INTRAURETHRAL ULTRASOUND CORRELATED WITH URETHRAL HISTOLOGY

Objective: To examine the anatomic identity of sonographically visible sphincteric structures of the female urethra. Methods: The urethra ur inary bladder, and vagina were removed from 11 fresh female cadavers a nd placed in a water bath. Intraurethral ultrasound was performed with a 360 degrees-rotating 7.5-MHz ultrasound probe. Afterward, the speci mens were fixed and cross sections were made transverse to the urethra l axis at 5-mm intervals. Corresponding ultrasonograms and histologic images were matched and depicted simultaneously side by side. The anat omic identity of sonographically visible structures was determined by histologic examination and thickness of the longitudinal smooth urethr al sphincter measured. Results: Structures visible sonographically wer e the striated and smooth urethral sphincter muscle layers, vagina, an d blood vessels with diameters exceeding 0.2 mm. The longitudinal smoo th muscle layer appeared as a well-defined internal hypoechoic ring. T he outer circular smooth muscle layers and the striated muscle layers were a more irregular and hyperechoic zone. The circular smooth muscle layers and the striated sphincter muscle layers could not always be d ifferentiated easily. With formalin fixation, tissue shrinkage resulte d in a smaller thickness of the longitudinal smooth muscle measured on the histologic specimen. Conclusion: With intraurethral ultrasound, t he longitudinal smooth muscle layer appears as a well-defined and meas urable hypoechoic ring. The region of the circular smooth muscle and t he striated muscle emerges as a hyperechoic and less definable outer z one. (C) 1998 by The American College of Obstetricians and Gynecologis ts.