Pelvis and Perineum

FINDING IMPORTANT NERVES AND VESSELS

  • Anal Triangle 
    • Lateral to the anus, the inferior rectal nerve, artery, and vein can be located. If you follow the nerve and vessels away from the anus, they will pass into the pudendal canal. In the pudendal canal, you will find the pudendal nerve, and the internal pudendal artery and vein.
  • Male Genitalia and Perineum 
    • Posterior to the ductus deferens is the pampiniform plexus of veins, and the testicular artery which runs with the plexus. You can tell the difference between the artery and vein because the artery has thicker walls. 
    • Located on the surface of the ductus deferens is the artery of the ductus deferens.
  • Male Urogenital Triangle
    • Posterior scrotal nerve, artery, and vein run lateral to the external anal sphincter → posterior part of the scrotum. 
    • Superficial dorsal vein drains into the superficial external pudendal vein in the inguinal region. 
    • Deep dorsal vein of the penis is a single vein at the midline of the penis on the dorsal side that drains into the prostatic venous plexus.
    • There are 2 dorsal arteries of the penis, one on each side of the deep dorsal vein on the penis.
      • If you follow the dorsal artery of the penis proximally, you will find its origin from the internal pudendal artery → also gives rise to the dorsal artery of the penis that runs through the corpora cavernosa (erectile tissue). 
    • There are 2 dorsal nerves of the penis, one on either side of the midline lateral to the deep dorsal artery. These nerves are branches of the pudendal nerve. 
    • *Midline of penis → lateral in either direction: vein, artery, nerve
  • Male Urinary Bladder, Rectum, and Anal Canal 
    • The anal columns are 5-10 longitudinal ridges of mucosa in the proximal part of the anal canal, and they contain the branches of the superior rectal artery and vein.
  • Male Internal Iliac Artery and Sacral Plexus
    • Aorta → Common iliac arteries → divide into external iliac and internal iliac arteries. (All arteries in this section are listed anterior to posterior anatomically)
      • External iliac artery supplies the lower limb (will be visited later in this unit).
      • Internal iliac artery supplies the pelvis. 
        • Anterior division
          • Find the medial umbilical ligament and follow it posteriorly to find the umbilical artery.
            • Superior vesicular arteries arise from the inferior surface of the umbilical artery and descend to the superolateral portion of the urinary bladder.
          • Obturator artery passes through the obturator canal. Follow the artery from the lateral portion of the canal → posterior to its origin. The obturator artery may have a branch (only in 20% people):
            • Aberrant obturator artery crosses the pelvic brim.
          • Inferior vesical artery → towards the fundus of the urinary bladder. (♂ cadavers only, ♀it is an unnamed branch of the vaginal artery)
          • Middle rectal artery → medially toward the rectum. This artery arises from the iliac artery with the inferior vesicular artery, so be sure to follow the vessels to their termination point.
          • Internal pudendal artery exits the cavity through the greater sciatic foramen inferior to the piriformis muscle.
          • Inferior gluteal artery passes out of the pelvic cavity between the ventral rami of spinal nerve S2 and S3 (S2-S3 arise at proximal attachment of piriformis muscle) → greater sciatic foramen inferior to the piriformis muscle.
        • Posterior division
          • Superior gluteal artery → exits pelvic cavity by passing between the lumbosacral trunk and the ventral rami of spinal nerve S1 exiting the pelvis superior to the piriformis muscle.
          • Lateral sacral artery arises inferior to the superior gluteal artery, and gives off an inferior and superior branch.
          • Iliolumbar artery → posterior and descends between lumbosacral trunk and obturator nerve.
    • Sacral plexus and coccygeal plexus are located in the endopelvic fascia. The sacral plexus can be found medial to the rectum near the anterior surface of the piriformis muscle.
      • Lumbosacral trunk is formed by the ventral rami L4-L5.
      • Sciatic nerve is formed by the ventral rami L4-S3, and can be found exiting the pelvis through the greater sciatic foramen and is inferior to the piriformis muscle.
