Inguinal, belonging to the groin. WILLIS’ REM. MED. WKS., Vocab. 1681
Development of the structures around the groin
Some of the tissue of the primitive myotome does not persist as muscle but degenerates into fibrous structures that form the aponeuroses of the muscles. The inferomedial aponeurotic attachments of three abdominal muscles, the external and internal obliques and the transversus abdominis, form the inguinal canal about the gubernaculum.
Differentiation of the inguinal canal
The development of the inguinal canal is not dependent on that of the testis, because it is similar in both sexes and virtually complete at 22 weeks, the time testicular descent begins in the male.
Development of the gubernaculum
At about 8 weeks, the testis is suspended from the posterior body wall by the urogenital mesentery that runs medial to the paramesonephric (müllerian) duct ( Fig. 9-1 ).
The gubernaculum is formed as mesenchymal cells condense and reinforce the more caudal portion of the mesentery. This structure extends as a short stalk from the lower pole of the testis and epididymis to the anterior abdominal wall at the site of the future inguinal canal. The mesonephric (wolffian) duct runs dorsal to the testis. (See also Chapter 17 .)
Opening of the inguinal ring
Between the sixth and tenth weeks, the peritoneum partially surrounds the gubernaculum , covering it on the anterior and lateral sides ( Fig. 9-2 A). Enlargement of the abdominal cavity by accumulation of the intestines displaces the anterior abdominal wall, which effectively pulls the testis and epididymis away from the posterior wall. As the gubernaculum tightens, it rotates the testis into a horizontal position with the epididymis below and holds it adjacent to the future canal.
The peritoneum evaginates as a pouch to form the processus vaginalis .
Because the head of the epididymis lies distal to the testis and is attached to the gubernaculum, it enters the internal ring of the new inguinal canal ahead of the testis. The epididymis follows the lead of the gubernaculum along with the processus vaginalis to the base of the scrotum.
The transversalis fascia that continues as the internal spermatic fascia about the gubernaculum thickens and forms an inverted U-shaped structure, the internal inguinal ring . The ring is at its greatest development around the 28th week, when the diameter of the gubernaculum is larger than that of the testis itself and testicular descent is imminent.
Evagination of the peritoneum occurs anterior and lateral to the spermatic cord ( Fig. 9-2 B). When an indirect hernia occurs, the sac exits through the deep inguinal ring in the same relationship to the cord.
Testicular descent
The peritoneal evagination forming the processus vaginalis progresses anterolateral to the gubernaculum until it has reached the base of the scrotum ( Fig. 9-3 A).
After the testis is in the scrotum, the tissues of the ring contract on the cord, leaving the oblique inguinal canal that is found in the adult. The peritoneal lining of the processus becomes obliterated ( Fig. 9-3 B).
The inguinal region in infants differs somewhat from that in the adult, and the differences are important for surgery at this age. With time, the initially thick superficial fascia resembling the aponeurosis of the external oblique assumes its normal thickness. The canal subsequently runs more obliquely, and the previously well-developed cremaster becomes thinned.
Cryptorchidism is the most common congenital abnormality of the testis. Approximately one-tenth of cryptorchid testes are intra-abdominal and the same proportion are ectopic, a fifth are prescrotal, two-fifths are inguinal, as many as a fifth are bilateral, and 3% or 4% are absent.
Coverings of the spermatic cord
(See also Chapter 17 .)
The four coverings of the spermatic cord arise from undifferentiated mesenchyme lying between the tissue destined to be the epithelium of the skin and that destined to be the mesothelium of the peritoneum. The mesenchyme develops three layers: (1) a subcutaneous layer, (2) a middle layer that becomes the body wall itself, and (3) a retroperitoneal layer. Late in fetal life, the subcutaneous layer differentiates into dermis, superficial fascia (eventually to become Camper’s and Scarpa’s fascias and the dartos), and deep investing fascia of the body wall (see Table 8-1 ).
During passage of the testis through the inguinal canal, the testis within the tunica vaginalis pulls with it a succession of layers from the anterior body wall (see Fig. 9-2 ). The exception is the cremaster, which probably forms from local mesenchyme.
The internal spermatic fascia is derived from the same layer of retroperitoneal connective tissue that forms the transversalis fascia. The cremasteric fascia and cremasteric muscle are continuations of the internal oblique and transversus abdominis; the external spermatic fascia is continuous with the innominate fascia over the external oblique (see Fig. 9-10 ).
Inguinal and femoral regions: structure and function
The anatomy of the inguinal region is complex because of adaptation to testicular descent and erect posture. The surgeon, by viewing the groin region from inside the pelvis as well as from the exterior and then mentally combining both views, can create a three-dimensional picture of the area to apply during an operation, whether for node dissection or for orchiopexy and hernia repair.
External approach to the inguinal region
Skin and fascia
The skin, in combination with two layers of superficial fascia, encloses the superficial vessels and nerves and the superficial inguinal lymph nodes.
