Micropenis

What is micropenis?

Micropenis is a penis that is normal in structure but whose length is much smaller than expected for age. The medical criterion: the stretched penile length is 2.5 standard deviations below the average for that age. In a baby born at term, this means less than about 2.5 cm.

Micropenis is rare. Most parents’ concerns that “the penis is small” are actually a buried penis: the penis is normal in size but hidden under fat and skin.

How is the penis measured correctly?

The measurement is done by a doctor: the fat pad above the pubic bone is pressed down to the bone, the penis is gently stretched, and the distance from the bone to the tip of the penis is measured. Measuring without pressing the fat pad makes the penis look falsely small.

Causes

The growth of the penis in the womb and in the first months of life depends on the hormone testosterone. Causes of micropenis:

• the pituitary gland in the brain producing too little of the hormones that stimulate the testicles (most common),
• the testicles themselves producing too little testosterone,
• the tissues responding poorly to testosterone,
• genetic syndromes,
• sometimes no cause is found.

Testing

• hormone tests (testosterone, LH, FSH), especially in the 1st–3rd months of life,
• genetic testing (karyotype) when needed,
• joint evaluation with a pediatric endocrinologist.

Treatment

The main treatment is testosterone: it is given in short courses as an injection or a cream. In most children the penis grows considerably. If there is a hormone deficiency, treatment continues in adolescence as well.