• CRM
• ERUS
• MRI

The aim of this study is to evaluate the correlation between endorectal ultrasound (ERUS) and magnetic resonance imaging (MRI) in preoperative staging of rectal cancer.
Materials and Methods: Fifty patients with rectal cancer underwent ERUS and 3-Tesla MRI for preoperative staging. With both imaging techniques were evaluated the following features: lesion site, tumour longitudinal extent, distance between lesion distal margins and puborectalis muscle, levator ani muscles infiltration, depth of extramural spread, mesorectal lymph nodes involvement and pelvic organs infiltration.
MRI evaluated also the following features: maximum thickness of the lesion, distance between externa margins of the lesion and mesorectal fascia and overcoming of the peritoneal reflection. All MR studies were evaluated by two experienced professionals board certified in radiology and experts in gastrointestinal imaging.
The correlation between MRI and ultrasound data was calculated for each measure using the Spearman rank test (p-values <0.05 were considered statistically significant).
The interobserver agreement for MRI was assessed by using the Cohen’s kappa statistics.
Eleven patients underwent directly to surgical resection without neoadjuvant therapy, and the surgical specimen was used as standard of reference for determination of depth of invasion (T stage) and perirectal nodal involvement (N stage).
Results: ERUS and MRI showed a statistically significant correlation for the lesion site (MRI observer A vs ERUS: rs=0.873, p<0.000001/ MRI observer B vs ERUS: rs=0.8485, p<0.000001), the tumour longitudinal extent (MRI observer A vs ERUS: rs=0.378, p=0.010393/ MRI observer B vs ERUS: rs=0.3794, p=0.010131), the distance between lesion and puborectalis muscle (MRI observer A vs ERUS: rs=0.7954, p<0.000001/ MRI observer B vsERUS: rs=0.7989, p<0.000001) and the depth of extramural spread (MRI observer A vs ERUS: rs=0.5107, p=0.000149/ MRI observer B vs ERUS: rs=0.5046, p=0.000186).
Moreover, TRUS and MRI were able to demonstrate the levator ani muscles infiltration with an overall agreement of 82% for MRI reader A and 80% for MRI reader B, the lymph nodes involvement with an agreement of 68% for MRI reader A and 76% for MRI reader B and the pelvic organs infiltration with an agreement of 80% for both MRI reader.MRI allowed, however, the evaluation of other staging parameters, as the distance between lesion and mesorectal fascia.
The interobserver agreement between MRI reader A and B was 0.91 for the lesion site, 0.914 for the distance between lesion and puborectalis muscle, 0.791 for the tumour longitudinal extent, 0.758 for the depth of extramural spread, 0.734 for the maximum thickness of the lesion and 0.48 for the distance between lesion and mesorectal fascia.
There was also an agreement between the two observers of 100% for the pelvic organs involvement, of 96% for the overcoming of the anterior peritoneal reflection, of 88% for the mesorectal lymph nodes involvement and of 82% for the levator ani muscles infiltration.
Conclusions: The good agreement between MRI and TRUS in preoperative staging of rectal cancer argues in favor of the use of MRI, because it also allows a more comprehensive local assessment.