Anorectal endosonography in benign anorectal disorders

Endosonography in anorectal disease: an overview

Anorectal endosonography (AE), which was introduced 20 years ago, derives from the study of urology. It was first used to evaluate rectal tumours and later also to investigate benign disorders of the anal sphincters and pelvic floor. The technique is easy to perform, it has a short learning curve and causes no more discomfort than a routine digital examination. A rotating probe with a 360 degrees radius and a frequency between 5 and 16 MHz is introduced to the rectum and then slowly withdrawn so that the pelvic floor and subsequently the sphincter complex are seen. Recently, it has become possible to reconstruct three-dimensional images. AE has been used for almost every possible disorder in the anal region and has increased our insight into anal pathology. The clinical indications for AE are: 1. Faecal incontinence in patients when surgery is an option. AE can show sphincter defects with excellent precision. There is a perfect correlation with surgical findings. Studies comparing AE with endoanal magnetic resonance imaging (MRI) have shown that both methods are equally good for demonstrating defects in the external anal sphincter; the internal anal sphincter is better visualized with AE. After sphincter repair, the effect is directly related to the decrease in the sphincter defect. 2. Perianal fistulae. AE has been shown to be accurate in staging perianal cryptoglandular fistulae and fistulae in Crohn's disease. When there is an external fistula opening, H2O2 can be introduced with a plastic infusion catheter. The tract then becomes visible as a hyperechoic lesion ("white"). It has been shown that this corresponds well with surgical findings. It is equally sensitive as endoanal MRI. Since recurrent cryptoglandular fistulae are complex in 50% and Crohn's fistula in 75%, it is mandatory to perform AE preoperatively in these patients to avoid missed tracts during surgery and subsequent recurrences. 3. Rectal tumors. In low tubulovillous adenomas or malignant polyps considered removable locally, confirming the local resectability (T0 or T1) is mandatory. Although larger rectal and more advanced tumours can be evaluated with AE, MRI is more sensitive in staging nodal involvement. 4. Anal carcinoma for staging. AE has been shown to stage better than the classical TNM classification for both local extension and prognosis. In conclusion, AE images the internal and external anal sphincter with high accuracy. It is easy to perform and is of particular value in the diagnosis of anal incontinence and perianal fistulae. It is excellent in staging anal carcinoma and can also be used in staging rectal carcinoma, especially very low large malignant polyps.

Endosonography of anal canal diseases

Anal endosonography became a valuable imaging method for diagnosis of anal diseases because of its accessibility, relative simplicity of performance, and low cost. It is used most often to detect anal sphincter defects, to classify anal fistulas and perianal abscesses, and to stage anal tumors. This review presents a normal anatomy of the anal canal, examination technique, and normal endosonographic anatomy of anal sphincters. The endosonographic findings of anal sepsis, malignancy, trauma, abnormalities in Crohn disease, and ulcerative colitis, as well as the role for anal endosonography among other imaging modalities, are discussed.

Use of endoanal ultrasound in patients with rectovaginal fistulas

PURPOSE

The purpose of our study was to define the role of endoanal ultrasound in the evaluation and management of patients with rectovaginal fistula.

METHODS

A retrospective review was performed of all patients with rectovaginal fistula who were evaluated by endoanal ultrasound at Barnes-Jewish Hospital at Washington University from 1992 to 1997.

RESULTS

Twenty-five females underwent endoanal ultrasound before rectovaginal fistula repair. Mean age was 34 years. Rectovaginal fistulas were caused by obstetric trauma (19 patients; 76 percent), cryptoglandular disease (5 patients; 20 percent), and Crohn's disease (1 patient; 4 percent). Previous rectovaginal fistula repair had been performed in ten patients (40 percent). A history of anal incontinence was present in ten patients (40 percent). Rectovaginal fistula location was above (15 patients), at (7 patients), or below (3 patients) the dentate line. Rectovaginal fistula size was <5 mm (19 patients; 76 percent) or >5 mm (6 patients; 24 percent). Anal manometry revealed decreased sphincter pressures (resting or squeeze) in 12 patients (48 percent). Pudendal nerve latency was abnormal in three patients (9 percent). Endoanal ultrasound identified the rectovaginal fistula in 7 patients (28 percent) and an anterior sphincter defect in 23 patients (92 percent). At surgery sphincter injuries were identified in 23 patients (92 percent). Treatment was either sliding flap repair with anal sphincter reconstruction (22 patients; 88 percent) or sliding flap repair alone (3 patients; 12 percent). Repair of the rectovaginal fistula was successful in 23 patients (92 percent). Complications occurred in 11 patients (44 percent): two recurrent rectovaginal fistulas, five infections, two skin separations, one ectropion, and one hematoma. The two patients with recurrent rectovaginal fistula had prior repairs, and both were subsequently repaired successfully. Of the 11 patients with preoperative anal incontinence, 6 patients (54 percent) were continent and 2 (18 percent) improved after surgery. Cause, size, location, and previous repair of fistula had no effect on final outcome.

CONCLUSIONS

Noncontrast endoanal ultrasound was not useful in imaging rectovaginal fistulas and cannot be recommended as a diagnostic or screening tool for the identification of a rectovaginal fistula. However, we recommend that endoanal ultrasound be performed preoperatively in all patients with known rectovaginal fistulas to identify and map occult sphincter defects. Concomitant anal sphincter reconstruction should be considered strongly in patients with rectovaginal fistula and an endoanal ultrasound-documented sphincter defect.

External anal sphincter defects: correlation between pre-operative anal endosonography and intraoperative findings

In order to correlate operative findings with external anal sphincter (EAS) defects identified on anal endosonography (AES), 30 faecally incontinent patients undergoing overlapping sphincteroplasty or total pelvic floor repair were investigated by AES before and after surgery. Endosonic findings were correlated with the appearance of EAS at operation. 21 out of 22 defects seen at surgery had been pre-operatively detected by AES (one false negative). Post-operatively the sphincteroplasty was clearly evident on AES. In three cases of failure it showed an extensive hypoechoic area and these patients underwent dynamic graciloplasty. Endosonography is the method of choice for pre-operative imaging of EAS, having an established role in identifying sphincter defects and correlating well with intraoperative findings. Post-operatively, it has the potential to identify breakdown of the previous repair, allowing prompt surgical intervention. Endosonography is helpful in planning the best type of operation following sphincter injury and is useful in auditing the results of surgery.