Microanatomical study of arteries of the fourth ventricle roof

Abstract

The arteries of the fourth velum) roof were investigated on 25 prepared rhombencephalons and 30 angiograms (adult persons). Superior portion of the roof (superior medullary vellum) is supplied by small branches originating from both the terminal branches of the superior cerebellar artery. These small branches descend over the superior medullary velum and superior cerebellar peduncles, and can be divided in the lateral and the medial group. In the apical area of fastigium there are anastomoses between the branches belonging to the systems of the superior and the posterior inferior cerebellar artery. The inferior portion of the fourth ventricular roof (inferior medullary velum and lamina tectoria) is supplied by numerous fine choroidal branches, usually originating from a retromedullary segment of the posterior inferior cerebellar artery (PICA). This artery is in a more or less close relationship to the inferior portion of the IV ventricular roof, but details of this relationship depend of the length of the arterial retromedullary segment. Further, this length depends mostly on the height of the point of origin of PICA from a. vertebralis. In over 80% of cases this point was in the level of the inferior pole of the olive and the length of retromedullary segment was then relatively great. When the point of origin of PICA was high (level of middle part or superior pole of olive) this segment was shorter and the artery relates only to upper neighbouring parts of the roof. In our material arteries from both sides were never in touch, being separated by the sharp incline of lamina tectoria (caudalmost part of roof) and by the presence of the vermis (more rostrally). The inferior vermian artery (one of the PICA terminal branches) may be in close relationship with the fourth ventricular roof too, usually when the opposite PICA is hypoplastic. In such cases the inferior vermian artery from the side with 'normal' PICA crosses the r481w1≠pyramis uvula or pyramics (10% cases right, 13% left).