Histomorphometry of the human dorsal nerve of the penis: analysis and clinical considerations

Abstract Background Little has been published on the histomorphometry of the human dorsal nerve of the penis (DNP), despite its growing importance in peripheral nerve surgeries aimed at restoring lost penile sensation or erectile function, and in gender-affirming surgeries which rely on the glans penis to reconstruct the neoclitoris with minimal histomorphometric data currently available to inform technique. Aim To quantify the number of axons in the human DNP and discuss potential clinical implications. Methods Bilateral DNP samples were obtained from 12 fresh frozen cadavers at the level of the inferior aspect of the pubic symphysis. Specimens were fixed and stained using validated techniques. Histomorphometric evaluation was performed at 1000× magnification using image analysis software to obtain myelinated nerve fiber count, fascicle number, and density. Outcomes Primary outcomes included myelinated axon count, fascicle number, and nerve fiber density of the DNP. Results Twenty-three DNP samples were analyzed. The mean axon count was 3634 (SD = 1575) with a range of 6299. Accounting for the bilaterality of the DNP, the mean total number of axons innervating the human glans penis was 7076 axons (SD = 2634 axons). The total myelinated axon count, fascicle number, and nerve density did not differ significantly by laterally, nor did these parameters differ significantly between individuals. Myelinated axon counts of the DNP were on average less than previously reported axon counts for the dorsal nerve of clitoris using identical methodology, despite the much larger size of the glans penis. The axon counts of the DNP varied more between individuals than demonstrated in our prior work on the dorsal nerve of clitoris. Clinical Implications These findings may suggest that variability in DNP axon composition may be one factor giving rise to outcome variability in nerve-based reconstructive and sensory restoration procedures and inform techniques in neoclitoris construction in gender-affirming genital surgery. Strengths and Limitations Unmyelinated axons are not counted using the technique employed. Samples were obtained from fresh frozen cadavers which may introduce heterogeneity into the tissue samples obtained. Conclusion This study reports axon count, fascicle number, and nerve density of the human DNP and discusses the clinical relevance therein.