Multimodal imaging evaluation in staging of rectal cancer

Table 1 Tumor nodes metastasis staging of rectal cancer based on the American Joint Committee on Cancer 7^th edition

Primary tumor (T)
Tx	Primary tumor cannot be assessed
T0	No evidence of primary tumor
Tis	Carcinoma in situ
T1	Tumor invades submucosa
T2	Tumor invades muscularis propria
T3	Tumor invades through the muscularis propria and into perirectal tissues
T4a	Tumor penetrates to the surface of the visceral peritoneum
T4b	Tumor directly invades or is adherent to other organs or structures
Regional lymph nodes (N)
Nx	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastases in 1-3 regional lymph nodes
N1a	Metastasis in 1 regional lymph node
N1b	Metastases in 2-3 regional lymph nodes
N1c	Tumor deposit(s) in the subserosa, mesentery, pericolic, or perirectal tissues without regional nodal metastasis
N2	Metastases in 4 or more regional lymph nodes
N2a	Metastases in 4-6 regional lymph nodes
N2b	Metastases in 7 or more regional lymph nodes
Distant metastasis (M)
M0	No distant metastasis
M1	Distant metastasis
M1a	Metastasis confined to 1 organ or site (e.g., liver, lung, ovary, non-regional node, external iliac lymph node)
M1b	Metastases in > 1 organ/site or the peritoneum

Note-Adapted from the American Joint Committee on Cancer staging system[3].

Table 2 Advantages and disadvantages of imaging modalities in preoperative staging

Imaging modalities	Advantages	Disadvantages
Preoperative staging
EUS	Depth of tumor invasion in early rectal cancer	Limited field of view Perirectal invasion and LN metastasis
CT	Wide availability Fast scanning time	Local staging and CRM involvement in lower rectal cancer
MRI	High soft tissue resolution Local staging and CRM involvement	Distant metastasis
PET/CT	Distant metastasis	Poor spatial resolution Perirectal invasion and CRM involvement
Post-therapeutic restaging
EUS	None	Low accuracy of T staging and LN staging
CT	Relatively high accuracy of CRM status	Relatively low accuracy of T staging and LN staging
MRI	High specificity of therapeutic response assessment High accuracy of CRM involvement	Relatively poor sensitivity
PET/CT	Distant metastasis	No standard parameter and follow-up protocol

MRI: Magnetic resonance image; EUS: Endorectal ultrasonography; CT: Computed tomography; PET: Positron emission tomography; CRM: Circumferential resection margin; LN: Lymph node.