Clinical presentation

Micropenis:

• Incidental finding on newborn examination.

• Finding on examination of an hypoglycaemic baby.

Definition

Penile size: measured from the pubic tubercle to tip of the stretched penis in a term baby is usually >3 cm. Micropenis is a measurement <2.2–2.5 cm (varies with ethnicity).

In the preterm baby the normal penile length (cm) is 2.27 + 0.16 GA, where GA is the gestational age in weeks.

Approach to the problem

History:

• Family history of ambiguous genitalia.

• Ethnic origin.

Examination:

• Dysmorphism.

• Midline defects: hypertelorism, cleft palate.

• Ophthalmic examination: Optic nerve hypoplasia/septo-optic dysplasia.

• Symptoms/signs hypothalamic–pituitary hormone deficiencies (see Chapter 7).

Differential diagnosis

• Normal variant.

• Anterior pituitary hormone deficiency.

• Ambiguous genitalia (see Chapter 8).

• Syndromes, such as CHARGE association, Prader–Willi syndrome.

Investigations

• Investigate as for hypopituitarism (see Chapter 7).

• It is essential to do pre-feed blood sugars until normal and stable.

• Temperature.

• Ultrasound of head for midline defects.

• Anterior pituitary hormone levels:

• – Adrenocorticotrophic hormone (ACTH) and cortisol.

• – Growth hormone (GH) (insulin-like growth factor (IGF-I), insulin-like growth factor binding protein-3 (IGFBP3)).

• – Luteinizing hormone (LH) and follicle stimulating hormone (FSH).

• – Thyroid-stimulating hormone (TSH) and free thyroxine (fT4).

• Magentic resonance imaging (MRI) of the head.

• Karyotype.

• Genetics opinion.

• Investigate as for ambiguous genitalia if appropriate (see Chapter 8).