Invited Commentary

Tracy L. Hull

Anal endosonography has revolutionized the treatment of fecal incontinence. In the early 1990s, research appeared that documented the normal anal sphincter complex and its components [1-3]. Mapping out the normal appearance of the internal and external sphincters allowed actual visualization of defects in the anal sphincter. Prior to this, patients with fecal incontinence (mostly women) were evaluated with physical exam, anal physiology, and needle electromyelogram (EMG) [4-6]. This limited evaluation was not precise, and probably many sphincter defects (usually as a result of childbirth) were missed [7]. Prior to anal endosonography, patients with fecal incontinence that manifested years after the injury were labeled as having "idiopathic" fecal incontinence. Whereas this category still exists, anal endosonography allows precise anatomical delineation in an effort to tailor treatment for the individual patient.

Currently, anal endosonography remains the most popular tool with which to study patients with fecal incontinence. Some patients have obvious defects, which do not require preoperative imaging studies, but many have sphincter defects that are difficult to quantify. Visualization of defects in this group of patients may be beneficial as a guide when planning surgical intervention.

As with any procedure, there are preferences in performing it and a learning curve in becoming proficient at it. The actual number of anal endosono-graphic exams needed to become skilled enough to identify defects is not clear but is probably low. The most difficult aspect of using the two-dimensional (2D) instrument is learning how to work the different tuning mechanisms, which intensify and manipulate the image. Once this is mastered, seeing defects in the black internal anal sphincter is quite easy. However, the striated external anal sphincter image is sometimes most difficult to visualize. Asking the patient to squeeze his or her anal muscle while the probe is rotating will sometimes delineate the ends of the muscle. Also, the examiner placing a finger in the patient's vagina while the probe is rotating may enhance visu alization of the anal sphincters, particularly the external anal sphincter. This is especially true for the inexperienced sonographer or when imaging a patient with a sphincter that is difficult to see.

I prefer to use a balloon around the crystal at the end of the probe rather than the hard plastic cone as discussed in the primary manuscript. I find the cone at times has a diameter that does not allow consistent coupling to the mucosa in patients with decreased tone, and thus shadowing from air distorts the image. The balloon is filled with degassed water and does not need to be overly filled and thus can be controlled to allow just the right amount of fluid to enhance balloon coupling against the anal canal mucosa.

Three-dimensional (3D) anal endosonography is relatively new and the machine expensive enough that many institutions do not have that equipment. The advantage of this modality is that it allows image acquisition and later reconstruction to study the sphincter complex in detail from multiple angles [8]. This can be an advantage, as it allows for intense study of the complex at a later time. However, this can also be a disadvantage, as it takes more time to configure and study the images versus the 2D procedure. The advantage of the degree of improved precision offered by the 3D unit is not clear, and at this point, particularly in light of the added time and expense, the 3D machine is not mandatory for optimal care.

Vaginal endosonography to view the muscle complex "through the rectovaginal septum" is practiced by some caregivers, particularly those from gynecologic backgrounds where transvaginal endosonogra-phy is also used to evaluate the ovaries and uterus. This could be considered a natural extension of its use. Without specific experience performing the procedure from this route, I cannot give a fair commentary other than to say that proponents feel they attain equivalent sphincter evaluation.

Other modalities have been examined to study the anal canal anatomy. The only one that provides information close to the endosonography machine is magnetic resonance imaging (MRI) with anal coil [9].

When consideration of time, expense, and degree of visualization is weighed against the MRI with coil, I consider endosonography superior.

At our institution, nearly all patients with fecal incontinence undergo anal endosonography when a surgical intervention is contemplated. We use the 2D machine, and the exam takes about 10 min or less. The exam is done in the office after the patient is given an enema. The enema also is an inexpensive test that crudely assesses the patient's ability to contain liquid in their rectal reservoir. The test is performed in the left lateral position with a 10-MHz probe. The anal endosonography, combined with a careful history and physical exam, guide us in treatment strategy.

As I practice at a teaching institution, anal physiology testing is also done; however, this is less helpful in my opinion. Considering the results from anal physiology testing, I particularly look at the pudendal nerve terminal motor latency (PNTML) and the compliance [10]. If the latency is prolonged, I will generally still repair a defect but explain to the patient that even with defect repair, the results will most likely be suboptimal. However, there is no good method to predict who will or will not be helped with sphincter repair. Therefore, I almost always offer repair to symptomatic patients, even those with a nerve prolongation. The other way I find anal physiology testing useful is to look at rectal compliance. This number reflects the elasticity of the rectum. If the compliance is low, the rectum is stiff and will not optimally store stool. Patients with low compliance can have an element of urgency, which negatively affects their defecation. Nonetheless, I still would repair a defective muscle in a patient with low compliance, as it may provide more time for the patient to reach the toilet. Even a few minutes may be a tremendous advantage.

The most common repair of the sphincter muscle is the overlapping anterior anal sphincteroplasty. This defect is usually a result of injury at the time of childbirth, and the woman's sphincter muscles may compensate for many years after the injury before debilitating symptoms develop. Long-term results of sphincter repair have been disappointing [11, 12], but if symptoms recur after surgery, anal endosonog-raphy is useful to verify that the muscle is optimally repaired. If a defect persists, surgical repeat repair is considered. Other novel treatments are being developed, but many will rely on accurate anatomy as outlined by anal endosonography to guide the treatment algorithm.

Other traumatic causes of fecal incontinence include consequences of surgery to address other anorectal disease. Fistulotomy and hemorrhoidecto-my can leave various degrees of defects in the muscle or anal topography that lead to leakage. Sometimes these problems can be surgically improved by smoothing the scar ridge or reapproximating the muscle ends. However, internal anal sphincter disruption from stretching or hemorrhoid excisional surgery that includes some muscle fibers may not respond to conventional muscle reapproximation and necessitate consideration of one of the novel approaches to improve fecal leakage. Once again, the ability to detect defects in specific sphincter components and the size and configuration is mandatory.

In conclusion, anal endosonography has emerged over the past 15 years as a primary tool used to evaluate the anal sphincters. Its use has led the way for new and exciting research geared toward improving fecal incontinence by selecting the appropriate patient based on anal anatomy. This evaluation tool continues to evolve, and the 3D unit may prove to be indispensable as treatment options diversify and become targeted for very specific sphincter problems.

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