Fiberoptic imaging of cavernous nerves in vivo

A critical intraoperative variable for the return of tumescence following radical prostatectomy is preservation of the cavernous nerves. We developed a nontoxic technique that would allow high resolution, in vivo real-time imaging specifically of the cavernous nerves.

The cavernous nerves were labeled by injecting a fluorescent retrograde nerve tracer into the corpus cavernosum of male rats. Nerves were subsequently imaged in vivo using fiberoptic confocal fluorescent microscopy. Initial screening trials were performed to decide on a nerve tracer capable of axonal labeling, optimize injection concentration and characterize retrograde transport time. Toxicity studies included intracavernous pressure monitoring following electrical nerve stimulation, apoptotic staining of injected cavernous tissue and measurement of lipid peroxidation in nerves exposed to laser emissions during imaging.

In vivo real-time video sequences of fluorescently labeled cavernous nerves were recorded. The screening trial indicated that the B subunit of cholera toxin conjugated to AlexaFluor 488 (Invitrogen) provided optimal imaging after 9 days of retrograde transport. Toxicity studies showed that maximal intracavernous pressure responses did not differ between labeled and unlabeled nerves (p = 0.9671). Tracer injection did not increase apoptosis in cavernous tissue and laser exposure did not increase lipid peroxidation in nerves.

In vivo real-time imaging of the cavernous nerves is possible with no measurable toxicity, allowing the maintenance of erection. This novel imaging modality may allow urologists to identify cavernous nerves during pelvic surgery.