Genitofemoral Nerve

Introduction

Genitofemoral neuralgia is a syndrome characterized by chronic neuropathic pain along the distribution of the genitofemoral nerve (GFN). The pain and subsequent impairment to quality of life can be quite debilitating for patients suffering from this condition.

Genitofemoral neuralgia is predominately reported as a result of iatrogenic nerve damage occurring during surgeries, trauma to the inguinal and femoral regions, and/or nerve entrapment. Failure to distinguish it from ilioinguinal nerve (IIN) and iliohypogastric nerve (IHN) neuralgia, due to their anatomic overlap, can obscure a definitive diagnosis and consequently delay the implementation of an effective treatment. For this reason, it is important to comprehensively understand the anatomy and distribution of the GFN in order to prevent the development of this neuropathy and manage it appropriately when it occurs.

The diagnosis is mainly based on the history and physical exam, but exclusion of other conditions, as well as diagnostic injections, are also part of the work-up. Some cases gradually improve with conservative measures; however, if they fail, the treatment is challenging and includes various minimally invasive modalities like hydrodissection, standard/pulsed radiofrequency treatment, cryoneuroablation, and spinal cord stimulation (SCS) or peripheral nerve stimulation (PNS). No high-quality studies support any of these modalities.

Clinical Presentation

Genitofemoral neuralgia was first described by Magee as “genitofemoral causalgia” and subsequently redefined by Lyon, introducing the current nomenclature.

Pain is typically unilateral. Clinical features can include intermittent or constant burning, tingling, itching or sharp pain, hypo- or hyperesthesia, allodynia, hyperalgesia, and paresthesia in the distribution of the GFN that may disturb sleep at night. These symptoms can be aggravated by coughing, sitting up, side-bending to the contralateral side, abducting the ipsilateral thigh, having peristaltic movements, and undergoing the Valsalva maneuver.

Pain radiating to the skin of the genitalia (scrotum or labia majora), especially with sensory changes in the groin area, also raises the possibility of genitofemoral neuralgia ( Fig. 18.1 ). Female patients often report pelvic pain and dyspareunia. Chronic unexplained vulvar pain has been reported in as many as 7% of woman aged 18 to 64 years in the United States and can be elicited by maximal hip flexion. In males, the cremaster reflex can be absent.

With regards to the great anatomical variability of the innervation of the groin and genital area, some authors suggest using the term “abdominoinguinal pain syndrome” to describe chronic pain conditions in this region.

Etiology

The etiology of GFN neuralgia could be traumatic or idiopathic. Most cases result from surgery (e.g., herniorrhaphy, appendectomy, hysterectomy, abdominoplasty, orchidectomy, aortic aneurism repair, failed lumbar surgery, nephrectomy, vasectomy, urethral sling, thermal damage from renal radiofrequency lesioning, laparoscopic procedures) or accidental causes such as blunt abdominal trauma, femoral catheterization, stretch trauma (e.g., pregnancy), retroperitoneal tumors, and endometriomas in the canal.

The incidence of clinically significant chronic postoperative inguinal pain (CPIP) ranges from 10% to 12% and decreases with time after surgery. The prevalence of this chronic debilitating pain affecting normal daily activities or work is approximately 0.5% to 6%.

Systematic reviews have found similar risk factors for developing CPIP, such as young age, female gender, a high level of preoperative and postoperative pain intensity, lower preoperative optimism, operation for a recurrent hernia, open repair technique, heavy-weight mesh, and postoperative complications (hematoma, infection).

Idiopathic GFN neuralgia is a rarity, although it has been reported. It could result from musculoaponeurotic pathology, such as tight fascial planes causing entrapment at the paravertebral or inguinal area, iliac crest, or rectus muscle border. Even in these “idiopathic” cases, a careful history often reveals a traumatic injury that includes heavy lifting, with a feeling of a “pop” in the abdominal area.

Differential diagnosis includes: important intraabdominal and pelvic pathologies (which are usually excluded by the time the patient gets to a pain physician), recurrent herniation (difficult to assess, may cause a diagnostic challenge as imaging modalities often do not give a definitive answer), infection, abscess, suture granuloma, IIN neuralgia and/or IHN neuralgia, lumbosacral radiculopathy and plexopathy, abdominal cutaneous nerve entrapment syndrome, and sacroiliac/iliolumbar pathology, which may refer pain to the groin. History-taking should include questions related to these conditions too.

Anatomy

The GFN is a component of the lumbar plexus. The GFN, IHN, and IIN are called “border nerves” of the lumbar plexus, as they are responsible for the innervation of the area (border) between the abdomen and legs.

The GFN (formerly also known as the genitocrural nerve) originates from ventral rami of the L1-L2 spinal nerve roots within the psoas muscle. It pierces the psoas muscle (at around the L3-L4 level), descends on the psoas’ anteromedial surface under the muscle’s fascia, passes the ureter posteriorly, and divides into two branches: the femoral and genital branches ( Fig. 18.2 ). In approximately 20% of the individuals, the nerve bifurcates more proximally, in the upper part of the psoas muscle.

The femoral branch (lateral and caudal) travels with and lateral to the external iliac artery, then goes through the fascia lata, enters the femoral sheath posterior to the inguinal ligament, runs lateral to the femoral artery, and gives off sensory branches innervating the skin area above the femoral triangle on the anterior superior part of the thigh ( Fig. 18.3 ).

The genital branch (medial and ventral), also known as the external spermatic nerve in males, descends along the psoas muscle toward the inguinal canal. On its course, it passes the inferior epigastric artery just lateral to the point where it converges with the external iliac artery and enters the inguinal canal via the ventral aspect of the deep inguinal ring. In males, it travels with the spermatic cord, innervating the cord itself and the skin of the scrotum. In males, the genital branch supplies motor innervation to the cremaster muscle (cremasteric reflex) by entering the inguinal canal through the deep inguinal ring and traveling along the posteromedial aspect of the spermatic cord parallel to the cremasteric vein. The location of the nerve within the spermatic cord can be variable (dorsal, ventral, inferior), but it also can travel outside of the spermatic cord in 3% of individuals.

In females, the GFN travels along the round ligament of the uterus and the adjacent vessels, giving off sensory branches to the labia majora and the skin of the mons pubis. The genital branch innervates the skin area just superior to the area supplied by the IIN. There can be significant overlap in the cutaneous innervation with other inguinal nerves (IIN and IHN). Iwanaga et al. suggested changing the nomenclature to medial and lateral branches instead of genital and femoral branches, respectively, due to the great variability of the originating branches and the innervated area.