Dissector Answers - Inguinal Region
Upon completion of this session, the student will be able to:
- Describe the anatomy of the inguinal canal.
- Describe the anatomy of the various kinds of abdominal wall hernias (indirect and direct inguinal, umbilical, lumbar).
- Define the layers of the anterior abdominal wall, their contributions to the coverings of the spermatic cord and round ligament, and the origin of these coverings as related to the descent of the gonads.
- Identify the anatomical landmarks on the deep surface of the anterior abdominal wall and their relationships to the types of inguinal hernias.
Learning Objectives and Explanations:1. Describe the anatomy of the inguinal canal. (W&B 433, M 193-198, N 250, 259,260, TG 5-10A, 5-10B, 5-11A)2. Describe the anatomy of the various kinds of abdominal wall hernias (indirect and direct inguinal, umbilical, lumbar). (W&B 434-435, M 205-207, N 261, TG 5-11A, 5-11B, 5-11C)
The inguinal canal can be thought of as a tunnel that travels from an "entrance", which is lateral and deep, to an "exit", which is medial and superficial. (As described below, during the development of the gonads there are structures that travel through the canal in this way.) It, like a tunnel, also has a roof, a floor, and two walls.Contents: spermatic cord (in males) or the round ligament of the uterus (in females) as well as blood vessels, lymphatic vessels, and the ilioinguinal nerve (which enters the canal from the side, rather than passing through the deep ring). Openings:
- deep (internal) inguinal ring: the entrance to the canal. The transversalis fascia pouches out, creating an opening through which structures can leave the abdominal cavity.
- superficial (external) inguinal ring: the exit from the canal. It is formed by the splitting of the diagonal fibers of the external abdominal oblique aponeurosis. Since the fibers split, anatomists get to give them different names. A lateral crus and a medial crus are formed. The lateral crus attaches to the pubic tubercle, while the medial crus attaches to the pubic crest. (Latin, crus = resembling leg or legs)
- roof: fibers of internal abdominal oblique and transversus abdominis muscles.
- floor: inguinal ligament throughout, with lacunar ligament added medially
- anterior wall: external abdominal oblique aponeurosis throughout, with internal abdominal oblique aponeurosis added laterally
- posterior wall: mostly transversalis fascia, with conjoint tendon (falx inguinalis), which is the joining of internal abdominal oblique and transversus abdominis aponeuroses, medially.
Note: The inguinal region can be tricky to put together, what with all of these layers mixing and matching and making structures. On top of that, it is important clinically! However, don't sweat it. Take a look at Netter's or pages 194-195 in Moore's, take a nap or have a coffee, then take another look. Talk to your friends about it, ask the professors, dig through its remnants in your cadaver, then take another look at the books. It will come together. Also, beware - there are other places in the body where some tissue defines a "passage" or a "canal" . You will see this type of thing again. Get used to thinking outside of the box!3. Define the layers of the anterior abdominal wall, their contributions to the coverings of the spermatic cord and round ligament, and the origin of these coverings as related to the descent of the gonads. (W&B 431-436, M 192-200, N 386, 387, TG 5-10B, 6-31, TG 5-02, 5-10B, 6-31)
See the Clinical Terms in the Anatomy Tables for full descriptions. The most important distinction to make is between direct and indirect inguinal hernias:
- Indirect: congenital, lateral to inferior epigastric vessels, enter canal via deep inguinal ring, often enter scrotum
- Direct: acquired, medial to inferior epigastric vessels, literally pierce the canal, seldom enter scrotum
Also, give some thought to what coverings each would have. (Latin, hernia = rupture)4. Identify the anatomical landmarks on the deep surface of the anterior abdominal wall and their relationships to the types of inguinal hernias. (W&B 435, N 253, 259, TG 5-07, 5-08, 5-09)
Layer of anterolateral abdominal wall Spermatic cord/testes covering skin scrotum superficial fascia scrotum/ dartos fascia&muscle external abdominal oblique aponeurosis external spermatic fascia internal abdominal oblique muscle cremaster muscle fascia from internal abdominal oblique muscle cremasteric fascia transversalis fascia internal spermatic fascia peritoneum processus vaginalis (obliterated)/ tunica vaginalis
