[Ultrastructural findings of arachnoid cysts and epithelial cysts]

Abstract

There may be several kinds of pathological conditions in the cystic lesion which are clinically diagnosed as benign intracranial cysts on CT scan. Light and electron microscopic studies on cyst walls were important in the differential diagnosis of benign intracranial cysts. We have studied 5 cases of intracranial arachnoid cysts and two epithelial cysts using the light and electron microscopy. Five cases of intracranial arachnoid cysts included two children and three adults (three females and two males). Three cases of them were localized in the middle cranial fossa, one case in the anterior and middle cranial fossa and one case in the lateral ventricle, giving headache and convulsion as the initial complaints. As for the epithelial cysts, one was localized at the para-collicular area complaining enlarged head and swollen anterior fontanelle and the other of four years was located in the fourth ventricle with headache and ataxic gait. On CT all of them demonstrated diffuse low density areas in both the arachnoid and the epithelial cysts without communicating findings between the cystic cavities and subarachnoid space on metrizamide CT cisternography. The arachnoid cyst walls were basically similar in structure to the normal arachnoid membrane and composed of elongated epithelial cells like the arachnoid cell and the connective tissues with lamellar collagen fiber bundles. However, 3 of the 5 cases had only fibrous tissues without epithelial cells. The inner sheath of the arachnoid cyst walls was composed of one or several layers of the arachnoid cells with flattened and relatively electron-dense cytoplasm on electron micrograph. They had a lot of elongated process and were tangled with each other, making large extracellular spaces between them. Below the electron dense arachnoid cells, compact packed cells with interdigitation partly demonstrated intercellular contacts such as numerous desmosomes and tight junctions. In those intercellular spaces collagen fibers and microfibrils were observed. The cells contained abundant cytoplasmic microfibrils and numerous organelles. They were separated from numerous collagen fibers and fibroblasts by non continuous basal lamina under the epithelial cells. Epithelial cyst wall had a layer of cuboidal or columnal epithelium in the inner layer of cyst wall. Those epithelial cells demonstrated granules having positive in PAS and mucicarmine stain in their cytoplasm. On electron microscopical study epithelial cells revealed a lot of microvilli and coating materials on the surface of them without cilia. The basement membranes were well developed under the epithelial cells separated from the connective tissues. In the intercellular clefts of the epithelial cells tight junctions and interdigitations were recognized.(ABSTRACT TRUNCATED AT 400 WORDS)