Paediatric Imaging

Cranium bifidum

persistence of wide fontanelles into childhood. The normal fontanelles are transient zones of non-ossified tissue lying between converging ossification centres in the frontal and temporal bone (anterior fontanelle) and parietal and occipital bones (posterior fontanelle). They narrow progressively after birth and close by 12 to 18 months in the case of the anterior and earlier for the posterior fontanelle. Persistence into adulthood is rare (less than 1%). Cranium bifidum is caused by delay in ossification of the anterior or posterior parietal bones which leads to large anterior or posterior or confluent frontoparietal skull defects. The underlying brain is covered by a membrane of dura and pericranium. The scalp is intact. Over time continued ossification of the vault may reduce a single parietal foramen to two defects which may persist or close over time. In 1in 25,000 individuals frontal or parietal foramina (Fig.1) may persist as full thickness defects in the skull vault. This may be seen in families in an autosomal dominant inheritance pattern. Midline cranium bifidum may be associated with cleidocranial dysostosis, midline cleft face syndrome, and aminopterin fetopathy. Clinically the abnormality is manifest as a soft spot in the skull vault and may bulge outward when a child cries.

EP

Fig.1

Skull radiograph showing typical parietal foramina. Note the lucent defects on either side of the mid line.

Cranium bifidum, Fig.1