High magnification chromoscopic colonoscopy or high frequency 20 MHz mini probe endoscopic ultrasound staging for early colorectal neoplasia: a comparative prospective analysis

Abstract

Background: Successful endoscopic management of early colorectal cancer using endoscopic mucosal resection requires the mandatory prediction of invasive depth and lymph node metastasis. Previous data using the Nagata crypt types Vn(B)/(C) as clinical indicators of T2/N+ disease have shown low specificity (50%) with a tendency to over stage lesions. New mini probe ultrasound "through the scope" imaging permits staging of lesions proximal to the rectum using direct endoscopic visualisation.

Aim: To compare the staging accuracy of the Nagata crypt type V with mini probe high frequency 20 MHz endoscopic ultrasound.

Methods: Sixty two patients with a Paris type II flat cancer were imaged using magnification colonoscopy followed by 20/12.5 MHz ultrasound in a "back to back" design. Crystal violet staining (0.05%) at 100x magnification permitted Nagata crypt criteria to be defined. Submucosal deep invasion (sm3+) was defined at ultrasound by the presence or absence of a disrupted third sonographic layer. Predicted T0/1:N0 lesions were resected using endoscopic mucosal resection with the remaining referred for surgery. Ultrasound and magnification staging were then compared with the resected histopathological specimens.

Results: One patient was excluded from the study due to poor bowel preparation. Fifty two lesions from 52 patients therefore met inclusion criteria (12 sm1/13 sm2/27 sm3+). Ultrasound (20 MHz) was significantly more accurate for invasive depth staging compared with Nagata stage (p<0.0001) (overall accuracy 93% and 59%, respectively). The sensitivity for lymph node metastasis detection using ultrasound and magnification was 80% and 31%, respectively (p<0.001). The negative predictive value of ultrasound for invasive depth was better than that observed using magnification (88%/47%, respectively). The prevalence of nodal disease overall was 19% (10/52), with 80% (8/10) node positive lesions occurring in the sm3+ lesion group.

Conclusions: High frequency 20 MHz ultrasound is superior to magnification alone when differentiating T1/2 disease with a high positive predictive value for sm3 differentiation. Sm3+ invasion was associated with nodal metastasis.