Experimental Pathologic Study at the Site of Carotid Endarterectomy

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Abstract
The authors previously reported the sequential morphological changes at the site of carotid endarterectomy (CE) in cats using light and scanning electron microscopy (SEM). The following problems remain unsolved; a) at the stage of restoration after CE, why do thrombi not increase at the site and why does cerebral embolism never occur? b) what is the nature of the amorphous material covering the CE site? c) what is the origin of new endothelial cells growing like islands far away from both ends of the CE? The present study was conducted to obtain some insight into these unsolved problems. The ultrastructural healing process of the endarterectomized carotid arterial wall was observed with a transmission electron microscopy (TEM). The authors found that the amorphous material covering the naked surface in the acute phase of CE consisted mainly of platelets. The platelets were loosely arranged on the luminal surface but were closely packed together in the deeper layer. In reparative phase, two kinds of cells could be recognized on the luminal surface of CE, namely, ovoid and flattened cells. Some of the ovoid cells were isolated from other cells. Most of the ovoid cells maintained contact with other cells by the cell membrane but without definite junctional structures. The rough endoplasmic reticulum (rERs) of these cells was remarkably enlarged and occupied most of the cell. There were many cells in the subendothelial space which resembled ovoid type cells but collagen fibrils were seldom recognized. In the third week after CE, the vessel surface was lined by two different cells as in the second week. However, the difference of intercellular organelles between the two types became minimal. In the deeper layer, there were many cells with myofilaments, dense bodies and basement membrane which had an appearance of modified smooth muscle cells, and the rER of the cells in the deeper layer developed more markedly than that of cells in the superficial one. In the mature phase, the luminal surface was covered with only flattened type cells. These cells satisfied a criterion of endothelial cells and had tight junctions. Beneath these cell layers, several layers of smooth muscle cell were seen although no elastic laminae was present. There were particular cells in the deeper layer of these muscle cells which possessed dense bodies and basement membrane but no intercellular filament. No collagen existed around these cells. These particular cells were neither fibroblasts nor smooth muscle cells and are more actually undifferentiated type cells. These findings suggested that undifferentiated cells, originating in the media (medial multipotential mesenchymal cells) became ovoid type cells during migration to the luminal surface, then differentiated to flattened type cells and finally matured to new endothelial cells.

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