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 underwentrectal EUS and curative surgery from July 1992 to September1994. We used a GF-UM20 instrument with both 12- and 7.5-MHztransducers. Compared with the histological findings, the diagnosticaccuracy rate for EUS was 76% (29/38) for the invasion depthand 85% (sensitivity) and 72% (specificity) for level one lymphnode metastasis, resulting in an overall preoperative stagingaccuracy of 74% (28/38). The diagnostic accuracy of invasiondepth was poor (only 45%: 5/11) in cases shown histologicallyto be a1 (tumor invasion through muscularis propria into parietalfat), but ranged from 90 to 100% when the a1 cases were excluded.The diagnostic accuracy for level one lymph node metastasiswas proportional to the nodal size. The size of lymph nodesthat had been diagnosed as metastatic and non-metastatic (P> 0.05) differed significantly. Eighteen (86%) of the 21metastatic nodes with histologically massive invasion were detectedpreoperatively by EUS. Eight of the 11 undetected metastaticnodes were either less than 4 mm in diameter or showed onlyslight invasion. Most (81%) of the level one metastatic nodeslarger than 5 mm were found. The worst preoperative stagingdiagnostic accuracy was for stage II cases (63%: 5/8), and infour of the 10 misdiagnosed cases, the stage was understimateddue to slight nodal invasion or skip metastasis (2 cases each).Although it was difficult to diagnose nodal metastasis correctlyin these cases, preoperative staging using EUS was considereduseful for diagnosing almost 80% of our rectal cancer cases.