Inguinal Region Anatomy

The inguinal region of the body, also known as the groin, is located on the lower portion of the anterior abdominal wall, with the thigh inferiorly, the pubic tubercle medially, and the anterior superior iliac spine (ASIS) superolaterally. The inguinal canal is a tubular structure that runs inferomedially and contains the spermatic cord in males and the round ligament in females. The floor of the inguinal canal is the inguinal ligament, otherwise known as the Poupart ligament, which is formed by the external oblique aponeurosis as it folds over and inserts at the ASIS down to the pubic tubercle. This folded edge is called the shelving edge and is important for surgeons in hernia repairs. The inguinal canal is a conduit where structures pass, which has significance from an embryological and pathological standpoint.

Embryology

Formation of the inguinal canal in males occurs concurrently with testicular descent prior to birth. The testes originate in the posterior abdominal cavity and, through certain signals, descend and ultimately reside in the scrotal cavity. This descent of the testis in males creates an inherent weakness in the abdominal wall at the inguinal canal. This weakness is important in the development of inguinal hernias. During normal testicular descent, the testis migrates caudally and traverses through various layers of the abdominal wall to end up in the scrotum. In females, the final event results in the ovum descending into the pelvis.

This process of testicular decent is assisted by a structure known as the gubernaculum, which forms on the inferior aspect of the gonad and signals descent and ultimately adherence of the gonad in its final destination. Failure for this event to occur in males leads to an undescended testis (testicle), otherwise known as cryptorchidism.

The muscle and fascial layers of the anterior abdominal wall continue inferiorly to form the layers covering the spermatic cord as it continues through the inguinal canal and into the scrotum. Around the 12th week of gestation, the processus vaginalis forms, which is an embryonic developmental outpouching of the peritoneum. ^[1] Ultimately, the connection of the processus vaginalis with the peritoneal cavity obliterates and it becomes a serous sac surrounding the testis, called the tunica vaginalis testis.

Inguinal region anatomy is illustrated in the image below.

The inguinal canal has 2 openings: the deep (internal) inguinal ring and the superficial (external) inguinal ring. The boundaries of the canal are as follows: ^[2]

• Posterior wall - Transversalis fascia laterally; conjoint tendon medially

• Anterior wall - Internal oblique muscle laterally and aponeurosis of external oblique muscle

• Roof - internal oblique and transversus abdominis muscles

• Floor - Inguinal ligament and lacunar ligament (medially)

The contents of the inguinal canal in males consist of the spermatic cord (with the genital branch of the genitofemoral nerve) and the ilioinguinal nerve. For females, the contents include the round ligament, genital branch of the genitofemoral nerve, and the ilioinguinal nerve. It should be noted that the ilioinguinal nerve passes through the superficial ring but does not completely run through the entire inguinal canal. ^[1]

The ilioinguinal nerve is a direct branch off the first lumbar nerve (L1). It provides sensation to the upper and medial thigh, as well as the perineum anteriorly. In men, it innervates the anterior aspect of the scrotum and the skin around the area of the root of the penis. In women, it provides sensation to the skin of the mons pubis and labia majora. This nerve also plays a role in the afferent portion of the cremasteric reflex, while the femoral branch of the genitofemoral nerve plays the major afferent role. ^[1]

The genital branch of the genitofemoral nerve is derived from L1/L2 spinal nerve roots. This nerve provides motor function to the cremaster muscle, as well as sharing in sensory innervation to the scrotum in males and labia in females. This nerve also provides the efferent portion of the cremasteric reflex. ^[1]

Special care must be taken to protect this nerve during Lichtenstein repair of a hernia, as it is quite susceptible to damage. Lichtenstein repair is one of the open methods used to treat inguinal hernias. While some techniques use suturing to repair the defects associated with inguinal hernias, the Lichtenstein technique uses mesh to cover the defect. The mesh is sutured at the internal oblique muscle. Since the nerve passes in between the internal and external oblique muscles, suturing the mesh at the internal oblique for the hernia repair makes the nerve vulnerable to damage. ^[3] If this occurs, the patient may experience hyperesthesia or hypoesthesia of the innervated area.

