Inguinal Canal

The inguinal canal [39] is an oblique tunnel that borders the anterior thigh and extends from the superficial to the deep inguinal ring, running parallel to and above the inguinal ligament. It develops between the 5th and the 32nd week of prenatal life, initially as the processus

. Peritoneum .Testis

Peritoneum

. Peritoneum .Testis

Peritoneum

Guberna Culum
Epididymis

Ductus (Vas) Deferens

Patent

Processus vaginalis

Ductus (Vas) Deferens

Patent

Processus vaginalis

Pampiniform Plexus Thrombosis

Epididymis Tunica Vaginalis

Obliterated Process vaginalis

Pampiniform Plexus Within the Spermatic cord

Epididymis Tunica Vaginalis

Obliterated Process vaginalis

Pampiniform Plexus Within the Spermatic cord

Fig. 1.18. Formation of the process vaginalis, descent of the testis, and the spermatic cord vaginalis, a peritoneal evagination that extends into the transversalis fascia. The processus vaginalis (Fig. 1.18) eventually loses its connection with the peritoneal cavity of the abdomen and persists as a double-walled serous layer, the tunica vaginalis, anterior and lateral to the testis. The transversalis fascia continues with the internal spermatic fascia in the form of a tubular sheath that travels forward, first by passing between the arched fibers of the aponeuroses of the transverse ab-dominis and internal abdominal oblique abdominis, and finally through the external abdominal oblique aponeurosis (Fig. 1.19). During the passage of the processus vaginalis and internal spermatic fascia through the aponeuroses of the internal and external abdominal oblique, they acquire additional coverings from the cremasteric muscle and fascia, and the external spermatic fascia.

The triangular gap proximal and lateral to the pubic crest that marks the continuation of the external spermatic fascia with the external abdominal oblique apo-neurosis is known as the superficial inguinal ring. This opening, formed by a division of the fibers of the external abdominal oblique aponeurosis, is bounded by medial and lateral crura. The medial crus passes supero-medially to join with the corresponding fibers of the contralateral side. The fibers of the lateral crus extend inferolateral to the superficial inguinal ring, forming the medial end of the inguinal ligament. Variable fibrous strands that run across the upper part of the superficial inguinal ring form the intercrural fibers. These fibers play a role in strengthening the superficial inguinal ring and preventing further splitting of the fibers of the external oblique aponeurosis.

The deep inguinal ring is a funnel-shaped opening in the transversalis fascia; it is located lateral and superior to the inferior epigastric vessels, and inferior to the arched lower margin of the aponeurosis of the transverse abdominis. Although size variations do exist, the deep inguinal ring is almost always larger in the male to accommodate the spermatic cord and its components. It is approximately 2.54 cm above the midpoint of the inguinal ligament, corresponding to the site of passage of the femoral artery under the inguinal ligament. The precise location of the deep inguinal ring as 0.52 cm lateral to the midinguinal point and 0.46 cm medial to the midpoint of the inguinal ligament has been documented by Andrews et al. [40]. Neither the midinguinal point nor the midpoint of the inguinal ligament can accurately predict the position of the deep inguinal ring.

The force exerted by the contraction of the internal abdominal oblique muscle on the margins of the deep inguinal ring may play an important role in preventing herniation. The oblique direction of the inguinal canal, the strength of the abdominal muscles, and the traction exerted by the internal oblique abdominis muscle during strenuous activity appear to compensate for weak-

External Abdominal. Oblique and Aponeurosis ^

Internal / Abdominal Oblique and Aponeurosis

Cremasteric Muscle and Fascia

^Transverse Abdominis

Processus Vaginalis

.Peritoneum

.Ureter

Internal Spermatic-Fascia

Parietal & Visceral, Layers of Tunica Vaginalis

.Peritoneum

Dartos Contraction

Dartos layer " (Subcutaneous Tissue)

External Spermatic Fascia

Epididymis ^Internal Spermatic fascia Fig. 1.19. Coverings of the testis and spermatic cord

Testis ness of the anterior abdominal wall. Presence of the conjoint tendon and the reflected inguinal ligament directly posterior to the superficial inguinal ring also play an important role in counteracting the weakness in the inguinal area. Contraction of the abdominal muscles forces the wall of the inguinal canal to collapse and thus act as a safety valve, preventing the occurrence of hernia in normal individuals.

The inguinal canal is bounded superiorly (on its roof) by the arched lower free fibers of the internal abdominal oblique and the transverse abdominis muscles and inferiorly (on its floor) by a combination of the inguinal and lacunar ligaments and the transversalis fascia. It is enclosed anteriorly by the aponeurosis of the external and abdominal internal oblique muscles and posteriorly by the transversalis fascia, falx inguinalis, and the reflected inguinal ligament. This canal contains the spermatic cord and ilioinguinal nerve in the male, and the round ligament of the uterus and ilioinguinal nerve in the female.

In the male (Fig. 1.18), descent of the gonads from the posterior abdominal wall follows the gubernacu-lum hunteri [41], a mesenchymal tissue that extends from the posterior abdominal wall to the deep inguinal ring. The processus vaginalis, guided by the guberna-culum, protrudes through the deep inguinal ring and descends to the scrotum, as additional fascial coverings are added to it. Variations in the attachments of the gu-bernaculum to the testis may determine the location of the testis. A recent study [42] found the proximal portion of the gubernaculum to be attached to the testes and epididymis in all fetuses that did not exhibit congenital malformations or epididymal alterations, such as tail disjunction or elongated epididymis. In unde-scended (cryptorchid) testes, an increased incidence of gubernacular attachment anomalies was accompanied by paratesticular structural malformations compared to the testes of normal fetuses. Cryptorchid testes are frequently located in the inguinal canal, sometimes in the femoral canal and suprapubic region (at the base of the penis), and rarely found in the contralateral scrotum or perineal region [43]. Tanyel et al. [44] reported neurogenic changes within all cremasteric muscles of boys with cryptorchid testis.

