How useful is rectal endosonography in the staging of rectal cancer?

Abstract

It is essential in treating rectal cancer to have adequate preoperative imaging, as accurate staging can influence the management strategy, type of resection, and candidacy for neoadjuvant therapy. In the last twenty years, endorectal ultrasound (ERUS) has become the primary method for locoregional staging of rectal cancer. ERUS is the most accurate modality for assessing local depth of invasion of rectal carcinoma into the rectal wall layers (T stage). Lower accuracy for T2 tumors is commonly reported, which could lead to sonographic overstaging of T3 tumors following preoperative therapy. Unfortunately, ERUS is not as good for predicting nodal metastases as it is for tumor depth, which could be related to the unclear definition of nodal metastases. The use of multiple criteria might improve accuracy. Failure to evaluate nodal status could lead to inadequate surgical resection. ERUS can accurately distinguish early cancers from advanced ones, with a high detection rate of residual carcinoma in the rectal wall. ERUS is also useful for detection of local recurrence at the anastomosis site, which might require fine-needle aspiration of the tissue. Overstaging is more frequent than understaging, mostly due to inflammatory changes. Limitations of ERUS are operator and experience dependency, limited tolerance of patients, and limited range of depth of the transducer. The ERUS technique requires a learning curve for orientation and identification of images and planes. With sufficient time and effort, quality and accuracy of the ERUS procedure could be improved.

Figure 1

Normal endorectal sonogram image acquired by flexible echoendoscope. The layers of the rectum are as follows: hyperechoic mucosa (m), hypoechoic muscularis mucosa (mm), hyperechoic submucosa (sm), hypoechoic muscularis propria (mp), and hyperechoic serosa (s).

Figure 2

Endorectal ultrasound (ERUS) image. A: A rectal carcinoma that appears to be T1 (penetration into submucosa) in one part (arrowheads show intact muscularis propria) and T2 (penetration into muscularis propria-arrows) in another part; B: A T3 rectal adenocarcinoma. Arrowheads show that the lesion penetrated into perirectal fat; C: A locally invasive cervical cancer, which invaded the rectum (arrows show tumor breach).