Imaging of appendiceal mucinous epithelial neoplasms: A narrative review

Table 1 TNM staging system for appendiceal mucinous epithelial neoplasm, according to the current classification criteria, including definitions of primary tumor (T), regional lymph node involvement (N), and distant metastasis (M), with corresponding stage groupings

TNM staging	Current classification criteria
Primary tumor (T)	Tx	Primary tumor cannot be assessed
	T0	No evidence of primary tumor
	Tis	Carcinoma in situ (intramucosal carcinoma; invasion of the lamina propria or extension into but not through the muscularis mucosae)
	T1	Tumor invades the submucosa
	T2	Tumor invades the muscularis propria
	T3	Tumor invades the subserosa or the mesoappendix
	T4 (T4a, T4b)	Tumor invades the visceral peritoneum, including acellular mucin or mucinous epithelium involving the serosa of the appendix or mesoappendix; tumor invades directly invades adjacent organs or structures
Lymph nodes (N)	NX	Regional lymph nodes cannot be assessed
	N0	No tumor involvement of regional lymph node(s)
	N1 (N1a, N1b, N1c)	Tumor involvement of one to three regional lymph nodes; tumor involvement of one regional lymph node; tumor involvement of two or three regional lymph nodes; no tumor involvement of regional lymph nodes, but there are tumor deposits in the subserosa or mesentery
	N2	Tumor involvement of four or more regional lymph nodes
Distant metastasis (M)	M0	No distant metastasis
	M1	Distant metastasis
	M1c	Metastasis to sites other than peritoneum