Endoluminal Ultrasonography of the Rectum and the Anal Canal

Abstract

Ultrasonography of the anal canal, the rectum and the surrounding tissues using intraluminal transducers with transanal/rectal imaging provides high-resolution imaging with clearly distinguishable tissue-dependent echo signals. Endorectal ultrasonography depicts rectal wall layers and adjuvant structures with a high degree of precision. Anal endosonography is carried out to examine the sphincter muscles and the pelvic floor. Detailed ultrasonographic anatomy is presented. Specific information is noted regarding the use of radial and linear scanning. The Doppler techniques depict the vascularization. Contrast-enhanced harmonic imaging and elastography are discussed in an integrative manner regarding their role in differentiating malignant from benign ano-rectal masses or lymph nodes. Three-dimensional endorectal ultrasonography provides superior visual images of tumor volume and the spatial relationships of tumor to surrounding anatomical structures. Endorectal ultrasonography technique accurately measures the size, circumference and distance of the tumor from various anatomic landmarks. It is capable of examining the anal sphincters for tumor infiltration, allowing the surgeon to decide whether a sphincter-sparing resection might be indicated. It can depict the relationship of tumor the to the pelvic peritoneal reflection, to determine whether local excision is possible. Endorectal ultrasonography in benign pathology is emphasized. Brief conclusions are given at the end of the chapter.