FETAL BRAIN LESIONS FOLLOWING ENDOSCOPIC LASER SURGERY IN TWIN TO TWIN TRANSFUSION SYNDROME: A MRI CLASSIFICATION

Background and purpose: Brain injury in monochorionic pregnancies complicated by twin-to-twin transfusion syndrome (TTTS) remains incompletely understood, and reported patterns vary widely due to heterogeneous imaging protocols. This study aimed to characterize fetal brain lesions after endoscopic laser surgery for TTTS using a structured MRI-based classification. Materials and methods: We conducted a retrospective observational study of TTTS pregnancies treated with endoscopic equatorial laser photocoagulation between January 2012 and January 2023. Fetuses with post-treatment brain abnormalities on MRI were included. MRI was performed 2-4 weeks after laser therapy following a standardized protocol. Lesions were independently reviewed and classified by neuroradiologists as ischemic or hemorrhagic, then categorized by radiologic pattern (focal, multifocal, diffuse) and vascular territory. Clinical variables, including donor/recipient status and Quintero stage, were compared using Fisher's exact test and the Mann-Whitney U test. Results: Thirty-six fetuses met inclusion criteria. Twenty (55.6%) were ex-recipients and 16 (44.4%) ex-donors. MRI was performed at a median gestational age of 22.7 weeks (range: 19.7-31.7). Ischemic lesions were identified in 31/36 fetuses (86.1%) and hemorrhagic lesions in 5/36 (13.9%). Among ischemic injuries, focal lesions predominated (22/31, 71.0%), most commonly within the middle cerebral artery (MCA) territory (18/22, 81.8%). Multifocal (6/31, 19.3%) and diffuse (3/31, 9.7%) patterns were less frequent. Hemorrhagic lesions involved the cerebellum (2/5, 40.0%) or thalamo-caudate sulcus (3/5, 60.0%). Ex-recipients more often exhibited focal ischemic lesions, while ex-donors showed a higher proportion of hemorrhagic injuries; however, no significant differences were detected by donor/recipient status or by Quintero stage. Conclusions: A structured MRI-based classification demonstrates that focal ischemia in the MCA territory is the predominant brain lesion after laser-treated TTTS, supporting thromboembolism as a likely mechanism. These findings contribute to understanding lesion patterns in TTTS and may aid future diagnostic and prognostic assessments. Abbreviations: ACA＝ anterior cerebral artery; DWI＝ diffusion-weighted imaging; GA＝ gestational age; ICA＝ internal carotidartery; IUD＝ intrauterine demise; IUGR/S-IUGR＝ (selective) intrauterine growth restriction; IVH＝ intraventricular hemorrhage; MC＝ monochorionic; PCA＝ posterior cerebral artery; TAPS＝ twin anemia-polycythemia sequence; TC＝ thalamo-caudate; TTTS＝twin-to-twin transfusion syndrome.