History
Sami, a 9-month-old boy, has been referred to the community paediatric clinic by his health visitor because his head circumference is on the 99.6th centile. He was born at 38 weeks’ gestation by spontaneous vaginal delivery, following an uneventful pregnancy to a Samoan woman. His birth weight was 4.3 kg (91st centile) and his head circumference at birth was 38 cm (98th centile). This is the mother’s third baby, but the other two children have a different father. Sami doesn’t sleep very well, waking up to three times per night, and this was the main reason his mother went to see her health visitor. Sami is otherwise well and has not had any previous medical problems. He has been able to sit unsupported for the last 2 months, he crawls, he can use either hand to pick up raisins or grains of rice. His mother has no concerns about his vision or hearing and he passed his newborn hearing screen. He is still breast-feeding but also eats purées and finger foods. The mother, her partner and the three children live in a two-bedroom flat. The growth chart in his parent-held child health record is shown in below
Examination
Sami is a well-looking child, who smiles and babbles continuously. He is not dysmorphic. His weight is 10.5 kg (91st centile), his length is 76.2 cm (98th centile) and his head circumference is 49.7 cm (99.6th centile). Cardiovascular and respiratory examinations are normal. His anterior fontanelle is almost closed. Neurological examination reveals normal tone, power and reflexes in the upper and lower limbs
1. What features in the history help to distinguish between the causes of a big head?
2. What other features should be sought on examination?
3. What is the most likely explanation for the large head circumference?