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42.2 Gross Anatomy
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359
create the blood–testis barrier that protects the haploid sperms from the autoimmune response from the organism and from hazardous bloodborne substances and
infections [20].
Structurally, the testis is delineated by the tunica albuginea, which is considered
the densest and toughest connective tissue in the body, carrying the important
mission of protecting the testis from environmental hazards. Septa from the tunica
albuginea divide the testis into 200–400 wedge-shaped lobes, each containing 3–10
coiled seminiferous tubules which constitute about 90% of the testicular mass. The
seminiferous tubules converge to a gathering point, the rete testis, located at the
testicular hilum or mediastinum testis. From here, efferent tubules (ductuli efferentes) carry the sperms to a single tube within the head, body, and tail of the epi-
didymis, which is continuous with the vas or ductus deferens [21] (Fig.42.2).
Fig. 42.2 Anatomy of the testis: This sagittal view shows the seminiferous tubules, the site of
sperm production. Formed sperm are transferred to the epididymis, where they mature. They leave
the epididymis during an ejaculation via the ductus deferens. (From Openstax.org books: Anatomy
and physiology of the testicular reproductive system. Creative Commons Attribution license.
https://openstax.org/books/anatomy- and- physiology- 2e/pages/27- 1- anatomy- and- physiology- ofthe- testicular- reproductive- system)
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42 Anatomy oftheScrotum andTesticles
The efferent ductules are unique because they are the sole part of the male
reproductive system that is lined by an epithelium containing both absorptive cells
and cells with motile cilia. On the one hand, these features allow the sperm to travel
rapidly into the epididymis, and on the other hand, the potential of ductal cells in
uid reabsorption favors sperm transport, concentration, and maturation, therefore
enhancing male fertility [22].
The testis has a triple arterial blood supply. The principal source is the testicular
artery, a branch of the abdominal aorta originating at L2–L3 just below the renal
arteries (remember that the embryological formation of the testes started near the
kidneys), but variations exist [23]. The other two suppliers are the cremasteric
artery arising from the inferior epigastric artery and the deferential artery or
artery to the vas which originates from the inferior vesical artery. A cadaveric
study showed that the testicular artery has a straight course in 85% and a convoluted
path in 15% and mostly terminates in the upper pole of the mediastinum testis
(78.8%) and divides into upper and lower polar branches in the majority of cases
(69.7%) [24]. There are anastomoses between the cremasteric artery and the lower
polar branch of the testicular artery and between the artery to the vas and branches
of the testicular artery through several capsular branches close to the mediastinum
testis. This study also classied the testis into three vascular areas according to the
arterial supply density (Fig.42.3):
• Rich vascular areas: upper polar, mediastinum testis, and posterolateral segments
• Moderate vascular areas: the middle third of the lateral surfaces
• Poor vascular areas: anterior border and anterolateral surfaces
Fig. 42.3 Schematic
diagram showing the
variation of arterial supply
according to the testicular
areas (lateral view). (From
Mostafa etal. [24], with
permission from Elsevier)
42.2 Gross Anatomy
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361
The testicular venous return is ensured by the pampiniform plexus2 which is
primarily drained by the testicular or gonadal vein, also called the internal sper-
matic vein, and the external pudendal vein, a tributary of the great saphenous
vein. The cremasteric vein, also referred to as the external spermatic vein, and
the vasal or deferential vein play a minimal role and empty into the inferior epigastric vein and the pelvic plexus, respectively [14]. The testicular vein drains into
the renal vein on the left side and the inferior vena cava on the right side. However,
there exist some individual variations [24].
In the lower third, as many as four to six trunks of testicular vein have been
described. Midway between the internal inguinal ring and the lower pole of the
kidney, the testicular vein divides into medial and lateral branches to form a delta.
The medial branch terminates into the left renal vein or the inferior vena cava (IVC)
after communicating with the ureteral veins and the contralateral renal vein: This
cross-communication exists only in 50% of individuals and is the only site
where the left and right testicular vein systems anastomose [25]. Here again,
many individual variations exist [26].
The lateral branch of the testicular vein communicates with colonic and renal
capsular veins before entering the perinephric space where it terminates.
The testicular veins are valveless and subjected to reux and possible development of varicoceles. The rationale behind varicocele ligation or embolization
lies in the interruption of blood ow in these valveless veins and the promotion of
the blood return through the external pudendal valved veins that drain into the great
saphenous vein (the longest vein in the body), a tributary of the femoral vein. It is
important to realize that the whole principle of varicocele treatment stands in this
anatomical detail as any testicular vein ligation would be catastrophic to the testis
(venous ischemia) if should alternative drainage be absent, or useless should it also
be valveless. Noteworthy cadaveric studies have revealed that varicocelogenesis is
not triggered by the sole valveless nature of the gonadal vein (if it were so, varicocele would be present in all men), and that reux is not the primum movens but is
rather secondary to a change in the pressure gradient at the junction between the
testicular and the renal veins [27].