As for the development of the region with respect to the descent of the gonads, the descriptions in both Woodburne&Burkel and Moore can be a bit confusing. Here is the basic gist (see also #5 below):
Male: testes begin as retroperitoneal structures in the posterior abdominal wall. They are attached to the anterolateral abdominal wall by the gubernaculum. As the gubernaculum "pulls" the testes into the pelvis and developing inguinal canal, it is preceded by the processus vaginalis, derived from the peritoneum which lies anterior to the testes. The processus vaginalis "pushes" the muscle and fascia layers, which will eventually make up the canal and spermatic cord, into the scrotum. After the testes are in position in the scrotum, the gubernaculum persists as the scrotal ligament, while part of the processus vaginalis remains as a bursa-like sac called the tunica vaginalis testis. (Latin, scrautum = quiver (with arrows), vagina = sheath)
Female: same as the male, up to a point. The gubernaculum is attached to the ovaries and the anterolateral abdominal wall. During development, though, it also attaches (in the middle) to the uterus. This attachment to the uterus prevents the ovaries from being pulled down. It also results in an adult derivative of the gubernaculum with two parts: the ovarian ligament and the round ligament. The former is between the ovary and the uterus, the latter between the uterus and the labium majus, running through the inguinal canal.
It should be noted that, at the time of birth, the inguinal canals run almost entirely posterior to anterior, with little medial deviation. With growth and development into an adult, they assume their oblique arrangement.
These diagrams are from the Loyola University Chicago - Stritch SOM LUMEN website. See an animation of this process here.
The basic idea is that there are five folds (covering ligaments) and some spaces, or fossae, around and between them. While not extremely important clinically, they do provide another way to think about the possible locations of hernias. Furthermore, these structures are interesting from the viewpoint of development, i.e., what they used to be.
Starting midaxillary on either side and going around to the midline, we have:
structure: lateral inguinal fossa lateral umbilical fold medial inguinal fossa* medial umbilical fold supravesicular fossa median umbilical fold contains: deep inguinal ring inferior epigastric vessels medial umbilical ligament median umbilical ligament clinical issue: indirect inguinal hernia direct inguinal hernia fetal remnant: fetal umbilical artery urachus
* part of this fossa is the inguinal triangle
Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.
The Muscles and Fasciae of the Abdomen -The Male Genital Organs - Surface Anatomy of the Abdomen -Surface Markings of the Abdomen
Questions and Answers:5. Review the descent of the gonads. (N 386, animations)Briefly, the testes start out behind the peritoneum below the kidney, in the lumbar region. From there, they descend through extraperitoneal connective tissue through the inguinal canal and into the scrotal cavity. A gubernaculum (fibrous tissue) helps to pull the testes down into the scrotal cavity through the inguinal canal. In adult life, the gubernaculum will become the scrotal ligament. The female case is similar, but the uterus develops near the middle of the gubernaculum and interrupts the descent of the ovary at the pelvic brim. The gubernaculum ends up as a short ligament from ovary to uterus (ovarian ligament) and a longer ligament passing from the uterus through the inguinal canal, inguinal rings (round ligament of the uterus) to the labia majora. Keep in mind that the descent involves an evagination of the abdominal wall and that this is where the inguinal canal starts (deep ring), this is also how the spermatic cord gets its layers from the layers of the abdominal wall. The peritoneum initially evaginates through the abdominal wall parallel to the round ligament (female) or spermatic cord (male) before birth. This normally closes but if it remains open constitutes a congenital inguinal hernia.6. What does the small genital branch of the