OC22.07: Magnetic resonance imaging of fetal cerebral lesions in severe twin–twin transfusion syndrome (TTTS): confrontation with ultrasound (US)

Abstract

Monochorial twins are subjected to ten fold increased risk of cerebral palsy, compared to the general population. This increased risk in TTTS is mainly related to intertwin through placental vascular anastomosis, hemodynamic imbalance, as well as anemia and prematurity. We reviewed all cases referred for TTTS, treated by either serial amnioreduction, laser coagulation, intrauterine transfusions or undergoing cord coagulation of an abnormal co-twin. We selected specific examples of cerebral lesions, in order to show the respectives advantages and pitfalls of prenatal cerebral ultrasound examination and Mri in the evaluation of the fetal prognosis. Serial US examination of the fetal brain aimed at obtaining transfontanellar views in axial, coronal and sagittal section. Doppler pic systolic velocity was also measured in the midcerebral artery. Fetal Mri was performed at 1Tesla with single shot fast spin echo T2sequences in the three directions, gradient echo T1 and diffusion weighted imaging in axial section. Fetal Mri is particularly contributive from 3 weeks following the insult to the brain. Fetal Mri is particularly helpful in peripheric lesions. It does allow a more precise identification of hemorrhagic or clastic lesion. Small cystic lesion may be difficult to appreciate because of a poor spacial resolution when compared with US. Diffusion weighted imaging is feasible in utero, but their results are not homogeneous and need further studies. The most frequent lesions were clastic, including hydranencephalia, supratentorial necrosis, uni or bilateral, ischemia of the corpus callosum and lenticulostriate area, multicystic encephalomalacia, periventricular leucomalacia, intraventricular periventricular and parenchymal hemorrhage, ventriculomegaly and brain atrophy. Post natal evaluation were performed with serial transfontanellar high resolution US examination. Mri was sometimes performed when the correct gestational age approached full term, as well as at 4 month or one year of life. Pathological confrontation were performed in severes cases that led to perinatal death or termination of pregnancy. The prognosis of fetal cerebral lesion in the context of TTTS is mainly evaluated by ultrasound and Mri is contributive in the most subtle lesions. Transfontanellar fetal cerebral ultrasound examination is facilitated by a transvaginal route and should be serially performed. Its value is close to postnatal examination. Mri at 32 weeks can accurately depict abnormal maturation as well as small peripheric lesions and more clearly identify periventricular lesions detected with high resolution US specially in the workup of a ventricular dilatation. Such detailed and serial evaluation should allow for mainly subtle lesion with a good prognosis to be recognized only postnatally.