Micropenis not only affects the growth and development of children and their psychological health, but also has different degrees of impact on the quality of life and fertility in adulthood, so it has received attention from parents and endocrinologists. So how to correctly diagnose and treat small penis? The size of the penis is related to race, age and the state of sexual development. It is generally considered that the anatomical structure and appearance of the penis are normal, and the length is lower than 2.5 standard deviations of the average length of the same age or the same pubertal development period as small penis. Clinically, the penis length value measured by the pay super is often used as the standard. The correct measurement of the penis is the basis of the diagnosis of micropenis, so that the penis is in a weak and extended state, along the dorsal side of the penis, the length measured from the root of the penis at the pubic symphysis to the tip of the glans (excluding the length of the foreskin). Obese or occult penis should be pushed away from the prepubic symphysis fat pad as much as possible. Second, determine the cause of penile shortening The development of the penis requires the action of the hypothalamic-pituitary-gonadal axis hormones. The hypothalamus produces gonadotropin-releasing hormone that stimulates the pituitary gland to secrete gonadotropins (luteinizing hormone LH and follicle-stimulating hormone FSH), which together with chorionic gonadotropin (HCG) stimulate the testes to secrete testosterone ( T), which is converted to dihydrotestosterone (DHT) by the action of 5α reductase 2, which in turn acts on androgen receptors to cause penile growth. Therefore, abnormalities in the hypothalamic-pituitary-gonadal axis and in any of the links of androgen synthesis and conversion, as well as abnormalities in the hormone receptors and their post-signaling systems, can affect the development of the penis, resulting in micropenis. The common causes of this disease include: (1) Hypothalamic-pituitary lesions: low gonadotropin production. (2) Abnormal testicular function: decreased production of testosterone. (3) Androgen conversion and androgen receptor abnormalities: low production of dihydrotestosterone and decreased androgen action. (4) Chromosomal abnormalities: sex chromosome abnormalities. This shows that the etiology of micropenis is complex and the clinical etiology is difficult to diagnose. (1) Karyotype analysis: Karyotype analysis is required for all children with micropenis. (2) Determination of hormone levels to determine whether the problem is hypothalamic-pituitary or testicular. Since the hypothalamic-pituitary-gonadal axis of infants and children is not yet well developed and is unresponsive, and the gonadal axis of prepubertal boys is not yet activated, the basal state sex hormone level has little significance for clinical diagnosis, so HCG excitation test and LHRH excitation test are needed; however, for small pubertal boys (from birth to 6 months after birth), if the hormone level can be measured, the testicular hormone level can be measured. However, for young adolescent boys (from birth to 6 months postnatal window), if the levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone (T) can be measured, the function of the hypothalamic-pituitary-gonadal axis can be initially determined. Generally, HCG stimulation test is performed first to understand the ability of the testes to produce testosterone and the presence of 5α reductase 2 deficiency or androgen resistance. If testicular function is normal, then LHRH stimulation test is performed to determine pituitary function. If adrenocortical insufficiency and growth hormone deficiency are suspected, ACTH excitation and growth hormone excitation tests should be performed. (3) If hypothalamic-pituitary lesions are suspected, cranial CT or MRI examination should be performed. Treatment of micropenis Previously, it was thought that the treatment of micropenis generally started at puberty, but now it is thought that treatment can be started once the diagnosis is confirmed. Some studies have reported that treatment given during the small adolescence (within 6 months after birth) can lead to better development of the penis and testes and improve the reproductive function in adulthood. The following treatments are often available: (1) GnRH micropump: for hypothalamic lesions, GnRH micropump treatment can be used to improve the pituitary gonadotropin secretion function of the child. (2) Gonadotropin: rh-FSH and rh-LH can be given to those with abnormal pituitary function. (3) HCG injection: HCG acts directly on the Leydig cells of the testis to increase the synthesis and secretion of testosterone, which is used for the treatment of insufficient gonadotropic secretion. (4) Androgens: Testosterone undecanoate can be given intramuscularly or orally. Currently, testosterone and dihydrotestosterone ointment are more commonly used in infants and children, especially after the better effect, but the use of such drugs requires regular check of androgens (T and DHT levels) in hospital to prevent their adverse effects.