Ulegyria refers to shrunken cortical gyri due to ischaemic damage in the neonatal period.
The main method of detecting ulegyria is MRI will reveal a focal gliosis of affected gyri. In addition, unaffected gyri are also present especially in watershed regions indicating delayed effects of perinatal hypoxic damage.
There are three main criteria for diagnosing ulegyria using MRI. The presence of a poorly demarcated lesion, atrophy and thinning of the cortex resulting in the characteristic “mushroom” like shape of ulegyria and presence of white matter signal abnormalities on FLAIR.
Ulegyria must be differentiated from polymicrogyria, which is a neuronal migration disorder, characterized by excessive folding of the surface gyri and a thickening of the cerebral cortex, rather than the sulcal scarring that is typical of ulegyria.
The period in which polmicrogyria and ulegyria emerge is also different. Polymicrogyria typically forms while the embryo's central nervous system is maturing. Ulegyria is acquired later in development during the perinatal period after neuronal migration has already occurred. It is also suspected that polymicrogyra is genetically linked, whereas ulegyria is caused by environmental factors like ischemia.
Polymicrogyria can lead to similar conditions that are linked to ulegyria such as mental retardation, cerebral palsy, and epilepsy. It has been observed that patients with polymicrogyria are not receptive to epilepsy surgery. However, responses of patients with ulegyria to similar surgeries are still not fully known, which makes distinction of these two disorders significant.