How is micropenis evaluated?

Evaluation of Micropenis

Micropenis should be diagnosed by measuring stretched penile length (SPL) and comparing it to age-specific normative data, with evaluation warranted when SPL is <2 cm at birth or <4 cm after age 5 years, followed by hormonal assessment during the mini-puberty period to determine the underlying etiology. 1

Definition and Measurement Technique

• Micropenis is defined as a structurally normal but abnormally small penis with SPL ≥2.5 standard deviations below the mean for age or stage of sexual development. 2, 1
• Use a standardized measurement technique: measure the stretched penile length from the pubic bone to the tip of the glans while applying gentle traction. 2
• Compare measurements to age-appropriate nomograms to confirm the diagnosis. 2
• All children above 1 year of age with SPL <1.9 cm require evaluation. 2
• At birth (term neonates), SPL <2 cm warrants investigation; after 5 years of age, SPL <4 cm requires evaluation. 1, 3

Differential Diagnosis

Before proceeding with evaluation, distinguish micropenis from:

• Buried or hidden penis (normal-sized penis obscured by suprapubic fat or abnormal penile skin attachment). 2
• Aphallia (complete absence of penile tissue). 2
• Webbed penis or other anatomical variants. 2

Clinical History

Obtain detailed information focusing on:

• Prenatal history: maternal medication use during pregnancy (iatrogenic causes), gestational age, intrauterine growth. 3
• Family history: consanguinity, similar conditions in relatives, genetic syndromes. 2
• Associated symptoms: cryptorchidism, hypospadias, incomplete scrotal fusion (suggestive of disorders of sex development). 1
• Growth velocity: critical for identifying hypothalamic or pituitary pathology. 2
• Developmental milestones: may indicate syndromic associations. 2

Physical Examination

Perform a comprehensive genital and systemic examination:

• Genital examination: assess for hypospadias, cryptorchidism, scrotal fusion abnormalities, and testicular size/consistency. 1
• Body habitus and secondary sexual characteristics: evaluate for syndromic features associated with hypogonadotropic hypogonadism. 2
• Growth parameters: height, weight, and growth velocity assessment. 2
• Dysmorphic features: look for clinical features suggestive of genetic syndromes (e.g., Prader-Willi, Kallmann, septo-optic dysplasia). 2

Laboratory Evaluation

Hormonal Assessment

The optimal time for hormonal evaluation is during the mini-puberty period (first 3-6 months of life), when gonadotropins and testosterone are physiologically elevated. 1, 4

• Basal hormone levels: measure LH, FSH, and testosterone. 1
• GnRH stimulation test: helpful in evaluating hypothalamic-pituitary function, particularly in hypogonadotropic hypogonadism. 2
• hCG stimulation test: assesses testicular function and testosterone production capacity; measure baseline and stimulated testosterone, DHT, and androstenedione levels. 2, 1
• Growth hormone assessment: if growth velocity is impaired or other features of hypopituitarism are present. 2

Genetic Studies

• Karyotype analysis: essential to rule out disorders of sex development, particularly when associated genital anomalies are present. 1
• Chromosomal studies: indicated when syndromic features are present or DSD is suspected. 2

Imaging Studies

• Consider imaging examinations when structural hypothalamic-pituitary abnormalities are suspected (e.g., MRI for septo-optic dysplasia, pituitary hypoplasia). 3

Etiologic Classification

Based on hormonal evaluation, classify into:

1. Hypogonadotropic hypogonadism (low LH/FSH, low testosterone): hypothalamic or pituitary failure. 2
2. Hypergonadotropic hypogonadism (elevated LH/FSH, low testosterone): testicular failure, partial gonadal dysgenesis, testicular regression. 2, 1
3. Disorders of testosterone biosynthesis or action: partial androgen insensitivity syndrome, 5α-reductase deficiency. 2, 1
4. Idiopathic: no identifiable cause after complete evaluation. 2

Multidisciplinary Consultation

Involve a pediatric endocrinologist for all cases; additionally consult genetics, pediatric surgery/urology, and psychology as needed based on findings. 2, 4

Common Pitfalls

• Failing to use standardized measurement technique: improper measurement leads to misdiagnosis. 2
• Delaying evaluation beyond the mini-puberty window: hormonal assessment is most informative during the first 3-6 months of life. 1, 4
• Assuming isolated micropenis without checking for associated anomalies: always examine for cryptorchidism, hypospadias, and scrotal abnormalities that suggest DSD. 1
• Omitting growth velocity assessment: this is critical for identifying GH deficiency and hypopituitarism. 2