A rectal ultrasound is a study looking at the wall of the rectum and surrounding lymph nodes using high-frequency sound waves, or ultrasound usually for the purpose of initial rectal cancer staging, follow-up for a history of rectal cancer, or evaluation of a rectal carcinoid. The test takes about 20 minutes and is performed on an outpatient basis in one of the clinics at Cedars Sinai Medical Center. This study is performed in conjunction with a rigid proctoscopy. Once the proctoscope has been inserted to the level of the upper rectum, the ultrasound probe is placed through the proctoscope and the ultrasound waves will be used to evaluate the rectal anatomy.
In the case of rectal cancer staging, the focus of the examination will be determining how deep into the rectal wall the primary cancer has invaded, and if the cancer has penetrated neighboring organs, such as the prostate gland in men or the vagina in women. This will determine the T, or tumor stage. The local lymph nodes will also be evaluated for evidence of spread, or metastasis, which will determine the N, or lymph node stage. Rectal ultrasound is not able to assess distant spread to organs such as the liver, lungs or brain, since it is only looking at the rectum and surrounding tissues.