Correlating structure and function: three-dimensional ultrasound of the urethral sphincter

Three-dimensional (3D) ultrasound facilitates assessment of the anatomy of the urethral sphincter, a decrease in sphincter volume being associated with stress incontinence. Urethral pressure profilometry (UPP) is used to assess urethral sphincter function although it is not diagnostic of stress incontinence. The aim of this pilot study was to determine whether 3D sphincter volume can be correlated with the area under the UPP curve.

Primigravid women were recruited antenatally between 32 and 42 weeks' gestation. 3D transvaginal ultrasound scans of the urethra were performed in modified lithotomy position with a comfortably full bladder. Length and cross-sectional area were measured allowing the sphincter volume to be calculated. UPP measurements were performed with a Gaeltec solid-state pressure transducer and the area under the curve mapped out and calculated. All scans and measurements were repeated between 3 and 6 months postpartum.

Nineteen women participated in the study. Antenatal and postnatal data were available in all cases. There was a statistically significant correlation between antenatal sphincter volumes and area under the UPP curve although this relationship was lost following delivery.

There appears to be a correlation between structural anatomy and functional anatomy in the antenatal period although following delivery this is lost.