The skin of the groin area is thick and relatively inelastic but because it is accessible and relatively hairless, it can be used for skin grafts during genital repair. The surface over a lower abdominal quadrant is suitable for excising full-thickness grafts or dermal grafts, and the anterolateral surface of the thigh can be flattened for cutting a split-thickness graft with a dermatome. In infants and obese adults, a fold of skin runs transversely above the skin crease at the bend of the thigh. This marks the lower border of the thickest part of the abdominal panniculus and is a useful crevice in which to hide an incision. In fact, the lines of skin tension run transversely and should be followed to favor healing of the wound, because the surrounding skin flaps can always be moved to allow surgical exposure of all parts of the groin.
The superficial fascia in the groin is a continuation of adjacent layers. Although an attempt is made to divide the superficial fascia into a superficial layer and a deep or membranous layer, the continuities are not precise, because some layers become attenuated and others acquire local importance. Buck’s fascia is a case in point. Although it is defined as being part of the membranous layer of the superficial fascia, it is covered by the dartos, which is an extension of Colles’ fascia, also part of the membranous layer of the superficial fascia. Table 9-1 defines the layers.
| Inguinal Region | External Genitalia | Thigh |
|---|---|---|
| Camper’s fascia | Subcutaneous fat | |
| Scarpa’s fascia | Dartos, Buck’s, Colles’ fascia | Cribriform fascia |
| Innominate fascia | External spermatic fascia | Fascia lata |
| Internal oblique | Cremasteric fascia and muscle | |
| Transversalis fascia | Internal spermatic fascia | Anterior, medial walls, femoral sheath |
| Peritoneum | Tunica vaginalis |
The superficial layer of the superficial fascia (Camper) is areolar tissue with its contained fat ( Fig. 9-4 ). This layer passes over the inguinal ligament to continue as the superficial fascia of the thigh. It is also continuous with the superficial fascia of the penis (often called the dartos layer). It descends into the scrotum with that of the areolar outer covering of the spermatic cord, the dartos proper, where the areolar tissue picks up nonstriated muscle fibers to become the dartos muscle . The layer then passes posteriorly to join the superficial layer of the superficial fascia of the perineum. The superficial epigastric vein and artery arise from the anterior surface of the femoral vein and artery 1 cm below the inguinal ligament and run across the line of an inguinal incision beneath the superficial layer to the level of the umbilicus. An incision through the neck of the scrotum may encounter the superficial external pudendal vessels as they cross from the fossa ovalis to supply the penis and scrotum.
The deep or membranous layer of the superficial fascia (Scarpa) is found in the groin as a distinct compact layer, but it becomes less identifiable over the upper portions of the flank and abdomen and may not be found in obese individuals. It should not be mistaken for the external oblique aponeurosis, especially because Scarpa’s fascia does not have parallel collagenous fibers. Also, traction on it moves with the skin to which it is attached. It is loosely connected to the innominate fascia of Gallaudet, which is the investing fascia overlying the external oblique aponeurosis . The membranous layer is firmly connected to the linea alba and to the symphysis pubis, contributing to the fundiform ligament .
The superficial inguinal pouch (Denis Browne) is a potential space between the membranous layer and the innominate fascia. The pouch lies lateral to the external ring and provides a space in which a cryptorchid testis may be found.
Between the pubic symphysis and the pubic tubercle, the membranous layer of the superficial fascia or Scarpa’s fascia is unattached, leaving an opening for the spermatic cord—the so-called abdominoscrotal passage that is felt as a ring around the examining finger. This ring is not to be confused with the external inguinal ring, which lies higher and is rarely palpable in the absence of a hernia. Scarpa’s fascia passes over the inguinal ligament, where it is attached only to the middle third, and blends with the superficial fascia of the thigh (over the superficial inguinal lymph nodes) and over the fossa ovalis and the fascia lata . It is continuous over the penis as the superficial fascia of the penis , the dartos layer, and it follows the spermatic cord into the scrotum as the membranous layer of the superficial fascia (dartos tunic). In the perineum it joins Colles’ fascia representing the membranous layer of the superficial fascia in that region.
Bony pelvis
Before describing the soft tissues, the bony surfaces and landmarks of the public portion of the pelvis are presented as a framework for attachment of the fascial structures about the inguinal canal. The pubis constitutes the lower medial third of the innominate bone ( Fig. 9-5 ).
The sites of attachment of inguinal structures are outlined in Table 9-2 .
