Image Spectrum of Anal Ultrasound in Patients with Peri Anal Disease

ABSTRACT

Endoanal ultrasonography has recently emerged as a popular diagnostic modality for mapping and imaging the anal sphincter. This procedure can be performed as an outpatient procedure; it is relatively quick and virtually painless. The imaging typically is performed in a proximal to distal manner with defining a variety of levels of the anal canal as it progresses. Anal ultrasond can provide a detailed image of the anal sphincter musculature. The internal anal sphincter appears endosonographically as a hypoechoic circular band that is most prominently seen at the level of the mid-anal canal. The external anal sphincter appears as a thicker circular mixed echogenic band outside of the hypoechoic internal sphincter. Anal ultrasond can be used to evaluate patients with anal fistulas with or without abscess. Imaging is performed and the fistulous tracts or abscesses are identified by hypoechogenicity within the external sphincter muscle or the ischiorectal fossa. Its ability to clearly image the anal sphincters has allowed its use for the evaluation of anal fistulas. Moreover, anal ultrasound has emerged as the technique of choice for imaging the anal sphincters and for evaluating incontinence. Each of the individual physiologic tests offers valuable information that is relevant to the continence mechanism, and the ultrasound yields results that are complementary to other tests. Ultrasound serves as a surveillance tool to monitor the results after sphincterplasty. We illustrate the endo-anal sonographic features of various anal diseases and the ultrasound-anatomic correlation for the anus.