Newborn Hypoxic Ischemic Brain Injury. Hisham Dahmoush, MBBCh FRCR Lucile Packard Children s Hospital at Stanford

Transcription

1 Newborn Hypoxic Ischemic Brain Injury Hisham Dahmoush, MBBCh FRCR Lucile Packard Children s Hospital at Stanford

2 NO DISCLOSURES

3 INTRODUCTION Neonatal hypoxic-ischemic encephalopathy (HIE) is a major cause of mortality and morbidity 1.5 per 1,000 live births in developed countries and up to 6 per 1,000 live births in developing countries HIE is a major contributor to perinatal deaths and poor neurodevelopmental outcomes in survivors

4 Modalities US: Good screening modality in the NICU setting demonstrating periventricular echogenicities, periventricular cysts, hemorrhagic infarcts, IVH CT: No role MRI: Gold standard and most sensitive modality. Predictor of outcome

5 PATIENT PREPARATION Communication with NICU staff to ensure scanner availability Nursing replace standard-length tubes with extension tubes in the NICU to allow the administration of supportive medications and fluids from outside the MR imaging suite Swaddling to decrease motion and prevent hypothermia Vacuum cushion to decrease motion Noise attenuation with sponge ear plugs and dedicated neonatal earmuffs.

6 PATIENT PREPARATION Continuous monitoring of vital signs including cardiac monitoring with a pulse oximeter and MR-compatible ECG MR-compatible infusion pump, ventilator, and resuscitation equipment should be ready MR-compatible incubators with built-in coils save time and improve safety Small diameter neonatal coils or knee coils improve SNR

7 PROTOCOLS Diffusion-weighted imaging (or diffusion tensor imaging) T2 T1 (Spin echo or 3D spoiled gradient) Susceptibility imaging (GRE, SWI, SWAN, QSM) MR Spectroscopy (TE 144 msec BG and 35 msec WM) ASL Perfusion (Challenging in newborns) To optimize SNR and contrast, TR must be increased

8 Abnormal neonatal brain MRI predicts unfavorable neurodevelopmental outcome Patterns of brain injury on MRI vary according to 1. Degree of brain maturity at the time of injury (Premature Vs Full term) 2. Severity of hypoperfusion 3. Duration of hypoperfusion

9 Many MR scoring systems to correlate imaging findings to clinical outcome Deep GM and PLIC injuries have worse neurodevelopmental outcomes Watershed pattern typically considered to be mild and with minimal effect on neurodevelopmental outcome However, recent data that watershed injury is significantly associated with poor cognitive outcomes later in life

10 THERAPEUTIC HYPOTHERMIA Effective if started within 6 hours Decreased mortality and morbidity in moderate to severe HIE Less extensive watershed and deep GM injuries and a greater proportion of normal MRI Does not change the prognostic value of neonatal brain MRI 40% of survivors still demonstrate a spectrum of varying severity of poor neurodevelopmental outcome

11 EVOLUTION OF SIGNAL CHANGES

12 EVOLUTION OF SIGNAL CHANGES Diffusion in the first 24 hrs (particularly with hypothermia) may underestimate injury Hypothermia does not delay appearance of diffusion changes beyond 24 hrs Hypothermia may delay appearance of T1/T2 changes Hypothermia delays the peak of findings on T1/T2 (days 8-10 compared to days 4-8 without hypothermia) Hypothermia delays pseudonormalization on diffusion (restricted diffusion persists up to days compared to days 5-8 without hypothermia) No major hypothermia effect on increased lactate early and decreased NAA after the first week

13 TIMING OF IMAGING American Academy of Neurology Practice Parameter on Neuroimaging of the Neonate Brain MRI between days 2 and 8 in term neonates for diagnostic assessment and for prognostic evaluation of neurodevelopmental outcome ACOG recommend two MRI scans when feasible early (24 96 h) useful in delineating the timing of perinatal injury second (7-21 days) important to determine the extent of injury (ideal timing at 10 days)

14 DIFFUSION IMAGING Diffusion changes as early as day 2 of life even in children treated with hypothermia are associated with poor developmental outcome Deep gray matter involvement is an independent marker of poor outcome Extensive microstructural alterations in white matter beyond severe punctate WM lesions appear to negatively impact neurodevelopmental outcomes

15 MR SPECTROSCOPY Lactate/NAA ratio has the highest diagnostic accuracy of predicting outcome Lactate is the metabolite which best predicts outcomes in non-cooled newborns Gray matter NAA was the only metabolite significantly differing between groups with normal outcome and infants that died NAA may be the better metabolite in predicting outcome in cooled infants

16 MR SPECTROSCOPY Small amount of lactate is normal in preterm newborns NAA peak is low in children before the age of 2 years Propylene glycol (preservative in phenobarbital and Dilantin) causes inverted doublet at 1.1 ppm on intermediate TE mimicking lactate

17 MR BRAIN THERMOMETRY Non invasively measure brain temperature mainly through MRS Temperature affects hydrogen bonding between water molecules Shift of spectral position of water with temperature compared with a reference metabolite (e.g NAA) Newborns who develop brain injury tend to have higher brain temperatures during and after hypothermia BLUE: During hypothermia RED: After hypothermia Wu et al. Brain temperature in neonates with hypoxicischemic encephalopathy during therapeutic hypothermia. J Pediatr Dec;165(6):