Neurokirurško značenje sfenoidnoga kuta i kuta klivus-tentorij u anatomskim varijacijama subtentorijskoga prostora [Neurosurgical importance of sphenoid angle and clivus-tentorium angle in anatomical variations of subtentorial space]

The complex relations of posterior fossa, posterior skull base area, and the base of the brain require precise preparation for neurosurgical operation and selection of the best approach. Being aware of anatomic variations in the operating field is of utmost importance for preventing complications arising from lack of knowledge of the anatomic relationships and variations of the region. Neurosurgical approach to skull base, brain base and brainstem are a great challenge because of anatomical stratification, especially in today's concept of minimally invasive surgery. Measurements and analysis of topographic anatomical relationship of skull base and infratentorial space using MRI allows a better selection of the apropriate approach to the needed region. In our study we investigated the influence of the independent variables sphenoid angle (SF angle) and clivus-tentorium angle (KT angle) with the dependent variables which are divided into the measured angles and distances. The angles are OK gornji, OK donji, OK prednji, OT prednji, OT stražnji, OT gornji and OT donji. Distances are GK-SKK, VER-SKK, PPCIS, GRP-DS, GRP-TC and DBA (position of basilar tip). In the study we used mediosagital T1 MRI images. The study included 410 subjects of both sexes; 247 women and 163 men. The average value of SF angle is 111°, KT angle 19°; GK-SKK 6.7 mm, VER-SKK 10.4 mm, PPCIS 5.9 mm, GRP-DS 17.2 mm GRP-TC 7, 9 mm. SF angle is positively correlated with the angles OK gornji, OT gornji and OT donji and with distances GK-SKK, PPCIS and GRP-DS while negatively correlated with KT angle, OK donji, OT stražnji and OT prednji. KT angle is positively correlated with the angles OK donji, OT gornji and OT donji and negatively correllated with the SF angle, OK gornji, OT prednji and OT stražnji, and with distances GRP-DS, GRP-TC and PPCIS. Predictive potential regression analysis of the SF angle and KT angle showed that both angles have statistically significant predictive potential of the dimensions of lamina tecti (GK-SKK), prepontine cistern (PPCIS) and interpeduncular cistern (GRP and GRP-DS-TC), while the dimension of the superior cerebellar cistern (VER-SKK) do not have statistically significant predictive potential. Dimensionality of the original multidimensional space of variables was reduced by factor analysis to four latent dimensions (factors). These factors were subjected to discriminatory analysis with the intention to find a dimension that should reveal the greatest difference between the groups of subjects defined as 10% lower and 10% upper extremes (10. and 90. percentile) of the group between the 10. and 90. percentile of SF angle and KT angle, separately. While analysing SF angle, the most of subjects (324) belonged to the middle group (between the 10. and 90. percentile), where the average SF angle is 111° with range from 103 to 120°. Under 10. percentile (41 subjects) average is 100° and range from 93 to 102°. Above the 90. percentile (45 subjects) average is 124° with the range 12-135°. With the KT angle, the largest number of subjects (314) belongs to the middle group (between the 10. and 90. percentile) with average 19° and range from 11 to 27°. Under 10. percentile (52 subjects) the average is 7° and range from 1 to 10°. Above the 90. percentile (44 subjects) the average is 31° and the range from 28 to 38°. In this study, due to our results, we point out that anatomical variations in subtentorial space and tentorial alignment depend on SF angle. Sphenoid angle is an important and indispensable tool when planning the neurosurgical operation in following regions: sellar and parasellar area, clivus, anterior brainstem, and craniovertebral junction. We propose clivus-tentorium angle as an important parameter when planning the neurosurgical operations in the pineal region, lamina tecti area, and posterior wall of the third ventricle.