42.2.3 The Epididymis
As mentioned above, the epididymis is a comma-shaped structure that contains a
single tube deriving from the efferent ductules. This tube is highly convoluted and
tightly compressed, with an estimated length of about 6m (20ft) when straightened
as reported in many old anatomical books. However, a recent study raised controversy by publishing lower values of only 30.48cm [28]. It is made of a head lying
at the upper pole of the testis, a body, and a tail which is continued by the vas deferens. The epididymis function is not just about the transportation of the sperms as
this would be more effective and rapid in a shorter duct. Its main functions are the
storage and maturation of sperm.
2
Pampiniform comes from the Latin word “pampinus,” tendril, and “forma,” form or shape.
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42 Anatomy oftheScrotum andTesticles
42.2.4 The Vas Deferens
The vas or ductus deferens originates as a continuation of the epididymal tail and
has approximately a 30–45cm length and a 2–3mm diameter in adults. It travels
within the spermatic cord through the scrotum and the inguinal canal to enter the
pelvic cavity. It then crosses above the ureter and approaches its opposite, both turning downward side by side and dilating to form the ampulla which lies parallel and
medial to the seminal vesicles. Each ampulla fuses with the duct of the corre-
sponding seminal vesicle to form the ejaculatory duct which crosses the prostate
to open into the prostatic urethra lateral to the urethral crest.
42.2.5 The Spermatic Cord
The spermatic cord’s diameter is 18.6mm (11–26mm) [29] and travels through the
inguinal canal.
It is formed by the invagination of three anterior abdominal wall fascial layers
and serves as the connecting channel between the abdominal and scrotal cavities.
The layers are as follows, from the outermost to the innermost: external spermatic
fascia (from the aponeurosis of the external oblique muscle), cremasteric fascia
(from the internal oblique fascia), and the internal spermatic fascia (from transversalis fascia). The cord contains the testicular artery, the vas deferens and its artery,
the cremasteric artery, the pampiniform venous plexus, the deferential vein, the
cremasteric vein, the genital branch of the genitofemoral nerve (supplies the cremasteric fascia and muscle), parasympathetic and sympathetic nerve bers, and lymphatics. The rule of “Three” helps recall these structures: three layers, three
arteries, three veins, three nerves, and three other things (vas deferens, lymphatics, and the closed processus vaginalis) [14].
Like the blood supply, lymph from the testis and epididymis recalls the embryological origins and drains into lymph nodes located in the retroperitoneum near the
renal vessels’ origins. Branches from the ilioinguinal nerve and the iliohypogastric
nerve travel outside the cord.
42.3 Congenital Abnormalities
Congenital anomalies of the testis, epididymis, and vas deferens have been reported
in 2% of normal male fetuses [30]. They include the following:
1. Undescended testis or cryptorchidism (from Greek words Kryptos, hidden,
and orchis, testis): This is the most frequent testicular abnormality after exclud-
ing congenital hydrocele which is considered physiological up to 1 year of age.
Studies have shown that the prevalence of undescended testis in boys with a
birth weight of ≥2500g has increased in several countries from around 2% to
4–8% in the last decades [31]. It is important to mention that not all mammals
have descended intrascrotal testes, and authors have proposed to group them in
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“four character state models”: (1) testicondy (the testicles remain intraabdominal, positioned close to the kidney and the scrotum is not present, e.g., sirenians
and cetaceans), (2) descended ascrotal (descended testicles but no developed
scrotum), (3) descended scrotal (descended testes and fully developed scrotum), and (4) marsupial model3 (descended testicles and well-developed scrotum, but in a prepenial position, contrary to Eutherians4 where the scrotum is
postpenial) [12].
2. Neonatal testicular torsion: About 150 cases have been reported in the litera-
ture and most of the cases (80%) occur before birth, justifying their presence in
this paragraph as “congenital abnormalities” [33, 34].
3. Testicular agenesis or anorchia: Anorchia is mostly associated with agenesis
of the vas deferens, and some are associated with unilateral renal agenesis [35].
4. Vanishing testis: This is also referred to as “Testicular regression syndrome,”
resulting from atrophy and disappearance of an initial normal testis during fetal
life. It should be differentiated from testicular agenesis. It is estimated to be
present in 5% of cryptorchidism [36].
