[Disproportionately large, communicating fourth ventricle; report of 4 cases].

Although both "Isolated Fourth Ventricle" (IFV) and "Disproportionately Large, Communicating Fourth Ventricle" (DLCFV) are the clinical-radiologic entities characterized by a dilatation of the fourth ventricle, DLCFV must be separated from IFV because of its apparent patency of the aqueduct. In some Japanese literature, however, there was some confusion concerning DLCFV and so-called "reversible DLCFV" or IFV with "one way aqueduct". In this paper, comparing DLCFV with IFV, a reasonable pathogenesis of DLCFV was discussed on the basis of clinico-radiological analysis of four cases of DLCFV. Our tentative conclusion is as follows: 1) Whether there is radiologic aqueductal patency or not, the term of DLCFV should not be primarily reserved for patients who have had shunting of the lateral ventricle for previous hydrocephalus." 2) It was strongly suggested that a mechanism involved in the development of DLCFV was the formation "membranous occlusion" in/or near the foramen Magendie.