The spermatic cord is covered with 3 layers, as follows: ^[1]

• The innermost layer consisting of the internal spermatic fascia, which is derived from the transversalis fascia

• The cremasteric fascia, which is derived from the internal oblique muscle

• The outermost layer consisting of the external spermatic fascia, which is derived from the deep fascia of the external oblique

The spermatic cord is formed by various nerves and vessels that connect to the testis. The classic description of the components of the spermatic cord is of 3 arteries, as follows:

• Artery to the ductus deferens (or vas deferens), testicular artery, cremasteric artery

• Pampiniform plexus, ductus deferens (vas deferens), lymphatics

• Genital branch of the genitofemoral nerve (L1/L2)

Testicular anatomy is illustrated in the image below.

Hernias

An inguinal hernia is the protrusion of intra-abdominal contents through a defect in the abdominal wall. It can be fat, bowel, or, in some cases, the genitourinary tract. The 2 types of inguinal hernias are direct inguinal hernias and indirect inguinal hernias.

An indirect inguinal hernia forms as a result of the failure of the processus vaginalis to fully obliterate. When it remains open, the potential for herniation occurs. This is why it is thought to be congenital in nature. This hernia lies lateral to the inferior epigastric artery. It passes through the deep (internal) inguinal ring and may pass through the entire inguinal canal and into the scrotum, depending on the patency of the processus vaginalis.

The second type of inguinal hernia is the direct hernia. This hernia forms as a result of weakening of the posterior wall of the inguinal canal, more specifically within a region called the "Hesselbach triangle." It is defined medially by the rectus abdominis muscle, laterally by the epigastric vessels, and inferiorly by the inguinal ligament.

Conditions that cause increased abdominal pressure rises the likelihood of direct inguinal hernia formation. Thus, it is known as an acquired hernia. The herniation protrudes medially to the inferior epigastric artery. ^[1]

Hydrocele

Hydrocele, like an indirect inguinal hernia, is the result of persistence of the processus vaginalis, and they may exist together. In this case, the persistence of the processus vaginalis leads to excessive fluid accumulation in the scrotum and around the testis. The amount of fluid present depends on the patency of the processus vaginalis. ^[2] If the processus vaginalis remains open, the hydrocele is termed communicating because persistent communication exists between the abdominal and scrotal cavities. The hydrocele can increase and decrease in size with gravity and throughout the day. This needs to be corrected with surgical excision of the hydrocele/hernia sac and repair of the hernia defect, if necessary.

Sexually Transmitted Diseases and Inguinal Symptoms

Certain sexually transmitted diseases (STDs) may manifest inguinal lymphadenopathy. Lymphogranuloma venereum (LGV) is an STD caused by the bacterium Chlamydia trachomatis. The first stage of this disease consists of small painless papules and papules that tend to ulcerate. Within 2-6 weeks, the second stage of the disease occurs, which involves painful inguinal lymphadenopathy. These lymph nodes may coalesce and form buboes. ^[4] Another STD known as chancroid causes inguinal lymphadenopathy. This disease is caused by the bacterium Haemophilus ducreyi. This disease is characterized by painful ulcerative lesions on the genitalia. Within 1-2 weeks, patients may experience painful inguinal lymphadenopathy. ^[5]

Surgical Considerations

The inguinal region is notable for the spectrum of diseases presenting in this anatomic location. Surgical implications ensue with many different approaches for these clinical entities.

Radical Orchiectomy

Testicular cancer is becoming one of the most curable forms of cancers, in part because of advances in chemotherapeutics and in surgical techniques. Patients with testicular cancer must have their testicle removed for ultimate cure. The testis is removed in a procedure known as a radical inguinal orchiectomy with high ligation of the spermatic cord. ^[6]

In this procedure, the testis is removed via an incision made superior and parallel to the inguinal canal. Once this incision is made and deepened through the Camper and Scarpa fascias, the external oblique aponeurosis is incised sharply heading inferomedially through the external ring. The ilioinguinal nerve is seen to lie over the spermatic cord. This is retracted gently, and the spermatic cord is then dissected around and freed up completely. A Penrose drain is used as a tourniquet to prevent the possible spread of cancer via the compression of vessels and lymphatics. The testis is then delivered through the inguinal canal and freed from its gubernacular attachments. The spermatic cord is then divided by double-clamping and is suture-ligated, tied, and excised. The external oblique aponeurosis is then closed by sutures to prevent hernias.

A scrotal approach for radical orchiectomy is not advised due to distinct lymphovascular drainage of testicle and scrotal wall and layers, avoiding any cancer dissemination.