5. Polyorchidism: A metanalysis published in 2009 revealed 140 cases of histo-
logically conrmed polyorchidism published in the literature with the great
majority being triorchidism and a predominance on the left side [37]. An exceptional case of ve testicles has also been reported [38] (Fig.42.4).
6. Isolated epididymal agenesis: This can be unilateral or bilateral.
7. Agenesis of the vas deferens: This may also be unilateral or bilateral.
Congenital bilateral absence of the vas deferens (CBAVD) occurs in 1in 1000
men and accounts for 1–2% of male infertility and for 6% of obstructive
azoospermia.
It is secondary to cystic brosis transmembrane conductance regulator
(CFTR) gene mutation and affects nearly 95% of men with cystic brosis [39].
8. Scrotal or penoscrotal transposition: In this anomaly, the scrotum is located
cephalic to the penis like in Marsupials. Fewer than 20 cases of complete penoscrotal transposition with an intact scrotum have been described in the literature
[40] (Fig.42.5).
9. Bid scrotum: This is dened as a midline cleft of the scrotum and may be
associated with hypospadias [41].
10. Accessory or ectopic scrotum [42].
3
Marsupials are mammals found in Australasia, Wallacia, and the Americas. They comprise a
handful of species such as kangaroos, koalas, opossums, bandicoots, wallabies, wombats, and
Tasmanian devils. They do not develop a well-dened anatomical placenta but have a functional
single layer of trophoblasts that produces hormones and a yolk sac. They do not have an umbilical
cord, and the placentation period is shorter than for eutherians. However, this is compensated by a
physiologically sophisticated and extended lactation allowing them “to exchange the umbilical
cord for the teat” [32].
4
Eutherians or placental mammals is a group of mammals comprising nearly 4000 species, including humans, monkeys, rodents, bats, elephants, whales, shrews, armadillos, dogs, cats, sheep,
cattle, horses, and so on.
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Fig. 42.4 Intraoperative view of polyorchidism in a 13-month-old boy operated for undescended
testes. (a) Three testes seen on the left side. (b) Two testes seen on the right side with a very long
epididymis connecting them. (From Zahirian Moghadam etal. [38], Commons Attribution 4.0
International License)
42 Anatomy oftheScrotum andTesticles
Fig. 42.5 Complete
penoscrotal transposition.
(From Somoza etal. [40].
Creative Commons
Attribution License)
11. Scrotal hemangioma: Hemangiomata are benign proliferations of vascular
endothelial cells. Congenital scrotal septum hemangiomas are very rare [42].
12. Splenogonadal fusion: This affects both sexes, but mostly the males with a
male-to-female ratio of 16:1. The left testicle connects in a continuous or
discontinuous fashion to splenic tissue, usually an accessory spleen. About 220
cases have been reported in the literature [43] (Fig.42.6).
42.3 Congenital Abnormalities
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a
c
b
d
e
Fig. 42.6 Continuous splenogonadal fusion on the left side and undescended right testis in an
8-month-old male infant. (a) Pre-operative B-mode ultrasound revealed possible fusion of the left
testis and the kidney; (b) single site laparoscopic examination revealed a closed right internal ring
and the right testis in the iliac fossa, at about the same height as the junction between the iliac vessel and the right vas deferens; (c) single-site laparoscopic examination visualized the right testis
located in the right iliac fossa, approximately 2cm above the right internal ring, with poorly developed right spermatic vessel; (d) complete fusion of the spleen and the left testis in the left iliac
fossa visualized by the single-site laparoscopic examination; (e) the left testis descended into the
scrotum after being separated from the spleen. (From Chen et al. [43]. Creative Commons
Attribution)
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42 Anatomy oftheScrotum andTesticles
13. Hemiscrotal agenesis: Extremely rare. Only eight cases are reported in the
English literature including some cases with heterotopic development of scrotal
tissue island in the inguinal region and extra-genital abnormalities [44, 45].
14. Scrotal agenesis: Complete congenital agenesis has been reported in only eight
cases [46, 47].
15. Scrotoschisis: Here the testicle eviscerates through a scrotal wall defect and
lies extracorporeally. Only a dozen of cases have been reported in the literature
[48, 49] (Fig.42.7).
16. Crossed testicular ectopia (CTE): This is dened by both testes being found
in one hemiscrotum subsequently to a descent error. The estimated global incidence of CTE is 1:4 million, and most of the time, the right testis is abnormally
located on the left side [50] (Fig.42.8).
a b
Fig. 42.7 (a and b) Congenital exposure of the right testis. (From Mohamed Mahfouz [49] with
permission from Elsevier)
References
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Fig. 42.8 Crossed
testicular ectopia. (From
Fahmy [50], with
permission from Springer
Nature)
367
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