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Few neuroimaging anatomic studies to date have investigated in detail the point of entry of cortical bridging veins (CBVs) into the superior sagittal sinus (SSS). Although we know that most CBVs join the SSS at an acute angle opposite to the direction of SSS blood flow, the three-dimensional (3-D) spatial configuration of these venous confluences has not been studied previously. This anatomical information would be pertinent to several clinically applicable scenarios, such as in planning intracranial surgical approaches that preserve bridging veins; studying anatomical factors in the pathophysiology of SSS thrombosis; and when planning endovascular microcatheterization of pial veins to retrogradely embolize brain arteriovenous malformations (AVMs). We used the concept of Euclidean planes in 3-D space to calculate the arccosine of these CBV-SSS angles of confluence. To test the hypothesis that pial AVM draining veins may not be any more acutely angled or difficult to microcatheterize at the SSS than for normal CBVs, we measured 70 angles of confluence on magnetic resonance venography images of 11 normal, and nine AVM patients. There was no statistical difference between normal and AVM patients in the CBV-SSS angles projected in 3-D space (56.2° [SD = 22.4°], and 46.2° [SD = 22.3°], respectively; P > 0.05). Hence, participation of CBVs in drainage of pial AVMs should not confer any added difficulty to their microcatheterization across the SSS, when compared to the acute angles found in normal individuals. This has useful implications for potential choices of strategies requiring endovascular transvenous retrograde approaches to treat AVMs. Clin. Anat. 33:293-299, 2020. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)

A high lumbar puncture (LP) at L2-L3 or above is often necessary to consider on technical grounds, but complications of conus medullaris (CM) damage during high LP are potentially concerning. We hypothesized that a high LP might be safer than previously thought by accounting for movements of the CM upon patient positional changes. We retrospectively reviewed standard normal supine lumbar spine magnetic resonance imaging of 58 patients and used electronic calipers on axial images at the T12-L1, L1-L2, and L2-L3 disc levels to measure the transverse diameter of the CM relative to the size of the dorsal thecal sac space (DTSS) through which a spinal needle could be inserted. On 142 axial images, the means for CM diameters were 8.2, 6.0, and 2.9 mm at the three levels, respectively. We then used known literature mean CM displacement values in the legs flexed and unflexed lateral decubitus position (LDP) to factor in CM shifts to the dependent side. We found that at all three levels, the likely positional shift of the CM would be too small and insufficient to displace the entire CM out of the DTSS. However, if needle placement could be confined to the midsagittal plane, an LP in the unflexed LDP would theoretically be entirely safe at both L1-L2 and L2-L3, and almost so at L2-L3 in the legs flexed LDP. Thus, high LPs at L1-L2 and L2-L3 are in theory likely safer than considered previously, more so in the legs unflexed than in the flexed LDP. Clin. Anat. 32:618-629, 2019. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)