Gynaecological Ultrasound in Clinical Practice

Anal endosonography is regarded as the gold standard investigation in patients presenting with faecal incontinence. The endosonography is also useful in the diagnosis of anal pain, anorectal tumours, fistulae, abscesses and anismus. The advent of anal endosonography has enabled considerable research into obstetric related anal sphincter trauma, the major aetiological factor in the development of anal incontinence. The internal anal sphincter is a thickened continuation of the circular smooth muscle layer of the bowel and appears homogeneously hypoechoic. The external anal sphincter usually appears hyperechoic, but has a heterogeneous appearance. Magnetic resonance imaging (MRI) defines the striated components of the sphincter with greater clarity. In 1994, Sultan et al. first described transvaginal endosonography to image the anal sphincters at rest with a rotating probe. The development of anal endosonography added a new dimension to understanding the pathogenesis of anal incontinence and the diagnosis of obstetric anal sphincter injuries.