Simultaneous endoluminal sonography and manometry to assess anal sphincter complex in normal subjects

The purpose of this study was to use simultaneous anal manometry and high-frequency endoluminal ultrasonography (EUS) to determine the relationship between resting anal pressure and cross-sectional area of the internal and external anal sphincters. Eleven normal subjects underwent simultaneous anal EUS and manometry using catheters containing both pressure ports and ultrasound transducers. Resting pressure and cross-sectional area of the sphincters were made throughout the anal sphincter complex. The length of the internal anal sphincter (IAS) by sonography (27+/-5 mm) was significantly less than the length of the high pressure zone (HPZ) by manometry (44+/-8 mm; P < 0.001). Maximum IAS cross-sectional area (CSA) occurred 10+/-6 mm proximal to the peak resting pressure. The resting anal pressure correlated with external anal sphincter (EAS) CSA (r = 0.77), but not with IAS CSA (r = -0.17). The sum of EAS CSA and IAS CSA correlated strongly with resting pressure (r = 0.85). In conclusion, the IAS is shorter than the HPZ, with a significant distance separating maximum IAS CSA from peak resting pressure. The sum of the IAS and EAS CSAs, but not that of the IAS alone, correlated with resting pressure. Thus, this study suggests that the EAS, in addition to the IAS, contributes to resting anal pressure.