Epididymis

The epididymis is a long, coiled tubular structure located along the posterior aspect of each testis. It functions primarily in the maturation, transport, and temporary storage of spermatozoa. It connects the efferent ductules of the testis to the vas deferens and plays a critical role in sperm physiology by enabling sperm to acquire motility and fertilizing capability. The epididymis is divided into three anatomical parts — head, body, and tail — and is encased within the tunica vaginalis along with the testis.

Structure

The epididymis is a single, highly convoluted duct — approximately 6 meters long if uncoiled — but compacted into a structure about 6 cm in length. It is composed of the duct of the epididymis, lined by pseudostratified columnar epithelium with stereocilia. The wall contains smooth muscle layers that increase in thickness from head to tail to aid sperm propulsion.

• Total duct length (uncoiled): ~6 meters
• Gross length (coiled form): ~6 cm

Parts of the Epididymis

• Head (Caput): Formed by the union of efferent ductules from the rete testis; lies on the upper pole of the testis
• Body (Corpus): Narrower middle portion; lies along the posterolateral aspect of the testis
• Tail (Cauda): Tapered, distal portion that continues into the vas deferens; serves as the primary sperm storage site

Histology

• Epithelium: Pseudostratified columnar with long stereocilia (non-motile microvilli for absorption and secretion)
• Lamina propria: Connective tissue supporting the epithelial lining
• Muscular wall: Smooth muscle — one layer in head, three layers in tail for peristalsis

Location

The epididymis is located along the posterior and superior aspect of the testis, within the scrotum. It lies between the testis and the tunica vaginalis. The tail of the epididymis continues directly into the vas deferens, which ascends in the spermatic cord.

Function

• Sperm Maturation: Enables sperm to acquire motility and fertilizing ability over several days
• Sperm Transport: Conducts sperm from efferent ductules to vas deferens via peristalsis
• Sperm Storage: Tail region stores mature sperm until ejaculation
• Secretion and Absorption: Contributes proteins, glycoproteins, and enzymes to the luminal environment

Blood Supply

• Arterial: Testicular artery (from abdominal aorta) and deferential artery (from inferior vesical artery)
• Venous: Pampiniform plexus → testicular vein → IVC (right) or left renal vein (left)

Lymphatic Drainage

• Para-aortic (lumbar) lymph nodes at L1 level

Innervation

• Autonomic fibers from testicular plexus
• Sympathetic: T10–T11 via renal and aortic plexuses

Embryological Development

• Derived from the mesonephric (Wolffian) duct
• Fully differentiated by the end of the first trimester

Clinical Significance

• Epididymitis: Inflammation often caused by bacterial infections or STIs; presents with scrotal pain and swelling
• Spermatocele: Benign cystic dilatation of the epididymal ducts, usually at the head
• Obstruction: Blockage can lead to obstructive azoospermia and infertility
• Congenital Absence: Seen in some cases of congenital bilateral absence of vas deferens (CBAVD), often associated with cystic fibrosis
• Surgical Relevance: Epididymectomy may be performed for chronic pain or infection unresponsive to treatment