METHODS

Clinical information was not often available; when available, it was usually brief, reporting mental retardation and seizures and, sometimes, family history; therefore, this report focuses almost exclusively on the imaging features. All MRIs were of good to excellent quality. Studies contained images that were found, after analysis, to have at least one small region of small gyri separated by thin or shallow sulci or an area of apparently thick cortex (5–7 mm) with irregularity of the cortical surface or the cortical-white matter junction; these images are the basis of this study. A total of 159 MRI scans were analyzed (7 excluded because of unsatisfactory images). All had images acquired in 3 planes (sagittal, axial, and coronal) and had both T1 and T2 weighted images. All images were reviewed by the author for the following characteristics: extent and location of the abnormal sulcation; characteristics of the gyri and sulci; associated anomalies. Based on the location, extent, and associated anomalies, as well as the clinical history (when available), the studies were classified into known categories of polymicrogyria that are largely based upon the location and extent of the morphologic abnormality. Several patients with known clinical diagnoses (9 patients with Aicardi syndrome, 9 with Zellweger syndrome, 3 with megalencephaly, polymicrogyria, and hydrocephalus (MPPH) syndrome, and 7 with congenital cytomegalovirus infection) were grouped together; other than CMV, all patients in a group had similar localization of PMG. Those that did not correspond to known genetic or familial disorders were grouped by morphology into the following nine categories: bilateral perisylvian PMG (Kuzniecky et al., 1993); unilateral hemispheric PMG (Chang et al., 2006); bilateral frontal PMG (Guerrini et al., 2000); bilateral frontoparietal PMG (Chang et al., 2004); bilateral parasagittal parieto-occipital PMG (Guerrini et al., 1997); bilateral lateral parietal PMG (Barkovich et al., 1999); bilateral asymmetric PMG; focal PMG (restricted to less than one lobe of a single hemisphere, grouped together despite they were in multiple different locations); and diffuse PMG (involving at least 3 of the 4 lobes in each hemisphere (Chang et al., 2004).

RESULTS

By far, the most common distribution of PMG in this group was bilateral perisylvian (Table); these 50 patients accounted for 31% of the studies analyzed. The next most common distribution was unilateral hemispheric, with 31 patients (19%); of note, all of these patients had PMG centered in the sylvian regions. The remainder of the distributions were considerably less common: focal PMG in 16 patients (10%), bifrontal PMG in 12 (8%); diffuse, Aicardi syndrome (with unilateral frontal PMG in all cases), and Zellweger syndrome (with bilateral perirolandic PMG) in 9 (6%) each; congenital infections (diffuse in 7 (4%), with cytomegalovirus infection in 6 and lymphocytic choriomeningitis infection in 1); bilateral frontoparietal in 6 (4%); bilateral asymmetric polymicrogyria and MPPH in 3 each; and bilateral parasagittal parieto-occipital and bilateral lateral parietal PMG in 2 each (Table).