ANATOMICAL VARIATION OF CEREBRAL VENOUS DRAINAGE - THE THEORETICAL EFFECT ON JUGULAR BULB BLOOD-SAMPLES

Recent studies have demonstrated significant variation in bilateral ju gular venous oxygen saturation measurements which may be of clinical s ignificance. We have therefore measured variations in normal dural sin us venous drainage to assess the possible effects of normal anatomical variations on measured jugular venous oxygen saturation. Normal volun teers (n = 25) were imaged using magnetic resonance venography to demo nstrate variations in venous anatomy. Flow was measured in the superio r sagittal sinus and bilaterally in the transverse sinus, sigmoid sinu s proximal to the jugular bulb and proximal jugular Vein using phase d ifference magnetic resonance imaging. Examination of magnetic resonanc e venogram images showed considerable variability in the symmetry of t ransverse sinus flow. Complete absence of one transverse sinus was see n in four cases and significant asymmetry in the size of the transvers e sinuses was present in 13. Quantitative flow studies demonstrated th at the ratio of superior sagittal sinus to combined jugular bulb flow showed remarkably little variation (0.46 +/- 0.06). Measurements of tr ansverse sinus flow showed significant asymmetry (< 40% of superior sa gittal sinus flow in one transverse sinus) in 21 of 25 volunteers. The effect of the observed asymmetry on jugular venous oxygen saturation was modelled based on the assumption of either a supratentorial or inf ratentorial lesion. This model predicted significant asymmetry in jugu lar venous oxygen saturation measurements (> 10%) in 65% of cases with a supratentorial lesion which is in close agreement with clinical obs ervations. This study suggests that normal variations in venous draina ge may account for observed asymmetry in jugular Venous oxygen saturat ion measurements.