Overview
Definition:
Micropenis is defined as a stretched penile length (SPL) that is more than 2.5 standard deviations (SD) below the mean for age and gestational age
in term newborns, this corresponds to an SPL of less than 1.9 cm
It is a congenital anomaly characterized by a disproportionately small penis
It can be an isolated finding or associated with other endocrine or genetic abnormalities.
Epidemiology:
Micropenis occurs in approximately 0.03% to 0.05% of male births
The prevalence can be higher in specific populations or associated with syndromes
It is essential to differentiate true micropenis from other conditions that may mimic it, such as buried penis or intersex disorders.
Clinical Significance:
Accurate and timely evaluation of micropenis is crucial for addressing potential underlying endocrine disorders, psychological impact on the child and family, and for planning appropriate management strategies, including hormonal therapy and surgical intervention, to optimize future sexual function and fertility.
Clinical Presentation
Symptoms:
Often noted at birth by parents or during routine newborn examination
Difficulty in voiding may be present if associated with severe hypospadias or other urethral anomalies
Absence of palpable testes in the scrotum suggests potential underlying hypogonadism.
Signs:
Stretched penile length (SPL) less than 1.9 cm in term newborns
The penis appears significantly smaller than expected for the infant's size
Associated findings may include hypospadias, undescended testes, bifid scrotum, or other signs of ambiguous genitalia
The glans and shaft are usually well-formed but small.
Diagnostic Criteria:
The primary diagnostic criterion is a stretched penile length (SPL) less than 1.9 cm in term male newborns, which is below -2.5 SD for age
Measurement technique is critical
the penis should be straightened without stretching, and the measurement taken from the pubic bone to the tip of the glans
Normal SPLs for premature infants are also available and should be used.
Diagnostic Approach
History Taking:
Detailed family history, including any history of endocrine disorders, infertility, or ambiguous genitalia
Maternal medical history, especially concerning hormone use (e.g., progestins) during pregnancy or maternal endocrine conditions
Gestational age assessment is vital
Ask about any concerns regarding voiding
Inquiry about the presence of testes in the scrotum.
Physical Examination:
Systematic physical examination focusing on the external genitalia
Measure stretched penile length accurately
Assess for hypospadias (subcoronal, megameatal, distal shaft, proximal shaft, perineal)
Palpate testes in the scrotum and assess their size and consistency
Examine for other congenital anomalies, including spinal defects, cardiac abnormalities, or limb malformations
Assess for clitoromegaly in suspected female infants or those with ambiguous genitalia.
Investigations:
Karyotype to determine chromosomal sex is essential, especially if ambiguous genitalia are present or if there is suspicion of Klinefelter syndrome (XXY)
Hormone levels: testosterone, LH, FSH, and hCG stimulation test to assess testicular function
17-hydroxyprogesterone for adrenal hyperplasia
Ultrasound of the scrotum and pelvis to identify testes and other pelvic structures
Imaging of the brain (MRI) may be considered if hypopituitarism is suspected
Genetic testing for specific syndromes if indicated
Serum electrolytes and glucose to rule out adrenal insufficiency.
Differential Diagnosis:
True micropenis vs
buried penis (adherent penis, webbed penis, webbed scrotum), intersex disorders (e.g., congenital adrenal hyperplasia, androgen insensitivity syndrome, ovotesticular DSD), primary hypogonadism (Kallmann syndrome, Prader-Willi syndrome), secondary hypogonadism (pituitary or hypothalamic disorders), pseudohermaphroditism, cloacal exstrophy, and penile agenesis.
Management
Initial Management:
The primary goal is to determine the underlying cause and initiate appropriate therapy
Reassurance and counseling for the parents regarding the diagnosis and potential treatment options
Referral to pediatric endocrinology and genetics is paramount
Avoid assigning a sex if genitalia are ambiguous until a full evaluation is complete.
Medical Management:
Hormonal therapy: Topical or intramuscular testosterone is the mainstay for stimulating penile growth in cases of true micropenis due to hypogonadism
A typical regimen involves topical testosterone cream (e.g., 2% or 5%) applied daily or intramuscular testosterone injections (e.g., 25-50 mg every 2-4 weeks) for a period of 3-6 months
The dose and duration depend on the infant's age, weight, and response
Regular monitoring of growth response and hormone levels is crucial.
Surgical Management:
Surgical intervention is generally considered for cosmetic or functional reasons and is typically deferred until puberty or later, after hormonal therapy has been completed and maximal growth achieved
Procedures may include phalloplasty or other reconstructive techniques for severe cases or associated anomalies like hypospadias
The goal is to achieve a functional penis suitable for voiding and sexual intercourse.
Supportive Care:
Psychological support for the child and family is critical throughout the evaluation and management process
Education on proper hygiene and potential long-term implications
Regular follow-up appointments with endocrinology, urology, and genetics are essential to monitor progress and address any emerging issues
Parents should be educated on penile grooming techniques to prevent buried penis recurrence.
Complications
Early Complications:
Poor response to hormonal therapy
Skin irritation or local reactions to topical testosterone
Undescended testes may require surgical correction if not responsive to hormonal treatment
Psychological distress in the family
Misassignment of sex leading to later gender dysphoria.
Late Complications:
Impaired sexual function and fertility
Psychological issues related to body image and self-esteem
Increased risk of urinary tract infections if hypospadias is severe
Infertility if testicular function is not restored or if genetic abnormalities are present
Risk of testicular tumors in certain genetic conditions.
Prevention Strategies:
Early and accurate diagnosis
Comprehensive genetic and endocrine workup
Appropriate and timely hormonal therapy
Careful sex assignment based on thorough evaluation
Multidisciplinary team approach involving pediatric endocrinologists, geneticists, urologists, and psychologists.
Prognosis
Factors Affecting Prognosis:
The underlying etiology is the most critical factor
Isolated micropenis with responsive hypogonadism generally has a good prognosis with hormonal treatment
Syndromic causes, severe hypospadias, or associated abnormalities can significantly impact the prognosis
The degree of penile growth achieved with therapy is a key indicator.
Outcomes:
With appropriate hormonal therapy, the penis can achieve a size that is considered functionally and aesthetically acceptable, allowing for normal voiding and sexual function in many cases
However, significant growth may not always be achieved, and some individuals may still require reconstructive surgery later in life
Long-term psychological well-being depends on comprehensive support.
Follow Up:
Lifelong follow-up may be necessary for individuals with underlying endocrine or genetic conditions
Regular monitoring of growth, sexual development, and hormone levels is crucial
Psychosocial support should be ongoing
Genetic counseling for the family and future reproductive planning should be discussed.
Key Points
Exam Focus:
Remember the SPL cutoff for term neonates (-2.5 SD, <1.9 cm)
Differentiate true micropenis from buried penis
Always investigate for underlying endocrine (hypogonadism, CAH) or genetic causes
hCG stimulation test is key for assessing testicular Leydig cell function.
Clinical Pearls:
Accurate measurement technique is paramount
use a standardized method
Consider a multidisciplinary team approach early in management
Counsel parents proactively about the condition, its implications, and treatment options
Emphasize that sexual function is not solely dependent on penis size.
Common Mistakes:
Failing to measure SPL accurately
Assuming isolated micropenis without a full endocrine and genetic workup
Delaying referral to specialists
Assigning sex prematurely in ambiguous genitalia cases
Over-reliance on surgery as the first-line management without addressing underlying hormonal issues.