Background and study aims: Miniprobe ultrasound technology allows in-vivo luminal staging of colorectal cancer with a probe that passes directly through the colonoscope's instrument port. Conventional rigid radial echoscopes are limited by the need for a second examination, an inability to image stenotic lesions, and the inaccessibility of proximal tumours. Since minimally invasive resection techniques are now possible, a sensitive preoperative staging tool is needed to optimize patient selection. The aim of this study was to examine the accuracy of miniprobe ultrasound imaging in the preoperative staging of colorectal cancer and to examine the value of the technique for management decisions.
Patients and methods: In a prospective study, a total of 131 consecutive patients with adenocarcinoma or broad-based polyps of the colorectum underwent 12.5-MHz miniprobe ultrasonography examinations conducted by a single endoscopist. Staging criteria for depth of tumour infiltration and nodal status were determined. Nodal disease was defined as the presence of a hypoechoic, round, defined boundary lesion larger than 10 mm in diameter. T0-T1N0 lesions were resected using endoscopic mucosal resection, and patients with lesions staged as T2N1 were referred for surgical resection. Tumour staging using endoscopic ultrasonography was then compared with the histopathological specimens.
Results: The accuracy of T staging using endoscopic ultrasonography was 96 % in comparison with the histopathological specimen. Five lesions (4 %) were incorrectly overstaged as T3 - pathology stage T2. Understaging occurred in three lesions (endoscopic ultrasound stage T3 - pathology stage T4). The overall accuracy of nodal staging using endoscopic ultrasonography was 87 % (sensitivity 0.95, specificity 0.71, positive predictive value 0.87, negative predictive value 0.88).
Conclusions: Miniprobe ultrasonography has a high overall accuracy for both T staging and N staging of colorectal cancer and may have an important role in selecting patients suitable for minimally invasive resection techniques.