Micropenis is an objective diagnosis made based on the meticulous measurement of the penile length. Given the significant anxiety, stress, and psychological impact, the accuracy of making the diagnosis is essential. A multidisciplinary team should manage micropenis once there is a definitive diagnosis. This finding can be isolated or part of other groups of symptoms and signs indicative of hormonal abnormalities or genetics association.
In human beings, the chromosomal sex combination is determined at fertilization either as female (XX) or male (XY). Early in fetal life, the embryo has both mesonephric duct (male) and paramesonephric ducts (females). Based on the presence or absence of the SRY gene (located on the Y chromosome), regression or development of one of these ducts will continue during organogenesis. The SRY gene stimulates gonadal differentiation into testicular tissue. At this early stage of development, the testes secrete three hormones that are very important in the sexual male differentiation process:
Under the influence of these three hormones, the male reproductive and genitourinary systems start to develop during the late third of the first trimester (8 to 12 weeks of gestation). The human chorionic gonadotropin (hCG) stimulates the Leydig cells to secrete testosterone. Further metabolism in utero converts testosterone to dihydrotestosterone. High levels of fetal androgens During the second-trimester further accelerate penile growth. In the postnatal period, further development of the male sexual characteristics takes place under the influence of the hormones regulated by the hypothalamic-pituitary axis (gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH)). The highest postnatal androgen levels occur between the first and third months of life. Undervirilization signs and micropenis usually result from disturbance of any of these steps. Such distribution can occur in any of the following:
In some cases, the etiology remains unclear even after performing an extensive evaluation.
Micropenis incidence in North America is about 1.5 per 10,000 male newborns. Research shows a slight statistical difference in the mean penile length between the White race, 2.6 cm, east Indian 2.5, and Chinese 2.3 newborns. Other studies proposed specific penile length standards for the Brazilian, Japanese, and Turkish infants and children.
Clinical diagnosis of micropenis often occurs after a detailed history and physical examination. After making the diagnosis, further testing to identify associated abnormalities and possible etiologies are necessary.
Detailed maternal history is the first step in evaluation for micropenis. Consanguinity and family history of ambiguous genitalia make inherited conditions more likely on the differential. Inquiry about maternal medication use is important, as the use of anti-androgen medications (flutamide, testolactone, enzalutamide, and spironolactone) can interfere with the in-utero virilization.
Physical examination assessment is the most crucial part of micropenis evaluation. Underverlization associated with low blood pressure and tachycardia can indicate adrenal gland insufficiency related to rare forms of congenital adrenal hyperplasia (CAH). Penile length accurate measurement is critical during the physical examination. The penis shaft should be maximally stretched. The distance is measured from the pubic symphysis (after pressing the suprapubic fat) to the tip of the glans (with the foreskin retracted as much as possible) dorsally. The average of multiple measurements can enhance accuracy.
Specific penile length less than two and a half standard deviations of the mean for the corresponding age confirm the diagnosis. Suggested lower limits of penile lengths in centimeters according to age are (represented graphically in figure 1):
Careful and thorough palpation of the gonads is another step in micropenis evaluation to narrow the differential diagnosis. The appearance and the maturity of the scrotal sac, the presence and the location of the urethral meatus, the curvature of the penile shaft, and any dysmorphic features require careful evaluation.
Following diagnosis by physical examination, work up to identify the etiology and to guide the treatment plan is necessary.
A standardized approach for micropenis evaluation consists of:
The goals of micropenis management include:
Medical or surgical interventions have had trials performed with variable responses. The primary etiology, age of presentation, degree of atrophy, and desired outcome usually dictate the treatment approach. A reasonable treatment plan for micropenis is a trial of medical therapy first, then surgical intervention if the medical treatment does not result in the desired outcomes.
A penile reconstruction is an option if the response to medical treatment is inadequate. Surgical treatment usually achieves acceptable results. However, dissatisfaction with penile appearance is common among treated patients.
The most crucial differential is to rule out is pseudo micropenis. In this condition, the penis appears small due to the surrounding tissue prominence or penile web that attaches the penis to the underlying skin. Meticulous thorough physical examination is essential to rule out pseudo-micropenis and avoid an invasive diagnostic evaluation and the associated patients' and their family's psychosocial stress. Chordee of the penis is another surgical condition that results in an abnormally curved penile shaft that can underestimate the penile length.
Micropenis is a physical finding that can be a sign of a systemic hormonal abnormality or a genetic process. Many conditions can present with micropenis. A systematic multidisciplinary team approach is crucial for evaluation and management. Pediatric endocrinologists and urologists are almost always involved in providing care for patients with micropenis. The ancillary services (geneticist, psychologist, social worker, and pharmacist) are essential to provide family support and maintain the mental well being of the patients and their families. As most micropenis patients present during the early neonatal period, the nursing assessment could be the first step in making the diagnosis.
Although experts have suggested a standardized evaluation and management plan, the variable presentation and the different etiological causes make it essential to do a comprehensive history and physical examination before ordering diagnostic tests. Medical and surgical treatments available for micropenis result in acceptable outcomes in most cases; however, social dissatisfaction remains a potential concern.
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