No Results

No Results


Microphallus, or micropenis, is defined as a stretched penile length of less than 2.5 standard deviations (SDs) below the mean for age. Traditionally, the term micropenis refers to a penis that is otherwise normally formed, and the term microphallus has been used when associated hypospadias is present.

The mean stretched penile length in a full-term newborn male is 3.5 cm. Measurements of less than 2-2.5 cm (2.5 SDs below the mean) in a full-term newborn male meet the definition of micropenis and warrant evaluation. [1, 2, 3, 4, 5] Penile growth is essentially linear during mid-to-late gestation. Tuladhar et al (1998) reported the following formula to describe the relationship between penile length and gestational age for infants born at 24-36 weeks gestation: [6]

Penile length in centimeters = -2.27 + 0.16 X (gestational age in weeks)

Although micropenis can be considered a form of ambiguous genitalia, the presence of a normal scrotum and palpable testes indicates a high probability of a normal male karyotype. If the testes are not palpable and/or the penile urethra is absent, the examination is better described as ambiguous, and an evaluation and counseling for disorders of sex development should be performed.

After the first few years of life, the penis grows very little until puberty when testosterone levels begin to rise. Mean stretched penile lengths and 2.5 SDs below the mean for various age groups can be found in the popular Harriet Lane Handbook (Table 10-15, 19th ed.). [7]

Occasionally, older boys are brought for evaluation because of concerns of small genitalia. These boys are usually prepubertal and obese. Most often, these individuals have normal penis size based on stretched penile length, and the apparent smallness is secondary to the penis being concealed in the suprapubic fat pad (“buried penis”). However, if the penis does measure less than 2.5 SDs below the mean (approximately 4 cm) or other abnormalities are present, such as cryptorchidism or hypospadias, further evaluation is indicated.

Fetal production of testosterone and its peripheral conversion to dihydrotestosterone (DHT) is necessary for normal male development. Early in gestation, placental human chorionic gonadotropin (hCG) stimulates the developing testes to produce testosterone by binding to the luteinizing hormone (LH) receptor. By approximately 14 weeks’ gestation, the fetal hypothalamic-pituitary-gonadal axis is active, and testosterone production falls under the control of fetal LH. Penile growth after the first trimester depends on fetal gonadotropin production. Testosterone is peripherally converted by the enzyme 5-alpha reductase to the more potent androgen DHT, which is responsible for virilization of the male external genitalia. Finally, intact peripheral androgen receptors are necessary for normal male development. [8, 9]

After an initial surge of LH and testosterone at birth, lasting about 12 hours, gonadotropin (LH and follicle stimulating hormone [FSH]) and testosterone levels are low during the first few days of life. At about 1 week of age, gonadotropin and testosterone levels begin to rise to pubertal levels, peaking at age 1-3 months, and then decreasing to prepubertal levels by age 6 months. [10, 11] After age 6 months, the little subsequent penile growth that occurs parallels general somatic growth. With the onset of puberty penis growth resumes because of increased testosterone production. Growth hormone also plays a role in penis growth as micropenis has been observed in children with isolated growth hormone deficiency.

Micropenis may be caused by a defect anywhere along the hypothalamic-pituitary-gonadal axis, a defect in peripheral androgen action, isolated growth hormone deficiency, a primary structural anomaly, or may be part of a genetic syndrome. The most common cause of micropenis is abnormal hypothalamic or pituitary function. In the absence of normal hypothalamic or pituitary function, a normally shaped penis may develop due to maternal hCG effect on fetal testosterone production, but adequate penile growth does not occur after 14 weeks’ gestation when testosterone production depends on intact fetal pituitary LH secretion. Failure of adequate testosterone production toward the end of gestation due to a primary testicular disorder can also result in inadequate penis growth.

Micropenis can also occur in children with LH-receptor defects and defects in testosterone biosynthesis (e.g. 17-beta hydroxysteroid dehydrogenase deficiency). [10] The genitalia of individuals with LH-receptor defects vary from normal female-appearing to male-appearing with micropenis. Individuals with 17-beta hydroxysteroid dehydrogenase deficiency most often have female-appearing genitalia and, less often, ambiguous genitalia. [12]

Defects in peripheral androgen action include 5-alpha reductase deficiency (failure of conversion of testosterone to DHT) and partial androgen insensitivity syndrome (PAIS) due to an androgen receptor defect. However, most children with these conditions have varying degrees of incomplete labioscrotal fusion, resulting in hypospadias and genital ambiguity. [12, 13]

Lastly, genetic syndromes in which micropenis may be a feature include Prader-Willi, Klinefelter, and Noonan syndromes, among others (see Causes). [12, 14]

By definition, microphallus is an exclusively male condition. However, distinguishing between a male with micropenis and bilateral cryptorchidism and a female with clitoromegaly is important and may be difficult.

Micropenis is most often recognized and evaluated in the immediate newborn period, but delays in evaluation may also occur.

Feldman KW, Smith DW. Fetal phallic growth and penile standards for newborn male infants. J Pediatr. 1975 Mar. 86(3):395-8. [Medline].

