Sonography is a non-invasive modality which has gained a place in the non-invasive evaluation of the rectum and anal canal. Studies are performed with intracorporeal probes as TRUS or transrectal sonography and with the addition of other more innovative techniques. These include transvaginal scan in woman and the use of transperineal scan in both sexes.

The two major arenas for transrectal sonography include the staging of rectal cancers and the evaluation of benign conditions of the anal canal, notably perianal inflammatory disease, in those with or without inflammatory bowel disease, and the evaluation of the anal sphincter in those with fecal incontinence.

Staging of rectal cancer prior to selection of a treatment regime is critical to identify those superficial tumours amenable to transanal excision and those invasive lesions better treated with neoadjuvant chemoradiation prior to surgery. The contrast and spatial resolution of state of the art ultrasound depicts the multi-layer appearance of the rectal wall making ultrasound the gold standard for preoperative evaluation of rectal tumours. Tumor invasion into the rectal wall and perirectal lymph nodes are staged using the TNM classification.

Perianal inflammatory disease affects two major populations, those with Crohn's disease and those with spontaneous inflammation according to the cryptoglandular theory. Inflammatory masses and tracts are shown and depicted in relation to the anal sphincters.

Fecal incontinence, an unfortunate sequela of childbirth trauma, is evaluated for demonstration of the morphologic damage to the anal sphincters.

Rectal and anal sonography are non invasive effective techniques for the study of the rectum and anal canal.