Abnormal cortical plate (polymicrogyria), heterotopias and brain damage in monozygous twins.

We report 5 cases of abnormal cortical plate (polymicrogyria or microgyric-like pattern) and heterotopias associated with hypoxic-ischemic brain injuries in monochorionic diamniotic twin fetuses of respectively 22, 26, 28, 31, 32 weeks gestation. These fetuses belonged to a series of 5 pairs of patients (10 cases) presenting with the characteristic features of the twin-to-twin transfusion syndrome. Three of them (2 donors and 1 recipient) were macerated and the brains were not available for study. Two (most likely recipient twins) survived. In the remaining 5 fetuses (3 donors and 2 recipients) with neuropathological study there were cortical plate abnormalities. In 2 cases, the cortex was dysmorphic and consisted of focal nodular distribution or vertical stripes of neurons. True polymicrogyria was focal in 2 cases and involved almost the entire surface of the hemispheres in another one. Heterotopias of immature cells were found in 4 cases, either in the white matter or in the cortex or in both sites. There was a focal laminar necrosis only in 2 cases. The morphological pattern of the anomalies depends on the time of occurrence of the insult and on its severity. These abnormalities, although similar to those already described in singleton fetuses, illustrate the variety of cortical dysmorphia which may be associated with fetal hypoxic-ischemic injuries and emphasize the particular vulnerability of the brain in monozygotic twins, whether it belongs to the donor or the recipient.