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Epididymis

Last revised by Dr Haiying Chen on 24 Nov 2021

The epididymis (plural: epididymides) is situated adjacent to the testis within the scrotal sac. Its primary function is the collection, maturation and transport of sperm via the ductus deferens.

The epididymis is an elongated structure, posterolateral to the testis. It can be subdivided into three anatomic regions: head (also known as globus major), body and tail (also known as globus minor). 

The total length of the epididymis is usually 6-7 cm but it is tightly coiled and would measure 6 m if uncoiled 3.

The head is the largest and most prominent part and is found at the superior pole of the testis. The head of the epididymis measures approximately 5-12 mm in length and may have a small projection called the appendix of the epididymis 3. The tail of the epididymis is found at the inferior pole of the testis 3.

Seminiferous tubules carry sperm via tubuli recti into a dilated space within the mediastinum testes known as the rete testis. The rete testis drains into the epididymis through 10-15 efferent ductules 1. Efferent ducts in the head of the epididymis unite to form a single duct in the body and tail region (globus minor), which continues as the ductus deferens.

The deferential artery (a branch of superior vesical artery or sometimes inferior vesical artery), a branch of the testicular artery (a branch off the aorta), and branches of the cremasteric artery (branch off the inferior epigastric artery) form anastomoses to supply the epididymis 5.

Some sources state that the epididymis is supplied only by branches of the testicular artery 5.

See article: Testicular and scrotal ultrasound

The normal epididymis is iso-to-hyperechoic to the testes, with equal or less vascularity on color and spectral Doppler. The head of the epididymis is visualized superior and lateral to the testes, while the body and the tail are smaller with variable locations 2.

  • T1: epididymis has homogenously intermediate signal
  • T2: epididymis has hyperintense signal, with slightly lower signal than testes

"Epididymis" derives from the Greek έπιδιδυμίς (έπί "upon" + δίδυμος "testis"). Δίδυμοι (meaning "twins") was an older term for both testes and ovaries. Galen originally used the term to refer to what we now call the tunica, and used the term "parastates" ("standing beside") for what we call the epididymis. Herophilos may have been the first to use it in the current sense.

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Cases and figures

  • Figure 1: testes and spermatic cord (Gray's illustration)
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  • Figure 2: testes and epididymis (Gray's illustration)
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  • Case 1
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