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Microphallus Clinical Presentation

  • Author: Karen S Vogt, MD; Chief Editor: Stephen Kemp, MD, PhD  more...
Updated: Jun 23, 2016


Neonatal hypoglycemia, often in the first 24 hours of life, is associated with other pituitary hormone deficiencies, including panhypopituitarism, growth hormone deficiency, and adrenal insufficiency. Other features that may be associated with hypopituitarism during the neonatal period include breech delivery, optic nerve hypoplasia or aplasia, nystagmus, other midline defects, and cholestasis with prolonged direct hyperbilirubinemia.

Poor growth or failure to thrive is also associated with other pituitary hormone deficiencies.

An abnormal sense of smell (anosmia or hyposmia) suggests Kallmann syndrome (hypogonadotropic hypogonadism with abnormal olfaction).

Other congenital anomalies may provide clues to a genetic syndrome.

Family history of similarly affected children could suggest a familial form of hypogonadism or other hormone deficiency, defect in steroidogenesis (autosomal recessive), or androgen insensitivity (X-linked). Family history of unexplained death in the first year of life could suggest pituitary hormone deficiencies, adrenal insufficiency, or both.



The infant or child with micropenis should be thoroughly examined for dysmorphic features and other congenital anomalies.

This examination should include careful inspection of the face and mouth for cleft lip or palate or other indications of midfacial hypoplasia.

Abnormal growth velocity after the first 6-12 months of life suggests growth hormone deficiency with or without other pituitary hormone deficiencies.

A thorough examination of the genitalia, including proper measurements of the stretched penis length, position of the urethral opening, and location and size of the testes, is important. One or both testes may be abnormally descended because testosterone also plays a role in testicular descent.

The proper technique for measuring the penis is to use a rigid ruler held firmly against the symphysis pubis at a right angle. Firm but gentle traction is placed on the penis to stretch it upward along the ruler to the point of increased resistance.[1]

An alternate, less traumatic method is to use the index finger of one hand as a gauge pressed against the symphysis. As gentle traction is placed on the penis, the index finger of the other hand is used to mark the length on the gauge finger, and a tape measure is used to determine the length.



Most cases of micropenis are due to fetal testosterone deficiency. Testosterone deficiency may be caused by a defect anywhere along the hypothalamic-pituitary-gonadal axis or a defect in peripheral androgen action (5-alpha reductase deficiency or PAIS). Micropenis may also be caused by isolated growth hormone deficiency. It can occur as a primary idiopathic structural anomaly or may be associated with a genetic syndrome. The most common cause of micropenis is abnormal hypothalamic or pituitary function that leads to hypogonadotropic hypogonadism. The next most common cause is a primary testicular disorder that leads to hypergonadotropic hypogonadism.

Conditions associated with hypogonadotropic hypogonadism

Kallmann syndrome

Anosmia (lack of sense of smell) or hyposmia is a prominent feature of Kallmann syndrome, which occurs in 1 per 10,000 males. The underlying abnormality is failure of migration of gonadotropin-releasing hormone (GnRH) and olfactory neurons from the olfactory placode to their proper locations in the hypothalamus and olfactory bulb, respectively. About half of males with Kallmann syndrome are born with a micropenis. The inheritance pattern is autosomal dominant (FGFR1/KAL-2 gene, among others), autosomal recessive, or X-linked recessive (KAL-1 gene). Associated anomalies may include cleft lip and palate, renal agenesis, sensorineural hearing loss, visual abnormalities, synkinesia (mirror image movements), cerebellar ataxia, agenesis of the corpus callosum, short metacarpals, or pes cavus. Abnormal or absent olfactory bulbs or sulci (folds) are seen on brain MRI in 90% of patients.[15, 16]

Isolated hypogonadotropic hypogonadism

Sense of smell is normal in this condition, differentiating it from Kallmann syndrome.[15]

Multiple pituitary hormone deficiencies

Hypoglycemia may occur due to growth hormone and adrenocorticotrophic hormone (ACTH) deficiencies. Midline defects and cholestatic liver disease can be associated. Hypopituitarism may be secondary to transcription factor mutations (eg, PROP-1, LHX3); however, in most instances, genetic evaluation is not part of the routine diagnostic evaluation.[17, 18]

Septo-optic dysplasia (SOD)

Major features of SOD include the triad of absent septum pellucidum, optic nerve hypoplasia, and hypopituitarism. Wandering nystagmus may be present. The multiple pituitary hormone deficiencies may be present at birth or develop over years. Mutations in the HESX1 gene (RPX) have been associated with SOD.[17, 18]

Conditions associated with decreased testosterone production and hypergonadotropic hypogonadism


In this condition, also known as vanishing testes or testicular regression syndrome, testes are absent in an individual with a normal male karyotype. Micropenis results when testicular degeneration occurs after 12-14 weeks' gestation. The testicular degeneration is likely due to torsion or other vaso-occlusive event in utero.[8, 9]

LH-receptor defects

Autosomal recessive mutations are found in the LHCGR gene in this rare condition and cause Leydig cell hypoplasia in males. The genital phenotype varies from normal-appearing female to male with micropenis.[14, 19]

Defects in testosterone steroidogenesis

Incomplete forms of 17 beta-hydroxysteroid dehydrogenase deficiency type 3 can cause micropenis, but the genitalia are most often female in appearance or less often ambiguous. The enzyme 17-beta-hydroxysteroid dehydrogenase normally converts androstenedione to testosterone. In the deficiency state, the androstenedione-to-testosterone ratio is elevated (after hCG stimulation in the prepubertal state) and is expressed as a testosterone-to-androstenedione ratio of less than 0.8. These individuals undergo profound virilization at puberty.[8, 20, 21]

