ROLE OF MAGNETIC RESONANCE SPECTROSCOPY IN PERINATAL ASPHYXIA IN TERM NEONATES AND ITS COMPARISON WITH DWI AND CONVENTIONAL MRI.

Abstract

Background and purpose: Neonatal hypoxic encephalopathy is one of the most important causes of neurological morbidity and mortality in term neonates. MR imaging is the most sensitive and specific imaging technique to assess perinatal asphyxia associated brain injury in full term neonates. In this study we investigated the usefulness of MR spectroscopy peak ratios, ADC values and conventional MR findings in term neonates following hypoxic/ ischemic insult.

Objectives: To compare the association between encephalopathy following hypoxia in term neonates with: proton MRS ratios, ADC values and with conventional MRI.

Study Design: prospective longitudinal study conducted over two years.

Participants: 25 term neonates with clinical, neurological and laboratory features of HIE.

Materials and Methods: Conventional MRI (T1 and T2 weighted sequences) was done within 72 hours and about one week of life along with diffusion-weighted imaging (DWI) and MR Spectroscopy was done in 25 inpatient term neonates with clinical and neurological features of encephalopathy following perinatal asphyxia. MR spectroscopy peak ratios in both basal ganglia and watershed zones were compared with ADC values and conventional MR findings for each grade of HIE.

Results: Out of 25 patients who were suspected of hypoxic encephalopathy based on clinical, neurological and laboratory features, 15 patients had early positive conventional MR findings (T₁ hyperintensity in basal ganglia/ thalami and watershed zone) , 16 patients had positive late positive conventional MR findings (T₁ hyperintensity in basal ganglia/ thalami and watershed zone, with T₂ hypointensity) , 19 patients positive diffusion weighted imaging based on diffusion restriction with low ADC values, and 22 patients had positive MRS findings with high lactate/choline and lactate/NAA ratio The most common abnormality detected on DWI was diffusion restriction with low ADC values. The most consistently noted abnormality on MR spectroscopy was presence of variable sized lactate doublet peak centered at 1.31 ppm. The peak area ratios of lactate/choline and lactate/NAA in both basal ganglia and watershed zones were compared with grade of HIE that showed a significant association. MRS ratios were compared with ADC values in both central grey matter and watershed zones for each HIE grade that also showed significant association. Higher association was found between spectroscopy findings and hypoxic ischemic injury compared to MR imaging and ADC.

Conclusion: MRS peak ratios of lactate /choline and lactate/NAA in both basal ganglia/thalami and watershed zones correlate well with the severity of hypoxic –ischemic encephalopathy. The combination of MRS, DWI with ADC values and conventional MRI may assist in localizing and predicting the severity of ischemic injury in HIE patients.

Implications: Proton MRS can be used to asses brain injury in term neonates following hypoxic / ischemic insult particularly when done within early neonatal period.