Perineum - LO 8

8. Understand the origins of the internal iliac a., and diagram its branches associated with the pelvis.

The common iliac a. bifurcates into its terminal branches, external & internal iliac aa., at approximately the level of the pelvic brim or the L5/S1 intervertebral disc.

The external iliac aa. are larger than the internal iliac aa., and supply the lower limb. The internal iliac aa. supply structures associated with pelvic and gluteal regions.

The internal iliac a. divides into anterior and posterior divisions at approximately the level of greater sciatic notch.

The posterior division of internal iliac a. primarily serves musculature of the back and hip. The anterior division of internal iliac a. supplies pelvic viscera & musculature.

Posterior division of internal iliac a. - branches

• • Iliolumbar a.

  • Lateral sacral aa.

  • Superior gluteal a.

    • • Continuation of posterior division

      • Largest branch of internal iliac a.

      • Exits greater sciatic foramen superior to piriformis m.

      • Supplies muscles associated with hip joint: gluteus maximus, medius, and minimus, piriformis, and obturator internus mm.

Anterior division of internal iliac a. branches

• • Umbilical a.

    • • Typically 1st branch of anterior division

      • Splits into:

        • • Superior vesical aa.: supplies superior bladder, distal ends of ureters, and proximal ends of ductus deferens and seminal vesicles

          • Medial umbilical ligament: obliterated umbilical a.

            • • Associated with medial umbilical ligament

  • Obturator a.

    • • Runs medially on the obturator fascia to exit the pelvis via the obturator canal

      • Supplies the medial compartment of thigh (adductors of hip), some pelvic muscles, skin

  • Inferior vesical a.

    • • Supplies inferior portion of the bladder

      • Variable in origin. Possible branching points include:

        • • Directly off anterior division, umbilical a., vaginal a., uterine a., & middle rectal a.

      • In males, has distinct prostatic brs. supplying the prostate, seminal vesicles, and ductus deferens

  • Vaginal a.

    • • Variable in origin, with the following possibilities:

        • • Branch of uterine a.

          • Independent origin from the internal iliac a.

          • Branch of middle rectal a.

      • Will often have branches that supply the inferior bladder (inferior vesical brs.)

  • Uterine a.

    • • At the internal os of cervix, the ureter crosses inferior (‘under’) the uterine a.

        • • This relationship is particularly important in uterine surgeries when the uterine a. is ligated.

            • • ‘Water under the bridge’

          • Anastomose with ovarian a. and vaginal a. branches

  • Internal pudendal a.

    • • Exits through the greater sciatic foramen, and then enters the ischio-anal fossa via the lesser sciatic foramen and pudendal canal

      • Primary source of blood to the perineum

      • Branches will be discussed in more detail in another learning objective

  • Inferior gluteal a.

    • • Supplies portions of the pelvic diaphragm, muscles of the hip (gluteus maximus m., piriformis m., quadratus femoris m.) and some portion of the hamstring mm.

        • • Provides collateral circulation to the thigh

      • Exits through the greater sciatic foramen inferior to the piriformis m.

      • May be a terminal branch of posterior division