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Paediatrics: Micropenis
Micropenis is often an incidental finding on newborn examination.
Micropenis
Micropenis is often an incidental finding on newborn examination.
An intact hypothalamic-pituitary-gonadal axis is required for the formation of a normal-sized phallus and for the descent of the testis. Both GH and the gonadotrophins are required for phallic growth.
The finding of micropenis warrants assessment of hypothalamic-pituitary function and exclusion of both GH deficiency and HH. Micropenis may also be part of a syndrome causing ambiguous genitalia.
Evaluation
Penile size
- Measured from pubic tubercle to tip of the stretched penis in a term baby.
- Normal size at birth is usually >3cm.
- Micropenis <2.2–2.5cm (varies with ethnicity).
General examination
- Dysmorphism.
- Midline craniofacial defects.
Ophthalmic examination
Optic nerve hypoplasia/septo-optic dysplasia.
Investigations
- The US of the head for midline defects.
- MRI head.
- Anterior pituitary hormone levels (basal and stimulated): ACTH and cortisol; GH (IGF-I, IGFBP3); LH and FSH; TSH and fT4.
- Karyotype.
Management
Referral to a paediatric urologist is often required. If severe micropenis is present a decision regarding sex assignment will be needed.
Treatment with a short course of IM testosterone or topical application of dihydrotestosterone cream may stimulate penile growth and improve appearances.