Although large cerebellar hemorrhages result in increased risk for mortality and severe neurodevelopmental deficits,[8
] the effects of smaller cerebellar hemorrhages seen on MRI and not cranial ultrasound have not been previously reported. This prospective cohort study suggests that smaller cerebellar hemorrhages seen only on MRI are associated with an increased risk for abnormalities on neurological examination. However, the presence of these hemorrhages is not associated with abnormalities on developmental testing at ages 3–6 years.
This study of neuroimaging in preterm newborns demonstrated a 2% incidence of ultrasound-detected cerebellar hemorrhage and an 8% incidence of cerebellar hemorrhage detected only on MRI. These rates are comparable with those reported by other groups.[1
] In agreement with previous studies,[8
] large cerebellar hemorrhages seen on ultrasound were associated with a high risk for adverse outcome – 67% mortality was seen during the initial hospitalization. However, due to the few cases of such hemorrhage in survivors in this cohort, we were unable to assess neurodevelopmental outcome.
This study highlights the power of MRI to detect cerebellar hemorrhages of 1 to 3mm in diameter – hemorrhages previously not detected on cranial sonograms. With increasing use of MRI in brain injury diagnosis in preterm newborns and a resulting increase in identification of these smaller hemorrhages, it is thus important to understand the neurodevelopmental consequences of such findings to guide parental counseling and patient therapy. Of note, the MRI sequences used in this study used a scan thickness of 4mm, and thus may have missed some incidences of these small hemorrhages. The actual incidence of these hemorrhages may be even more common than reported here.
Higher rates of abnormalities on neurological examination were seen in children with MRI-only cerebellar hemorrhages, with a 5-fold increased odds compared with those without cerebellar hemorrhage. Due to the variability of the physician examining the subjects in follow-up, there may be nondifferential misclassification of this outcome measure. As a result, this study may have underestimated the magnitude of the association between MRI-only cerebellar hemorrhages and abnormal neurological examination. Abnormalities tend to include hypertonia and hyperreflexia normally associated with spastic diplegic cerebral palsy. These associations were not dampened after adjusting for the severity of IVH and WMI. Notably, however, these deficits are less severe than those previously reported in children with larger ultrasound-detected cerebellar hemorrhages, and do not prevent ambulation.
That the neurological deficits observed with cerebellar hemorrhage are the same as those classically described with IVH and WMI raises new questions as to the neural pathways that may be involved in these findings. One possibility is that cerebellar injury directly results in changes in tone and reflexes. Another possibility is that limitations in cerebellar function magnify the deficits associated with IVH and WMI, resulting in increased recognition of these findings by the evaluating clinician.
In contrast with previous studies showing cognitive and language impairment associated with cerebellar hemorrhages, this study did not show an association between MRI-only cerebellar hemorrhages and deficits in performance or verbal domains using the WPPSI-III test. This suggests a dramatic difference between the effects of these smaller MRI-only hemorrhages on cognitive outcome compared with previous reports in larger ultrasound-visible hemorrhages. A wide range of ages at developmental testing may be a limitation in this study, although there was no difference between the ages of assessment between those with and without cerebellar hemorrhage, and the variability in scores were small. In addition, more subtle neurocognitive deficits that might result from these cerebellar hemorrhages may only become evident at a later age than tested for this study.
Although we were able to study the effect of overall cerebellar injury on outcome, there were not enough cases of cerebellar hemorrhage to compare effects of bilateral versus unilateral cerebellar hemorrhage or left hemisphere versus right hemisphere hemorrhages, or to look at the association between particular regions of injury and specific neurological findings. Larger studies of preterm newborns with localized cerebellar hemorrhage on MRI would help elucidate whether the location of cerebellar hemorrhage can further inform us regarding the specific deficits that would ensue.
The finding of increased risk of neurological deficits after cerebellar hemorrhage not visible on ultrasound adds to the growing body of evidence that shows additional benefit of the use of MRI to screen for brain injury in preterm newborns in addition to the routine use of cranial ultrasound.[17
] Considering that preterm newborns with cerebellar hemorrhage not visible on cranial ultrasound have 5-fold increased odds of abnormal neurological examination by school age, this would provide additional information to aid in deciding which children require closer follow-up after hospital discharge and earlier interventions.
With an increasing awareness of the risk of cerebellar hemorrhage in preterm newborns and its associated risk for mortality and severe developmental delay, it has become important to understand the range of cerebellar hemorrhage which can occur and the associated outcomes. Compared with large cerebellar hemorrhages previously identified by cranial ultrasound, small 1 to 3 mm hemorrhages seen by MRI in the preterm cerebellum are associated with an increased risk of abnormalities on neurological examination, but not with cognitive impairment. These findings will be important to aid physicians in counseling parents regarding potential outcomes in their newborn children, and highlight the utility of MRI scans in the assessment of preterm cerebellar injury.