Paediatrics: Micropenis

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.