Endorectal ultrasonography for the assessment of wall invasion and lymph node metastasis in rectal cancer

Abstract

Endorectal ultrasonography (ERUS) with a flexible-type radial scanner (Aloka Co. Ltd., Tokyo, Japan; 7.5 MHz) was applied to 120 patients with rectal cancer for the assessment of wall invasion and pararectal lymph node metastasis. Normal rectal wall was described as a five- or seven-layer structure excluding the lowest part within 3 cm from the anal verge. Loss of normal layers basically indicated the existence of cancer invasion. According to UICC classification, we divided the depth of wall invasion into four ultrasonographic levels (uT1–uT4), and results were correlated with histopathologic findings. Overall accuracy of the assessment was 92.0 percent (103/112). Overestimation occurred in 5 of 60 cases with T3 cancer (8.3 percent), and underestimation occurred in 1 of 19 cases with T2 cancer (5.3 percent) and 3 of 60 cases with T3 cancer (5 percent). Inflammatory cell infiltration was found around the cancer in a considerable number of cases. However, the assessment of wall invasion was hardly affected in our hands. Because the muscularis propria of the rectal wall was often recognized as a three-layer structure, uT2 cancer was subdivided into three subgroups of uPM1, uPM2, and uPM3. The assessment of invasion of sublayers in muscularis propria was possible in 14 of 19 cases (73.7 percent), and correct assessment was achieved in 57 percent of the cases. The ultrasonographic demonstration of pararectal lymph nodes was studied on 98 patients. No swollen lymph nodes were detected ultrasonographically in 35 of 98 cases (35.7 percent), but cancer metastasis was found histopathologically in 5 of these 35 cases (14.3 percent). The metastasis was observed more frequently in lymph nodes with a diameter of more than 5 mm (53.8 percent) and in those with a well-defined boundary and with an uneven and markedly hypoechoic pattern (72.3 percent). Although unable to detect minimal cancer foci, ERUS was considered a very useful tool for the assessment of the depth of cancer invasion in the rectal wall and pararectal lymph node metastasis.