 |
|
Cranial ultrasound is an excellent tool for screening high-risk neonates, particularly when performed serially. Scanning through the posterior or mastoid windows also improves the ability of cranial ultrasound to assess less readily visualized brain structures (eg, the cerebellum). Although MRI complements ultrasound, it has the additional benefit of being able to capture the appearance of the immature brain in all planes with superb resolution. The application of advanced MRI techniques, such as diffusion-tensor sequences, allows us to identify early ischemia and to map developing white matter tracts.
How? The majority of commercial scanners operate at 1.5 Tesla, but imaging at 3 Tesla has advantages for the neonatal brain.1 (Note: Tesla is the unit used to measure the strength of a magnetic field.) In order to avoid patient injury, attention must be paid to ensuring that any internal or attached devices, such as reservoirs or ventriculoperitoneal shunts, are compatible with the field strength being used. A coil that fits closely to the neonatal head and an imaging protocol optimized for the neonatal brain are both required.
The latter should include diffusion-weighted or tensor imaging.2 Motion artifact is the main reason for an unsuccessful examination, and sedation is usually required. It may be necessary to resort to fast sequences or motion correction techniques in order to obtain clinically relevant data.3 Neonates require cardiovascular monitoring throughout an MRI examination. In sick neonates who die without antemortem imaging, a postmortem examination may be useful.4
Why? Neonatal imaging can provide information about the pattern of acquired brain lesions in high-risk neonates5-10 that will vary with the clinical history.11-16 This, in turn, is closely associated with specific patterns of later impairment. Neonates who develop signs of hypoxic-ischemic encephalopathy (HIE) following an acute sentinel event (eg, placental abruption) sustain bilateral and usually symmetrical lesions within the basal ganglia and thalami (BGT), and exhibit an abnormal appearance in the posterior limb of the internal capsule (PLIC).
The appearance of the PLIC is a powerful predictor of later cerebral palsy.5 The severity of lesions within the BGT determines the severity and nature of this motor impairment, and the likelihood of associated difficulties with cognition, feeding, and, later, seizures. The appearance of the PLIC facilitates the prediction of outcome in term-born neonates with perinatal stroke6 and in preterm infants imaged at term-equivalent age with focal lesions or periventricular leukomalacia (PVL).17-19
Who? Neonates who should be imaged include all those with such neurologic signs as poor feeding, abnormal tone, seizures, and abnormal head circumference. Neonates may have had a brain abnormality diagnosed antenatally on ultrasound or MRI (eg, ventricular dilation, a small cerebellum, or absent corpus callosum). Although the quality of fetal MRI scanning is improving, a neonatal MRI will still provide superior-quality images and should be performed. To date, no evidence suggests that MRI should replace ultrasound as a screening tool for the preterm infant at discharge or at term-equivalent age. The majority of preterm infants will have evidence of mild ventricular dilation, slightly reduced cortical folding, and areas of long T1 and long T2 — so-called diffuse excessive high-signal intensity — in the white matter.
The more obvious these changes, the more likely it is that there will be future developmental problems.20 MRI in preterm infants should be reserved for those in whom the ultrasound is abnormal or there are unexplained neurologic signs. In the case of an abnormal ultrasound, MRI should provide additional, complementary information for predicting motor impairment.21 Neonates with evidence of central nervous system infection, whether preterm or term, warrant the use of MRI as well.
When? The optimum timing for the use of MRI in the term infant with suspected perinatal injury is within 1 to 3 weeks postdelivery, when the lesions are the most obvious on conventional sequences. In the severely ill neonate, information may be required earlier, in order to make informed decisions about the withdrawal of intensive care. In such situations, diffusion-weighted imaging should always be used, as recently acquired lesions may not be obvious on conventional sequences. In the preterm infant, the best prognostic information may be obtained at term-equivalent age, although with severe lesions, an earlier image may have the ability to predict a poor outcome.
In summary, MRI is a valuable adjunct to ultrasound in preterm and term infants. Correct timing and appropriate imaging techniques are critical in obtaining relevant information.
Commentary References
| 1. |
Rutherford M, Malamateniou C, Zeka J, Counsell S. MR imaging of the neonatal brain at 3 Tesla.
Eur J Paediatr Neurol. 2004;8(6):281-289. |
 |
| 2. |
Rutherford MA, Ward P, Malamatentiou C. Advanced MR techniques in the term-born neonate with perinatal brain injury. Semin Fetal Neonatal Med.
