Fig. 3.1
An anterior view of the pelvis illustrating the large vessels traversing the inguinal region
Superficial Arterial Supply
Proximal superficial branches of the femoral artery supply this part of the groin. The specific branches, from lateral to medial, are the superficial circumflex iliac artery, the superficial epigastric artery, and the superficial external pudendal artery (Fig. 3.2).
Fig. 3.2
Illustration of the superficial branches that supply the inguinal area
Superficial Circumflex Iliac Artery
The superficial circumflex iliac artery is the smallest of the three main superficial branches. It pierces through the fascia lata as its origin is usually lateral to the saphenous opening. It travels superolaterally, in the direction of the anterior superior iliac spine, to become highly branching and supplies the region of the skin over the lateral third of the inguinal ligament and the iliac crest. This artery also supplies the superficial fascia and superficial inguinal nodes along its course. It anastomoses with branches of the deep circumflex iliac, superior gluteal, and lateral circumflex femoral artery.
The superficial circumflex artery can be divided into three subtypes: type 1, type 2, and type 3. In type 1 or archetype, it originates below the inguinal ligament and may have branches. Type 2 is seen when it arises from the deep circumflex iliac artery. In type 3, the artery is absent. Type 3 has a prevalence of about 17%.
Superficial Epigastric Artery
Medial to the superficial circumflex iliac artery, and following a more vertical course, is the superficial epigastric artery . Typically, it originates from the anterior aspect of the femoral artery about 2–5 cm distal to the inguinal ligament. It ascends anterior to the inguinal ligament up to the region just below the umbilicus. It supplies the skin, superficial fascia, and inguinal nodes in midinguinal area. Branches of the superficial epigastric artery anastomose with those of the contralateral artery. It also communicates with the inferior epigastric artery.
Variations in the origin of the superficial epigastric artery have been previously reported. It often originates from a trunk that is shared with the superficial circumflex iliac artery. It may also branch from the pudendal artery or the profunda femoris artery. Results from studies on the prevalence of this vessel vary widely from 58 to 90%.
Superficial External Pudendal Artery
The superficial external pudendal artery has a medial origin on the femoral artery. It has a medial route, coursing in the direction of the pubic symphysis where it traverses the spermatic cord in males and the round ligament in females. It supplies cutaneous blood flow to the inferior abdomen, the penis, and the scrotum in males and the labia majora in females. It anastomoses with branches of the internal pudendal artery.
The source of the superficial external pudendal artery is almost always the femoral artery, but rarely it may originate from the profunda femoris artery. It has also been observed to share a common trunk with the superficial epigastric artery.
Deep Arterial Supply
The deep layer of the groin obtains its blood supply mainly from two arteries: the deep circumflex iliac and the inferior epigastric (Fig. 3.3). More superiorly, some of its supply may be derived from the anterior branches of the subcostal and lumbar arteries. The ascending branch of the deep circumflex iliac, along with the anterior branches of the subcostal and first four lumbar arteries, can be found between the internal oblique and transversus abdominis muscles. Here, their vascular networks supply the muscles that they come into contact with.
Fig. 3.3
Illustration of the deep vessels that supply the inguinal area
Deep Circumflex Iliac Artery
The deep circumflex iliac artery branches off of the lateral aspect of the external iliac artery and supplies the deep lateral groin. It’s a laterally running nerve that forms many anastomoses. Its initial direction is toward the anterior superior iliac spine. Up to this point, it remains enclosed in a sheath of connective tissue formed from fibers of the transversalis fascia and the iliac fascia. Near the anterior superior iliac spine, three important things occur: (1) it anastomoses with the ascending branch of the lateral circumflex femoral artery, (2) the artery pierces the transversalis fascia and continues laterally along the inner lip of the ilium, and (3) a large ascending branch is given off. The deep circumflex iliac artery continues laterally and posteriorly to anastomose with the iliolumbar and superior gluteal arteries. The ascending branch passes through the transversus abdominis muscle just superior to its origin and continues in a cephalad direction. Here, it runs between, and supplies, the transversus abdominis and inner oblique muscles. It continues in this intermuscular plane to form anastomoses with the lumbar and inferior epigastric arteries. Small proximal branches may also anastomose with the superficial circumflex iliac artery.
Inferior Epigastric Artery
The inferior epigastric artery , a branch of the external iliac artery, has its origin just medial to that of the deep circumflex iliac artery. The inferior epigastric gives off two branches: the pubic and the external spermatic (or cremasteric). The pubic branch crosses the conjoint tendon to travel inferiorly toward the obturator artery. It forms an anastomosis with the obturator artery. When this pubic branch is large (20–30% of cases), it takes the place of the obturator to become the aberrant obturator artery. Notably, this pubic branch may also enter the inguinal (Hesselbach’s) triangle. The external spermatic branch joins with the contents of the spermatic cord in the male. Here it supplies the cremasteric muscle and other fascial layers within the cord. It also anastomoses with the testicular artery. In females, the artery is relatively smaller and supplies the round ligament.
