Micro Penile Syndrome (Disorder)

What is Micro Penile Syndrome?

Micro Penile syndrome, also known as Microphallus is a medical condition, which is measured after birth. This syndrome is diagnosed if stretched penile length is below the value of – 2.5 standard deviations of the mean value; internal and external genitalia are normally formed. Micro Penile syndrome usually occurs due to lack of testosterone during fetal development [1, 2].


Micro Penile Syndrome can be considered to be a part of disease group with ambiguous genitalia. The genitalia are otherwise normal. In most cases, this syndrome occurs due to lack of testosterone during fetal development. Testosterone deficiency occurs due to disruption in the hypothalamic-pituitary-gonadal axis or due to defected periphery action of androgens. Another possible cause is isolated growth hormone deficiency. The most common cause of Micro Penile syndrome occurs due to hypergonadotropic hypogonadism- hypogonadism due to lack of response from gonads to sex hormones.

Micro Penile Syndrome

Infant presented with Micro Penis
Image source:ncbi.nlm.nlh.gov

Hypergonadotropic Hypogonadism

Syndromes associated with hypergonadotropic hypogonadism include:

  • Kallmann syndrome- rare condition, in which the main feature is anosmia (loss of sense of smell) and micropenis. It is also associated with cleft lip, vision and hearing anomalies, and renal agenesis.
  • Isolated hypogonadotropic hypogonadism- syndrome is similar to Kallmann syndrome, but in this case the sense of smell is normal
  • Pituitary hormone deficiencies due to hypopituitarism. Hypopituitarism can also be a part of a syndrome, like Septo-optic dysplasia, which is characterized with absence of septum pellucidum (membrane between two brain hemispheres), optic nerve hypoplasia and hypopituitarism.

Hypogonadotropic hypogonadism

Hypogonadotropic hypogonadism and decreased testosterone production is associated with:

  • Anorchia- absent testes in male with normal karyotype. If testicular degeneration occurs after 12-14 week of pregnancy, it can result with Micro Penile syndrome.
  • Mutation in the Luteinising hormone/choriogonadotropin gene (LHCGR), which causes defect in luteninising hormone receptors, which can cause micropenis.
  • Defects in genesis of testosterone.

Genetic Syndromes

Genetic syndromes that are associated with Micro penile syndrome:

Other syndromes that can cause Micro penile syndrome:

  • 5-alpha reductase deficiency- lack of this enzyme, that usually converts testosterone to a much more potent form- dihydrotestosterone, can cause ambiguously appearing genitalia in various degrees.
  • Partial androgen insensitivity
  • Robinow syndrome
  • Rud syndrome [1,2]

Micro Penile Syndrome in Adults

In some cases, older children before puberty might be concerned of small genitalia. In most cases these patients are obese and the stretched penile length is normal. Further investigations should be done in case cryptorchidism is present [1].

Adult men can present with concerns about small penis size, when their penis size is in the normal range. This occurrence is called Small Penis Syndrome and it is psychiatric disorder that belongs to a larger psychiatric condition group called Body Dysmorphic disorders. This syndrome can cause a variety of psychological symptoms, like anxiety, depression, and social dysfunction with social withdrawal or isolation [3].


burried penis

Image showing burried penis
Image source: gvsc.hk

The first step to diagnosing micropenis in newborns is physical examination of external genitalia. When examining, the penis should have following characteristics:

  • Small size, that has to be measured by gently stretching the penis, to exclude “buried penis”- a condition where penis seems small, due to a fat fold in the pubic area.
  • Normal foreskin
  • Normal localization of the opening of urethra

After initial examination, laboratory studies should be done. It is important to do genetic analysis and confirm the chromosomal sex- normally for males it should be 46 XY. If the karyotype is abnormal, further investigations should be done, that can prove the suspected diagnosis. Other laboratory studies that are done for baby with 46 XY karyotype are:

  • Levels of gonadotropins- Luteinizing hormone and follicle stimulating hormone
  • Anti- Müllerian hormone and Inhibin-B. These substances are markers for the presence of testicular tissue, in case the baby is presented with cryptorchidism (one or both testes have not descended in the scrotum).


Possible location of testes in criptorchidism
Image source: medical-dictionary.thefreedictionary.com

  • Testosterone and dihydrotestosterone levels. Levels of these hormones have to be measured before and after stimulation with synthetic human chorionic gonadotropin (hCG). Usually the ratio between testosterone and DHT is measured, to evaluate possible 5-alpha-reductase deficiency
  • If hypopituitarism is suspected, glucose, insulin, growth hormone, total tyroxine, thyrotropin stimulating hormone and cortisol levels should be obtained[1,2]

Some of the possible causes for Micro penile syndrome, like chromosomal abnormalities, can be found using diagnostic tests during pregnancy. Ultrasound during pregnancy can also detect possible genital abnormalities [4].

Imaging Studies

In case genitalia are ambiguous, pelvic ultrasonography can be used. If ultrosonagraphy detects uterus and ovaries, it suggests that the karyotype is female, but infant has virilized genitalia

Magnetic resonance imaging of the head is used when hyopituitarism is suspected. In case of Kallmann syndrome, olfactory abnormalities can be detected [1,2].


First line of treatment is testosterone therapy. Usually intra muscular injections are used for three months. It is effective if the underlying cause is testosterone deficiency. Testosterone therapy can also be a diagnostic measure. If after three month therapy there is no increase in the size of the penis, it suggests androgen insensitivity syndrome. With appropriate therapy, infant or child can achieve normal adult penis size. It is important to start this therapy before the puberty, because it primes the penis for later growth.

Human chorionic gonadotropin has also been used to improve testicular steroidogenesis and growing of the penis. It can be used in cases of idiopathic hypogonadotrophic hypogonadism that presents with micropenis. By using hCG, serum testosterone levels increase, as well as penile length and testicular volume [5].

In severe cases, for example, in case of testosterone insensitivity, gender reasignement and genitoplasty can be performed. Usually surgical intervention is not necessary, because mostly infants who present only with micropenis are sensitive to medication therapy.

In case of this syndrome, circumcision should be avoided until all the diagnostic and treatment measures have been done [1, 2].

ICD 10 Code

Micro Penis Syndrome is classified in the International Classification of Diseases and related health problems (World Health Organization). This condition is classified under Q55.62- Hypoplasia of penis. Letter Q stands for congenital malformations, deformations and chromosomal abnormalities.

Small penis syndrome, a body dysmorphic disorder is classified under Mental, Behavioral and Neurodevelopmental disorders with code F45.22 [6].

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  1. http://emedicine.medscape.com/article/947504-overview
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3890219/
  3. http://small-penis-facts.com/?page_id=12
  4. http://www.jultrasoundmed.org/content/28/10/1389.full
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3214853/
  6. http://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.22

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