Endorectal ultrasound
Endorectal ultrasound (ERUS) is a medical imaging technique that involves the insertion of an ultrasound transducer through the anus to create detailed images of the rectal wall and surrounding tissues. This procedure is commonly used to diagnose various cancers, including colorectal, anal, and prostate cancer, by determining tumor boundaries and assessing potential spread to lymph nodes and pelvic organs. ERUS can also serve as a surveillance tool to detect local recurrence of tumors.
Prior to the procedure, patients may need to stop certain medications and prepare the rectum through cleansing. During the examination, patients typically lie on their side while the physician performs a digital rectal exam and then inserts the transducer, which emits sound waves to generate images displayed on a monitor. The procedure is generally safe, although there are minor risks such as perforation, bleeding, and infection. After the imaging, any abnormal tissues can be biopsied for further analysis.
ERUS images are interpreted based on established criteria that help differentiate between healthy and abnormal tissues. Despite some similarities in appearance between cancerous and inflamed tissues, cytologic evaluations are often necessary to confirm the presence of cancer.
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Endorectal ultrasound
ALSO KNOWN AS: Endorectal echoscopy, endorectal ultrasonography, rectal endosonography, transrectal ultrasound
DEFINITION: Endorectal ultrasound (ERUS) is the insertion of an ultrasound transducer through the anus to construct detailed images of the rectal wall and adjacent tissues. ERUS instruments vary in insertion tube design (such as size, flexibility, and view), ultrasound technology (such as frequency, orientation, and scanning), imaging capabilities (such as fiber-optic or electronic and two- or three-dimensional), and configuration (that is, the ultrasound transducer is either mounted on or passed through an endoscope).
Cancers diagnosed:Colorectal cancer, anal cancer, prostate cancer
Why performed: ERUS may be performed either as a diagnostic procedure to determine tumor boundaries and to assess spread into lymph nodes and pelvic organs or as a surveillance procedure to detect local recurrence.
Patient preparation: A few days before the procedure, the patient may need to stop certain medications, such as aspirin products and blood thinners. The day before the procedure, the patient cleans the rectum, as with an enema.
Steps of the procedure: ERUS is scheduled in a physician’s office or other outpatient setting. The patient wears a gown and lies on the side. The patient is awake; if needed, sedation or local anesthetic can be given. First, the physician performs a digital rectal exam (DRE). Then, the ultrasound transducer is inserted through the anus into the rectum, and a lubricated latex balloon (or alternative for a latex-sensitive patient) covering the ultrasound transducer is inflated. The ultrasound transducer is turned on, sending pulses of sound waves through the balloon into the rectal wall and adjacent tissues. As each pulse of sound waves hits different tissues, some sound waves bounce back and become a gray-scale 2-D or 3-D image on a video monitor. The physician views the images as the ultrasound transducer is moved through the rectum. Tumor dimensions and lymph node sizes are measured. Abnormal tissues are sampled (biopsied) with a fine needle; all tissue samples are taken to the laboratory for cytologic evaluation.
After the procedure: The patient leaves and resumes normal activities, unless sedation or local anesthetic was needed. In the latter case, the patient will need to be driven home by another individual.
Risks: ERUS is relatively safe, with a small risk of these side effects: perforation, bleeding, and infection.
Results: ERUS images are interpreted with criteria developed by Ulrich Hildebrandt and Gernot Feifel in 1985 or those later developed by J. Beynon et al. Boundaries of the tumor in the rectal wall are accurately determined from the thickness and continuity of each layer of the rectal wall. Lymph nodes and pelvic organs are assessed for size, shape, and irregularities. Because cancerous and inflamed tissues look similar in ERUS images, however, cytologic evaluation must verify whether abnormalities in lymph nodes or pelvic organs are cancerous.
Bibliography
Bisset, R. A. L., A. N. Khan, and Durr-e-Sabih. Differential Diagnosis in Abdominal Ultrasound. 3rd ed. New Delhi: Elsevier, 2008. Print.
"Colorectal Cancer: Diagnosis." Cancer.net. Amer. Soc. of Clinical Oncology, Sept. 2013. Web. 2 Oct. 2014.
Dietrich, Christoph Frank. Endoscopic Ultrasound: An Introductory Manual and Atlas. 2nd ed. Stuttgart: Thieme, 2011. Digital file.
Edelman, Bret R., and Martin R. Weiser. "Endorectal Ultrasound: Its Role in the Diagnosis and Treatment of Rectal Cancer." Clinics in Colon and Rectal Surgery 21.3 (2008): 167–77. PDF file.
"Prostate Cancer." Cancer.org. Amer. Cancer Soc., 12 Sept. 2014. Web. 2 Oct. 2014.
"Ultrasound - Pelvis." RadiologyInfo.org. Radiological Soc. of North Amer., 2014. Web. 2 Oct. 2014.