EN | DE | PT Get help How to study Login Register

Inguinal canal: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Inguinal canal

Throughout the human body there are numerous openings that allow structures to pass from one area to another. They are referred to by different names, such as foramina, canals, or hiatus. The anterior abdominal wall – which extends in a craniocaudal fashion from the xiphisternum and adjacent lower borders of the lower eight ribs to the inguinal ligaments and the pubis – has naturally occurring paired canals in the lower regions known as the inguinal canals. More specifically, the inguinal canals are found in the inguinal region, which extend from the lower abdomen into the medial part of the proximal thighs on each side.

The oblique tunnels serve as a conduit that allows passage of the male gonads from their intra-abdominal point of origin to the final destination in the scrotal sac. The boundaries of this hiatus are formed by the muscles of the anterior abdominal wall in the left and right iliac fossa. The size of the canals increase with age and are significantly more developed in males than in females.

Key facts about the inguinal canal
Walls Roof - formed by Muscles: internal oblique, transversus abdominis
Anterior - formed by Aponeuroses: internal oblique, external oblique
Floor - formed by Ligaments: inguinal ligament, lacunar ligament
Posterior - formed by Tendon and transversalis fascia
Mnemonic: MALT
Openings Deep inguinal ring - at the midpoint of the inguinal ligament
Superficial inguinal ring - 'V' shaped defect in the external oblique aponeurosis within the Hasselbach's triangle
Content Male: spermatic cord and ilioinguinal nerve
Female: round ligament of the uterus and ilioinguinal nerve (*ilioinguinal nerve enters the scrotum through superficial ring, but does not travel through the inguinal canal)
Spermatic cord content 3 arteries: testicular, cremasteric, ductus deferens artery
3 fascial layers: external spermatic, cremasteric, internal spermatic
3 nerves: genital branch of genitofemoral nerve, sympathetic fibers, ilioinguinal nerve 
Clinical importance Herniations

This article will discuss the embryology and anatomy of the inguinal canals. Furthermore, disorders of the inguinal canal and how they are treated will also be addressed.

Anatomy 

Landmarks

The inguinal canal is an oblique intramuscular slit that may range from 3 – 5 cm long in an adult. It originates superolaterally at the deep inguinal ring. This opening occurs at the medial half of the inguinal ligament of Poupart at the midpoint between the anterior superior iliac spine (ASIS) and the pubic tubercle; also known as the midpoint of the inguinal ligament. Please note that this is different from the mid inguinal point, which is the midpoint between the ASIS and pubic symphysis. However, the deep inguinal ring can also be found 1.25 cm above the mid inguinal point.

Inguinal canal in a cadaver: While dissecting the inguinal canal, you will find the vas deferens coursing laterally to the inferior epigastric vessels. In addition, the hard, cord-like and firm thread felt on palpation is the vas deferens.

The canal then terminates at the superficial inguinal ring, which can be found about 1 cm superolateral to the pubic tubercle. Also, the superficial inguinal ring is bordered medially by the inferolateral border of rectus abdominis, laterally by the inferior epigastric vessels and inferiorly by the medial third of the inguinal ligament. These three borders are often referred to as Hesselbach's (inguinal) triangle and serve as an important landmark for the superficial ring.

Learn everything about the anatomy and function of the inguinal canal with our articles, video tutorials, quizzes, and diagrams.

Borders 

The various layers of tissue of the lower abdominal wall play an important role in the formation of the inguinal canal. The canal has four borders – a roof and a floor, and anterior and posterior walls. It should be noted that the deep ring and thinnest part of the postural wall (i.e. the lateral aspect) is supported by the thickest part of the anterior wall. Similarly, the reflected inguinal ligament and conjoint tendon provide additional support to the posterior wall immediately behind the superficial inguinal ring.

A simple mnemonic to recall the borders of the inguinal canal is MALT:

  • The roof is formed by Muscles (internal oblique and transversus abdominis).
  • The anterior wall is derived from Aponeuroses (internal and external oblique aponeuroses).
  • The floor is formed by Ligaments (inguinal and lacunar ligaments).
  • The posterior wall is formed by the conjoint Tendon and Transversalis fascia.

Have you been learning the anatomy of the inguinal canal as efficiently as possible? Find out how to avoid these common learning mistakes.

Deep inguinal ring

The initial opening of the inguinal canal is located at the midpoint of the inguinal ligament, and is referred to as the deep (lateral) inguinal ring. It is an oval defect in the transversalis fascia, which is widest along the vertical axis of the opening. The defect is significantly larger in males than in females, as it is meant to accommodate the passage of the testes into the scrotal sac.

