DIFFUSION WEIGHTED MAGNETIC RESONANCE IMAGING AND QUANTITATIVE APPARENT DIFFUSION COEFFICIENT IN EVALUATION OF PARENCHYMAL CHANGES IN TERM NEONATES WITH HYPOXIC ISCHEMIC BRAININJURY

SUMMARY

The primary objective of this study was to elucidate the role of diffusion weighted MR imaging and quantitative assessment of apparent diffusion co efficient (ADC) in evaluation of parenchymal changes in normothermic term neonates with hypoxic ischemic injury to brain. A total of forty normothermic term neonates underwent MR imaging with diffusion weighted imaging and were followed up for a period of 6 months. Topographic distribution of signal abnormalities, diffusion abnormalities, radiological pattern of injury and ADC values were correlated with the radiological severity and outcome at 6 months. Neonates with clinical diagnosis of HII were classified based on Thompson score, according to which 17 (42.5%), 16 (40%) and 7 (17.5%) neonates had mild, moderate and severe HII respectively. Most of the neonates with HII were males with a male- female ratio of 12.3:1. The associated risk factors were low birth weight, prolonged second stage of labour, MSAF, fetal growth restriction and oligohydramnios. Of the 40 neonates, 30 (75%) neonates required some form of respiratory support at birth or during the course. Radiological abnormalities and extent of involvement of white matter and deep gray nuclei were better assessed on conventional MR imaging than on DWI. Conventional MR imaging was sensitive in detecting the involvement of cortical gray matter but underestimated the extent of involvement which was better evaluated on DWI. DWI was more sensitive in evaluating the involvement and subjectively quantifying the degree of involvement of corpus callosum, PLIC, cerebellum and brain stem when opposed to conventional MRI. Proportion of neonates showing cortical involvement was higher in neonates with moderate and severe HII. Overall, occipital and temporal cortices had the highest frequency of involvement in 24 (60%) neonates each. Involvement of temporal and parietal cortices was more conspicuous on DWI than cMRI. Among the deep gray nuclei, putamen and thalamus were involved frequently in 27(67.5%) neonates of whom 14 (87.5%) and 7 (100%) neonates had moderate and severe HII respectively. Caudate and globus pallidus were involved in 5 (71.4%) and 4 (47.1%) neonates with clinically severe HII. Periventricular white matter was commonly involved than subcortical white matter. Out of the total 40 neonates, 25 (62.5%) and 34 (85%) neonates showed involvement of subcortical and periventricular white matter respectively on cMRI while 20 (50%) and 28 (70%) neonates respectively showed involvement on DWI. Parietal white matter was most commonly involved in 32 (80%) neonates of whom 12, 15 and 5 neonates had clinically mild, moderate and severe HII respectively. PLIC involvement was seen in 19 (47.5%) neonates on cMRI and 27 (67.5%) neonates on DWI and was frequently seen in neonates with clinically moderate and severe HII. Basal ganglia- thalamic pattern of injury was the most common pattern seen in 16 (40%) neonates. Global HII, multicystic encephalomalacia and multifocal hemorrhage were seen in 5 (12.5%) neonates each. Uncommon patterns of HII in term neonates included gangliothalamic necrosis, neonatal porencephaly, periventricular leucomalacia and germinal matrix hemorrhage. Radiological severity was assessed by a MRI based scoring system validated by Rutherford M et al. Out of 40, 4 neonates had radiologically mild HII, 11 had moderate HII and 24 had severe HII. We observed discordance between clinical and radiological severity assessment of HII, especially in neonates with mild and moderate HII. Out of 17 neonates with clinically diagnosed mild HII, 8 had radiologically moderate and 4 had severe HII. Of the 16 neonates with clinically diagnosed moderate HII, 14 had radiologically severe HII. We observed significant difference in the ADC values between abnormal regions of brain and the corresponding normal appearing areas. Mean ADC values of abnormal appearing cortex, deep gray nuclei, periventricular and subcortical white matter were 836.77, 783.48, 920.83 and 950.24 x 10-6sq.mm/s respectively while that of the corresponding normal appearing areas were 1216.12, 1211.06, 1544.72 and 1522.75±287.70 x 10-6sq.mm/s respectively. In our study, out of 40 neonates, 35 (87.5%) neonates had abnormal outcome at 6 months which comprised of death in 8 (20%) neonates and motor neurological abnormality in 27 (67.5%) neonates. Watershed pattern, basal ganglia- thalamic pattern, global HII and multicystic encephalomalacia were associated with abnormal motor neurological outcome at 6 months in 2 (100%), 12 (75%), 3 (60%) and 3 (60%) neonates respectively. Of the 8 neonates who expired within 6 months of age, 6 had radiologically severe HII with basal ganglia- thalamic pattern, global HII, multicystic encephalomalacia and massive intracranial hemorrhage in 3 (37.5%), 2 (25%), 2 (25%) and 1 (12.5%) neonates respectively. Radiological severity score of more than 6 was predictive of abnormal outcome at 6 months with specificity and PPV of 100%. Irrespective of the severity and pattern of HII. low ADC values in PLIC, corpus callosum and thalamus were significantly associated with abnormal outcome at 6 months.