micropenis

Last reviewed 01/2018

Micropenis is, literally, small penis.

• term inconspicuous penis is used for conditions including trapped or buried penis (as well as micropenis)
  • micropenis
    • condition where there is a morphologically normal penis (including penile urethra) - however the penile length is more than two standard deviations below the mean length for age (when stretched)
      • average stretched penile lengths are:
        • preterm (30 weeks' gestation) 2.5+/- 0.4 cm
        • term infants 3.5 +/- 0.4 cm
        • age of 2-3 years 5.1 +/- 0.9 cm
        • age of 11 years 6.4 +/- 1.1 cm
        • in full term infants - micropenis is defined as a stretched penile lenght of < 2.5 cm
      • micropenis usually reflects hypogonadism
  • buried penis
    • is a penile shaft that is normal size but is buried in an overbundance of prepubic fat - penis may appear to have a redundant foreskin and apparently require circumcision when it is in fact a buried penis
  • webbed penis
    • in this condition the penile shaft is attached by webbing to the scrotum
      • may be poor penile suspension (because the penile suspensory ligament only poorly anchors the penis to the pubic bone and so the penis droops and the normal contour of the penile phallus is lost) - thus presents as an inconspicuous penis
• diagnosis
  • best recognised and evaluated in the when neonatal examination occurs
    • if micropenis - examine for dysmorphic features - should include inspection of the face and mouth and for cleft lip or palate or other indications of mid-facial hypoplasia (associated with Kallman's syndrome)
    • if there is a family history of micropenis - suggests familial form of hormonal deficiency, androgen insensitivity or defect in steroidogenesis
  • measurement
    • thorough examination of genitalia
      • proper measurement of stretched penis length (gentle traction is placed on the penis during measurement) and testicular size
        • measurement of penile length should be undertaken using a rigid ruler held firmly against the pubis symphysis at a right angle - an alternative method is to use the index finger of one hand as a guage pressed against the pubis symphysis
      • note that it can be difficult to distinguish a boy with a microphallus and a girl with clitoromegaly - the finding of a normal scrotum with palpable testes indicates that the child has a high probability of being chromosomally male
  • other considerations:
    • consider Kallman's syndrome in patient has a lack of ability to smell
    • consider adrenal insufficiency, isolated growth hormone deficiency, or hypopituitarism if history of neonatal hypoglycaemia, visual abnormalities or poor growth
    • if a diagnosis of micropenis is considered in an older boy who is prepubescent and obese - usually have a normal sized penis (5-7cm) but apparent smallness is because penis is buried in fat
      • if however penile length is less than 4cm, particularly if other findings are also present, then further investigation/evaluation is required
        • consider possible causes such as chromosomal abnormalities e.g. Klinefelter's, Noonan's; gonodotrophin releasing hormone deficiency; pituitary lesion e.g. cranipharyngioma; gonadal failure
• management
  • it is important to consider the psychological impact of this condition - there may be stress and anxiety from the child and family
    • prompt referral and early surgical reconstruction can prevent psychological trauma for both parent and child
  • weight reduction - some believe that this is the treatment of choice if there is a buried penis where there is an overlapping abdominal fat pad

Notes:

• GP must consider the possibility of a buried penis if a patient requests a circumcision because of an apparent redundant foreskin. If circumcision occurs in this case then this might make optimal surgical revision impossible for the buried penis.Also a circumcision may result in a case of trapped penis with scarring and phimosis - repair of a trapped penis is much more difficult than a simple circumcision

Reference:

• (1)GP magazine (23/11/2007):32.