The genital and femoral branches of the genitofemoral nerve. (Reprinted with permission from Dr. Maria Fernanda Rojas)
The genitofemoral nerve (GFN) arises from the L1 and L2 spinal nerves predominantly. It is part of the lumbar plexus. It is mainly a sensory nerve except for motor fibers of the cremasteric muscle. The GFN lies on top of the psoas muscle and crosses the ureter on descent. It divides into the genital and femoral branches which could happen anywhere during its course above the inguinal ligament (Fig. 7.1).
The femoral branch, a sensory branch, courses below the inguinal ligament and supplies the triangular dermatomal part over the femoral triangle. The area supplied by the genital branch is in the inguinal area inferior to that supplied by the ilioinguinal nerve (Fig. 7.2).
The genital branch crosses the inferior epigastric artery (IEA) at its lower end lateral to the junction between the external iliac artery (EIA) and IEA and enters the inguinal canal through the deep inguinal ring (Fig. 7.3). It travels along with other contents of the inguinal canal along with the spermatic cord in men and the round ligament of the uterus in women. The canal also contains the ilioinguinal nerve and testicular vessels in men or the vessel following the round ligament of the uterus in females.
Select patients with suspected genitofemoral neuralgia. Diagnosis is mainly clinical based on the history and the dermatomal distribution of pain, which is mainly neuropathic in nature (burning, paresthesia, or numbness in the lower abdomen radiating to medial thigh and into the labia majora in women and the anterior surface of the scrotum in men). Patients tend to hold a “novice skier’s” position to relieve the strain on the nerves. Spinal extension tends to exacerbate the pain. Physical examination reveals cutaneous neuropathic sensory changes and Tinel’s sign may be present on tapping along the inguinal ligament. Cremasteric reflex may be absent.
There are three different methods to scan and identify the genital branch of the genitofemoral nerve (GFN). No validated standardized technique has been described yet. Two methods are already described in the literature and the third one (method 1) is from author’s clinical experience especially from scanning female patients.
Probe: High-frequency linear probe (6–13 MHz).
Place the probe in transverse plane just below the inguinal ligament and identify the femoral artery and place it at the middle of the screen (Fig. 7.4).
The probe is then rotated to long axis to visualize the femoral artery (FA) longitudinally and moved cranially to identify the FA that becomes the external iliac artery (EIA) and dives deep into the abdomen (Fig. 7.5).
At this point, the inguinal canal appears as an oval structure (bold arrows) superficial to the FA with the round ligament (left) of the uterus or spermatic cord (right) (Fig. 7.6). Note the spermatic cord is a structure with multiple tubular structures inside (vas deferens, arteries, and vein). The probe is moved medially tracing these structures to move away from the FA.