Morphological aspects of the female pig bladder neck and urethra: quantitative analysis using computer assisted 3-dimensional reconstructions

PURPOSE: To investigate whether the pig is a suitable model for studies of lower urinary tract function and dysfunction, we sought to determine the morphology of the female pig bladder neck and urethra. Computer assisted 3-dimensional (D) reconstructions from step serial histological sections were used for visualization of the spatial relationships between neighboring urethral wall components, and the quantification of these components in the bladder neck and along the urethra. MATERIALS AND METHODS: Step serial histological paraffin sections from the bladder neck and urethra of 6 female pigs, stained with Masson's trichrome, were used to generate computer assisted 3-D reconstructions using MacStereology (Ranfurly MicroSystems Ltd., Airdrie, United Kingdom) as the 3-D software package. RESULTS: The bladder neck and urethral anatomy revealed well defined smooth and striated muscle layers that varied in location, regional distribution and orientation. Circular smooth muscle was maximally developed in the mid urethra, at which point maximal urethral pressure was observed. The longitudinal smooth muscle layer appeared continuous with the detrusor, implicating a possible role in urethral shortening at the onset of voiding. A small circular and longitudinal striated muscle component was present in the distal urethra. CONCLUSIONS: Anatomical differences exist between the female pig and human bladder neck and urethra, which were successfully highlighted using computer assisted 3-D reconstructions from step serial histological paraffin sections.