Purpose or Case Report: Perinatal Hypoxic Ischemic Injury (HII) has a higher prevalence in the developing world. One of the primary concepts for suggesting that an imaging pattern reflects a global insult to the brain is when the injury is noted to be bilateral and symmetric in distribution. In the context of HII in term neonates, this is either bilateral symmetric (a) peripheral/watershed injury (WS) or (b) bilateral symmetric Basal-ganglia-thalamus (BGT) pattern, often with the peri-Rolandic and hippocampal injury. Unilateral, asymmetric or unequal distribution of injury may therefore be misdiagnosed as perinatal arterial ischemic stroke. This has been previously reported in the typical distribution patterns, without a clear indication of the prevalence. We aimed to determine the prevalence of unilateral, asymmetric and unequal degree HII and to characterize the distribution on MRI in a large database of patients with Cerebral Palsy (CP) from South Africa.
Methods & Materials: We retrospectively reviewed MRI findings in 1213 children diagnosed with HII on MRI. Those with unilateral and/or asymmetric and/or symmetric but unequal distribution of HII were extracted for further evaluation.
Results: 1213 MR reports in patients with reported diagnosis of HII were reviewed. Of these, 156 (13%) had unilateral, asymmetric or unequal distribution of HII features, ranging in age from 1-20 years, (median 7 years, IQR: 4-9 years). These were unilateral HII in 2/1213 (0.2%) - involving only the WS in both instances. Asymmetric HII was present in 48/1213 (4%) - asymmetric BGT in 4 (0.3%), asymmetric watershed in 6 (0.5%) and asymmetric combined BGT and WS in 38 (3.1%). There was bilateral, symmetric but unequal degree of HII in 106/1213 (8.7%) – BGT in 17 (1.4%), WS in 20 (1.6%) and combined BGT and WS in 69 (5.7%).
Conclusions: Even though the vast majority of children with CP due to HII demonstrate a characteristic bilateral symmetric pattern of injury, 13% demonstrate a unilateral, asymmetric, bilateral, symmetric but unequal degree of HII. Differentiation from PAIS, which is mostly unilateral and distributed typically in the MCA territory should be possible and recognition of the BGT or WS MRI injury patterns add confidence to the diagnosis in such scenarios.