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Tail of epididymis

The tail of the epididymis is the most distal, enlarged portion of the epididymis, located at the inferior pole of the testis. It serves as a key storage site for mature spermatozoa and connects directly to the vas deferens. The tail is highly coiled and surrounded by dense connective tissue, making it structurally robust. It plays a major role in the maturation, storage, and transport of sperm and is an important landmark in scrotal imaging and urological surgery.

Synonyms

  • Cauda epididymis

  • Epididymal tail

  • Inferior epididymal segment

Location and Relations

  • Location:

    • Situated at the inferior pole of the testis, continuous with the body of the epididymis superiorly and the vas deferens posteriorly

  • Relations:

    • Anteriorly: Inferior pole of testis

    • Posteriorly: Vas deferens and pampiniform plexus

    • Laterally: Scrotal wall and tunica vaginalis

    • Medially: Testicular hilum and vessels

Function

  • Acts as a major storage site for mature spermatozoa

  • Provides environment for sperm survival until ejaculation

  • Connects with the vas deferens for transport of sperm during ejaculation

  • Contributes to sperm maturation through biochemical interactions

Clinical Significance

  • Common site of epididymitis (inflammation, often bacterial)

  • May be involved in tuberculosis or granulomatous disease

  • Cysts and spermatoceles often originate here

  • Important landmark in vasectomy procedures (near junction with vas deferens)

  • Enlargement or mass may mimic testicular tumor on imaging

  • Trauma may lead to hematoma or rupture

MRI Appearance

T1-weighted images:

  • Tail appears as low-to-intermediate signal intensity relative to fat

  • Hemorrhage or proteinaceous cysts may appear bright

T2-weighted images:

  • Tail appears as intermediate to hyperintense signal

  • Dilated tubules or cysts appear very bright

STIR (Short Tau Inversion Recovery):

  • Normal tail: Intermediate to hyperintense signal

  • Inflammation, edema, or cysts: bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal tail: mild homogeneous enhancement

  • Epididymitis: diffuse or focal strong enhancement

  • Abscess: rim enhancement with central non-enhancing cavity

3D T2 SPACE / CISS:

  • Tail shows intermediate to mildly hyperintense signal compared to muscle

  • Surrounded by bright fluid (tunica vaginalis or cysts if present)

  • Excellent for mapping fine tubular structure and detecting cysts or nodules

CT Appearance

Non-Contrast CT:

  • Tail appears as a soft tissue density at inferior pole of testis

  • Difficult to separate from testis without pathology

  • Calcification may be seen in chronic infection or granulomatous disease

Post-Contrast CT:

  • Mild homogeneous enhancement in normal tail

  • Epididymitis: diffuse or focal increased enhancement

  • Abscess: rim-enhancing lesion with central low density

  • Cysts: low attenuation, non-enhancing

MRI images