[Preoperative assessment of perirectal lymph nodes by ultrasound].

Endorectal ultrasound is a new technique which is having an increasing impact on the surgical community. Beyond the assessment of tumor penetration depth two kinds of lymph nodes are to be differentiated by ultrasound in the perirectal fat. 1) Inflammatory enlarged lymph nodes which appear hyperechoic, unsharply limited to the surrounding tissue and 2) lymph node metastases which are hypoechoic having the same density as the tumor. Sensitivity and specificity of endorectal ultrasound in the detection of lymph node metastases in 97 patients was 80%, the positive predictive value was 78%, the negative 82%. In an in vitro study we examined 27 lymph nodes of patients with either inflammatory or cancerous colon diseases by computerized B-scan texture analysis. An HP-77020 A realtime electronic sector-scanner was connected with HP-1000 microcomputer which permitted the selection and texture-analysis of a region of interest (ROI). Afterwards the lymph nodes were examined histologically. Independent of size and surrounding fat tissue there was a highly significant difference between inflammatory and cancerous enlarged lymph nodes concerning mean grey level and mean gradient. Tumor infiltrated lymph nodes are hypoechoic with poor contrast within the node whereas inflammatory enlarged nodes are more hyperechoic and show more contrast. Thus, we can state that it is possible by consideration of echogenity and contrast to distinguish sonographically between tumor infiltrated and inflammatory enlarged lymph nodes.