Inguinal Region Tumors

Tumors of the spermatic cord or inguinal region are quite rare. Clinical distinction between inguinal hernias, which are very common in this region, and tumors, a rare entity, is even more challenging when based on history and physical exam.

Tumors of the spermatic cord are usually benign (70-80%), and most are simple lipomas that are also found accompanying most of the inguinal hernias. Among malignant tumors of the spermatic cord, sarcomas are the most common type. Rhabdomyosarcomas are the most aggressive type and are the predominant type in children. The other histological types of sarcomas, namely liposarcomas, leiomyosarcomas, and fibrosarcomas, are most frequently encountered in the adult population. Of all liposarcomas in the body, only 12% are found in the inguinal region and the spermatic cord more specifically, making them relatively infrequent in the clinical setting.

The treatment is usually orchiectomy with a large local excision to ensure negative margins of resection, since these tumors can recur. ^[7]

Cryptorchidism

Cryptorchidism refers to a testis that has not completely descended and, as such, is not found in the scrotum. Prior to birth, the testes reside within the abdomen in the fetus. The testis then begins to migrate towards the internal inguinal ring. Between 28 and 40 weeks’ gestation, the testes begin transinguinal migration, which ultimately leads to placement within the scrotum. For patients with cryptorchidism, it is recommended that the testis be placed in the scrotum if it has not migrated on its own within 6 months.

The undescended testis is found most of the time along the inguinal canal and is referred to as cryptorchid. With surgical exploration and orchiopexy of the testicle in the scrotum, the patient has a better chance of fertility and is able to perform testicular self-examinations to check for cancer. It is important for the patient to be able to examine himself because patients with cryptorchidism have a significantly increased risk of testicular cancer. ^[8]

Lymph Nodes

Lymph nodes in the inguinal region receive drainage from the penis, scrotum, and vulva. Patients with cancer or STDs may acquire lymphadenopathy in this region.

Penile cancer

Penile cancer is a rare but serious disease found in certain parts of Africa and South America. This is one of the types of cancer in which primary metastasis occurs through the lymphatic system. The first site of penile cancer spread is the superficial inguinal lymph nodes. It is very important to identify these nodes because they are important in the staging and treatment of patients with penile cancer.  Inguinal lymph node dissection are performed by urologists without any signs of nodal spread or metastasis in order to allow a more accurate staging. This helps guide further treatment in achieving cure for some patients. ^[9]

Testicular cancer

Patients with testicular cancer do not primarily have inguinal lymphadenopathy. Testicular cancer typically spreads to lumbar lymph nodes, specifically to preaortic and lateral aortic nodes. However, testicular cancer may metastasize to the superficial inguinal nodes if there is excessive retroperitoneal involvement, scrotal invasion, or if scrotal orchiectomy is performed. ^[10]

The following image shows the template for superficial inguinal lymph node dissection for a patient with penile cancer.

Inguinal Hernia Repair: Laparoscopic Versus Open Repair

Symptomatic inguinal hernias require surgical repair. The major indication for repair is to prevent incarceration. This occurs when the bowel becomes trapped and strangulated in the hernia defect, thus stopping blood flow to the bowel segment. This can lead to bowel necrosis if not reduced within 6 hours when the obstruction is complete.

Hernias can be repaired using either an open technique or a laparoscopic technique. In both procedures, the goal is to remove the hernia sac, with repair of the inguinal canal. The repair can be performed by reapproximating the patient’s own tissues to minimize and close the defect. If the defect is severe enough or the abdominal muscle wall is very weak, a heterogenous material such as a polypropylene mesh is used for reinforcement.

With laparoscopic repair, the 2 techniques used are the completely extraperitoneal repair and the transabdominal preperitoneal patch.

Many studies compared use of mesh that is strongly advised in laparoscopic inguinal hernia repair; other studies compared the use of glue and other alternatives like staples or sutures for mesh fixation. Postoperative pain is better with glue, with similar outcomes. ^[11]  Amidst discussions of raising costs for inguinal hernia repair procedures, the new introduced robotic approach comes to add even more costs to an increasingly expensive surgery.

The advantages of open versus laparoscopic procedures have been debated. Laparoscopic procedures have the advantage of a less invasive approach with decreased morbidity, decreased pain, and faster recovery. However, compared with open procedures, laparoscopic repair also involves other potential risks including bowel obstruction, bladder damage, and potential neurovascular damage. ^[12]