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ANATOMY: EPIDIDYMIS & VAS DEFERENS

Epididymis

• Gross Structure
  • A duct/tubule attached to the posterolateral aspect of the testis
  • Divided into 3 parts:
    1. Caput (head)
    2. Corpus (body)
    3. Cauda (tail)

  

  A. Head of epididymus

  B. Body of epididymus

  C. Tail of epididymis

  D. Vas deferens

  Source: Wikipedia

   

  • Appendix of the epididymis
  • A pedunculated or sessile cystic body on the upper pole of the caput epididymis
  • Wolffian (mesonephric) duct remnant
    • Recall that appendix testis is a Mullerian (paramesonephric) duct remnant

  

  Source: Wikipedia

• Microanatomic Architecture
  • Primary cell types (2):
    1. Principal cells
    • Have absorptive and secretive functions
    2. Basal cells
       • Believed to be derived from macrophages and to be precursors of principal cells
• Arterial supply
  • Main blood supplies (2):
    1. Superior and the medial epididymal arteries
       • Arise from the testicular artery, which arises from the aorta
       • Supply the caput and corpus epididymis
    2. Inferior epididymal artery
    • Arises from the artery of the vas (vasal/deferential artery), which arises from the superior vesical artery, which arises from the internal iliac artery
    • Supplies the cauda epididymis
    • These form an extensive interconnection
      • Clinical implications (3)
        1. If the artery of the vas is ligated from previous vasectomy, the blood supply to the epididymis from the testicular artery is adequate
        2. If the testicular artery is ligated, the blood supply to the epididymis from the artery of the vas is adequate
        3. During vasoepididymostomy or vasovasostomy, the epididymis can be intentionally dissected off the testis and mobilized to the caput, with the inferior and medial epididymal arteries intentionally ligated without adverse consequence. As long as the superior epididymal artery remains intact, the blood supply to the epididymis will be adequate

• Radiology
  • Ultrasound
    • The epididymis appears either hyperechoic or isoechoic in comparison to the testis

Vas Deferens

• Gross structure
• Measures between 30-35 cm in length from the cauda epididymis to its termination at the ejaculatory duct
• Tortuous for 2-3 cm as it leaves the epididymis (the convoluted vas deferens)
• Lumen ranges between 0.2-0.7 mm in diameter, depending on the segment
• Travels posteriorly along the spermatic cord, posterior to the vessels in the cord. The vas deferens passes through the inguinal canal and enters the pelvis lateral to the epigastric vessels. On entering the pelvis, after passing through the internal inguinal ring, the vas deferens separates from the testicular vessels. The vas deferens ultimately reaches the posterior base of the prostate after traveling medial to the pelvic sidewall.
• Arterial supply

• The seminal vesical (abdominal) end of the vas derives its blood supply from the artery of the vas (vasal/deferential artery)
• The testicular end of the vas receives additional blood supply from the inferior epididymal arterial interconnections, which extend onto the vas deferens
• The two blood supplies to the vas deferens freely anastomose with each other
• After vasectomy, if [branches of] the vasal vessels are ligated, the testicular end of the vas receives all of its blood supply from the superior and middle epididymal arteries, which arise from the testiclar artery, whereas the seminal vesical (abdominal) end of the vas receives all of its blood supply from [remaining intact branches] from the artery of the vas.
• The vas deferens receives no blood supply from the surrounding cremaster muscle or from any blood vessels from the spermatic cord. Therefore, if the vas deferens is sectioned or obstructed in two different locations, the intervening segment will fibrose owing to lack of blood supply. Therefore, two simultaneous vasovasostomies cannot be safely performed on the same vas if the vasal vessels have been interrupted in both locations

Questions

1. What are the functions of the epididymis?
2. What the is embryologic origin of the appendix testis? Appendix epididymis?
3. What is the bloods supply to the epididymis?
4. What is the normal length of the vas deferens?
5. What is the position of the vas deferens in relationship to the a) vessels of the spermatic cord and b) inferior epigastric vessels?

Answers

1. What are the functions of the epididymis?
   1. Sperm transport
   2. Sperm storage
   3. Sperm maturation
2. What the is embryologic origin of the appendix testis? Appendix epididymis?
   • Appendix testis from Mulerrian duct
   • Appendix epididymis from Wolffian duct
3. What is the bloods supply to the epididymis?
   • Head of epididymis: superior epididymal artery from testicular artery
   • Body and tail of epididymis: inferior epididymal artery from vasal (deferential) artery
4. What is the normal length of the vas deferens?
   • 30-35cm
5. What is the position of the vas deferens in relationship to the a) vessels of the spermatic cord and b) inferior epigastric vessels?

 

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 21