Purpose The cerebral arterial inflow, venous outflow, and Cerebrospinal fluid volume and flow are highly regulated in an equilibrium to maintain adequate cerebral perfusion as governed by the Monro-Kellie doctrine. Multiple neurological conditions had been associated with abnormalities in the cerebral venous system including multiple sclerosis and idiopathic intracranial hypertension, among others. We aim to quantitatively study the relationship and discrepancy between total cerebral blood flow (TCBF) and cerebral venous outflow (CVO), as well as the TCBF as a proportion of the cardiac output in adults and how it compares to the pediatric patients, and highlight the discrepancies.

Materials and Methods 31 healthy volunteers (24 adults and 7 children) underwent 4D flow MR imaging for arterial evaluation and 2D CINE PC-MRI for venous evaluation in an IRB approved study. 3D volumetric ECG-gated PC-MRI data with 3-directional velocity encoding (4D flow MRI) was acquired for the arterial system. 2D CINE PC MRI was acquired for the venous system at both transverse sinuses. 4D flow MRI data was processed using in-house software tools in Matlab. We calculated the cumulative TCBF in ml/sec as the sum of inflow in the bilateral ICAs and basilar artery. The CVO was calculated as the sum of the flow in the bilateral transverse sinuses. The ratio of CVO to TCBF was calculated. Also, the TCBF as a percentage of cardiac output was calculated.

Results A significant positive correlation between TCBF and CVO (r=0.81 and P<0.001) was seen. The TCBF (20.21±4.58 ml/s versus 11.78±2.03 ml/s; P<0.001) and CVO (12.80 ± 3.82 ml/s versus 9.03 ±2.31 ml/s; P=0.010) were significantly higher in children compared to adult volunteers. The CVO/TCBF ratio was significantly lower in children versus adult volunteers (0.63 ± 0.01 versus 0.76 ± 0.02, P=0.025). In adults, the correlation of TCBF with age remains strong (rho = -0.69, t-stat = -4.5, P=0.00018). However, CVO (rho = -0.29, t-stat = -1.42, P=0.171) and CVO/TCBF ratio (r=0.16, P=0.446) were not significantly associated with age in the adult cohort. The ratio of cerebral arterial inflow to systemic aortic outflow was significantly higher in children compared to adults (0.45±0.08 versus 0.15±0.02, P<0.001).

Conclusions Both TCBF and CVO decrease with age, however unlike TCBF, there is no correlation between the decrease in CVO through the Transverse sinuses and age, which could suggest the early development of alternative venous drainage pathways through the emissary and extracranial veins. This could also explain the differential ratio of CVO to TCBF, which suggests that more than 20% of cerebral venous outflow in adults and more than 35% of outflow in Children are not through the Transverse sinuses in the supine position. Understanding the quantitative differences between TCBF and CVO in healthy volunteers could help identify and manage changes related to venous outflow abnormalities.

Disclosures R. Abdalla: None. S. Schnell: None. M. Aristova: None. M. Hurley: None. S. Ansari: None. A. Shaibani: None.