Origin and Location
The cremaster muscle originates from the internal oblique muscle of the abdomen (m. obliquus internus abdominis). Some of the lower muscular fascicles of this muscle, running along the inguinal ligament, separate to form the m. cremaster.
Topographically, the muscle passes through the inguinal canal (canalis inguinalis). It forms part of the contents of the inguinal canal in males, accompanying the spermatic cord. From the inguinal canal, the muscle descends into the scrotum, where it becomes part of the fascial and muscular layers enclosing the testis and spermatic cord.
Structure and Coverings
Unlike the superficial dartos fascia (tunica dartos) of the scrotum, which contains smooth muscle cells, the m. cremaster is composed of skeletal muscle.
The muscle is enclosed by its own fascia — the cremasteric fascia (fascia cremasterica). Within the spermatic cord (funiculus spermaticus) and scrotal wall, it forms a distinct layer:
- Superficial to it lies the external spermatic fascia (fascia spermatica externa), derived from the aponeurosis of the external oblique muscle of the abdomen.
- Deep to it lies the internal spermatic fascia (fascia spermatica interna), derived from the transversalis fascia (fascia transversalis).
In the layered structure of the testicular coverings, the m. cremaster constitutes a separate muscular layer (the 6th layer from the skin inward). In the context of the scrotal wall layers, it is generally considered the 5th layer.
Function and Cremasteric Reflex
The muscle's primary role is elevation of the testis in response to thermal or tactile stimuli to protect it from injury and help regulate testicular temperature.
The muscle is evaluated clinically via the cremasteric reflex:
- Elicitation: Stroking the skin of the upper medial thigh with a blunt instrument.
- Response: Immediate elevation of the testis due to contraction of the m. cremaster.
- Reflex arc level: Spinal cord segments L1 – L2.
Blood Supply
The muscle is supplied by the cremasteric artery (a. cremasterica), a branch of the inferior epigastric artery.
Venous drainage occurs via scrotal veins into the external pudendal veins and the pampiniform plexus (plexus pampiniformis), which eventually forms the testicular vein (v. testicularis).
Clinical Significance (Hernia Surgery)
Knowledge of the topography of the m. cremaster is crucial during inguinal hernia repairs, such as Bassini or Lichtenstein repairs.
During surgical exposure and isolation of the hernia sac, the surgeon secures the spermatic cord. To locate the wall of the hernia sac—which has a characteristic whitish appearance—the coverings of the spermatic cord, including the fibers of the cremaster muscle (m. cremaster), are incised. The sac is then identified among the cord structures, isolated, opened, and managed, followed by posterior inguinal canal wall reinforcement.