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Topic

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Fetal penis

The fetal penis is the external male genital organ that develops from the genital tubercle during embryogenesis. It plays a critical role in urinary excretion in utero and sexual function postnatally. Prenatal evaluation of the penis is important for assessing fetal sex, growth, and congenital anomalies of the genitourinary tract.

Development begins around the 7th week of gestation, with differentiation under the influence of fetal testicular androgens. By the second trimester, the penis becomes externally visible and can be evaluated with ultrasound and, when needed, MRI.

Synonyms

  • Prenatal penis

  • Male fetal genitalia

  • Fetal phallus

Structure and Development

  • Glans penis: Derived from the genital tubercle; forms the distal end

  • Shaft: Contains developing corpora cavernosa and corpus spongiosum

  • Urethra: Forms via urethral groove closure on the ventral aspect of penis

  • Prepuce (foreskin): Develops from ectodermal folds surrounding glans

  • Development is complete by late second trimester, though growth continues throughout pregnancy

Relations

  • Anteriorly: Amniotic fluid and anterior abdominal wall

  • Posteriorly: Fetal scrotum and perineum

  • Superiorly: Lower abdominal wall and bladder

  • Inferiorly: Perineal region

Function

  • Provides a conduit for urine excretion from bladder into amniotic sac

  • Serves as an anatomical marker for fetal sex determination

  • Plays a role in identifying congenital anomalies of genital development

Clinical Significance

  • Sex determination: Identification of penis confirms male sex

  • Hypospadias/Epispadias: Urethral closure defects detected prenatally in some cases

  • Micropenis: May indicate endocrine or chromosomal disorders

  • Ambiguous genitalia: Requires detailed evaluation of external and internal genitalia

  • Urethral obstruction (posterior urethral valves): May cause bladder distension and oligohydramnios

  • Imaging role: MRI is supportive when ultrasound is inconclusive, especially in ambiguous genitalia or pelvic malformations

MRI Appearance

T2 HASTE (T2 GRE):

  • Shaft and glans: Low-to-intermediate signal intensity

  • Surrounding amniotic fluid: Very bright, providing contrast for identification

  • Corpora cavernosa/corpus spongiosum: Low-to-intermediate signal intensity

T1 GRE:

  • Shaft and glans: Low-to-intermediate signal intensity

  • Developing fat around genital region: Appears bright, improving contrast

  • Hemorrhage or abnormal content (rare in utero): Hyperintense focal signal if present

MRI image

fetal Penis MRI axial anatomy image-img-00000-00000

MRI image

fetal Penis MRI sagittal image