The deep ring is lateral to the inferior epigastric vessels as well as the interfoveolar ligament (fibrous band extending from the lower margin of the transversalis fascia to the superior pubic ramus) when they are present. The deep ring may also function as a valve whenever it is made taut by contractions of the internal oblique muscle in response to raised intra abdominal pressure. 

Anterior wall 

Beneath the skin and Scarpa’s fascia, sandwiched between two layers of Camper’s fascia, are the anterior abdominal wall muscles. The most superficial anterior abdominal muscle plays a crucial role in the formation of the anterior wall of the inguinal canal. The external oblique muscle has numerous points of origin along the lower eight ribs and their associated costal cartilages.

While some of the caudal fibers have attachments to parts of the iliac crest, some fibres continue caudally as the anterior aponeurosis. This fibromuscular structure, coupled with fibers of the internal oblique muscle form the anterior wall of the inguinal canal. The medial third of the anterior wall is formed by the patent superficial inguinal ring.

Inferior wall (floor) 

The free lower border of the external oblique aponeurosis rolls inwards to form the inguinal ligament. Extending from the anterior superior iliac spine to the pubic tubercle, this ligament has an antero-inferior convexity toward its lower limit. It commences as a tubular, oblique structure at the lateral extent.

As it travels medially, the ligament then begins to widen as it approaches the pubis. The abdominal surface of the ligament contains a groove, which forms the floor of the inguinal canal. The fibres that do not insert at the pubic tubercle diverge to form the lacunar ligament (posterolaterally) and to join the linea alba (superomedially). The lacunar ligament also contributes to the floor of the canal.

Superior wall (roof) 

Deep to the thick, bulky external oblique muscle is the internal oblique muscle. Unlike its superficial counterpart, it originates from the groove in the lateral two thirds of the inguinal ligament as well as the iliac crest. It has superior attachments to the lower border of the lower four ribs and their associated cartilages. Additionally, other fibres also join the anterior aponeurosis to attach to the costal cartilages of the 7th to  9th ribs.

However, it is the set of fibers that arise from the inguinal ligament that are needed to form the roof of the inguinal ligament. These fibers travel superiorly, and then arch inferomedially as it crosses the contents of the canal. The roof is further supported by fibers of the transversus abdominis muscle and the transversalis fascia

Posterior wall 

Like the internal oblique muscle, the transversus abdominis muscle also (albeit, partly) arises from the lateral third of the inguinal canal and curves inferomedially to join the internal oblique aponeurosis as both structures insert at the pectineal line and pubic crest as the conjoint tendon. This robust tendon provides additional support to the medial third of the posterior abdominal wall. The lateral part of the posterior wall is also supported by the in-rolled part of the inguinal ligament, alongside the transversalis fascia.  

Superficial inguinal ring

The medial opening of the inguinal canal occurs within Hesselbach's triangle and is known as the superficial inguinal ring. It is a ‘V’ shaped defect in the external oblique aponeurosis, whose apex is parallel with the deep aponeurotic fibres. The side walls of the superficial ring are formed from the aponeurotic crura of the external oblique. The lateral crus is thicker than the medial one, as the former is reinforced by the inguinal ligament.

The medial crus inserts at the pubic crest, while the lateral crus attaches to the pubic tubercle. There is also grooving of the lateral crus (not observed in females) that provides an atraumatic area for the spermatic cord to lay. The base of the triangular opening falls along the pubic crest. While there is variability in the size of the ring among individuals, it is also markedly larger in males than in females in order to accommodate testicular descent. 

Contents 

The contents of the inguinal canal vary dramatically between males and females; as there are significantly less structures that traverse the female inguinal canal. The ilioinguinal (arising from T12 and L1) and genital branch of the genitofemoral nerves (arising from L2) are the only structures that are found in both male and female inguinal canals. Note that the ilioinguinal nerve does not pass through the deep inguinal ring. Instead, it gains access to the canal by piercing its roof midway along the length of the canal.

Recall that the ilioinguinal nerve provides general somatic afferent innervation to the anterior perineum and medial part of the proximal thigh. Additionally, it innervates the mons pubis and labia majora in females, as well as the base of the penile shaft and anterior scrotal sac in males. The genital branch of genitofemoral nerve participates in the general somatic efferent supply to the cremasteric muscle (in males) and general somatic afferent to the labia and scrotum.

