Tentorial Venous Anatomy: Variation in the Healthy Population

Schematic representation of 3 transtentorial vein configurations. The 2 groups of tentorial sinus configurations are shown; group 1, which is subdivided, has an RC, while group 2 does not. Regions of variation are shaded in purple, cross-hatching denotes sinuses, and veins are blue. The split confluens is shown for groups 1A and 1B. The degree of petrous apex pneumatization for each group is also shown. A, Configuration 1A has a medialized RC, and the ITV is interrupted by plexiform anastomosis to the RC or LTS. B, Configuration 1B has a lateralized RC, and the ITV is uninterrupted. C, In configuration 2, the RC is absent; the LTV connects the MTS to the LTS and the LTS to the superior petrosal sinus. Relevant draining sinuses are also shown. CS indicates cavernous sinus; ATV, apical tentorial vein; CBV, cerebellar bridging vein; ICS, intercavernous sinus; ISS, inferior sagittal sinus; MBV, mesencephalic bridging vein; PA, plexiform anastomosis; SpPS, sphenoparietal sinus; SS, straight sinus; SSS, superior sagittal sinus; VGC, vein of Galen confluens; VG, vein of Galen; TS, transverse sinus; SPS, superior petrosal sinus; C, confluens; TBV, tentorial bridging vein; ICV, internal cerebral vein.

Association and correlation with clustering highlights common tentorial vein configurations. Left, Cramér V association heat map, a symmetric measure of associations among categoric variables, presents 2 intercorrelated variable groupings. The first shows a high-to-perfect association among the MTS origin, RC, ITV, and LTV. The second shows a moderate-to-high association among the cavernous sinus, LTS origin, transverse sinus, and MTV. Right, The Pearson correlation heat map reveals 2 primary configurations, one of which also has an alternate configuration based on the presence or absence of the ring connection of the MTS and LTS. In the first configuration, the RC is medialized. Due to the presence of the medialized RC originating from the MTS at the straight sinus, the tentorial veins have the following connections: The ITV is interrupted by the RC, and the LTV is lateralized, draining to the superior petrosal sinus. An alternate and slightly less common configuration comprises a lateralized RC and resultant medialized LTV. The second primary configuration has no RC, the ITV is interrupted by the LTS, and the LTV is also interrupted by the LTS. In this configuration, the MTS may be present or absent. IAC-PCF (left) and (right) (degrees); petrosagittal angle (left) and (right) (degrees); CC-JB distance (left) and (right) (millimeters); remaining variables are categoric. The ITV was categorized as 0 through 4 as per the result of preliminary categorization. LTV was categorized as 1 through 3 per results of preliminary categorization. female = 0; M1, male = 1.

Tentorial vein and skull base measurement subset correlation with clustering and distribution plots. Left, The Pearson correlation heat map further characterizes the medialized RC with the ITV and LTV. This characterization confirms that when the RC of the MTS and LTS is present and medialized, the ITV and LTV originate from this connection and are lateralized (group 1A). The strongest associated configuration comprises this; the lateralized RC is confirmed (group 1B). The configuration with the absent RC between the tentorial sinuses is also again confirmed (group 2). This configuration appears related to the CC-JB distance and the tentorial angle in the heat map. Right, Y-axes in all charts are patient numbers. Probability density functions and kernel density estimates for skull base measurements, grouped by tentorial vein categories, reveal additional relationships. The distribution plots are shown for the right side of the tentorium only because symmetry is upheld as shown in the heat map. The probability density functions for LTV 3 and ITV 4 (configuration 1A) are nearly identical; this is inversely related to male sex, CC-JB distance, and petrous apex pneumatization 0 (less complete). This group is positively correlated to petrous apex pneumatization 1 (more complete). Group 1B has no correlation with petrous apex pneumatization; however, it is distinguished from group 2 by oppositional correlation to the IAC-PCF. The probability density functions and kernel density estimates of ITV 2 and LTV 1 (group 2) are very similar. IAC-PCF (left) and (right) (degrees); petrosagittal angle (left) and (right) (degrees); CC-JB distance (left) and (right) (millimeters); the remaining variables are categoric. ITV was categorized as 0 through 4 per the results of preliminary categorization. LTV was categorized as 1 through 3 per the results of preliminary categorization. F0 indicates female = 0; M1, male = 1; R, right; L, left.