How to evaluate and manage a child's concern about having a small penis?

Evaluation of Perceived Small Penis in Children

The first critical step is to distinguish true micropenis (stretched penile length <2.5 SD below mean for age) from normal anatomical variants like buried/hidden penis, which requires proper measurement technique and age-appropriate nomograms. 1, 2

Initial Assessment and Measurement Technique

• Measure stretched penile length using standardized technique: gently stretch the penis to resistance and measure from pubic symphysis to tip of glans on the dorsal surface 1, 2
• Compare measurements against age-specific normograms; any child >1 year with stretched length <1.9 cm requires full evaluation 1
• Differentiate true micropenis from:
  • Buried/hidden penis (normal-sized penis obscured by suprapubic fat or abnormal penile-scrotal attachment) 1, 2
  • Webbed penis (penoscrotal web extending onto ventral shaft)
  • Aphallia (complete absence of penis) 1

Testicular Examination

• Palpate and measure testicular volume using Prader orchidometer at each visit 3
• Bilateral small testes (<12 ml) with small penis suggests hypogonadotropic or hypergonadotropic hypogonadism requiring immediate endocrine evaluation 3, 1
• Bilateral nonpalpable testes with small penis is a medical emergency requiring immediate specialist consultation to rule out disorders of sex development, including congenital adrenal hyperplasia 4
• Unilateral or bilateral undescended testes require referral to pediatric urology by 6 months of age (corrected for gestational age) 4

Growth and Developmental Assessment

• Measure height, weight, and growth velocity as poor growth suggests hypothalamic-pituitary pathology (combined growth hormone and gonadotropin deficiency) 1
• Document pubertal staging (Tanner staging) in older children 1
• Assess for dysmorphic features or syndromic associations (Prader-Willi, Kallmann, septo-optic dysplasia) 1, 2

Laboratory Evaluation for True Micropenis

When micropenis is confirmed by measurement:

• Obtain baseline hormones: LH, FSH, total testosterone, and inhibin B to assess hypothalamic-pituitary-gonadal axis 3, 1
• GnRH stimulation test to differentiate hypogonadotropic hypogonadism (hypothalamic/pituitary failure) from hypergonadotropic hypogonadism (testicular failure) 1, 2
• hCG stimulation test (1500-2000 IU intramuscularly 3 times weekly for 3 weeks) to assess testicular androgen production capacity 1, 2
• Consider karyotype analysis if bilateral small testes, ambiguous features, or syndromic presentation 1, 2
• Anti-müllerian hormone (AMH) may help assess Sertoli cell function if testicular dysgenesis suspected 3

Etiological Classification

True micropenis falls into four categories:

• Hypogonadotropic hypogonadism (low LH/FSH, low testosterone): hypothalamic or pituitary failure 1, 2
• Hypergonadotropic hypogonadism (high LH/FSH, low testosterone): primary testicular failure 1, 2
• Partial androgen insensitivity syndrome: normal/elevated testosterone with inadequate response 1, 2
• Idiopathic: normal hormonal axis, unclear etiology 1, 2

Treatment Approach for True Micropenis

Regardless of underlying etiology, a trial of testosterone therapy should be attempted in all prepubertal children with confirmed micropenis to assess penile response. 1

Testosterone Treatment Protocol:

• Testosterone enanthate or cypionate: 25-50 mg intramuscularly monthly for 3 months in prepubertal children 1, 2
• Transdermal dihydrotestosterone (DHT) is an alternative in prepubertal children 1
• Reassess penile length after 3-month course; most patients show satisfactory growth response 1, 5
• Critical timing: Early diagnosis and androgen therapy initiation between 11-12 years prevents psychological sequelae of undersized genitals and delayed puberty 6

Long-term Management:

• Children with hypogonadotropic hypogonadism and growth hormone deficiency require appropriate hormonal replacement 1
• Surgical correction is NOT indicated for endocrine-responsive micropenis 1
• Sexual reassignment is rarely performed now, as testosterone-treated children achieve satisfactory penile length and sexual function 1, 5

Management of Normal Variants (Buried/Hidden Penis)

• Reassure parents that penile length is normal when properly measured 1, 2
• Weight loss if obesity is contributing factor
• Surgical correction (escutcheonectomy, scrotoplasty) reserved for severe cases affecting urination or causing psychological distress
• No hormonal therapy indicated 1

Critical Pitfalls to Avoid

• Never dismiss bilateral small testes without full hormonal evaluation and consideration of disorders of sex development 3
• Do not delay referral of undescended testes beyond 6 months of age, as spontaneous descent is unlikely and fertility damage progresses 4
• Avoid ultrasound screening for undescended testes prior to specialist referral, as imaging rarely changes management and delays appropriate care 4
• Do not assume normal variant without proper stretched penile measurement against age-specific norms 1, 2
• Recognize that topical testosterone in childhood increases relative penile size before puberty but provides no adult size advantage over untreated micropenis, though it may postpone psychological coping needs 5

Multidisciplinary Referral Indications

• Immediate endocrinology referral: confirmed micropenis, bilateral small/nonpalpable testes, poor growth velocity 1, 2
• Pediatric urology referral by 6 months: undescended testes 4
• Genetics consultation: syndromic features, ambiguous genitalia, abnormal karyotype 1, 2
• Psychology/social work: all children with micropenis benefit from long-term psychological support 7