2005; 10(5):445-460. |
|
| 3. |
Jiang S, Xue H, Glover A, Rutherford M, Rueckert D, Hajnal JV. MRI of moving subjects using multislice snapshot images with volume reconstruction (SVR): application to fetal, neonatal, and adult brain studies. IEEE Trans Med Imaging. 2007;26(7):967-980.
|
|
| 4. |
Nicholl RM, Balasubramaniam VP, Urquhart DS, Sellathurai N, Rutherford MA. Postmortem brain MRI with selective tissue biopsy as an adjunct to autopsy following neonatal encephalopathy. Eur J Paediatr Neurol. 2007;11(3):167-174.
|
|
| 5. |
Rutherford MA, Pennock JM, Counsell SJ, Mercuri E, Cowan FM, Dubowitz LM, et al. Abnormal magnetic resonance signal in the internal capsule predicts poor neurodevelopmental outcome in infants with hypoxic-ischemic encephalopathy. Pediatrics. 1998;102(2 pt 1):323-328.
|
|
| 6. |
Mercuri E, Rutherford M, Cowan F, Pennock J, Counsell S, Papadimitriou M, et al. Early prognostic indicators of outcome in infants with neonatal cerebral infarction: a clinical, electroencephalogram, and magnetic resonance imaging study. Pediatrics. 1999;103(1):39-46.
|
|
| 7. |
Mercuri E, Ricci D, Cowan FM, Lessing D, Frisone MF, Haataja L, et al. Head growth in infants with hypoxic-ischemic encephalopathy: correlation with neonatal magnetic resonance imaging. Pediatrics. 2000;106(2 pt 1):235-243.
|
|
| 8. |
Miller SP, Ramaswamy V, Michelson D, Barkovich AJ, Holshouser B, Wycliffe N, et al. Patterns of brain injury in term neonatal encephalopathy. J Pediatr. 2005;146(4):453-460.
|
|
| 9. |
Cowan FM, de Vries LS. The internal capsule in neonatal imaging. Semin Fetal Neonatal Med. 2005;10(5):461-474.
|
|
| 10. |
Logitharajah P, Rutherford MA, Cowan FM. Hypoxic-ischemic encephalopathy in preterm infants: antecedent factors, brain imaging and outcome. Pediatr Res. 2009 Apr 22. [Epub ahead of print].
|
|
| 11. |
Okereafor A, Allsop J, Counsell SJ, Fitzpatrick J, Azzopardi D, Rutherford MA, et al. Patterns of brain injury in neonates exposed to perinatal sentinel events. Pediatrics. 2008;121(5):906-914.
|
|
| 12. |
Burns CM, Rutherford MA, Boardman JP, Cowan FM. Patterns of cerebral injury and neurodevelopmental outcomes after symptomatic neonatal hypoglycemia. Pediatrics. 2008;122(1):65-74.
|
|
| 13. |
Foran A, Cinnante C, Groves A, Azzopardi DV, Rutherford MA, Cowan FM. Patterns of brain injury and outcome in term neonates presenting with postnatal collapse. Arch Dis Child Fetal Neonatal Ed. 2009; 94(3):F168-F177.
|
|
| 14. |
Gkoltsiou K, Tzoufi M, Counsell S, Rutherford M, Cowan F. Serial brain MRI and ultrasound findings: relation to gestational age, bilirubin level, neonatal neurologic status and neurodevelopmental outcome in infants at risk of kernicterus. Early Hum Dev. 2008;84(12):829-838.
|
|
| 15. |
Leijser LM, de Vries LS, Rutherford MA, Manzur AY, Groenendaal F, de Koning TJ, et al. Cranial ultrasound in metabolic disorders presenting in the neonatal period: characteristic features and comparison with MR. imaging. AJNR Am J Neuroradiol. 2007;28(7):1223-1231.
|
|
| 16. |
Mercuri E, Cowan F, Rutherford M, Acolet D, Pennock J, Dubowitz L. Ischaemic and haemorrhagic brain lesions in newborns with seizures and normal Apgar scores. Arch Dis Child Fetal Neonatal Ed. 1995;73(2):F67-F74.
|
|
| 17. |
Rademaker KJ, Uiterwaal CS, Beek FJ, van Haastert IC, Lieftink AF, Groenendaal F, et al. Neonatal cranial ultrasound versus MRI and neurodevelopmental outcome at school age in children born preterm. Arch Dis Child Fetal Neonatal Ed. 2005;90(6):F489-F493.
|
|
| 18. |
de Vries LS, Roelants-van Rijn AM, Rademaker KJ, van Haastert IC, Beek FJ, Groenendaal F. Unilateral parenchymal haemorrhagic infarction in the preterm infant. Eur J Paediatr Neurol. 2001;5(4):139-149.
|
|
| 19. |
Roelants-van Rijn AM, Groenendaal F, Beek FJ, Eken P, van Haastert IC, de Vries LS. Parenchymal brain injury in the preterm infant: comparison of cranial ultrasound, MRI and neurodevelopmental outcome. Neuropediatrics. 2001;32(2):80-89.
|
|
| 20. |
Krishnan ML, Dyet LE, Boardman JP, Kapellou O, Allsop JM, Cowan F, et al. Relationship between white matter apparent diffusion coefficients in preterm infants at term-equivalent age and developmental outcome at 2 years. Pediatrics. 2007;120(3):e604-e609.
|
|
| 21. |
Spittle AJ, Boyd RN, Inder TE, Doyle LW. Predicting motor development in very preterm infants at 12 months’ corrected age: the role of qualitative magnetic resonance imaging and general movements assessments. Pediatrics. 2009;123(2):512-7.
|
|
|
