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ANATOMY OF INGUINAL CANAL

Dr Vishnu Mohan 29/11/2014

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Inguinal Canal

This is an oblique intermuscular passage in the lower part of the anterior abdominal wall , Situated just above the medial half of the inguinal ligament

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Inguinal Canal

LocationInferior part of the anterolateral abdominal wall

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Length & direction

It is about 4cm(1.5 inches) long, and is directed downwards, forwards and medially

The inguinal canal extends from the deep inguinal ring to the superficial inguinal ring

A Box?

Anterior wallRoof

Posterior wallFloorMedialImagine the right side inguinal canal viewed from the front as a box with anterior & posterior walls, a roof & floor. The arrow indicates that structures can run through it from lateral to medial e.g. in males it transmits the spermatic cord, and in females, the round ligament of the uterus.

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Deep inguinal ring

An oval opening in the fascia transversalis situated 1.2 cm above the midinguinal point, and immediately lateral to the stem of the inferior epigastric artery

Inguinal canal

Deep inguinal ring

FloorHere are the posterior wall, which has the DEEP inguinal ring situated laterally, and the floor. (Roof and anterior wall removed).

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Superficial inguinal ring

Is a triangular gap in the external oblique aponeurosis . It is shaped like an obtuse angled triangle . The base of the triangle is formed by the pubic crest, the two sides of the triangle from the lateral or lower and the medial or upper margins of the opening. It is 2.5 cm long and 1.2 cm broad at the base these margins are referred as crura. At and beyond the apex of the triangle 2 crura are united by intercrural fibers

Inguinal canal

Anterior wall

RoofSuperficial inguinal ring

FloorHere are the anterior wall (which has the SUPERFICIAL inguinal ring situated medially), and the roof.

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BOUNDARIES OF INGUINAL CANALTHE ANTERIOR WALL 1.In its whole extenta. Skinb. Superficial fasciac. External oblique aponeurosis2.In its lateral one-thirdThe fleshy fibres of the internal oblique muscle.

Inguinal canal13

Anterior wallSuperficial inguinal ring

The anterior wall is made up of the external oblique muscle throughout, and is reinforced by theinternal oblique m. laterally.The transversus abdominus m. lies even more laterally as part of the anterior abdominal wall.

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1.In its whole extenta. The fascia transversalisb. The extra peritoneal tissuec. The parietal peritoneum.2.In its medial two-thirdsa. The conjoint tendonb. At its medial end by the reflected part of the inguinal ligament.

THE POSTERIOR WALL

Posterior wall of the inguinal canal15

Deep inguinal ring

The posterior wall is formed by transversalis fascia (orange) throughout and the conjoint tendon (red) medially. The wall is particularly weak over the deep inguinal ring

Conjoint tendon mediallyPosterior wall

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Inguinal canal16

Posterior wallFloorSpermatic cord

Anterior wall

The transversus abdominis and internal oblique mm. combine to form the CONJOINT tendon that arches over the contents of the inguinal canalThe conjoint tendon attaches to the pubic crest, reinforces the posterior canal wall medially and also forms the ROOF of the canalConjoint tendon

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ROOF OF THE INGUINAL CANALIt is formed by the arched fibres of the internal oblique and transverse abdominis muscles.

Roof and anterior wall of the inguinal canal18The anterior wall of the canal is formed by external oblique muscle (orange) throughout and by internal oblique muscles (red/black/white) laterally. This wall is weak medially because of the hole in the external oblique muscle (= superficial inguinal ring).

Anterior wall

Roof is formed by the conjoint tendon and the meeting of the anterior and posterior walls of the canalSuperficial inguinal ring

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FLOORIt is formed by the grooved upper surface of the inguinal ligament; and at the medial end by the lacunae ligament

Floor of the inguinal canal20

Floor

The floor is formed by an incurving of the inguinal ligament, which is part of the external oblique muscle, forming a gutter. (Medially it forms the lacunar ligament which is not illustrated).

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SEX DIFFERENCEThe inguinal canal is larger in males than in females.

STRUCTURES PASSING THROUGH THE CANAL1.The spermatic cord in males, or the round ligament of the uterus in females, enters the inguinal canal through the deep inguinal ring and passes out through the superficial inguinal ring.2.The ilioinguinal nerve enters the canal through the interval between the external and internal oblique muscles and passes out through the superficial inguinal ring.