Inguinal canal in females

The round ligament of the uterus (ligamentum teres uteri) passes through the inguinal canal to insert on the posterior surface of the labia majora. It is a derivative of the embryonic gubernaculum that originates at the uterotubal junction (also called the uterine horn) and functions as a uterine anchor that keeps the uterus in the anteverted positio

Inguinal canal in males

In the simplest form, the male inguinal canal contains only the spermatic cord in addition to the same nerves found in the female inguinal canal. However, the spermatic cord contains several layers of fascia, and houses several arteries, nerves, and other reproductive structures. These structures can be readily recalled using the mnemonic “FANO x 3”, which translates to:

  • Fascia – these are continuations of the muscular and fascial layers that were traversed by the processus vaginalis during development.
    • The deepest of the three fascial layers is the internal spermatic fascia. It is a continuation of the transversalis fascia that was pulled through the canal during development.
    • The cremasteric muscle and fascia form the middle musculofascial layer of the spermatic cord. Both are continuations of the internal oblique muscle and fascia, respectively.
    • Finally, the external spermatic fascia is the outermost layer, which developed from the external oblique aponeurosis.
  • Arteries – the testes maintain the arterial supply it acquired during early development. These vessels migrate caudally with the gonad during its descent.
    • The testicular artery is responsible for supply the testes. Also historically known as the internal spermatic arteries, these vessels are direct branches of the aorta.
    • The cremasteric artery (formerly known as the external spermatic artery) supplies the cremaster as well as other fascial layers of the spermatic cord. The artery arises from the inferior epigastric artery and traverses the inguinal canal. It also shares anastomoses with the testicular artery.
    • The third artery in the inguinal canal is the artery of the vas (ductus) deferens. The ductus deferens is responsible for transporting sperm from the testes to the urethra. The arteries that supply it arise indirectly from the internal iliac artery via either the superior or inferior vesical arteries.

Nerves – in addition to the general somatic afferent and efferent nerves mentioned earlier, there are also autonomic nerves that pass through the canal to supply the gonads and associated structures.

  • Ilioinguinal nerves
  • Genital branch of genitofemoral nerve
  • Autonomics

Other – miscellaneous structures found in the cord include:

  • The ductus deferens.
  • The pampiniform plexus of veins - These vessels encircle the arterial structures and participate in a countercurrent heat exchange process that ensures that the blood being carried to the testes is at ambient temperature.
  • Testicular lymphatics will drain lymph from the testes to the para-aortic lymph nodes.

Ready to consolidate your knowledge even more? Try out our quiz below:

Embryology 

The sole purpose of the inguinal canal is to provide a conduit that facilitates gonadal descent. In males, this results in the testes leaving the lumbar region of the posterior abdominal wall to enter the scrotal sac. In females, however, this means movement of the ovaries from the same area, to the pelvic region. The presence of the inguinal canal in both males and females are indicative of the stage of sexual development before the differentiation of sexes. Since the formation of the canal is more pronounced males, it will be discussed as the prototype for inguinal canal development. 

Initially, around the eighth week of gestation, the testis shares a urogenital mesenteric attachment with the mesonephros (primitive kidney) to the posterior abdominal wall. The bilateral formation of the ligamentous gubernaculum occurs shortly after the degeneration of the mesonephros (the mesentery is left attached to the gonads). These mesenchymal derivatives have proximal attachment to the caudal pole of each ipsilateral testis. Distally, each ligament takes an oblique course through the developing anterior abdominal wall before inserting on the internal surface of the ipsilateral labioscrotal swellings. Gonadal descent is also facilitated by testicular enlargement and loss of the paramesonephric ducts (under the influence of Müllerian inhibiting substance [MIS]). The latter event allows the testis to migrate across the abdomen from the posterior abdominal wall to the anterior abdominal wall. In addition to these processes, an increase in intra abdominal pressure (as a result of gastrointestinal organogenesis), along with foetal testosterone also promote the descent of the glands into the scrotum.

However, the key feature that supports formation of the inguinal canal is the development of the processus vaginalis (during the 12th gestational week) in the region ventral to the gubernaculum. The flask-shaped processus vaginalis is an evaginated portion of peritoneum that bulges through the anterior abdominal wall. As the processus vaginalis migrates along the path created by the gubernaculum, it takes the layers of the anterior abdominal wall with it; resulting in the formation of the inguinal canal.The deep and superficial inguinal rings correspond to the openings created by the processus vaginalis through the transversalis fascia and external oblique aponeurosis, respectively. Under normal circumstances, the testicular descent begins around the 26th gestational week and may conclude over the course of three days. In other instances, it spans the course of six weeks and by the 32nd gestational week both testes are present in the scrotal sac. A small percentage of infants are born with undescended testes (cryptorchidism). This is likely to resolve by the 3rd month of extrauterine life.

In genotypic females, although the gonads never leave the pelvic cavity, there decent is also preceded by the formation of a relatively smaller processus vaginalis. Similarly, this promotes the formation of the inguinal canal in females as well. The processus vaginalis often fuses long before birth. 

Inguinal canal: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Register now and grab your free ultimate anatomy study guide!