Tentorial alignment and its relationship to cisternal dimensions of the pineal region: MRI anatomical study with surgical implications using the new clivotentorial method

•There is no consensus regarding methods of measurement of the tentorial alignment.•Our clivotentorial method provides a simple and effective means of measurement.•Tentorial alignment and dimensions of pineal region cisterns are correlated. Tentorial alignment and dimensions of posterior fossa cisterns are measurements whose variability can decrease surgical freedom if not taken into account when choosing the approach to the pineal region. The aim is to provide quantitative anatomical information regarding these dimensions, and to discuss their relevance in two most commonly used approaches to this region: the occipital transtentorial and supracerebellar-infratentorial approach. A retrospective study of midsagittal T1-weighted MRI images of 410 randomly selected healthy subjects was performed. The clivus-tentorium (C–T) angle was measured to assess tentorial alignment. The following distances were used as craniocaudal cisternal measurements: quadrigeminal cistern = superior colliculi - inferior part of the splenium of corpus callosum (SC-ISCC), and superior cerebellar cistern = vermis - inferior part of the splenium of corpus callosum (VER-ISCC). Median C–T angle value was 19 ± 7°, the quadrigeminal cistern height 6.7 ± 1.6 cm, and the superior cerebellar cistern height 10.4 ± 2.6 cm. The C-T angle was negatively correlated with the SC-ISCC distance (r = −0.271; p 0.001). The SC-ISCC distance was positively correlated with the VER-ISCC distance (r = 0.282; p < 0.001). Our new method of measuring tentorial alignment provides a simple and effective aid in preoperative planning. For the first time, we present data on craniocaudal dimensions of posterior fossa cisterns, their relationship with tentorial alignment, and discuss their relevance in SCIT and OT approaches.