Anatomy of diplegia: an hypothesis.

Periventricular leukomalacia (PVL) occurring in relation to the body of the lateral ventricle could account for damage to the corticospinal tracts. However, PVL in this location is relatively rare, and the view that it causes the diplegia of preterm birth is challenged on the anatomical grounds that the corticospinal tracts to the legs are some distance away from the main sites of PVL, which are at the collateral trigone and near to the interventricular foramen. If PVL lesions do cause permanent nerve damage, it is surprising that cortical blindness in diplegia is so uncommon. A dying-back neuropathy caused by selective damage to corticospinal neurons could be considered as an alternative hypothesis to account for the paralysis of diplegia.