Perinatal hypoxia is a vital cause of long-term neurologic complications ranging from mild behavioral deficits to intractable seizures, mental retardation, and cerebral palsy. With improvements in care of at-risk neonates, more and more children survive. This makes it increasingly important to assess, soon after birth, the prognosis of children with hypoxic–ischemic encephalopathy .
Magnetic resonance imaging (MRI) is a leading source of brain injury biomarkers in perinatal HIE. Different patterns of brain injury by conventional MRI have been related to severity and phenotype of neurodevelopmental sequel after HIE. However, conventional MRI requires availability of an experienced pediatric neuro radiologist, can be subjective, and provides broad severity classification on an ordinal scale . Quantitative MRI techniques such as MRS can overcome these limitations by providing continuous, reproducible measures of brain microstructural and metabolic injury .
MRS outperforms MRI in detecting abnormalities of metabolism even when normal structures are present on magnetic resonance (MR) imaging studies. Therefore, combination of MR studies and 1 HMRS may make it possible to evaluate severity and help predicting outcome of HIE .
MRI examination was normal in nearly half of the patients (16 cases) (all had lac peak on MRS examination), the remaining 14 cases showed multiple abnormalities as periventricular leukomalacia (PVL) and ventriculomegaly, reduced myelination (absent of high signal intensity of PLIC in T1WI), white matter injury displaying hypo intensity signal in T1WI and hyper intensity in T2WI, germinal matrix hemorrhage, brain atrophy, and smudged grey white matter differentiation (brain edema). These findings are in agreement with Zhu et al.  who examined 31 neonates with HIE classified in 3 groups underwent follow-up MRI. All patients in group I died. In group II (moderate HIE), the abnormalities observed in the brains of patients included extensive extracerebral spaces and encephalatrophy, cerebral infarction, focal encephalomalacia and encephalatrophy, multiple cyst-like encephalomalacia, marble-like basal ganglia, periventricular leukomalacia, myelin hypoevolutism, gliosis, and thinning of corpus callosum. In group III, normal or slightly extensive extracerebral spaces were observed. For 11 cases in group III, MRI detected slightly extensive extracerebral spaces in 2 cases. The MRI examination was normal in 9 cases. Also in the study of Guo et al.  out of the total of 29 cases, 13 cases had no MRI abnormalities; 10 had minor to moderate abnormalities; 4 cases had severe abnormalities; with two mortality cases (one after 6 days and one after 12 days).
Patients were classified by MRS into 3 groups according to the value of Lac/Cr ratio; Group I had Lac/Cr lower than 0.5, Group II in which Lac/Cr ranging between 0.5 and 1.5 and Group III in which Lac/Cr ratio was higher than 1.5.
It was found that Lac/Cr ratio positively correlates with clinical staging, severity of brain abnormalities in MRI examination and patients’ outcome on neurological examination at 1 year so it promotes worse prognosis. As in group III with the highest Lac/Cr ratio which included 14 patients all from stage III Sarnat, highest incidence of brain abnormalities on MRI examination and the worst prognosis (2 cases died, 10 cases developed cerebral palsy and 2 cases had delayed development), in group II which included 6 patients all from Sarnat II stage showing normal MRI examination, 4 cases had developmental delay and 2 cases had cerebral palsy, but in group I included 10 patients (6 patients were clinically classified as Sarnat stage I and 4 patients as Sarnat stage II) all of them had normal neurological examination on follow-up.
These results are in agreement with the Egyptian study Noaman et al.  who studied the role of MRS and chemical biomarkers in grading and assessing the severity and prognosis of HIE non-invasively in 30 newborn with HIE (15 stage I Sarnat, 11 stage II Sarnat, 4 stage III Sarnat) and concluded that Lac/Cr was a good indicator in recognition of the outcome as in the group whom Lac/Cr greater than 1.5 severe clinical symptoms and signs (Sarnat stage III) were present and then all neonates were died.
These results also matches with Fan et al.  who studied MRI and MR spectroscopy in 38 full-term neonates suffered from HIE (9 neonates with Sarnat stage I, 13 Sarnat stage II and 16 stage III according to clinical signs and the presence of a history of asphyxia) and illustrated that the group whose Lac/Cr ratio more than 1.5 had severe lesions detected by MRI and poor outcome and they concluded that MRS is a very useful tool in diagnosis patients with HIE and predicting their outcome.
In 1HMRS peak metabolites ratios: At the level of basal ganglia, Lac/Cr and NAA/Cho ratios had higher sensitivity 95 than NAA/Cr 90 while highest specificity was for Lac/Cr 90.1 versus NAA/Cr 90 then NAA/Cho 87. At the level of thalamus, each of Lac/Cr, NAA/Cr and NAA/Cho ratios had equal sensitivity 80, while Lac/Cr ratio had higher specificity 100 versus NAA/Cr 92 then NAA/Cho 89. At the level of frontal white matter, NAA/Cr and NAA/Cho showed higher sensitivity 95 than Lac/Cr while Lac/Cr and NAA/Cho showed higher specificity 80 than NAA/Cr 70. At the level of occipital white matter NAA/Cho was the highest sensitivity 95 versus NAA/Cr and Lac/Cr 90 and 87 while Lac/Cr was the highest specificity 100 versus NAA/Cr and NAA/Cho 80 and 75, respectively. Lac/Cr ratio higher than 0.38, 0.36, 0.42 in basal ganglia, thalamus and white matter was significantly predictive of pathological outcome. NAA/Cr ratio lower than 0.9, 0.75, 0.9, 0.8 in basal ganglia, thalamus, frontal and occipital white matter was significantly predictive of pathological outcome. NAA/Cho ratio lower than 0.29, 0.25, 0.31, 0.3 in basal ganglia, thalamus, frontal and occipital white matter was significantly predictive of pathological outcome.