      • Pudendal nerve receives its contribution from the ventral rami of spinal nerves S2-S4.
    • Pelvic splanchnic nerves are branches of ventral rami of spinal nerves S2-S4.
    • Sacral portion of sympathetic trunk located on the anterior surface of the sacrum medial to the ventral sacral foramina.
      • Sympathetic trunk travels from the abdomen to the pelvis and the sympathetic trunks join at the midline near the level of the coccyx to form the ganglion impar.
      • Sacral splanchnic nerves arise from 2-3 sacral sympathetic ganglia and pass to the inferior hypogastric plexus.
  • Female Urogenital Triangle
    • Posterior labial nerve, artery, and vein enter the urogenital triangle passing lateral to the external anal sphincter muscle.
  • Female Urinary Bladder, Rectum, and Anal Canal
    • Superior rectal artery and vein are located within the 5-10 longitudinal ridges of mucosa in the proximal part of the anal canal.
  • Female Internal Iliac Artery and Sacral Plexus
    • Aorta → Common iliac arteries → divide into external iliac and internal iliac arteries. (All arteries in this section are listed anterior to posterior anatomically)
      • External iliac artery supplies the lower limb (will be visited later in this unit)
      • Internal iliac artery supplies the pelvis
        • Anterior division
          • Find the medial umbilical ligament and follow it posteriorly to find the umbilical artery.
            • Superior vesicular arteries arise from the inferior surface of the umbilical artery and descend to the superolateral portion of the urinary bladder.
          • Obturator artery passes through the obturator canal. Follow the artery from the lateral portion of the canal → posterior to its origin. The obturator artery may have a branch (only in 20% people):
            • Aberrant obturator artery crosses the pelvic brim.
          • Uterine artery courses along the inferior attachment of the broad ligament → lateral aspect of the uterus.
            • Divides into superior → body and fundus of uterus
            • Smaller branches → cervix and vagina.
          • Vaginal artery passes along the floor of the pelvis, inferior to the ureter. *Ureter passes between the vaginal artery and the uterine artery.
          • Middle rectal artery courses medially toward the rectum.
          • Internal pudendal artery exits the pelvic cavity through the greater sciatic foramen inferior to the piriformis muscle. *Often arises from a common trunk as inferior gluteal artery.
          • Inferior gluteal artery passes out of the pelvic cavity between the ventral rami of spinal nerve S2 and S3 (S2-S3 arise at proximal attachment of piriformis muscle) → greater sciatic foramen inferior to the piriformis muscle.
        • Posterior division
          • Superior gluteal artery exits the pelvic cavity by passing between the lumbosacral trunk and the ventral rami of spinal nerve S1, exiting the pelvis superior to the piriformis muscle.
          • Lateral sacral artery gives rise to inferior and superior branches. Inferior branches pass anterior to the sacral ventral rami. 
          • Iliolumbar artery passes posterior and ascends between the lumbosacral trunk and the obturator nerve. 
    • Sacral plexus and coccygeal plexus are located in the endopelvic fascia. The sacral plexus can be found medial to the rectum near the anterior surface of the piriformis muscle.
      • Lumbosacral trunk is formed by the ventral rami L4-L5.
      • Sciatic nerve is formed by the ventral rami L4-S3 and can be found exiting the pelvis through the greater sciatic foramen and is inferior to the piriformis muscle.
      • Pudendal nerve receives its contribution from the ventral rami of spinal nerves S2-S4.
    • Pelvic splanchnic nerves are branches of ventral rami of spinal nerves S2-S4.
    • Sacral portion of sympathetic trunk located on the anterior surface of the sacrum medial to the ventral sacral foramina.
      • Sympathetic trunk travels from the abdomen to the pelvis, and the sympathetic trunks join at the midline near the level of the coccyx to form the ganglion impar.
      • Sacral splanchnic nerves arise from 2-3 sacral sympathetic ganglia and pass to the inferior hypogastric plexus.

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