In a day and age where medicine and surgery have an increasing drive for less invasive measures, there is a rising need to find the greatest possible amount of information prior to definitive intervention. The use of ultrasound for the evaluation of anal and rectal disorders has become a mainstay in the workup of anorectal disease for many years and has seen numerous improvements in technology as well as in the understanding of normal and abnormal anatomy. As with many other innovations, this technology was initially borrowed from urologists, who had been using it as a means of examining the prostate. Since that time, adjustments have been made to optimize it for the evaluation of the rectum and anus.
Endoluminal ultrasound, specifically of the rectum and anus, can be an extremely useful adjunct in the diagnosis of various conditions. As with any other ultrasound modality, this technique is very user-dependent, so specialized training is quite important for reproducible results. A practice that provides a consistent need for this test is also valuable.
Endoanal ultrasound is used most commonly in the evaluation of the anal sphincters in the workup of fecal incontinence. In women who have a history of vaginal delivery or any patient with a history of anal trauma, symptoms of incontinence may indicate scarring of the internal sphincters. Ultrasound, in conjunction with anal manometry, pudendal nerve testing, and defecography, can help determine the cause of the loss of fecal control and guide optimal surgical options.
Endorectal ultrasound is key to staging and evaluation of rectal cancers. In the hands of an experienced ultrasonographer, depth of invasion as well as nodal status can be measured with a fair degree of certainty. Advanced techniques include ultrasound-guided biopsy of lymph nodes for stage verification, which can guide decisions regarding the need for neoadjuvant therapy.
Standard ultrasound images are in 2-D, requiring frozen images to display normal and abnormal anatomy. Newer models include 3-D imaging, which capture the anatomy within a cube; this can be manipulated on the unit or on a computer at leisure to reveal anatomy through various cuts along multiple axes or through spinning the cube to allow views from different angles.
Normal Anatomy, Normal Ultrasound
The normal anatomy of the anus can be evaluated through ultrasound with great accuracy. The structures include the anal mucosa, the internal anal sphincter (IAS), the external anal sphincter (EAS), the puborectalis, the perineal body, the seminal vesicles in a man, and any bowel that may fall into a particularly deep cul-de-sac at the level of the upper anal canal.
The anal canal is divided into three general levels, each of which demonstrates different characteristics: upper, mid, and lower. The upper anal canal is marked by the visualization of the puborectalis muscle, which appears as a U-shaped sling surrounding the anus at the superior-most border of the sphincters. Here, ...