The current study found that NAA/Cr and NAA/Cho were significantly lower in patients with poor outcome than patients with favorable outcome. This is in agreement with Lally et al.  who examined 223 neonates of whom 160 examined by MRS in a multi-centric cohort study to assess prognostic accuracy of MRS biomarkers as early predictors of the neurodevelopmental abnormalities observed years after neonatal encephalopathy and found that each of NAA/Cr, NAA/Cho, Lac/NAA and NAA concentration are specific and sensitive in predicting patient’s outcome. Cutoff value of NAA/Cho within the thalamus was < 0.22 (close to found in current result 0.25) showing significant correlation with poor outcome.
These results also are in consistent with Ancora et al.  who studied 20 full-term neonates with different stages of perinatal hypoxia and found that MR spectroscopy is an accurate early predictor for poor neurologic outcome in neonates as the difference of NAA/Cr, NAA/Cho and Lac/NAA between normal neonates and others with pathological outcome was statistically significant. NAA/Cr ratio ≤ 0.67 within the basal ganglia (close to study’s cutoff 0.75 in thalamus and 0.9 within basal ganglia) was significant of poor outcome.
There is disagreement with Guo et al.  who examined 24 neonates and found that MRS is a useful technique for distinguishing between HIE and normal newborns. However, with regard to differentiating between grades, MRS should be interpreted in conjunction with performances on T1WI in reverse to current study in which the differences of Lac/Cr, NAA/Cr and NAA/Cho ratios between mild, moderate and severe cases were statistically significant (P = 0.05). Also the ascent in Lac/Cr ratio was not marked in contrast to present study. It seems likely that this difference of results is related to the time of the MRS examination with respect to the hypoxic–ischemic event. The mean time from injury to MRS in patients in the current study was 23 days; for patients in Guo et al.  was 7 days.
The present results proved that in all examined regions HIE stage III had significantly higher Lac/Cr ratio than stage II than stage I. This matches Thayyil et al.  who reviewed all studies that compared MR biomarkers performed during the neonatal period (including conventional MRI, DWI and MRS) with neurodevelopmental outcome at age of 1 year and found that MRS specifically Lac/NAA and Lac/Cr ratio had better diagnostic accuracy than conventional MRI performed at any time during the neonatal period.
On the other hand, a larger recent study was done by Alderliesten et al.  who studied 88 neonates, 22 of whom died and 7 had unfavorable motor outcome. They documented that infants with poor outcome had obviously higher Lac/NAA ratios than infants with a normal outcome. This current study has relied on Lac/Cr ratio in adverse to many studies which depended on Lac/NAA ratio as it is an unreliable index of Lac accumulation as NAA is often reduced in hypoxic–ischemic injury as mentioned by Cady .
At the level of parieto-occipital cortex and basal ganglia Ancora et al.  had examined 23 patients with mean age from 7 to 10 days and concluded that NAA/Cr and Lac/Cr measured at parietal–occipital level were the best predictors of outcome. Cutoff value of Lac/Cr > 0.3 (close to current study > 0.42) at parietal-occipital level was able to discriminate between newborns that developed CP and those that did not until 2 years of age. Similar to this recent study which found that Lac/Cr ratio was significantly higher in patients with poor outcome than patients with favorable outcome and that NAA/Cr ratio was significantly lower in patients with poor outcome than patients with favorable outcome.
Other studies match current results as Shanmugalingam et al.  who studied 21 newborns with HIE and documented that compared with normal outcome, lactate/Cr and lactate/NAA were higher and NAA/Cr was lower in patients who had severe outcome and Cheong et al.  who studied the value of MRS in the thalamus in 17 newly born infants suffered from perinatal HIE and also concluded that Lac/Cho, Lac/Cr and Lac/NAA in neonates with neonatal encephalopathy with severe outcome were all increased compared with control values and with those infants with normal or mild outcome. In addition, NAA/Cr and NAA/Cho in the severe outcome group were reduced compared with both control and normal or mild groups.
It was found that in all examined regions HIE stage III had significantly higher Lac/Cr ratio and lower NAA/Cr and NAA/Cho ratios than stage II than stage I. This is in agreement with Zhu et al.  who examined 46 patients to investigate the prognostic values of MRS obtained from neonatal brains with hypoxic–ischemic encephalopathy and found that, Glx-a/Cr and Lac/Cr values were higher in the moderate and severe HIE groups than in the mild HIE group, whereas the NAA/Cho and NAA/Cr values in severe HIE group were much lower than in mild and moderate HIE. Additionally, there was positive correlation between the values of Glx-a/Cr and Lac/Cr and the severity of brain injury. But there was a negative correlation between the values of NAA/Cr and NAA/Cho and the severity of brain injury in HIE (in current study glutamine was not measured by MRS machine).
The results in the present study were also consistent with those of the study of Barkovich et al.  in which patients experienced injury within an average of 7 days prior to MRS and found associations with NAA levels in HIE and a preliminary study of Cady  in which metabolite concentrations in neonates with neonatal encephalopathy documented increases in (Lac) and reductions in (NAA), (Cho), and (Cr) similar to those reported in this current study.