Cremasteric Reflex

Excerpt

Superficial reflexes are motor responses that occur when the skin is stroked. The cremasteric reflex is a superficial reflex found in human males that is elicited when the inner part of the thigh is stroked. Stroking of the skin causes the cremaster muscle to contract and pull up the ipsilateral testicle toward the inguinal canal. Like other superficial reflexes, it is simply graded as present or absent. A female counterpart of the cremasteric reflex is the Geigel reflex. In the female, it involves the contraction of muscle fibers along the upper part of the Poupart or inguinal ligament and is sometimes called the inguinal reflex. Similar to the other superficial reflexes, such as the abdominal and the normal plantar reflexes, the cremasteric reflex is not usually tested in contrast to the deep tendon, the brainstem, and primitive reflexes. The cremasteric reflex is most commonly performed in the evaluation of acute scrotal pain and the assessment for testicular torsion that is commonly associated with an apparent loss of the reflex.

Anatomy

The cremaster muscle is a paired structure made of thin layers of striated and smooth muscle. The muscle's name is derived from a Greek word meaning “suspender.” In reality, the muscle has 2 parts, a lateral and medial cremaster muscle. The lateral muscle originates from the internal oblique muscle and inguinal ligament, and the medial cremaster muscle usually originates from the pubic tubercle but sometimes from the lateral pubic crest. The muscles that are covered by a fascia loop over the spermatic cord and testicles and insert into the testicle tunica vaginalis. In the female, the cremaster muscle is found on the round ligament.

The cremasteric artery, a branch of the inferior epigastric artery, along with anastomotic flow from the other arteries supplying the scrotum, provides blood flow to the muscles.

The innervation for the cremasteric reflex is provided by the sensory and motor fibers of the genitofemoral nerve that originates from the L1 and L2 spinal nerve nuclei. Stroking of the inner thigh stimulates the sensory fibers of the genitofemoral and ilioinguinal nerves. After these sensory nerves synapse in the spinal cord, the motor fibers of the genitofemoral nerve are activated, and the cremaster muscle is caused to contract with the resultant elevation of the ipsilateral testicle. Because it is a superficial reflex, it is different from muscle stretch reflexes. For the cremasteric reflex, the sensory signal has to ascend the cord to the brain before descending again to reach the motor neurons.

Indications

The cremasteric reflex can be performed in assessing scrotal pain. While some studies report a high correlation between loss of cremasteric reflex and testicular torsion, there are a surprising number of studies reporting the persistence of the reflex during verified cases of torsion. Additionally, other studies confirm that it is also absent from significant numbers of males and more so at younger ages. The frequency of the intact reflex has been reported in 61.7% to 100% of boys between 24 months and 12 years of age.