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Head of epididymis

The head of the epididymis, also known as the caput epididymis, is the enlarged superior portion of the epididymis. It is formed by the coiled efferent ductules that emerge from the posterior superior aspect of the testis. The epididymal head is the largest segment of the epididymis and is positioned at the upper pole of the testis. It serves as the initial storage and maturation site for spermatozoa.

Because of its location and intimate relation to the testis, the head of the epididymis is often evaluated in scrotal imaging for conditions such as epididymal cysts, spermatocele, torsion, infection, or tumors.

Synonyms

  • Caput epididymis

  • Globus major

  • Superior pole of epididymis

Location and Structure

  • Location:

    • Situated at the superior pole of the testis

    • Attaches to the upper posterior aspect of the testis

  • Structure:

    • Formed by the convergence and coiling of 12–20 efferent ductules from the testis

    • Enlarged and rounded in shape compared to the body and tail of epididymis

    • Continuous inferiorly with the body of the epididymis

Relations

  • Superiorly: Upper pole of the testis

  • Anteriorly: Tunica vaginalis (visceral layer)

  • Posteriorly: Testicular vessels and pampiniform plexus

  • Inferiorly: Body of epididymis

  • Medially: Closely related to mediastinum testis and efferent ductules

Function

  • Collects sperm from efferent ductules of the testis

  • Provides initial storage and maturation environment for spermatozoa

  • Contributes to absorption of testicular fluid

  • Acts as a conduit to the body and tail of the epididymis before sperm pass into the vas deferens

Clinical Significance

  • Common site for epididymal cysts or spermatoceles (benign fluid-filled swellings)

  • May be involved in epididymitis (infection/inflammation), presenting with pain and swelling

  • Can be involved in torsion of appendix of epididymis, causing acute scrotal pain in children

  • Epididymal head lesions may mimic intratesticular tumors on imaging

  • Frequently assessed in scrotal ultrasound and MRI for differentiating cystic vs solid pathology

MRI Appearance

T1-weighted images:

  • Head of epididymis shows intermediate signal intensity

  • Cysts/spermatoceles: low signal intensity (fluid-filled)

  • Hemorrhagic content: may appear bright

T2-weighted images:

  • Normal tissue: intermediate to mildly hyperintense signal

  • Cysts/spermatoceles: bright hyperintense fluid signal

  • Inflammatory changes: increased signal intensity with surrounding edema

STIR (Short Tau Inversion Recovery):

  • Normal head: intermediate to mildly hyperintense signal

  • Fluid collections or inflammatory changes: bright hyperintensity

  • Fat suppressed for better lesion contrast

T1 Fat-Sat Post-Contrast:

  • Normal head: mild homogeneous enhancement

  • Epididymitis: diffuse intense enhancement

  • Abscess: rim enhancement with central non-enhancing core

  • Tumor: nodular or heterogeneous enhancement

3D T2 SPACE / CISS:

  • Epididymal head and ducts appear as intermediate to mildly hyperintense structures

  • Surrounded by bright fluid of tunica vaginalis (if present)

  • Excellent for delineating small cysts, ductal anatomy, or subtle lesions

CT Appearance

Non-Contrast CT:

  • Epididymal head not well delineated; appears as a small soft tissue density adjacent to superior testis

  • Calcifications may be visible in chronic epididymitis or post-infection

  • Fat in scrotum appears as low attenuation, providing background contrast

Post-Contrast CT:

  • Normal epididymal head: mild, homogeneous enhancement

  • Inflammatory lesions: diffuse or focal enhancing enlargement

  • Abscess: rim-enhancing collection

  • Tumors: irregular or heterogeneous enhancement

MRI image