external iliac and in inguinal, mesorectal and internal iliac nodes. — **Fig. 198**

M – Distant Metastasis

M0	No distant metastasis
M1	Distant metastasis

TNM Pathological Classification

The pT and pN categories correspond to the T and N categories.

pM1	Distant metastasis microscopically confirmed

Note

pM0 and pMX are not valid categories.

pN0

Histological examination of a regional perirectal/pelvic lymphadenectomy specimen will ordinarily include 12 or more lymph nodes; histological examination of an inguinal lymphadenectomy specimen will ordinarily include 6 or more lymph nodes. If the lymph nodes are negative, but the number ordinarily examined is not met, classify as pN0.