Layers of the Scrotum (Superficial to Deep)

1. Skin

• Thin, corrugated (wrinkled), and more darkly pigmented than surrounding skin due to a high concentration of melanocytes in the basal layer of the epidermis.
• Consists of keratinized stratified squamous epithelium.
• The dermis contains hair follicles, apocrine and eccrine sweat glands, and sebaceous glands.
• No subcutaneous adipose tissue - this is replaced by the dartos layer below.
• Corresponds to the skin of the abdominal wall.

2. Dartos Layer (Tunica Dartos)

• Replaces the subcutaneous fat (hypodermis) of the abdominal wall.
• Contains smooth muscle fibers arranged in two sublayers: a superficial dartos muscle layer (DMSL) and a deep dartos muscle layer (DMDL).
• Also contains myofibroblasts embedded in elastic-fiber-rich extracellular matrix.
• Contraction of the dartos wrinkles the scrotal skin, reducing surface area and heat loss to maintain optimal temperature for spermatogenesis (about 2-3°C below body temperature).
• Apocrine and eccrine sweat glands and hair follicle roots are found between its two layers.
• Corresponds to Camper's and Scarpa's fascia (superficial abdominal fascia / Colles' fascia in the perineum).

3. External Spermatic Fascia

• An extension of the external abdominal oblique aponeurosis.
• Thin but organized layer with thick collagen bundles, nerve fibers, and blood vessels.
• A few smooth muscle fibers are detectable on its outer surface.

4. Cremaster Muscle and Cremasteric Fascia

• An elongation of the internal oblique muscle into the scrotal wall.
• Contains loosely arranged striated (skeletal) muscle fascicles surrounded by cremasteric fascia.
• Predominantly type I (slow oxidative) fibers - fatigue resistant.
• Innervated by the genital branch of the genitofemoral nerve (L1-L2).
• The cremasteric reflex (stroking the inner thigh causes ipsilateral testicular elevation) tests this at spinal levels L1-L2; it is absent on the side of testicular torsion.

5. Internal Spermatic Fascia

• Derived from the transversalis fascia (deep to the transversus abdominis muscle).
• Positioned between the cremaster muscle and the parietal layer of the tunica vaginalis.
• Mostly dense irregular connective tissue containing nerves, blood vessels, and lymphatics.

6. Parietal Layer of Tunica Vaginalis

• The innermost layer; derived from the parietal peritoneum of the abdominal cavity (processus vaginalis).
• A serous membrane lined by simple squamous (mesothelial) epithelium supported by a thin submesothelial connective tissue layer.
• Together with the visceral layer (adherent to the testis), it forms the tunica vaginalis cavity, which contains a small amount of lubricating fluid.
• Abnormal fluid accumulation here = hydrocele (congenital if processus vaginalis remains patent; acquired from infection, injury, or malignancy).

Histological Section of the Scrotal Wall

Summary Table

Mnemonic

• Skin
• Dartos
• External spermatic fascia
• Cremaster muscle and cremasteric fascia
• Internal spermatic fascia
• Tunica vaginalis (parietal layer)

• Histology: A Text and Atlas with Correlated Cell and Molecular Biology, pp. 2158-2161
• Smith and Tanagho's General Urology, 19th Edition, p. 526