Inguinal canal

Anterior wall

Spermatic cord enters the inguinal canal through the deep inguinal ringPosterior wall

FloorSpermatic cord exits through the superficial inguinal ring

Deep inguinal ringSuperficial inguinal ring

Medial

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Inguinal canals why have them?Allow contents of the scrotum to communicate with intra-abdominal contentsPrevent mobile intra-abdominal contents (e.g. intestine) from entering the scrotum and possibly becoming damaged, while at the same time permitting blood vessels, nerves, lymphatics, vas deferens etc. to supply the scrotal contents

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MECHANISM OF INGUINAL CANALThe presence of the inguinal canal is the cause of weakness in the lower part of the anterior abdominal wall. This weakness is compensated by the following factors

Obliquity of the inguinal canalThe two inguinal rings do not lie opposite to each other. Therefore, when the intra-abdominal pressure rises the anterior and posterior walls of the canal are approximated, thus obliterating the passage. This is known as the flap valve mechanism.

The superficial inguinal ring is guarded from behind by the conjoint tendon and by the reflected part of the inguinal canal.

The deep inguinal ring is guarded from the front by the fleshy fibres of the internal oblique.

Shutter mechanism of the internal oblique This muscle has a triple relation to the inguinal canal. It forms the anterior wall, the roof, and the posterior wall of the canal. When it contracts the roof is approximated to the floor, like a shutter.

Ball valve mechanismContraction of the cremaster helps the spermatic cord to plug the superficial inguinal ring

Slit valve mechanismContraction of the external oblique results in approximation of the two crura of the superficial inguinal ring . The integrity of the superficial inguinal ring is greatly increased by the intercrural fibres.

Hormonesmay play a role in maintaining the tone of the inguinal musculature

Whenever, there is a rise in intra abdominal pressure as in coughing , sneezing, lifting heavy weights all these mechanisms come to play, so that the inguinal canal is obliterated, its openings are closed, and herniation of abdominal viscera is prevented.

STRUCTURES RELATED WITH INGUINAL CANAL

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From within outwards, these are as follows:

1.The internal spermatic fascia , derived from the fascia transversalis; it covers the cord in its whole extent .

2.The cremasteric fascia is made up of the muscle loops costituting the cremaster muscle, and the intervening areolar tissue. It is derived from the internal oblique and transversus abdominis muscles.

Round ligament of uterus The round ligaments are two fibro muscular flat bands ,10 to 12 cm long, which lie between the two layers of broad ligament , begins at the lateral angle of the uterus, passes through the deep inguinal ring ,traverses the inguinal canal and merges with the areolar tissue of the labium majus

Hesselbachs (Inguinal) Triangle is an important structure as it is the site for direct hernias. The triangle has the following borders:1) Medial border of rectus abdominus(medially)2) Inguinal ligament (inferiorly)3) Inferior epigastric vessels(laterally)

HESSELBACHS TRIANGLE

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CLINICAL ANATOMY OFINGUINAL CANAL

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A Brief Mention of Hernias

Hernias are abnormal outpouchings of the abdominal contents (such as the small intestine) from the cavity in which they belong. There are two main types of hernias that occur at the inguinal region. Direct hernia and indirect hernia.

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The posterior wall of the canal is particularly weak laterally because of the deep inguinal ringThe anterior wall opposite the deep ring is reinforced laterally by the internal oblique muscles.A hernia (e.g. of small bowel) that comes through the deep inguinal ring will have to travel along the inguinal canal as it cannot push into the reinforced layers of muscle in the anterior wall of the canal directly opposite the deep inguinal ring

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The anterior wall of the canal is weak medially where the superficial inguinal ring is situatedThe posterior wall, opposite the superficial ring, is reinforced medially by the conjoint tendon that is formed by fibres of the internal oblique and transversus abdominis musclesAbdominal contents cannot normally force themselves through the superficial ring directly because of the reinforced posterior wall medially

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Indirect or oblique hernia These are the most common inguinal hernias, in this the contents of the abdomen enter the deep inguinal ring and traverse the whole length of the inguinal canal to come out through the superficial inguinal ring

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Coverings of indirect herniasPeritoneumInternal spermatic fascia(from transversalis fascia)Cremaster muscle & fascia(from transversus abdominis andinternal oblique mm.)External spermatic fascia(from external oblique m.)Superficial fasciaSkin44

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Direct Hernias Direct hernias occurs lateral to the epigastric vessels. They do not protrude through any ring, but through an area of weakness in the posterior wall of the inguinal canal; this area is likely to be Hesselbachs Triangle. The hernia is often parallel to the spermatic cord, but almost never enters the scrotum

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Coverings of direct herniasPeritoneumTransversalis fasciaConjoint tendonExternal oblique aponeurosisSuperficial fasciaSkin46

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Inguinal hernia results because pressure finds weak spot at inguinal canal

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THANK YOU

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