In a male patient undergoing abdominoperineal resection (APR) for low rectal carcinoma, the autonomic nerve most responsible for erectile function that is at risk of injury is:

• A Hypogastric nerves (L1, L2 sympathetic) at the aortic bifurcation, controlling ejaculation only
• B Pudendal nerve at the ischial spine, which carries all autonomic supply to the penis
• C Inferior hypogastric plexus parasympathetics from the superior mesenteric ganglion
• D Pelvic splanchnic nerves (S2, S3, S4 parasympathetic) forming the nervi erigentes; they travel in the neurovascular bundle of Walsh lateral to the prostate ✓

Explanation

Erection is mediated by the pelvic splanchnic nerves (nervi erigentes, S2–S4 parasympathetics), which travel laterally in the neurovascular bundle along the posterolateral aspects of the prostate and rectum. These nerves are at highest risk during APR, low anterior resection, and radical prostatectomy. The Walsh nerve-sparing technique in radical prostatectomy aims to preserve these bundles. Hypogastric nerves (sympathetic) control bladder neck closure and seminal emission/ejaculation. The pudendal nerve supplies somatic innervation for erection through the bulbocavernosus and ischiocavernosus muscles.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.