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Lobule of testis

The lobule of the testis is a well-defined structural unit within each testis. Each testis contains 200–300 lobules, separated by fibrous septa extending from the tunica albuginea. Each lobule contains 1–4 seminiferous tubules, which are tightly coiled structures responsible for spermatogenesis.

The lobules converge toward the mediastinum testis, where the seminiferous tubules connect to straight tubules (tubuli recti) that drain into the rete testis. This arrangement provides an efficient and compartmentalized organization for sperm production.

Synonyms

  • Testicular lobule

  • Lobulus testis

  • Seminiferous lobule

Structure and Contents

  • Boundaries: Fibrous septa from tunica albuginea separate lobules

  • Contents:

    • Seminiferous tubules: 1–4 per lobule; site of sperm production

    • Interstitial tissue: Contains Leydig cells (produce testosterone), connective tissue, lymphatics, and blood vessels

    • Myoid cells: Surround seminiferous tubules, aiding sperm transport

  • Drainage: Seminiferous tubules → straight tubules → rete testis → efferent ductules → epididymis

Relations

  • Surrounded by tunica albuginea of the testis

  • Converge toward the mediastinum testis

  • Externally related to tunica vaginalis and scrotal coverings

Function

  • Spermatogenesis: Seminiferous tubules generate spermatozoa

  • Hormone secretion: Interstitial Leydig cells produce testosterone, crucial for male secondary sexual characteristics and spermatogenesis

  • Transport: Seminiferous tubules direct developing sperm toward rete testis

Clinical Significance

  • Testicular tumors: Can arise from seminiferous epithelium (germ cell tumors) or interstitial cells (Leydig cell tumors)

  • Orchitis: Infections may inflame lobules, impairing spermatogenesis

  • Infertility: Structural or functional damage to seminiferous tubules may lead to oligospermia or azoospermia

  • Cryptorchidism: Undescended testes may have malformed lobules, increasing cancer risk

  • Imaging relevance: Recognition of lobular structure helps identify focal lesions on ultrasound, MRI, and CT

MRI Appearance

T1-weighted images:

  • Testicular lobules show homogeneous low-to-intermediate signal intensity

  • Fat between lobules or in tunica shows bright signal

  • Hemorrhage or tumor may show areas of bright signal

T2-weighted images:

  • Lobules show intermediate to high signal intensity due to seminiferous tubule fluid content

  • Pathology (edema, inflammation, tumor) appears as focal bright or heterogeneous signal

STIR (Short Tau Inversion Recovery):

  • Normal lobules show intermediate to high signal intensity 

  • Inflammation, edema, or tumor: bright hyperintensity

  • Fat is suppressed and appears dark, improving lesion visibility

T1 Fat-Sat Post-Contrast:

  • Normal testis enhances homogeneously

  • Tumors show heterogeneous, nodular, or diffuse enhancement

  • Abscess or necrosis: rim enhancement with central non-enhancement

3D T2 SPACE / CISS:

  • Lobules and seminiferous tubules show intermediate to mildly hyperintense signal compared to muscle

  • Surrounded by bright tunica and fluid, giving high contrast

  • Useful for fine anatomic detail of rete testis and intratesticular lesions

CT Appearance

Non-Contrast CT:

  • Testicular lobules appear as soft tissue density within the scrotum

  • Fat planes and tunica may outline testis margins

  • Hemorrhage or calcification may be visible in pathology

Post-Contrast CT:

  • Testicular parenchyma enhances homogeneously in normal lobules

  • Tumors or inflammation show heterogeneous or focal enhancement

  • Abscess: rim enhancement with low-density center

MRI image

Lobule of testis mri axial anatomy image-img-00000-00000