Presentation
Stage 3 twin-twin transfusion syndrome.
Patient Data
Two fetuses present.
Lower twin: smaller and stuck against the uterine wall with its head positioned nearest the cervix. This is the donor twin. There is borderline asymmetric lateral ventriculomegaly with the left lateral ventricular trigone measuring 10 mm and the right 8 mm.
Upper twin: surrounded by a large amount of amniotic fluid and was highly mobile as a result, during the examination. 3 mm focus of susceptibility related signal loss and subtle localized brain parenchymal volume loss in the left frontoparietal region. The findings are most consistent with a small, established hemorrhagic cortical infarct. Generalized symmetric widening of the CSF spaces is consistent with the recipient status of this twin and is a well recognized and often transient finding in such fetuses. Otherwise normal apperance of the brain and normal cerebral biometry.
The deepest pocket of amniotic fluid surrounding this twin is approximately 10 cm.
Placenta: The placenta is anterior and somewhat thin for this gestation measuring 16 mm in maximum AP diameter.
Fetal MRI obtained 5 days post laser photocoagulation.
Discordant amniotic fluid is no longer seen and the smaller of the 2 twins is now mobile and situated in the right side of the amniotic cavity.
Twin 1 (previous upper twin - now left cephalic)
Established hemorrhagic infarction again noted in the left frontal lobe. This is now more obviously associated with localized disruption of the zonal anatomy, but otherwise has not changed since the previous examination. No new hemorrhage or infarction is identified.
Twin 2 (previous lower twin now right breech)
Persistent borderline lateral ventriculomegaly which is stable, with each lateral ventricular trigone measuring 10 mm.
For ease of anatomic assessment, views of both fetal heads have been cropped and rotated into standard orientation. Please refer to sequence labels to distinguish the cephalic vs breech twins.
Cerebral development at 20 wks
At 20 weeks gestation, the interhemispheric and Sylvian fissures are always present. Note the shallow, rounded appearance of the Sylvian fissure at this stage. Over the next few weeks, it will become deeper, more squared and then angular as the temporal lobe folds over to cover the operculum. Other fissures have not yet appeared.
Also at this stage, we begin to see the normal 5 layered laminar appearance, which will persist until approximately 30 weeks gestation. From inner to outer, the layers are: 1.Ventricular zone (arrowhead); 2. periventricular fiber-rich zone (dotted arrow); 3. intermediate zone (curved arrow); 4. sub-plate (long thin arrow); 5. cortex (short thick arrow).
Note on the right side, localized disruption of the normal laminar pattern near the site of previous antenatal hemorrhage in this fetus (marked #).
The ganglionic eminences are low signal, highly cellular areas present within the subventricular zone, and still prominent at this stage; they will become less so as cells migrate from the ganglionic eminences to the neocortex, grey matter nuclei, thallami and hippocampi. Normal ganglionic eminences (short arrow) and germinal matrix (long arrow)
Case Discussion
This case demonstrates features of twin-twin transfusion syndrome with fetal MRI, prior to and after successful laser photocoagulation.
Both fetal brains are mildly abnormal. The donor twin has borderline ventriculomegaly, and the recipient twin has a small, established left frontal hemorrhagic infarct. Fetal cerebral appearances including sulcation and lamination are otherwise normal and age appropriate. Annotated images address the features of normal fetal brain development at 20 weeks which are seen in this case.
Case courtesy of Prof Stacy Goergen.