Testis

The testes (also known as the testicles) are the male gonads and are contained within the scrotum. The testes are responsible for production of sperm and testosterone.

Gross anatomy

At birth, testes measure approximately 1.5 cm (length) x 1 cm (width), reaching ~4 mL volume at puberty ¹.

Normal adult testes are ovoid and measure approximately 3 cm (AP) x 2-4 cm (TR) x 3-5 cm (length), with a volume of 12.5-19 mL ².  However, the size of the testes decreases with age.

From the mediastinum testis, several radiating septa extend into the testis forming 250-400 lobules. Each of these lobules contains 2-3 seminiferous tubules. Seminiferous tubules carry the sperm via tubuli recti into a dilated space within the mediastinum testis which is known as the rete testis, which drains into the epididymis through 10-15 efferent ductules ¹. Efferent ducts in the head of the epididymis (globus major) unite to form a single duct (globus minor) in the body and tail region, which continues as the ductus deferens (a.k.a. vas deferens). 

Blood supply

The testes are supplied by testicular arteries, arising from the aorta, just below the origin of renal arteries. The testes are drained by a plexus of veins (pampiniform plexus), which continue as the testicular veins. The right testicular vein directly drains into the inferior vena cava (IVC), while the left testicular vein drains into the left renal vein.

Lymphatic supply

Lymphatic drainage of the testes is through lymphatics running with the testicular arteries, draining into para-aortic lymph nodes.

Innervation

Testes receives autonomic (sympathetic) innervation from the spermatic plexus, originating from the para-aortic ganglia.

Variant anatomy

• polyorchidism (very rare)
  • bilobed testes: thought to be a variant of polyorchidism
• testicular appendages: may arise from the testes and have a variable incidence

Radiographic appearance

Ultrasound

See also: Testicular and scrotal ultrasound

The normal testes have a homogenous, moderately echogenic pattern. A testicle is surrounded by a thin echogenic fibrous band, which represents the visceral component of the tunica vaginalis and the tunica albuginea. In the absence of intrascrotal fluid, the tunica is usually visualized only at its hilum as an echogenic structure, where it invaginates into the testis, to form the mediastinum testis.

Doppler

Intratesticular arteries are low resistance vessels with a mean resistive index (RI) of 0.62 (0.48-0.75) ¹.

MRI

• T1: testes and epididymides have homogenously intermediate signal
• T2: testes have hyperintense signal, with slightly lower signal in the epididymides

Tunica albuginea has hypointense signal on both T1 and T2 weighted images.

History and etymology

"Testicle" is thought to arise from the Latin word "testis" (witness, one who "testi"fies"testifies). The connection between a witness and the term for a male sex organ is thought to be that the testicles are a sign of virility and under Roman law no person was allowed to be a witness unless his testicles were present (i.e. neither eunuchs nor women were felt to be reliable witnesses!) ⁴

Related pathology

• undescended testes
• torsion testes
• orchitis
• testicular tumours