In the female, the gonads follow a much shorter course, and the gubernaculum attaches to the ovary and the uterus during its descent toward the anterolateral abdomen. The portion of the gubernaculum that connects the ovary to the uterus becomes the proper ovarian ligament. The remaining part, which extends through the anterolateral abdomen, develops into the round ligament of the uterus that travels through the inguinal canal to the major labium. Since the round ligament attaches to the anterolateral abdomen before the inguinal canal is completely formed, it does not have the same fascial coverings as the processus vaginalis in the male. In the female, the coverings are so thin that they are indistinguishable from the round ligament itself.

In the male, obliteration of the processus vaginalis, and thus the connection between the peritoneal cavity in the abdomen and scrotum, is usually complete at birth. However, this process may begin late, and when it does, it becomes completed by the first few weeks of postnatal life. Closure begins at the deep inguinal ring and extends downward to involve all the intervening regions.

The only postnatal remnant of the processus vaginalis is a closed sac anterior and lateral to the testis, known as the tunica vaginalis. Failure of the processus vaginalis to close (patent processus vaginalis) may allow part of the abdominal viscera to protrude through the deep inguinal ring and follow the course of the inguinal canal to the superficial inguinal ring, producing an indirect inguinal hernia. Kahn et al. [45] published a report that objectively confirms that presence of a patent processus vaginalis is not a prerequisite to the development of indirect inguinal hernia.

The tunica vaginalis (Fig. 1.18) consists of visceral and parietal layers separated by a cavity that contains a thin film of fluid. Accumulation of fluid in this cavity produces hydrocele, a condition that exhibits transillu-minating scrotal swelling anterior to the testis. Hydro-cele can be a primary (idiopathic) or secondary condition. A primary hydrocele is usually large and rigid, occurs over the age of 40, and develops slowly. A secondary hydrocele tends to occur in younger individuals as a sequel to inflammation or tumors of the testis. A congenital hydrocele associated with indirect inguinal hernia is usually large and full during the day and shrinks during the night. A spermatic cord hydrocele tends to move downward when traction is applied to the testis.

The blood supply, venous and lymphatic drainage, and innervation of the testis are associated with the posterior abdominal wall and are contained within the spermatic cord (Figs. 1.7, 1.18, 1.19). This cord is a composite bundle that contains the vas deferens (duc-tus deferens), testicular artery, pampiniform venous plexus, deferential artery, and the genital branch of the genitofemoral nerve. It is covered by the external spermatic fascia, cremasteric muscle and fascia and the internal spermatic fascia. Separation of the vas deferens and associated vessels within the spermatic cord from the processus vaginalis and attainment of inguinal or-chiplexy can successfully be accomplished by division of the internal spermatic fascia [46].

The vas deferens (Figs. 1.18,1.19), a cord-like structure rich in smooth muscle fibers, begins as a direct continuation of the tail of the epididymis and ascends in the center of the spermatic cord, entering the abdominal wall via the superficial inguinal ring. Subsequent to its course through the deep inguinal ring into the pelvis, it joins the duct of the seminal vesicle to form the ejaculatory duct. Bilateral congenital absence of the vas deferens is associated with azoospermia and may determine the likelihood of cystic fibrosis [47].

The testicular artery (Fig. 1.19) emanates from the abdominal aorta and descends anterior to the ureter, coursing within the inguinal canal to supply the testis. The angle between the ductus deferens and the testicu-lar vessels, and the thickness of the adjacent tissue around the deep inguinal ring, show great variations. This angle, which constitutes the apex of what is called the "triangle of doom", maybe used as a point of reference to predict the position of the ductus deferens, thereby preventing accidental surgical stapling of the underlying external iliac vessels during herniorraphy [48]. The thickness of the peritoneum, transversalis fascia, and intervening connective tissue is greatest lateral to the testicular vessels and least over the ductus deferens.

The deferential artery, a branch of the inferior vesical artery, forms an extensive anastomosis with the tes-ticular and the cremasteric arteries. The cremasteric artery arises from the inferior epigastric artery and supplies the cremasteric muscle and fascia. The pampiniform plexus (Fig. 1.18) travels through the inguinal canal and gives rise to a number of veins that coalesce to form the right and left testicular veins, which drain into the inferior vena cava and the left renal vein, respectively. Dilation of the pampiniform plexus produces varicocele, a condition that is usually visible when standing or straining. It is associated with defective valves in the plexus, thrombosis of the left renal vein, renal diseases, and rarely with superior mesenter-ic artery syndrome.

The round ligament of the uterus, a remnant of the gubernaculum, follows the inguinal canal from the deep to the superficial inguinal ring and eventually reaches the major labium. It is considerably stretched during pregnancy and maintains the anteverted position of the uterus. The wall of this ligament contains great numbers of smooth muscle fibers near the uterus; these diminish toward the deep inguinal ring, converting into fibrous strands as it reaches the major labium. The round ligament courses diagonally within the me-sometrium toward the pelvic floor anterior to the external iliac, obturator, and vesical vessels, and the obliterated umbilical artery. The round ligament allows some lymphatics from the cervix and fundus of the uterus to follow its course to the superficial inguinal lymph nodes.

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