The inferior epigastric artery , together with its accompanying vein, forms the lateral border of the inguinal (Hesselbach’s) triangle. The artery courses superomedially toward the rectus abdominis muscle, passing near the medial border of the deep inguinal ring. Thus it lies deep to the origin of the spermatic cord. While traveling anterior to the parietal peritoneum, the artery causes an observable elevated fold that is evident from an intraabdominal view of the anterior abdominal wall. This fold is called the lateral umbilical fold. Near the lateral border of the rectus abdominis muscle, in the region of the apex of the inguinal triangle, the artery pierces the transversalis fascia. It continues superiorly, just lateral to the midline, along the posterior aspect of the rectus abdominis where it passes anterior to the arcuate line. It remains between the rectus abdominis and the posterior lamina of the rectus sheath to anastomose with the superior epigastric artery (above the umbilicus) and the lower posterior intercostal arteries. During its ascension, the inferior epigastric artery also gives off several branches that anastomose with other arteries. Its branches join with branches of the superficial epigastric, circumflex iliac, and lumbar arteries. In the end, the inferior epigastric artery supplies muscles of the abdominal wall, peritoneum, and even some areas of skin over the lower abdomen via its cutaneous branches.
A few variations in the origin of the inferior epigastric artery have been noted. It may sometimes branch off of the femoral artery, in which case it ascends to enter the abdominal cavity. It is also not uncommon to have it arising from the external iliac artery via a common trunk with the obturator artery. Rarely, it may originate from the obturator artery itself from the internal iliac artery.
Veins
The veins of the inguinal region generally tend to accompany their similarly named arteries. Thus, the superficial groin will be drained by the superficial circumflex iliac , the superficial epigastric , and the superficial external pudendal veins . These three superficial veins transport their deoxygenated blood to the saphenous vein. The deeper structures of the groin will be drained mainly by the deep circumflex iliac veins and the inferior epigastric veins . These veins usually occur in pairs, or venae comitantes, for each artery, eventually combining to form one common vein. These deep veins drain into the external iliac vein—about 1 cm above the inguinal ligament for the inferior epigastric vein and about 2 cm above the inguinal ligament for the deep circumflex iliac vein.
The great saphenous vein usually joins with the femoral vein at the saphenous opening. However, it may also pierce the fascia lata prior to reaching the saphenous ring, it may be duplicated, or a venous network may replace it. Variations of the venous drainage in the vicinity of the saphenous opening are numerous. Most commonly, the superficial circumflex iliac and the superficial epigastric veins combine before joining the saphenous vein. In one variant, all three superficial veins drain directly into the femoral vein.
An inconstant vein, the thoracoepigastric vein, may be observed on the anterior abdominal wall and connects the inferior epigastric vein, or the femoral vein, with the lateral thoracic veins. This essentially communicates the inferior vena cava drainage area to that of the superior vena cava.
Variation of the external iliac vein, which drains the inferior epigastric vein and the deep circumflex iliac vein, is uncommon. Unilateral aplasia, bilateral aplasia, and duplication have all been reported.
Nerves of the Groin
The lumbar plexus originates from the ventral rami of lumbar nerves one to four. The inguinal region receives its somatic motor and sensory innervation from the terminal branches of the lumbar plexus (Fig. 3.4). The groin receives its innervation mainly from three nerves: the iliohypogastric, the ilioinguinal, and the genitofemoral. The femoral and obturator nerves, though they don’t innervate the groin, are at risk of damage due to pathology or intervention in this region. Thus, they will also be briefly mentioned as knowledge of their course is a necessity prior to manipulation of this area.
Fig. 3.4
This illustration highlights the innervation of the inguinal region by nerves originating from the lumbar plexus
Iliohypogastric Nerve
The iliohypogastric nerve commonly shares its origin with the ilioinguinal nerve. Its fibers originate mainly from L1, but it may also have some contribution from T12. It emerges anterior to the quadratus lumborum and posterolateral to the origin of the psoas muscles. It continues to course on the anterior belly of the quadratus lumborum muscle until it crosses its lateral margin. At this point, it pierces the transversus abdominis muscle and continues in the intermuscular plane between the transversus abdominis and the internal oblique muscles. It continues superior and parallel to the iliac crest and gives off a lateral cutaneous branch (iliac branch) near to the anterior superior iliac spine. The lateral cutaneous branch sits between the internal and external oblique above the iliac crest. It innervates the skin in the posterolateral gluteal region. An anterior cutaneous branch (hypogastric branch) continues between the internal oblique and the transversus abdominis. As it continues on its medial course, it penetrates the internal oblique and the external oblique aponeurosis to enter the subcutaneous area about 3 cm above the superficial inguinal ring. It innervates the skin just superior to the pubic symphysis. Apart from this sensory function, it also innervates the abdominal muscles that it comes into contact with. The iliohypogastric nerve communicates with neighboring nerves, namely, the subcostal and ilioinguinal nerves.