Deficiency of 5-alpha reductase

5-alpha reductase peripherally converts testosterone to the more potent DHT, which is necessary for virilization of the male external genitalia. The genitalia in most children with this autosomal recessive condition are usually more ambiguous, with varying degrees of incomplete labioscrotal fusion and hypospadias. The hallmark biochemical abnormality is an elevated testosterone-to-DHT ratio (usually >30:1) after hCG stimulation if prepubertal. These individuals also undergo profound virilization at puberty. Genetic testing for SRD5A2 gene mutations is commercially available.[13, 22, 23]

Partial androgen insensitivity syndrome

PAIS is caused by a defect in the androgen receptor. Isolated micropenis is not typically a manifestation of PAIS because the genitalia are usually more ambiguous. Gonadotropin and testosterone levels are elevated in this condition. Because the gene that codes for the androgen receptor is located on the X chromosome, PAIS is inherited in an X-linked manner.[9]

Genetic syndromes

Klinefelter syndrome (47,XXY) and other poly X syndromes

Features of this syndrome include hypergonadotropic hypogonadism, tall stature, gynecomastia, small firm testes, increased leg length in proportion to height, and increased risk for learning difficulties.[24]

Prader-Willi syndrome (PWS)

Hypogonadism is a feature of PWS and usually manifests in males as cryptorchidism and an underdeveloped scrotum. Some also have a micropenis. Characteristic features of PWS include hypotonia, weak suck, feeding difficulties and failure to thrive in infancy with later development of hypothalamic hyperphagia and often obesity. Motor and language developmental delay, short stature, small hands and feet, emotional instability (perseveration, obsessions and compulsions), almond-shaped eyes, and triangular mouth are additional features. PWS occurs in 1:20,000 live births. The underlying genetic abnormality is the lack of expression of genes on the Prader-Willi critical region, 15q11.2-13, of the paternally inherited chromosome 15, which may be due to deletion (70%), maternal uniparental disomy (25%), or a imprinting defect (5%).[25]

Bardet-Biedl syndrome

Features of this syndrome include hypogonadotropic hypogonadism, rod-cone dystrophy with progressive visual impairment, obesity, short stature, polydactyly, developmental delay, renal anomalies leading to end-stage renal disease, and hepatic fibrosis. Inheritance of this syndrome is in an autosomal recessive pattern and mutations in 14 genes have been implicated.[26]

Noonan syndrome

Features of this syndrome include short stature, webbed neck, hypertelorism, ptosis, low posterior hairline, low-set ears, pectus excavatum, cryptorchidism, valvular pulmonary stenosis, lymphedema, and bleeding abnormalities. Noonan syndrome is inherited in an autosomal dominant manner, although approximately half of all cases represent new mutations. Mutations in the PTPN11 gene are found in 50% and smaller percentages have mutations in KRAS, SOS1, and RAF1.[27]

CHARGE syndrome

The syndrome is defined by coloboma, heart disease, atresia choanae, retarded growth and development, genital anomalies and hypogonadism, and ear anomalies and deafness. Neuropathic bladder, hydronephrosis, vesicoureteral reflux, and ureteropelvic junction obstruction may also occur. Given these potential renal and urinary tract abnormalities, bladder and renal ultrasonography and voiding cystourethrography (VCUG) are indicated in those suspected of having this syndrome. Sixty to seventy percent have a mutation in the CHD7 gene.[28, 29]


More rare genetic syndromes associated with micropenis include Robinow syndrome, Rud syndrome, and IMAGe syndrome.[12]

Contributor Information and Disclosures

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.

Specialty Editor Board

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.

Chief Editor

Stephen Kemp, MD, PhD Former Professor, Department of Pediatrics, Section of Pediatric Endocrinology, University of Arkansas for Medical Sciences College of Medicine, Arkansas Children's Hospital

Stephen Kemp, MD, PhD is a member of the following medical societies: American Academy of Pediatrics, American Association of Clinical Endocrinologists, American Pediatric Society, Endocrine Society, Phi Beta Kappa, Southern Medical Association, Southern Society for Pediatric Research

Disclosure: Nothing to disclose.

Additional Contributors

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.

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

  2. 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].

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

  4. 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].

  5. 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].

  6. 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].

  7. 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.

  8. 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.

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

  10. 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].

  11. 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].

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

  13. 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].

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

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

  16. Pallais JC, Au M, Pitteloud N, et al. Kallmann Syndrome. GeneReviews. Available at Accessed: 3 July 2011.

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

  18. 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.

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

  20. 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].

  21. 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].

  22. 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].

  23. 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].

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

  25. Cassidy SB, Schwartz S. Prader-Willi Syndrome. GeneReviews. Available at Accessed: 2 July 2011.

  26. Waters AM, Beales PL. Bardet-Biedl Syndrome. GeneReviews. Available at Accessed: 2 July 2011.

  27. Allanson JE. Noonan Syndrome. GeneReviews. Available at Accessed: 2 July 2011.

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

  29. Lalani SR, Hefner MA, Belmont JW et al. CHARGE Syndrome. GeneReviews. Available at Accessed: 2 July 2011.

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

  31. 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].

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

  33. 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].

  34. Drugs: Testosterone. MD Consult. Available at Accessed: 2 July 2011.

  35. Menon RK, Trucco M, Stratakis CA. Molecular Endocrinology and Endocrine Genetics. Sperling MA. Pediatric Endocrinology. 3rd ed. Philadelphia, PA: Elsevier Saunders; 2008. Chapter 1.

  36. Styne DM, Grumbach MM. Puberty: Ontogeny, Neuroendocrinology, Physiology, and Disorders. Melmed S. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011. Chapter 25.

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