Diagnostic utility of endoscopic ultrasonography for preoperative rectal cancer staging estimation

The preoperative staging accuracy of endoscopic ultrasonography (EUS) was assessed in 38 rectal cancer patients who underwent rectal EUS and curative surgery from July 1992 to September 1994. We used a GF-UM20 instrument with both 12- and 7.5-MHz transducers. Compared with the histological findings, the diagnostic accuracy rate for EUS was 76% (29/38) for the invasion depth and 85% (sensitivity) and 72% (specificity) for level one lymph node metastasis, resulting in an overall preoperative staging accuracy of 74% (28/38). The diagnostic accuracy of invasion depth was poor (only 45%: 5/11) in cases shown histologically to be a1 (tumor invasion through muscularis propria into parietal fat), but ranged from 90 to 100% when the a1 cases were excluded. The diagnostic accuracy for level one lymph node metastasis was proportional to the nodal size. The size of lymph nodes that had been diagnosed as metastatic and non-metastatic (P < 0.05) differed significantly. Eighteen (86%) of the 21 metastatic nodes with histologically massive invasion were detected preoperatively by EUS. Eight of the 11 undetected metastatic nodes were either less than 4 mm in diameter or showed only slight invasion. Most (81%) of the level one metastatic nodes larger than 5 mm were found. The worst preoperative staging diagnostic accuracy was for stage II cases (63%: 5/8), and in four of the 10 misdiagnosed cases, the stage was underestimated due to slight nodal invasion or skip metastasis (2 cases each). Although it was difficult to diagnose nodal metastasis correctly in these cases, preoperative staging using EUS was considered useful for diagnosing almost 80% of our rectal cancer cases.