Neurovasculature of the pelvis and perineum

Question 1

What is the anatomical origin of the superior rectal artery?

Answer 1

Inferior mesenteric artery.

Question 2

Describe the general vasculature of the perineum and pelvis, listing the exceptions.

Answer 2

Most of the pelvis and perineum are supplied by branches of the internal iliac artery, and drained by tributaries of the internal iliac vein. Exceptions are the gonads and the majority of the rectum.

Question 3

What are the anatomical origins of the testicular and ovarian arteries?

Answer 3

Both are branches or the abdominal aorta.

Question 4

How does blood reach the inferior vena cava from the ovarian and testicular veins?

Answer 4

the right testicular/ovarian vein generally joins the inferior vena cava; the left testicular/ovarian vein, unlike the right one, joins the left renal vein instead of the inferior vena cava.

Question 5

Which branches usually arise from the posterior trunk of the internal iliac artery, and what areas do they supply?

Answer 5

Supplies posterior pelvic wall and part of gluteal region. Iliolumbar a., Lateral sacral aa., Superior gluteal a.

Question 6

Which branches usually arise from the anterior trunk of the internal iliac artery?

Answer 6

Obturator a., Superior vesical a. (may be multiple aa), Umbilical a. (becomes medial umbilical ligament), Uterine and vaginal aa. (female) or Inferior vesical a. (male), Middle rectal a., Internal pudendal a., Inferior gluteal artery .

Question 7

Describe the anatomical relationships of the superior and inferior gluteal arteries to the piriformis muscle and the sacral plexus.

Answer 7

Inferior gluteal usually exits the pelvis between S1-2 or more commonly S2-S3. It runs anterior to the piriformis m.
Superior gluteal exits above S1 and is posterior to the piriformis m.

Question 8

How does the internal pudendal artery reach the perineum from the pelvis?

Answer 8

The internal pudendal artery runs in the pudendal canal (Alcock’s canal).

Question 9

Which branch of the internal pudendal a supplies the anal triangle?

Answer 9

Inferior rectal a. supplies the anal canal, from internal pudendal a. (from internal iliac a)

Question 10

Which branches of the internal pudendal a supply the clitoris or penis and associated erectile tissues?

Answer 10

Dorsal and deep aa of penis / clitoris (erectile tissues)

Question 11

How does blood return to the right atrium of the heart, via the portal route, and via the systemic (caval) route, from the portal-caval anastamoses in the inferior part of the rectum.

Answer 11

Mostly by superior rectal vein to inferior mesenteric vein to splenic vein (or sup mesenteric v) to hepatic portal vein. (portal route)

Middle rectal veins to internal iliac veins. Inferior rectal veins drain the anal canal to the internal pudendal vein to internal iliac vein (systemic route)

Question 12

For example, lymph from the bladder will follow the blood vessels to which set of nodes? What is the alternative drainage?

Answer 12

Superior and inferior vesical arteries from internal iliac artery in males and the superior vesicle and vaginal arteries in females. Vesical venous plexus drains to the internal iliac veins but also anastomoses with veins of bony pelvis and to internal vertebral plexuses.
Bladder and prostatic lymphatics drain to the external (alternative) and internal iliac nodes.

Question 13

To which sets of lymph nodes does lymph from the rectum and anal canal first drain?

Answer 13

follows the arteries; along superior rectal and inferior mesenteric aa. to inferior mesenteric nodes. Along middle rectal a. to internal iliac nodes or from anal canal to internal iliac nodes and superficial inguinal nodes.

Question 14

The lymphatic drainage of the ovary, uterine tube, uterus and vagina are rather complex, draining initially to three sets of nodes – which?

Answer 14

Body of uterus, cervix, vagina to internal and external iliac nodes, part of fundus along round ligament through inguinal canal, to superficial inguinal nodes, superolateral uterus, uterine tube, ovary along suspensory ligament of ovary to lumbar nodes, lower vagina to superficial inguinal nodes

Major routes follow the arterial blood supply (see station 1), but one route follows the round ligament of the uterus.

Question 15

Where does lymph from the testes drain?

Answer 15

lumbar and preaortic nodes, urethra and cavernous bodies to internal iliac and deep inguinal nodes.

Question 16

How does lymph from the pelvis and perineum ultimately return to the bloodstream?

Answer 16

CHECK

Question 17

Where are the preganglionic parasympathetic neuron cell bodies, and how do their axons reach ganglia?

Answer 17

Parasympathetic fibers enter the pelvis in pelvic splanchnic nerves that originate from spinal cord levels S2 to S4.

Question 18

What are the affects of PSNS innervation on the pelvis and perineum?

Answer 18

Causes engorgement of erectile tissues during sexual arousal (erection), and controls the smooth muscle of the bladder, rectum, and to some extent the female reproductive tract.

Question 19

What are the affects of SNS innervation on the pelvis and perineum?

Answer 19

contraction of smooth muscles of the ductus deferens, seminal glands, and prostatic ducts during the emission phase of ejaculation.

Question 20

Where are the preganglionic neuron cell bodies of the pelvic SNS, and how do their axons reach ganglia where synapses occur?

Answer 20

Sympathetic fibers enter the inferior hypogastric plexuses from the hypogastric nerves and from branches (sacral splanchnic nerves) of the upper sacral parts of the sympathetic trunk. Ultrimately, these nerves are derived from preganglionic fibers that leave the spinal cord in the anterior roots, mainly of T10 to L2.

Question 21

Which spinal cord segments process afferent information from visceral organs? What do these fibers travel with?

Answer 21

Visceral afferent fibers follow the course of the sympathetic and parasympathetic fibers to the spinal cord.
Pain carried by PS nerves includes: the rectum (S2-S4), the inferior bladder (S2-S4), prostate (S2-3), cervix (S2-4).
Sympathtic includes: superior bladder (T12-L2/3), prostate (probably - T12-L2/3), fundus and body of vagina (T12-L2) and ovaries (T11-L1).

Question 22

Which spinal nerve anterior rami contribute to the obturator nerve.

Answer 22

L2-L4

Question 23

Which muscle compartment in the lower limb does the obturator nerve supply?

Answer 23

Medial compartment of the thigh

Question 24

What does the sacral plexus form from?

Answer 24

The sacral plexus forms in the pelvic cavity from the ventral rami of spinal nerves L4- S4 (the small S5 & coccygeal (Co) nerves may be included as well). The lumbosacral trunk joins the sacral plexus from the lumbar region, and contains some axons from L4 ventral ramus and all L5 ventral ramus.

Question 25

What are the major branches of the sacral plexus? Which spinal segments contribute to each?

Answer 25

The superior gluteal nerve (L4-S1)
The inferior gluteal nerve (L5-S2)
The sciatic nerve (L4-S3)
The pudendal nerve (S2-4)

Question 26

What structures does the superior gluteal nerve innervate?

Answer 26

Gluteus medius, gluteus minimus, tensor fascia latae

Question 27

What structures does the inferior gluteal nerve innervate?

Answer 27

Gluteus maximus

Question 28

What structures does the sciatic nerve innervate?

Answer 28

Lateral rotator group (except piriformis and quadratus femoris) and the posterior compartment of thigh

Question 29

What is the main somatic nerve innervating the skeletal muscles and skin of the perineum? What are the main cutaneous nerves?

Answer 29

Mainly pudendal S2-4 – Branches are Inferior rectal nn, Perineal nn (muscular and posterior scrotal/labial) and Dorsal n of penis/clitoris. Also Perineal branches of posterior femoral cutaneous n and branches of ilioinguinal and genitofemoral.