Background and Objective Injury to the developing cerebellum is an increasingly recognised complication of extreme prematurity, with possible major implications for neurodevelopmental outcome. On routine cranial ultrasonography (cUS) through the anterior fontanelle (AF), visualisation of the posterior fossa structures is limited. The mastoid fontanelle (MF) provides a better view of the posterior fossa and improves the detection of cerebellar injury. In this study we investigated the incidence and characteristics of cerebellar injury in a cohort of very preterm infants, using the MF approach in addition to routine cUS through the AF, and compared cUS findings with magnetic resonance imaging (MRI).

Methods A cohort of 63 preterm infants (<32 weeks) was studied prospectively during the neonatal period with cUS, using the AF and MF. MRI was performed around term equivalent age.

Results Seven infants (11%) were identified with posterior fossa haemorrhage, using the MF approach. In only two of seven infants were the lesions seen on routine AF views. MRI confirmed the findings on cUS in all cases. MRI showed punctate haemorrhages in the cerebellum in six other infants with normal cUS findings. Combining the findings on cUS and MRI, cerebellar injury was diagnosed in 13/63 infants (21%).

Conclusions Cerebellar injury is a frequent finding in very preterm infants. cUS through the MF can demonstrate injury missed by the routine AF approach. However, punctate haemorrhagic lesions may still remain undetected even when the MF approach is used. The prognostic implications of these smaller lesions need further attention.