Question
To provide anesthesia to a patient in the third stage of labor, an obstetrician palpates the structure marked by a “red arrow” transvaginally in the picture below, then injects a local anesthetic.
Injection of anesthetic at this approximate location will most likely block which of the following nerves?
A. Inferior gluteal nerve.
B. Lateral femoral cutaneous nerve.
C. Lateral femoral cutaneous nerve.
D. Pudendal nerve.
Show Answer
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Correct Answer » D
Explanation
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The structure marked by a red arrow represents ischial spine.
The pudendal nerve is often anesthetized to provide obstetric anesthesia (although epidural blocks are now more commonly used in preparation for delivery).The pudendal nerve arises from sacral segments 2, 3, and 4.
It exits the pelvis by way of the greater sciatic foramen and then courses around the ischial spine (and sacrospinous ligament) to pass through the lesser sciatic foramen.It then runs through Alcock’s canal to supply the muscles and skin of the perineal area.
- The inferior gluteal nerve leaves the pelvis by passing through the greater sciatic foramen to supply the gluteus maximus muscle.
- The lateral femoral cutaneous nerve courses by the anterior superior iliac spine and supplies the anterolateral skin of the thigh.
- The obturator nerve passes through the obturator foramen to supply muscles and skin in the medial thigh.