Bin-Abbas B, Conte FA, Grumbach MM. Congenital hypogonadotropic hypogonadism and micropenis: effect of testosterone treatment on adult penile size why sex reversal is not indicated. J Pediatr. 1999 May. 134(5):579-83. [Medline].

Schonfeld WA, Beebe GW. Normal growth and variation in male genitalia from birth to maturity. J Urol. 1942. 64:759-777.

Wessells H, Lue TF, McAninch JW. Penile length in the flaccid and erect states: guidelines for penile augmentation. J Urol. 1996 Sep. 156(3):995-7. [Medline].

Bhakhri BK, Meena SS, Rawat M, Datta V. Neonatal stretched penile length: relationship with gestational maturity and anthropometric parameters at birth. Paediatr Int Child Health. 2014 Jan 26. [Medline].

Tuladhar R, Davis PG, Batch J. Establishment of a normal range of penile length in preterm infants. J Paediatr Child Health. 1998 Oct. 34(5):471-3. [Medline].

Cohee, L. Endocrinology: Table 10-19: Mean Stretched Penile Length. Tschudy MM, Arcara KM. The Harriet Lane Handbook. 19th ed. Philadelphia, PA: Elsevier; 2012. Chapter 10.

Hughes IA. The Testes: Disorders of Sexual Differentiation and Puberty in the Male. Sperling MA. Pediatric Endocrinology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2008. Chapter 16.

Achermann JC, Hughes IA. Disorders of Sex Development. Melmed. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011. Chapter 23.

Grumbach MM. A window of opportunity: the diagnosis of gonadotropin deficiency in the male infant. J Clin Endocrinol Metab. 2005 May. 90(5):3122-7. [Medline].

Quigley CA. Editorial: The postnatal gonadotropin and sex steroid surge – Insights from the androgen insensitivity syndrome. J Clin Endocrinol Metab. 2002. 87:24-28. [Medline].

Witchel SF, Lee PA. Ambiguous Genitalia. Sperling MA. Pediatric Endocrinology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2008. 127-164. Chapter 4.

Maimon L, Philibert P, Cammas B, et. al. Phenotypical, biological, and molecular heterogeneity of 5-alpha-reductase deficiency: An extensive international experience of 55 patients. J Clin Endocrinol Metab. Feb 2011. 96(2):296-307. [Medline].

Achermann JC, Ozisik G, Meeks JJ. Genetic causes of human reproductive disease. J Clin Endocrinol Metab. 2002. 87:2447-2454. [Medline].

Hayes FJ, Seminara SB, Crowley WF. Hypogonadotropic hypogonadism. Endocrinol Metab Clin North Am. 1998. 27:739-763. [Medline].

Pallais JC, Au M, Pitteloud N, et al. Kallmann Syndrome. GeneReviews. Available at http://www.ncbi.nlm.nih.gov/books/NBK1334/. Accessed: 3 July 2011.

Bonomi M, Vezzoli V, Krausz C, et al. Characteristics of a nationwide cohort of patients presenting with isolated hypogonadotropic hypogonadism (IHH). Eur J Endocrinol. 2018 Jan. 178 (1):23-32. [Medline].

Toogood AA, Stewart PM. Hypopituitarism: clinical features, diagnosis, and management. Endocrinol Metab Clin North Am. 2008 Mar. 37(1):235-61, x. [Medline].

Melmed S, Kleinberg D, Ho K. Pituitary Physiology and Diagnostic Evaluation. Melmed S. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011. Chapter 8.

Tsigos C, Latronico C, Chrousos GP. Luteinizing hormone resistance syndromes. Ann N Y Acad Sci. 1997 Jun 17. 816:263-73. [Medline].

Boehmer AL, Brinkmann AO, Sandkuijl LA, et al. 17Beta-hydroxysteroid dehydrogenase-3 deficiency: diagnosis, phenotypic variability, population genetics, and worldwide distribution of ancient and de novo mutations. J Clin Endocrinol Metab. 1999 Dec. 84(12):4713-21. [Medline].

Lee YS, Kirk JM, Stanhope RG, et al. Phenotypic variability in 17beta-hydroxysteroid dehydrogenase-3 deficiency and diagnostic pitfalls. Clin Endocrinol (Oxf). 2007 Jul. 67(1):20-8. [Medline].

Gad YZ, Nasr H, Mazen I. 5 alpha-reductase deficiency in patients with micropenis. J Inherit Metab Dis. 1997 Mar. 20(1):95-101. [Medline].

Sinnecker GH, Hiort O, Dibbelt L. Phenotypic classification of male pseudohermaphroditism due to steroid 5 alpha-reductase 2 deficiency. Am J Med Genet. 1996 May 3. 63(1):223-30. [Medline].

Palmer JS. Genitourinary manifestations in boys and girls associated with genetic disease. J Men’s Health Gend. March 2006. 3(1):71-79.

Cassidy SB, Schwartz S. Prader-Willi Syndrome. GeneReviews. Available at http://www.ncbi.nlm.nih.gov/books/NBK1330/. Accessed: 2 July 2011.

Waters AM, Beales PL. Bardet-Biedl Syndrome. GeneReviews. Available at http://www.ncbi.nlm.nih.gov/books/NBK1363/. Accessed: 2 July 2011.

