Rigi10™ Malleable Penile Prosthesis
Also Known As
Musculus cremaster, Cremasteric muscle, Muscle of Riolan, Entire cremaster muscle of spermatic cord
Definition
The cremaster muscle is a paired anatomical structure primarily found in the male pelvis and perineum, playing a crucial role in testicular thermoregulation and protection.1 It is a thin layer of muscle that covers the testes and the spermatic cord, situated between the internal and external layers of the spermatic fascia.1 The primary function of the cremaster muscle is to elevate the testes (retraction) towards the inguinal canal, an action known as the cremasteric reflex. This reflex is vital for protecting the testes and ensuring optimal conditions for spermatogenesis by moving the testes closer to the body in response to cold temperatures or other stimuli, and allowing them to descend when the ambient temperature is warmer.1
Structurally, the cremaster muscle is complex. While traditionally considered a striated (skeletal) muscle, detailed histological studies have revealed that it is composed of distinct bundles of both striated and smooth muscle fibers embedded within connective tissue.2 The smooth muscle fibers are more abundant than previously understood and are dispersed among the striated muscle fibers rather than being arranged in distinct layers.2 This mixed composition contributes to its unique physiological properties, including a tendency for spontaneous electromyographic discharges, which are attributed to the presence of multiple motor end-plates on individual striated muscle fibers and an overall dense innervation pattern.2 Myosin immunostaining has further characterized the cremaster muscle as a slow-twitch muscle.2 Remnants of the cremaster muscle are also found in females, located adjacent to the round ligament of the uterus, though it is not as developed or functionally significant as in males.1
Clinical Context
The cremaster muscle and its associated reflex, the cremasteric reflex, are clinically significant in several contexts, primarily in urology and neurology. The cremasteric reflex is routinely tested during physical examinations to assess the integrity of the nerve pathways involved (ilioinguinal nerve for sensory input, and the genital branch of the genitofemoral nerve for motor output, corresponding to spinal cord levels L1-L2).1 Its absence or alteration can indicate neurological damage, spinal cord injury, or testicular torsion, a urological emergency where the spermatic cord twists, cutting off blood supply to the testicle. A diminished or absent cremasteric reflex on one side can be a key diagnostic sign of testicular torsion, prompting urgent surgical intervention.2
In pediatric urology, the cremaster muscle is relevant in the context of retractile testes. A retractile testis is one that has descended into the scrotum but is periodically pulled up into the inguinal canal by an overactive cremasteric reflex. This condition is common in young boys and usually resolves spontaneously as they grow and the cremasteric reflex becomes less active. However, it needs to be differentiated from undescended testes (cryptorchidism), which require medical or surgical intervention.1
The muscle itself can also be a source of chronic groin or testicular pain, sometimes referred to as cremaster muscle dysfunction or spasm. This can occur due to nerve irritation, post-surgical changes (e.g., after hernia repair), or idiopathic reasons. Treatment can range from conservative measures like physiotherapy and medication to, in refractory cases, surgical denervation or excision of cremasteric fibers.1
During surgical procedures in the inguinal region, such as hernia repair or orchiopexy (surgical fixation of a testis), the cremaster muscle is an important anatomical landmark. Surgeons must carefully identify and handle the cremasteric fibers and the associated neurovascular structures within the spermatic cord to avoid iatrogenic injury.1