genitofemoral nerve innervate?The small genital branch of the genitofemoral nerve innervates the cremaster muscle. It also anastomoses with the anterior scrotal/labial nerve (from the ilioinguinal nerve) to supply the skin of the area.7. Does the weak fascia between the falx inguinalis and inguinal ligament have a thickened lateral border (an interfoveolar ligament)?This depends on your cadaver. Netter 259 or TG 5-08, 5-09 shows it from the internal view.8. What tissue forms the deep (internal) inguinal ring, and how does it do so?The deep inguinal ring is formed by transversalis fascia above the midpoint of the inguinal ligament. It is not really "ring"-like, but is more of a sleeve.9. What passes through the deep ring? (N 262, 369, TG 5-08, 5-09)In the male, the structures that make up the spermatic cord traverse the ring (actually, the cord is formed at the ring). In the female, it is the round ligament of the uterus.10. What are the relationships of the medial inguinal fossa and lateral inguinal fossa to the weak fascia and the deep inguinal ring? (N 253, TG 5-07, 5-08, 5-09)Direct inguinal hernias start in the inguinal triangle, which is at the base of the medial inguinal fossa, between the medial and lateral umbilical folds. This triangle, since it is covered by weak fascia, allows direct hernias to pierce the anterior abdominal wall. Indirect inguinal hernias start at the base of the lateral inguinal fossa, lateral to the lateral umbilical fold. The deep inguinal ring, which transmits indirect hernias, is just lateral to the inferior epigastric vessels at the base of this fold.11. Define the inguinal triangle. (N 259, TG 5-07)This is the weak area defined by the lateral border of rectus abdominis muscle, the inferior epigastric artery, and the inguinal ligament.12. What is the relationship between direct and indirect inguinal hernias and the falx inguinalis, weak fascia, deep and superficial inguinal rings, inguinal canal, and inguinal ligament? (N 259, TG 5-07, 5-08, 5-09, 5-11A, 5-11B, 5-11C)OK... here we go AGAIN! (Are you getting the impression that this is something you should know?) Direct inguinal hernias pass through the inguinal triangle (see #2, #10, and #11), which is an area of weak fascia. They almost never go into the scrotum. Both the superficial inguinal ring and the inherent weakness of abdominal wall lateral to the falx inguinalis make this area susceptible to hernias. Indirect inguinal hernias start at deep inguinal ring, pass down inguinal canal, through superficial ring, and, in the male, usually descend into scrotum along with the spermatic cord. In the female they travel along the round ligament.13. Define the inguinal canal, noting location, orientation, rings, walls, shape, and relationships.See #1 above.14. How are the coverings of the spermatic cord represented in the scrotum? (N 387, TG 5-10B, 6-31)From superficial to deep, the cord is covered by skin, tunica dartos muscle, external spermatic fascia, cremaster muscle, internal spermatic fascia. In the area of the testis, there is an additional deepest layer, the tunica vaginalis (anterior and lateral). The external spermatic fascia, cremaster muscle, and internal spermatic fascia are the coverings of the spermatic cord proper, i.e., they wrap around it.15. Compare the inguinal canal in male and female: (N 260, 378, TG 5-08A, 5-08B, 5-08C, 5-08D, 5-09A, 5-09B, 5-09C, 5-09D)The inguinal canal is essentially the same in both sexes (see questions above). The character of the layers is diminished in the female and, of course, the contents are different.16. To what does the round ligament of the uterus attach? (N 378, 369, TG 5-09A, 5-07)The round ligament, derived from the gubernaculum, is attached to the uterus on the lateral surface below the uterine tube. From there, it runs through the inguinal canal to end in the labia majora.17. What is its male homologue? (N 386)The scrotal ligament is the male remnant of the gubernaculum. It, however, does not run through the inguinal canal, since it pulled the testes through.18. What is the scrotal ligament? (N 386)
The remains of the embryonic gubernaculum, the fibrous tissue which helps to pull the testes into the scrotal cavity. It attaches the inferior end of the testis to the inner aspect of the scrotal sac.
Updated: 30 November 2011
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