Allanson JE. Noonan Syndrome. GeneReviews. Available at http://www.ncbi.nlm.nih.gov/books/NBK1124/. Accessed: 2 July 2011.

Ragan DC, Casale AJ, Rink RC. Genitourinary anomalies in the CHARGE association. J Urol. 1999 Feb. 161(2):622-5. [Medline].

Lalani SR, Hefner MA, Belmont JW et al. CHARGE Syndrome. GeneReviews. Available at http://www.ncbi.nlm.nih.gov/books/NBK1117/. Accessed: 2 July 2011.

Bourgeois MJ, Jones B, Waagner DC. Micropenis and congenital adrenal hypoplasia. Am J Perinatol. 1989 Jan. 6(1):69-71. [Medline].

Becker D, Wain LM, Chong YH, et al. Topical dihydrotestosterone to treat micropenis secondary to partial androgen insensitivity syndrome (PAIS) before, during, and after puberty – a case series. J Pediatr Endocrinol Metab. 2016 Feb. 29 (2):173-7. [Medline].

Xu D, Lu L, Xi L, et al. Efficacy and safety of percutaneous administration of dihydrotestosterone in children of different genetic backgrounds with micropenis. J Pediatr Endocrinol Metab. 2017 Nov 27. 30 (12):1285-91. [Medline].

Stoupa A, Samara-Boustani D, Flechtner I, et al. Efficacy and Safety of Continuous Subcutaneous Infusion of Recombinant Human Gonadotropins for Congenital Micropenis during Early Infancy
. Horm Res Paediatr. 2017 Jan 12. [Medline].

Krishnan A, Chagani S, Rohl AJ. Preoperative Testosterone Therapy Prior to Surgical Correction of Hypospadias: A Review of the Literature. Cureus. 2016 Jul 8. 8 (7):e677. [Medline]. [Full Text].

Calikoglu AS. Should boys with micropenis be reared as girls? [editorial]. J Pediatr. 1999 May. 134(5):537-8. [Medline].

Wisniewski AB, Migeon CJ, Gearhart JP, et. al. Congenital micropenis: Long-term medical, surgical, and psychosexual follow-up of individuals raised male or female. Hormone Research. 2001. 56:3-11. [Medline].

Drugs: Testosterone. MD Consult. Available at http://www.mdconsult.com. Accessed: 2 July 2011.

Karen S Vogt, MD Pediatric Endocrinologist, Department of Pediatrics, Division of Endocrinology, Walter Reed National Military Medical Center

Karen S Vogt, MD is a member of the following medical societies: American Academy of Pediatrics, American Diabetes Association, Endocrine Society, Pediatric Endocrine Society

Disclosure: Nothing to disclose.

Michael J Bourgeois, MD Director of Pediatric Undergraduate Medical Education, Associate Professor, Department of Pediatrics, Division of Pediatric Endocrinology and Metabolism, Texas Tech University School of Medicine

Michael J Bourgeois, MD is a member of the following medical societies: American Academy of Pediatrics, American Diabetes Association, Texas Medical Association

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

George P Chrousos, MD, FAAP, MACP, MACE, FRCP(London) Professor and Chair, First Department of Pediatrics, Athens University Medical School, Aghia Sophia Children’s Hospital, Greece; UNESCO Chair on Adolescent Health Care, University of Athens, Greece

George P Chrousos, MD, FAAP, MACP, MACE, FRCP(London) is a member of the following medical societies: American Academy of Pediatrics, American College of Physicians, American Pediatric Society, American Society for Clinical Investigation, Association of American Physicians, Endocrine Society, Pediatric Endocrine Society, Society for Pediatric Research, American College of Endocrinology

Disclosure: Nothing to disclose.

Sasigarn A Bowden, MD Associate Professor of Pediatrics, Section of Pediatric Endocrinology, Metabolism and Diabetes, Department of Pediatrics, Ohio State University College of Medicine; Pediatric Endocrinologist, Associate Fellowship Program Director, Division of Endocrinology, Nationwide Children’s Hospital; Affiliate Faculty/Principal Investigator, Center for Clinical Translational Research, Research Institute at Nationwide Children’s Hospital

Sasigarn A Bowden, MD is a member of the following medical societies: American Society for Bone and Mineral Research, Central Ohio Pediatric Society, Endocrine Society, International Society for Pediatric and Adolescent Diabetes, Pediatric Endocrine Society, Society for Pediatric Research

Disclosure: Nothing to disclose.

Arlan L Rosenbloom, MD Adjunct Distinguished Service Professor Emeritus of Pediatrics, University of Florida College of Medicine; Fellow of the American Academy of Pediatrics; Fellow of the American College of Epidemiology

Arlan L Rosenbloom, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Epidemiology, American Pediatric Society, Endocrine Society, Pediatric Endocrine Society, Society for Pediatric Research, Florida Chapter of The American Academy of Pediatrics, Florida Pediatric Society, International Society for Pediatric and Adolescent Diabetes

Disclosure: Nothing to disclose.


Research & References of Microphallus|A&C Accounting And Tax Services