Table 1. Anal endosonography studies.

Aim	Cohort assessed	Probe characteristics	Technique	2D/3D	Outcome
Gold et al [15]	51 patients referred for possible anal sphincter abnormalities	Axial endoscopic probe, 10 MHz	Position: left lateral position	2D	Overall interobserver agreement for diagnosis of EAS and IAS was found to be very good; κ=0.8
Intra-observer and interobserver agreement of sonographic measurements of the anal structures			Probe: positioned at level of PR, probe withdrawn at increments of 1.25 mm until lower limit of anal canal
Gold et al [16]	20 controls and 24 patients with faecal incontinence	NS	NS	3D	3D multiplanar imaging revealed a direct relationship between the length of anal sphincter tear and radial extent
Relationship between radial and linear extent of anal sphincter tear
Williams et al [17]	55 females scanned at a median of 33 weeks′ gestation and 10 weeks post partum	B&K Sirius 3D system,a rotating transducer, 10 MHz	Position: left lateral position	3D	Total incidence of obstetric sphincter trauma was 29% with 11% affecting the EAS
Incidence of obstetric trauma to the EAS and related structures			Probe: inserted into distal rectum and automated data acquisition
Williams et al [18]	22 females with no evidence of tears on post-delivery scans	B&K Sirius 3D system,a rotating transducer, 10 MHz	Automated dataset acquired while probe withdrawn from anal canal	3D	Multiplanar anal endosonography allows longitudinal measurement of anal sphincter; after a vaginal delivery there are changes in the anal sphincter morphology
Assess morphological change in anal sphincter in absence of endosonographic evidence of trauma after vaginal delivery

2D, two-dimensional; 3D, three-dimensional; EAS, external anal sphincter; NS, not stated; PR, puborectalis.

^aBruel & Kjaer, Naerum, Denmark.