Histologic study of arteriovenous shunts in the normal dura mater adjacent to the transverse sinus

BackgroundAlthough AV shunts are known to exist in the normal dura mater, their histologic appearance has not been examined in detail. Arteriovenous shunts in the normal dura mater adjacent to the transverse sinus, the most frequent site of DAVFs, were studied histologically.MethodsNormal dura mater adjacent to the transverse sinus was obtained from 8 cadavers. Each specimen was cut into approximately 4-μm-thick serial sections; these were stained by the elastic Masson method and examined under a light microscope.ResultsOf the 8 specimens, 5 harbored a total of 6 AV shunts; no shunts were found in the other 3 specimens. The shunts, located in the supratentorial (n = 1) and infratentorial dura mater (n = 4) and in the tentorium cerebelli (n = 1), were classified into 2 types. In direct-type shunts, the artery connected directly to the vein; the diameter of these shunts ranged from 40 to 80 μm. In indirect-type shunts, the artery and vein were parallel and were indirectly connected by a shunt vessel, producing an H shape. The diameter of these shunt vessels ranged from 30 to 45 μm. All 6 shunts were connected to veins or the venous lake; none connected directly to the transverse sinus.ConclusionsThe existence of direct- and indirect-type AV shunts in the normal dura mater was confirmed histologically. Both types exhibited the histologic features of DAVFs, suggesting that AV shunts in the normal dura mater might be involved in the etiology of DAVFs.