Sixty-four autopsied brains of schizophrenic patients were neuropathologically examined and compared with 10 brains of non-schizophrenic controls. Clinical diagnoses were established retrospectively according to the Research Diagnostic Criteria and the International Classification of Diseases. We found: brains without deviations of the sulcogyral pattern of the temporal lobe or abnormal gross configuration (n = 22); brains with abnormal sulcogyral pattern of the temporal lobe or abnormal gross configuration (n = 42): with definite cytoarchitectonic abnormalities of the rostral entorhinal region in the parahippocampal gyrus and, in 16 cases only, in the ventral insular cortex (n = 20); with equivocal changes of the cytoarchitecture in these two regions (n = 22). Generally, these anatomical abnormalities were asymmetric. The histological findings in the two limbic regions consisted mainly of poorly developed structure in the upper layers, with a heterotopic displacement of single groups of nerve cells in the entorhinal region. Particularly, the disturbed structure of the second layer Pre-alpha in medial and central fields of the entorhinal region, situated in the parahippocampal gyrus (group 2a), suggests a disturbance of neuronal migration in a later phase of cortical development.

A postmortem histological comparison of 5 selected cases of schizophrenia with 5 non-schizophrenic controls showed a circumscribed malformation of the entorhinal cortex. The cortical alterations consisted mainly of a lack or a change of the characteristic island formations in layer II pre-alpha. Further, there were atypical neurons in layers II and III showing a conspicuous decrease of volume, often a change of the shape. They lay either in clusters or in columnar formations. These cells were considered "young neurons". The changes varied considerably from case to case and sometimes extended to all entorhinal layers. In one case the extension of the changes is described by means of serial sections in steps which extend over the whole rostral entorhinal region. Here, the striking architectural changes were formed in an exactly circumscribed sector and did not extend to the rostral hippocampal formation. On the whole, the changes are regarded as local migrational disturbances that occur during the second trimester of brain development. Neuronal displacements like these could give rise to various aberrant connections within the limbic system and related structures (e.g. the central position of the entorhinal region in circuits such as the entorhino-hippocampal loop, entorhinol-insula and entorhino-orbitofrontal reciprocal connections). Whereas alterations of the genetic programming of cell migrations may be suspected, various environmental influences (e.g. viral infections during the months III-V of pregnancy) appear to play a significant role. The malformations may be a decisive vulnerability factor for the later manifestation of the illness.

Both types of functional psychosis schizophrenia and manic depressive illness (MDI) share several epidemiological, clinical and genetic characteristics. Subtle morphological changes as evidenced by neuroimaging techniques have also been reported in both entities. Thus far, neuropathological changes have been described in schizophrenia only. We report four cases of MDI with neuropathological changes similar to those found in schizophrenia, i.e. definite disturbances in the cytoarchitecture within the entorhinal region indicating a migrational malformation in the superficial layers possibly originating in the second fetal trimester. A limited sector of the rostro-ventral insula showed a diminution of the nerve cell population. We suggest a vulnerability factor secondary to fetal developmental impairment in the entorhinal region common to both schizophrenia and MDI.

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