Key Terms: Anal, Anatomy, Biopsy, Cancer screening, Colon, Digital rectal examination, Endorectal probe, Enema, Metastasis, Rectal.
Definition
Ultrasound is a type of imaging technique that painlessly uses sound waves to produce an image of internal structures, organs, and masses. Endorectal ultrasound, also called transrectal ultrasound, is a special ultrasound technique in which the transducer is directly inserted through the anus and into the patient's rectum. The sound wave echoes detected by the transducer are converted by a computer into an image.
Purpose
Ultrasound technology has been used in medicine since World War II and is recognized as a non-invasive, non-radiative, real-time and inexpensive imaging capacity. It has become standard medical practice to produce fetal images and to identify and assess various anatomical features of the body.
Endorectal ultrasound is a specialized ultrasound application and it represents one of the most useful diagnostic tools for diseases of the anal and rectal regions of the body, especially for rectal, anal, and prostrate cancer screening and staging.
For rectal cancer, endorectal ultrasound is the most preferred method for staging both depth of tumor penetration and local lymph node metastatic status. Endorectal ultrasound:
- differentiates areas of invasion within large rectal adenomas that seem benign
- determines the depth of tumor penetration into the rectal wall
- determines the extent of regional lymph node invasion
- can be combined with other tests (chest x rays and computed tomography scans, or CT scans) to determine the extent of cancer spread to distant organs, such as the lungs or liver The resulting rectal cancer staging allows physicians to determine the need for—and order of—radiation, surgery, and chemotherapy.
For patients diagnosed with anal cancer, endorectal ultrasound may help to stage the lesion and may be used as follow-up care to check for recurrence of cancer after treatment.
In the diagnosis of prostrate cancer, endorectal ultrasound has become a companion technique to digital rectal examination (DRE). It is also the most frequent method used to guide biopsy needle insertion. If surgery is indicated, endorectal ultrasound can also assist the preoperative evaluation of the depth of cancer penetration and of the presence of metastases, as required to design appropriate surgical procedures.
Endorectal ultrasounds can also be used to check the overall treatment results.
Precautions
This is a very easy procedure. Unlike other imaging techniques, it uses no radiation and thus requires no special precautions.
Description
The instrumentation used for endorectal ultrasound consists of a hand-held probe, the transrectal transducer, a scanner, and an imaging screen. During the procedure, high-frequency acoustical (sound) waves are sent out by the small microphone-like transducer, which is inserted into the rectum. The waves bounce off the organ being examined and produce echoes sent by the transducer to a computer so as to generate a picture called a sonogram. Doctors examine the sonogram for echoes that may represent abnormal areas.
Usually, the patient lies on his side during the test. An endorectal probe is covered with a protective covering and inserted into the patient. The probe looks like a small enema tip and there is a minimal amount of discomfort associated with the procedure itself. Once inserted, the sonographer or radiologist gently moves the probe forward and backward to best evaluate the organ being examined. An endorectal ultrasound generally takes five to ten minutes. After the procedure, the radiologist interprets the results and sends a report to the referring physician.
Preparation
The patient requires no anesthetic or sedation, but needs an enema about two hours before the test in order to provide a clean rectal wall through which to scan. The evening before the procedure, it is recommended that the patient eat a small dinner, drinking only clear liquids and avoiding coffee, tea, or soft drinks after dinner.
Aftercare
The patient should enjoy a good meal and remember to keep a follow-up appointment if scheduled. In some cases, there may be some bleeding from the rectum, though this usually settles within a few days. Antibiotics may be prescribed in some cases.
Risks
Multiple studies have shown that the sound waves used with ultrasound imaging are harmless and may be directed at patients with complete safety. However, some patients may develop infections following the procedure, which could require further treatment. These may cause shivering and fever. Any manifestation of such symptoms should be immediately reported to the treating physician. Generally speaking, the entire procedure is well tolerated and there is usually minimal bleeding afterwards.
Normal Results
Normal sonograms produce images that have the correct shape of the organ or tissue examined by the procedure, meaning that it corresponds to the true anatomy.
Abnormal Results
Abnormal sonograms produce images which highlight abnormal features of the organ being scanned. In a tumor is present, it will show up as a distinct contrast feature on the sonogram.
Resources
Books
Bankman, I. Handbook of Medical Imaging. Academic Press, 2000.
Bushong, S. C. Diagnostic Ultrasound. New York: McGraw-Hill & Co., 1999.
Edelstein, Peter, M.D. Colon and Rectal Cancer. New York: Wiley-Liss, 2000.
Periodicals
Gavioli, M., A. Bagni, I. Piccagli, S. Fundaro, and G. Natalini. "Usefulness of endorectal ultrasound after preoperative radiotherapy in rectal cancer: comparison between sonographic and histopathologic changes." Diseases of the Colon and Rectum 43 (August 2000): 1075-83.
Hsieh, J.-S., C.-J. Huang, J.-Y. Wang, and T.-J. Huang. "Benefits of Endorectal Ultrasound for Management of Smooth-Muscle Tumor of the Rectum." Diseases of the Colon and Rectum 42 (August 1999): 322-8
Sudhanshu, G., et al. "Staging of prostate cancer using 3-dimensional transrectal ultrasound images: a pilot study." Journal of Urology 162 (1999): 1318-1321.
van den Berg, J. C., J. P. van Heesewijk, and H. W. van Es. "Malignant stromal tumour of the rectum: findings at endorectal ultrasound and MRI." British Journal of Radiology 73 (September 2000): 1010-12.
Questions to Ask the Doctor
- How many endorectal ultrasounds will I have to undergo?
- Are any other imaging tests indicated?
- How will this test help you diagnose my cancer?
—Monique Laberge, Ph.D.
