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Bulb of Penis

The bulb of the penis is the expanded posterior part of the corpus spongiosum located in the superficial perineal pouch. It represents the proximal enlargement of the erectile tissue through which the spongy (penile) urethra passes. The bulb is intimately related to the perineal membrane, pelvic floor, and bulbospongiosus muscles.

It serves as an anchoring structure of the penis and contributes to erection, ejaculation, and urination by supporting the penile urethra. Its strategic location makes it clinically important in trauma, infections, and in imaging interpretation of pelvic and perineal structures.

Synonyms

  • Penile bulb

  • Bulbus penis

  • Posterior expansion of corpus spongiosum

Location and Boundaries

  • Location: Situated in the midline of the superficial perineal pouch, posterior to the penile shaft

  • Superiorly: Attached to the perineal membrane

  • Inferiorly: Covered by the bulbospongiosus muscle

  • Anteriorly: Continuous with the corpus spongiosum of the penis

  • Posteriorly: Related to the perineal body

Relations

  • Anteriorly: Corpus spongiosum of the penile shaft

  • Posteriorly: Perineal body

  • Laterally: Ischiocavernosus and bulbospongiosus muscles

  • Superiorly: Urogenital diaphragm (perineal membrane)

  • Inferiorly: Superficial perineal fascia (Colles’ fascia)

Function

  • Forms the posterior part of the corpus spongiosum, supporting the urethra

  • Participates in penile erection by engorgement of venous sinusoids

  • Assists in ejaculation by contraction of bulbospongiosus muscles, expelling semen and urine from urethra

  • Acts as an anchor, stabilizing the penis at its perineal attachment

Clinical Significance

  • Urethral injury: Bulbar urethra is vulnerable in straddle injuries

  • Infections: Can be a site of abscess formation spreading into perineum or scrotum

  • Oncology: May be involved in penile or urethral carcinoma, seen on imaging

  • Surgical relevance: Landmark in perineal urethrostomy and reconstructive procedures

  • Erectile dysfunction: Pathology in corpus spongiosum may impair function

MRI Appearance

T1-weighted images:

  • Bulb shows intermediate signal intensity from erectile tissue

  • Surrounding fat appears bright, delineating the structure

  • Urethral lumen appears dark

T2-weighted images:

  • Bulb of penis demonstrates heterogeneous intermediate-to-bright signal due to vascular sinusoids

  • Urethra seen as central dark tubular structure

STIR (Short Tau Inversion Recovery):

  • Erectile tissue shows intermediate signal

  • Inflammation, trauma, or edema appear as areas of bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Bulb enhances homogeneously due to vascularity

  • Pathology (abscess, tumor, inflammation) shows heterogeneous or rim enhancement

3D T2 SPACE / CISS:

  • Bulb appears with intermediate to mildly hyperintense signal compared to muscle

  • Urethra seen clearly as a central hypointense channel

  • Excellent for high-resolution urethral anatomy and pathology

CT Appearance

Non-Contrast CT:

  • Appears as a soft tissue density structure in the midline perineum, posterior to penile shaft

  • Urethra not well visualized without contrast

  • Trauma may show hematoma as hyperdense regions

Post-Contrast CT:

  • Bulb enhances homogeneously due to vascular erectile tissue

  • Pathologic lesions (abscess, tumor, trauma) appear as irregular or rim-enhancing areas

  • Urethral contrast studies can outline lumen within the bulb

MRI image

CT image

Bulb of Penis ct axial anatomy image-img-00000-00000