FIGURE 7.

Drainage of blood from superficial cortical veins into the superior sagittal sinus with and without presence of a bridging vein. On the left, absence of the bridging portion of the superficial cerebral/cortical vein crossing the subarachnoid cerebrospinal fluid and subdural space to the superior sagittal sinus leads to impaired drainage causing cyanotic engorgement and enhancement of vessels within the leptomeninges. Redirection of cortical venous blood into the deep venous drainage system occurs via engorged, corkscrew medullary veins. The increased venous pressure reduces arterial perfusion, causing eventual brain atrophy. Higher leptomeningeal venous pressure is also transmitted via variable emissary veins to venous lacunae within the dura mater. This, in turn, reduces venous and lymphatic drainage from the scalp. Such impaired drainage produces visible port-wine stains, with variable lymphedema, as well as hypertrophy of both bone and skin. The right side of the schema depicts normal venous structure and blood flow when bridging veins are present.