Magnetic resonance imaging anatomy of the female urethra: a direct histologic comparison.
Academic Article
Overview
abstract
OBJECTIVE: To define the urethral structures visible on magnetic resonance imaging (MRI) relevant to stress urinary incontinence. METHODS: The urethra and surrounding tissues were harvested from 13 female cadavers (ages 21-81) and fixed in 10% buffered formalin. High-resolution T1- and T2-weighted images were obtained at 1.5 tesla. Mallory trichrome-stained histologic sections were prepared in corresponding planes from the cadaveric specimens. Immunohistologic stains for smooth muscle (actin) and vascular endothelium (CD-34 and factor VIII) were obtained on two specimens. Histology and MRI were compared using side-by-side correlation of projected images and by superimposing projected images. Comparison was also made to a non-cadaveric urethral MRI of a 29-year-old woman and to the MRI of another specimen imaged pre- and post-fixation. RESULTS: Distinct layers of the cadaveric urethra were seen best on proton density and T2-weighted images. From the center to the periphery, a series of concentric rings were visible: an inner bright ring, the mucosa; a dark ring, the submucosa; an outer bright ring, the smooth muscle of the urethra in a loose connective tissue matrix; and a peripheral dark ring, the striated urogenital sphincter muscle of the urethra in dense connective tissue. No significant alterations were caused by fixation. These cadaveric images matched the non-cadaveric MRI of the 29-year-old woman. CONCLUSION: The internal urethral anatomy visible on high-resolution MRI can be identified and confirmed histologically, and these findings may form the basis for future anatomic investigation of stress urinary incontinence and other urethral abnormalities.
