Lab Manual - Pelvic Neurovasculature

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Describe the formation of the two sciatic foramina. List the muscles, nerves, and vessels which pass through each. (explanation)
  2. Demonstrate the origins of the piriformis and obturator internus muscles and describe two specializations of the obturator fascia. (explanation)
  3. Identify the pelvic diaphragm and differentiate its components. (explanation)
  4. Trace the branching pattern of the internal iliac vessels in each sex, identifying branches by their relationships to pelvic organs or wall structures. (explanation)
  5. Demonstrate the formation of the sacral plexus, its relationship to the piriformis muscle and gluteal vessels, and its pelvic splanchnic nerves. (explanation)
  6. Identify and describe the inferior hypogastric (pelvic) plexus and its connections to the superior hypogastric plexus via the hypogastric nerves. (explanation)
  7. Identify and describe the sacral sympathetic trunks and the sacral sympathetic nerves. (explanation)
  8. Trace the sympathetic and parasympathetic nerve supply to any pelvic organ, listing the location of the preganglionic cell body, the course of preganglionic fibers, the location of the postganglionic cell body, and the course of postganglionic fibers. (explanation)

Readings and Modules:

Procedure:

1. Examine the bony pelvis. (Play movie; View images: N 248, 352, 486, 503, TG 3-04, 3-05, 3-07, 6-03, 6-06A, 6-06B)

Examine the bony pelvis and identify the obturator foramen and groove, the greater sciatic notch (foramen), ischial spine, the lesser sciatic notch (foramen), ischial tuberosity. Locate the sacroiliac joint. Review how the sacrotuberal and sacrospinal ligaments help to form the greater and lesser sciatic foramina.

2. Clean and identify the branches of the internal iliac artery, removing the corresponding veins. (Play movie; View images: N 253, 255, 264, 267, 363, 364, 398, 400, 401, 402, 403A, 403B, 404A, 404B, 405, 487, 502, 503, TG 3-27, 3-28, 3-55, 5-05, 5-07A, 5-07B, 5-08D, 5-09D, 6-07, 6-09A, 6-09B, 6-17A, 6-17B, 6-22, 6-29A, 6-29B)

Reflect the peritoneum off the side wall in order to mobilize the viscera and access the neurovasculature in the space deep to the peritoneum. In female specimens, strip the peritoneum from the broad ligament to appreciate the blood supply to the uterus and vagina. Pull the viscera (rectum, uterus, vagina, bladder) toward the midline of your hemisected pelvis. Review the course of the ureter in both male and female.

Locate the common iliac artery and vein, note course and relations and point of bifurcation. Trace the external iliac artery and vein along the brim of the pelvis and note their relationship as far as the inguinal ligament. Review the inferior epigastric artery and its relationships.

Identify the internal iliac vein. Trace its major tributaries, then remove the veins to expose the internal iliac artery. The internal iliac artery commonly divides into anterior and posterior divisions. The posterior division gives rise to the iliolumbar artery, the lateral sacral artery (sending branches into the anterior sacral foramina), and the superior gluteal artery (passes out of the pelvis over the superior border of the piriformis muscle). Locate the anterior division and note how it terminates by dividing into the inferior gluteal and the internal pudendal arteries. These exit the pelvis below the lower border of the piriformis muscle (other relations?). Return to the proximal part of the anterior division and trace the branches to pelvic viscera: the umbilical artery and its superior vesical branches (note its continuation as the medial umbilical ligament or obliterated umbilical artery); identify the uterine artery, the vaginal artery, the middle rectal artery, and the obturator artery. Do you have an "aberrant obturator artery", which arises from the inferior epigastric artery and accompanies the obturator nerve? Organize the blood supply to the base of the bladder, prostate, seminal vesicles.

Arteriogram of pelvic vessels
Arteriogram of occluded vessels

3. Identify the nerves of the pelvis. Identify the muscles of the pelvic wall and floor. (Play movie; View images: N 367A, 367B, 368, 369, 370, 402, 403, 409, 410, 412, 415, 416, 417, 497, 499A, 499B, 502, 503, TG 3-25A, 3-25B, 3-26, 3-28, 6-04, 6-15A, 6-15B, 6-18A, 6-18B, 6-17, 6-18A, 6-18B, 6-19A, 6-19B, 6-21A, 6-21B, 6-22A, 6-22D, 6-23A, 6-23B, 3-27)

Locate the first four sacral nerves as they emerge from the anterior (pelvic) sacral foramina. Locate the lumbosacral trunk; note its course, the relation of the superior gluteal artery to it and the first sacral nerve. Examine the formation of the sacral plexus.

Pick up the superior hypogastric plexus on the bifurcation of the aorta and trace it into the pelvis. Note its division into hypogastric nerves and their continuity into the inferior hypogastric (pelvic) plexus. Locate the sympathetic trunk entering the pelvis along the medial border of the pelvic sacral foramina. Note ganglia (number? ), gray rami communicantes, sacral splanchnics. Now return to the sacral nerves and identify the pelvic splanchnic nerves. How many are there? Trace them to the inferior hypogastric plexus and search for branches passing up into the sigmoid mesocolon and to the descending and sigmoid colon. Consider subsequent distribution to rectum, vagina, uterus, bladder, prostate. Organize your knowledge of the autonomic (sympathetic and parasympathetic) supply to the pelvic viscera.

On one side only, pull the viscera medially in order to see the muscles of the pelvic diaphragm or floor. Locate the obturator internus muscle and define its fascia. Locate its thickening, the arcus tendineus levator ani. Determine the parts of the pelvic diaphragm and trace each. Distinguish between the levator ani and the coccygeus muscles. What is the puborectalis muscle; significance? Define the urogenital hiatus. What does it transmit?

Examine the piriformis muscle and note its attachment to the sacrum, as well as its relation to the sacral nerves, to the sacral plexus and to the superior and inferior gluteal arteries.

Lymphangiogram of iliac lymph nodes and vessels