| BONES | |
| Pectineal line | Lacunar ligament |
| Fascial lacunar ligament | |
| Pectineal ligament | |
| Falx inguinalis | |
| Lowest fibers of internal oblique | |
| Conjoined tendon | |
| Lowermost portion of the transversus | |
| Pubic tubercle | Medial end of inguinal ligament |
| Lacunar ligament | |
| Cremaster | |
| Pubic crest | Lateral head of rectus abdominis |
| Aponeurosis of external oblique | |
| Conjoined tendon | |
| Symphysis | Membranous layer of superficial fascia |
| Aponeurosis of external oblique | |
| Medial head of rectus abdominis | |
| Anterior superior iliac spine | Lateral end of inguinal ligament |
| Transversalis fascia (deep crural arch) | |
| LIGAMENTS | |
| Superior pubic ligament (Cooper) | Transversus abdominis |
| Iliopsoas fascia | Inguinal portion of internal oblique |
| Inguinal portion of transverses | |
The pectineal surface (see Figs. 9-18 and 9-19 ) on the superior ramus of the pubis has a triangular shape that is oriented forward and slightly upward. This surface extends from the pubic tubercle (also see Figs. 9-9 A, 9-10 , 9-11 A, and 9-19) to the iliopubic eminence (see Figs. 9-17 and 9-18 ) that marks the junction of the ilium and the pubis. In front is the obturator crest (also see Fig. 9-19 ) and behind is a sharp edge, the pectineal line (pecten pubis) (also see Figs. 9-7 , 9-11 B, and 9-19 ).
The pubic crest (also see Figs. 9-9 A and 9-19 ) is the free upper border of the body of the pubis medial to the obturator crest. The lateral head of the rectus abdominis arises from its lateral part; the medial part of the rectus crosses its medial part before attaching to the symphysis and adjacent pubis. The pubic tubercle lies near the medial end of the pubis and is an important landmark in surgery of the groin because it indicates the medial attachment of the inguinal ligament. The tubercle provides part of the floor of the external inguinal ring.
The joint between the pubic bones, the pubic symphysis , has a thickness of 2 to 3 mm and is composed of hyaline and fibrous cartilage. It has an oval shape and commonly has a primitive cavity. It is connected by a heavy anterior pubic ligament and a smaller posterior pubic ligament, structures that are more likely to pull off from the bone rather than rupture.
External oblique layer
Each of the three muscles of the anterior abdominal wall is covered on both sides with investing fascia. The layer covering the external surface of the external oblique, the innominate fascia of Gallaudet, is the thickest and becomes the fascia lata in the thigh. The internal surface of the muscle has a thinner fascial coat and both the inner and outer fascias fuse at the inferior, free border, where the external oblique forms the inguinal ligament.
The fibers of the external oblique aponeurosis, following the direction of the fibers of the muscle, run downward and medially to end in and form part of the linea alba ( Fig. 9-6 A). The aponeurosis is also attached medially to the upper border of the pubic symphysis and to the pubic crest as far as the pubic tubercle . It forms the anterior wall of the inguinal canal, supplemented laterally by fibers of the internal oblique aponeurosis that attach to the lateral part of the inguinal ligament.
The external spermatic fascia results from fusion of the innominate fascia and the fascia associated with the internal surface of the external oblique and its aponeurosis ( Fig. 9-6 B). It forms the outer tubular sheath surrounding the spermatic cord and testis. It is important surgically during exposure of the spermatic cord: If this fascia is incised along with the underlying external oblique aponeurosis to the point where its sheath widens near the upper pole of the testis, the scrotal contents, even if enlarged, may be drawn into the wound. It covers the cremasteric fascia and internal spermatic fascia .
Aponeurosis, fascia, and ligament are defined in Table 9-3 .
| Aponeurosis: A flat, dense structure composed of strong collagenous parallel fibers that form a white tendon of insertion of the external oblique, the internal oblique, and the transversus abdominis into the sheath of the rectus abdominis muscle and into the pubis |
| Fascia: Layers formed from condensations of connective tissue covering muscles or derived from the retroperitoneal connective tissue |
| Ligaments: Condensations of connective tissue distributed between structures |
The superficial inguinal ring is the most medial of the three inguinal rings (superficial, external, and internal) that provide passage for the spermatic cord while preventing herniation of the peritoneum and its contents (see Fig. 9-10 ). It is a triangular opening based on the pubic crest. Its sides are the medial and lateral crura formed by the edges of the external oblique aponeurosis as that structure splits to join the crest. The lateral edge, as the inferior or lateral crus , is the inguinal ligament itself reinforced by the intercrural fibers that come from the innominate fascia. The intercrural fibers run at right angles to the fibers of the aponeurosis and may arch over the superficial ring. The medial edge of the superficial inguinal ring, the superior or medial crus , is a thin extension of the external oblique aponeurosis that is attached to the front of the pubis and also to the linea alba, where its fibers interlace with those from the opposite side.
Inguinal ligament
The inferior margin of the aponeurosis of the external oblique extends between the anterior superior iliac spine , where it is attached to the iliopsoas fascia, and the pectineus fascia at the pectineal line on the inner aspect of the pubis ( Fig. 9-7 A). The aponeurosis becomes somewhat thicker as it arches over the femoral nerve, vessels, and canal and folds internally on itself before ending as a free edge. This inward fold forms a shelf along its inner aspect, the inguinal ligament (Poupart). The ligament is rounder laterally but becomes flatter medially as it joins the pubic tubercle . The fibers of the external oblique aponeurosis change their oblique course to a more transverse direction to follow the line of the ligament. The deeper fibers posteromedially spread out to join the pectineal line. The ligament itself forms the floor of the inguinal canal.
