Clinical Cases - Perineum & External Genitalia

A 24-year-old woman pregnant with her first child had been in the second stage of labor (pushing) for several hours. The crown of the child's head was just visible through the vaginal orifice, but the obstetrician was concerned that the woman was exhausted and was no longer able to push effectively. She decided to perform an episiotomy to enlarge the opening of the birth canal and assist the delivery of the baby.

Questions to consider:

1. What is an episiotomy and when is it performed?

   An episiotomy is an incision made in the perineum to enlarge the distal end of the birth canal. Episiotomies are performed in order to ease delivery, especially in difficult cases like breech and forceps deliveries.
   
   During delivery, as the infant proceeds to move down the vaginal canal, the infant stretches the perineum, levator ani, and pelvic fascia. Specifically, the pubococcygeus muscle is at risk for stretching to the point of tearing. The pubococcygeus muscle supports the urethra, vagina, and vaginal canal and damage to this muscle could lead to urinary stress incontinence post delivery whenever the patient coughs or increases her intraabdominal pressure by bearing down.

2. Episiotomies are generally made as a midline incision. If the incision were to continue tearing, what structures could be damaged?

   If the incision tears further during the delivery, a median incision is more likely than a posterolateral incision to extend posteriorly through the perineal body, the external anal sphincter, the internal anal sphincter, and the rectum.

3. What health risks to mother and child are associated with perineal tears?

   Serious tears (those that involve the anal sphincter and the rectum) may become infected by bowel contents, as may the child as it passes through the birth canal. This may delay or impair adequate healing for the mother or even present significant health risks (i.e. septicemia) for mother or child.

4. What are some potential complications if the perineal body is damaged and not repaired correctly?

   The integrity of the perineal body is critical to the strength of the entire perineum in women. Unrepaired injury can cause dysfunction of the external anal sphincter, internal anal sphincter, and/or sexual dysfunction (e.g. dyspareunia).

A 26-year-old woman pregnant with her second child experienced considerable anxiety when she thought about the pain that she would experience during childbirth. Her obstetrician explained that there were several options that involved the use of local anesthetics which would relieve the pain and said that he usually preferred to use a bilateral pudendal nerve block.

Questions to consider:

1. What is the distribution of the pudendal nerve and its branches?

   The pudendal nerve (from S2, S3, and S4) is the major nerve of the perineum, providing motor and sensory fibers to the perineum. Its branches in the female include: the perineal nerve, which provides branches to the posterior labial region and the muscles of the urogenital triangle; the dorsal nerve of the clitoris, which supplies the prepuce and glans of the clitoris; and the inferior rectal nerves, which supply the perianal region.

2. What other nerves would need to be blocked to provide complete anesthesia to the perineal region?

   Complete anesthesia of the perineal region requires anesthetization of the genital branches of the genitofemoral nerve, the ilioinguinal nerve, and the perineal branch of the posterior femoral cutaneous nerve. This can be accomplished by making an injection along the outer margin of the labia majora.

3. Where is the best place to deliver anesthetic to perform a pudendal nerve block?

   The location to deliver anesthetic to the pudendal nerve is as the nerve wraps around the ischial spine and before it sends out its branches.

4. What landmarks would an obstetrician use to deliver the anesthetic accurately?

   Two different methods may be used for a pudendal nerve block. In the transvaginal procedure, the ischial spine is palpated through the wall of the vagina and the needle is then passed through the vaginal mucous membrane toward the ischial spine, at which point the pudendal nerve is bathed with anesthetic. In the perineal procedure, the ischial tuberosity is palpated through the buttock and the needle is inserted about one inch deep medial to the ischial tuberosity. The anesthetic can then be injected to bathe pudendal nerve.

5. What other methods of anesthesia might be used to provide pain relief during childbirth?

   There are two other methods for delivering anesthetic to reduce the pain of childbirth: spinal anesthesia and epidural anesthesia. In spinal anesthesia, local anesthetics are injected into the subarachnoid space in the lower lumbar region. In epidural anesthesia, local anesthetic is infused into the epidural space through a catheter inserted into the vertebral canal. The methods have the advantage of blocking pelvic pain in general while allowing the mother to remain awake without interfering with uterine contractions.