The lateral cutaneous branch of the inguinal nerve may sometimes be replaced by the lateral thoracic branch of T12. Another possible variation occurs when the anterior cutaneous branch supplies the pyramidalis muscle. At times the hypogastric branch may be replaced by the ilioinguinal nerve in the region of the external inguinal ring. The fibers of the hypogastric branch may also combine with those of the twelfth thoracic nerve. Instead of originating from L1, the iliohypogastric nerve may also originate from T12 and may even obtain some of its fibers from T11. The nerve may be absent in up to 20.6% of persons.
Ilioinguinal Nerve
Though the ilioinguinal nerve shares a common origin with the iliohypogastric nerve, its nerve fibers are usually solely from the L1 nerve root. It takes a similar but more inferior course to the iliohypogastric nerve. It travels above the iliac crest, piercing the transversus abdominis near the anterior superior iliac spine. Further medially it penetrates the inner oblique. It provides motor innervation to these muscles that it comes into contact with. It exits medially through the superficial inguinal ring and branches into an anterior scrotal (labial) branch, a small pubic branch, and crural branches. The anterior scrotal (or labial) branches conduct sensory stimuli from the anterior scrotum or labia majora. The small pubic branch innervates a small area at the base of the penis or clitoris and mons pubis. The crural branches innervate the upper inner thigh and inguinal crease.
Several deviations from the textbook norm have been observed with the ilioinguinal nerve. One such example is seen when it originates from L2 instead of L1. Additionally, in about 5% of cases, it may be formed from two spinal nerve roots. Previous studies have shown that the nerve originates from the lumbar plexus in about 72.5%. In 25% of cases, it arises from a common trunk with the iliohypogastric nerve.
It is surgically important to note that the ilioinguinal nerve may completely bypass the inguinal ring. At times it may pass deep to the inguinal ligament. Also, the ilioinguinal nerve may join with the iliohypogastric in cases where the former is very small. In such cases, it is replaced by a branch of the iliohypogastric nerve. In cases where the ilioinguinal nerve is absent, the iliohypogastric nerve (most commonly), the genital branch of the genitofemoral, or the femoral branch of the genitofemoral innervates its region. On the other hand, the ilioinguinal nerve may innervate nearby areas if other nerves are absent. It may partially or totally replace the lateral femoral cutaneous nerve or the genital branch of the genitofemoral nerve.
Genitofemoral Nerve
The first and second lumbar nerves both contribute to the genitofemoral nerve. As the nerve emerges, it pierces through the cephalad portion of the psoas major muscle. It continues caudally, anterior to the belly of the psoas major muscle and deep to the psoas fascia before it divides into a lateral femoral branch and a medial genital branch. The femoral branch travels lateral to the external iliac artery and continues deep to the inguinal ligament into the femoral sheath. It then pierces the anterior lamina of the femoral sheath and the fascia lata superficial and lateral to the origin of the femoral artery. The femoral branch provides sensation to an area of skin on the anterior central thigh, just inferior to the inguinal ligament. It also provides sensory innervation to the femoral artery through its connections with the femoral intermediate cutaneous nerve. The genital branch enters the deep ring of the inguinal canal and innervates the cremasteric muscle within the wall of the spermatic cord in men. Alternatively, it may pass superficial to the deep inguinal ring, traveling in the aponeurosis of the external abdominal oblique. This branch also provides sensory innervation to the anterior scrotum in men and the mons pubis and anterior labia majora in women.
The genital and femoral branches can arise from different locations in the lumbar plexus, either from L1, L2, or occasionally L3. The genital branch may also contain fibers from the T12 ventral ramus. The nerve may divide prior to exiting the psoas muscle in about 20% of cases. When the genitofemoral nerve is absent, the distribution for the genital branch is covered by the ilioinguinal nerve, while the anterior and lateral cutaneous femoral nerves innervate the territory of the femoral branch. Similarly, when the ilioinguinal nerve is absent, branches of the genitofemoral nerve may replace it.
Femoral Nerve and Obturator Nerve
The femoral nerve contains fibers originating from the L2–L4 spinal nerve roots. Initially, it travels between the lateral aspect of psoas major and the iliacus muscle. On its way to the inguinal region, it innervates the iliacus muscle. It then passes deep to the inguinal ligament and into the femoral sheath that is formed, in part, by the transversalis fascia. Also within the femoral sheath are the femoral artery and vein and the node of Cloquet. Within the femoral canal, it lies lateral to the femoral artery, though it may at times be found between the artery and the vein. The femoral nerve innervates the flexors of the hip and the extensors of the knee. It provides sensorineural innervation to the anterior thigh, anteromedial knee, medial leg, and medial foot.
Similar to the femoral nerve, the obturator nerve has contributions from L2–L4 lumbar nerves. It emerges medial to the psoas major muscle and enters the lesser pelvis dorsal to the common iliac vessels then lateral to the internal iliac vessels. It exits the pelvis through the obturator foramen after dividing into anterior and posterior branches. The anterior branch innervates the medial thigh, the hip joint, and the adductors. The posterior branch passes posterior to the adductor brevis to also supply innervation to the adductors of the hip.
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