Diagnostic Ultrasound - Abdomen and Pelvis

Testes
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Anatomy: Pelvis
GROSS ANATOMY
Testis
• Densely packed seminiferous tubules separated by thin
fibrous septa
○ 200-300 lobules in adult testis
○ Each has 400-600 seminiferous tubules
○ Total length of seminiferous tubules 300-980 meters
• Seminiferous tubules converge posteriorly to form larger
ducts (tubuli recti)
○ Drain into rete testis at testicular hilum
• Rete testis converges posteriorly to form 15-20 efferent
ductules
○ Penetrate posterior tunica albuginea at mediastinum to
form head of epididymis
• Tunica albuginea forms thick fibrous capsule around testis
• Mediastinum testis is thickened area of tunica albuginea
where ducts, nerves, and vessels enter and exit testis
• Testicular appendage (appendix testis)
○ Small, nodular protuberance from surface of testis
○ Remnant of müllerian system
Epididymis
• Crescent-shaped structure running along posterior border
of testis
• Efferent ductules form head (globus major)
○ Unite to form single, long, highly convoluted tubule in
body of epididymis
• Tubule continues inferiorly to form epididymal tail (globus
minor)
○ Attached to lower pole of testis by loose areolar tissue
• Tubule emerges at acute angle from tail as vas deferens
(a.k.a. ductus deferens)
○ Continues cephalad within spermatic cord
○ Eventually merges with duct of seminal vesicle to form
ejaculatory duct
• Epididymal appendage (appendix epididymis)
○ Small nodular protuberance from surface of epididymis
○ Remnant of wolffian system
Spermatic Cord
• Contains vas deferens, nerves, lymphatics, and connective
tissue
• Begins at internal (deep) inguinal ring and exits through
external (superficial) inguinal ring into scrotum
• Arteries
○ Testicular artery
– Branch of aorta
– Primary blood supply to testis
○ Deferential artery
– Branch of inferior or superior vesicle artery
– Arterial supply to vas deferens
○ Cremasteric artery
– Branch of inferior epigastric artery
– Supplies muscular components of cord and skin
• Venous drainage
○ Pampiniform plexus
– Interconnected network of small veins
– Merges to form testicular vein
– Left testicular vein drains to left renal vein
– Right testicular vein drains to inferior vena cava
• Lymphatic drainage
○ Testis follows venous drainage
– Right side drains to interaortocaval chain
– Left side drains to left paraaortic nodes near renal
hilum
○ Epididymis may also drain to external iliac nodes
○ Scrotal skin drains to inguinal nodes
EMBRYOLOGY
Testis
• Testis develop from genital ridges, which extend from T6-
S2 in embryo
• Composed of 3 cell lines (germ cells, Sertoli cells, Leydig
cells)
• Germ cells
○ Form in wall of yolk sac and migrate along hindgut to
genital ridges
○ Form spermatogenic cells in mature testes
• Sertoli cells
○ Supporting network for developing spermatozoa
○ Form tight junctions (blood-testis barrier)
○ Secrete müllerian inhibiting factor
– Causes paramesonephric (müllerian) ducts to regress
– Embryologic remnant may remain as appendix testis
• Leydig cells
○ Principal source of testosterone production
○ Lies within interstitium
○ Causes differentiation of mesonephric duct (wolffian)
ducts
– Each duct forms epididymis, vas deferens, seminal
vesicle, ejaculatory duct
– An embryologic remnant may remain as appendix
epididymis
• Scrotum derived from labioscrotal folds
○ Folds swell under influence of testosterone to form twin
scrotal sacs
– Point of fusion is median raphe, which extends from
anus, along perineum, to ventral surface of penis
○ Processus vaginalis, a sock-like evagination of
peritoneum, elongates through abdominal wall into twin
sacs
– Aids in descent of testes, along with gubernaculum
(ligamentous cord extending from testis to
labioscrotal fold)
– Results in component layers of adult scrotum
• Testicular descent
○ Between 7-12th week of gestation, testes descend into
pelvis
– Remain near internal inguinal ring until 7th month,
when they begin descent through inguinal canal into
twin scrotal sacs
– Testes remain retroperitoneal throughout descent
– Testes intimately associated with posterior wall of
processus vaginalis
○ Component layers of spermatic cord and scrotum form
during descent through abdominal wall
○ Transversalis fascia → internal spermatic fascia
– Transversus abdominis muscle is discontinuous
inferiorly and does not contribute to formation of
scrotum