A 62-year-old man is incapable of penile erection after rectal surgery with prostatectomy. The patient most likely has a lesion of which of the following nerves?
**Core Concept**
The patient's inability to achieve penile erection after rectal surgery with prostatectomy suggests a lesion of a nerve that is crucial for erectile function. The penis receives parasympathetic innervation from the pelvic splanchnic nerves, which are derived from the sacral spinal cord (S2-S4). However, for erection to occur, there must be a simultaneous relaxation of the smooth muscle in the corpus cavernosum, which is mediated by the sympathetic nerves.
**Why the Correct Answer is Right**
The correct answer involves the sympathetic nerves that run along the inferior hypogastric plexus. The sympathetic nerves to the penis arise from the T10-L1 spinal cord segments and travel through the inferior hypogastric plexus. These nerves release norepinephrine, which stimulates the smooth muscle in the corpus cavernosum to relax, allowing blood to flow into the penis and cause an erection. In this scenario, the patient's inability to achieve an erection suggests that the sympathetic nerves to the penis were damaged during the rectal surgery.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the pelvic splanchnic nerves, which are derived from the sacral spinal cord (S2-S4), are responsible for the parasympathetic innervation of the penis and are not directly involved in the relaxation of the smooth muscle in the corpus cavernosum.
**Option B:** This option is incorrect because the pudendal nerve, which is derived from the S2-S4 spinal cord segments, is responsible for the somatic innervation of the external genitalia, including the skin and muscles of the penis, but not the autonomic innervation of the penis.
**Option C:** This option is incorrect because the superior hypogastric plexus, which is formed from the aortic plexus, is involved in the sympathetic innervation of the abdominal organs, but not the pelvic organs.
**Option D:** This option is incorrect because the obturator nerve, which is derived from the L2-L4 spinal cord segments, is responsible for the motor innervation of the adductor muscles of the thigh, but not the autonomic innervation of the penis.
**Clinical Pearl / High-Yield Fact**
Damage to the sympathetic nerves to the penis can result in a condition known as retrograde ejaculation, where semen is ejaculated into the bladder instead of out of the penis.
**Correct Answer: C. The superior hypogastric plexus is not the correct answer but the actual answer is D. The obturator nerve is not the correct answer. The correct answer is actually the nerves that are affected during the surgery and the nerves that are involved in the sympathetic innervation of the penis. The nerves that are most likely affected during the surgery are the nerves that are in close proximity to the prostate gland and the nerves that are involved in the sympathetic innervation of the penis. These nerves are the nerves that arise from the T10-L1 spinal cord segments and travel through the inferior hypogastric plexus. However, the correct answer is not listed among the options.**