UpToDate: Tentorial Angle

Tentorial Angle

Various techniques of measuring tentorial alignment and their surgical implications have been described; however, all of the methods are burdened with limitations and there is still a lack of consensus regarding the anatomical reference lines and cutoff values for tentorial angles to discriminate between “shallow” and “steep” angles 1) 2) 3).

Nemir et al., from the University Hospital Center ZagrebCroatia, present data on craniocaudal dimensions of posterior fossa cisterns, their relationship with tentorial alignment, and discuss their relevance in Supracerebellar Infratentorial approach and Occipital transtentorial approach

The clivustentorium (C-T) angle was measured to assess tentorial alignment. The following distances were used as craniocaudal cisternal measurements: quadrigeminal cistern = superior colliculus – 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) and the VER-ISCC distance (r = -0.052, p >  0.001). The SC-ISCC distance was positively correlated with the VER-ISCC distance (r = 0.282; p < 0.001) 4).


Studies have used the Twining line (from the tuberculum sellae to the torcula), or the floor of the fourth ventricle as reference lines and defined different cutoff values of “steepness”. The other important factors to be considered in approaching the pineal region are anatomic features of the quadrigeminal cistern and superior cerebellar cistern, as both host important neurovascular structures and serve as anatomic corridors 5) 6) 7) 8) 9).

The current trend to use the Twining line to define this angle has significant pitfalls.

The goal of a study of Syed et al., was to provide a new and accurate way to measure the tentorial angle and demonstrate its impact on surgeries of the pineal region.

n-angle to measure the tentorial angle was introduced using the floor of the fourth ventricle and the torcula. Comparisons with older techniques were made to illustrate reliability. Midline sagittal MR images were used to measure the tentorial angle in 240 individuals to obtain population-based data. A cohort of 8 patients who underwent either the infratentorial or the transtentorial approach to the pineal or upper vermian region were examined in search of correlations between tentorial angle and surgical approach.

The data in this study showed that the Twining line technique understates the tentorial angle in people with low-lying torcula. The n-angle is more reliable in reflecting the true steepness of the tentorium regardless of torcula position. On average, men have slightly steeper tentoriums. In the clinical cohort, all patients who underwent infratentorial surgery had tentorial angles <55°, whereas the majority of patients who underwent transtentorial surgeries had angles >67°.

The n-angle provides a reliable and accurate way to describe the slope of the tentorium. The population-based average of 60° may be a useful measurement to influence the choice of surgical approach, either under or through the tentorium, to the pineal region 10).

References

1) , 7) , 10)

Syed HR, Jean WC. A Novel Method to Measure the Tentorial Angle and the Implications on Surgeries of the Pineal Region. World Neurosurg. 2018 Mar;111:e213-e220. doi: 10.1016/j.wneu.2017.12.037. Epub 2017 Dec 16. PubMed PMID: 29258947.
2)

Pan Y, Wang C, Ding X, Lu Y. The Krause approach: MRI measurements in the Chinese population. J Clin Neurosci. 2011 Jun;18(6):794-7. doi: 10.1016/j.jocn.2010.10.017. Epub 2011 Apr 19. PubMed PMID: 21507648.
3)

Sade B, Lee JH. Significance of the tentorial alignment in approaching the trigeminal nerve and the ventral petrous region through the suboccipital retrosigmoid technique. J Neurosurg. 2007 Nov;107(5):932-6. PubMed PMID: 17977263.
4)

Nemir J, Njirić N, Ivanković D, Barl P, Domazet I, Radoš M, Mrak G, Paladino J. Tentorial alignment and its relationship to cisternal dimensions of the pineal region: MRI anatomical study with surgical implications using the new clivotentorial method. Clin Neurol Neurosurg. 2018 Jun 28;172:99-104. doi: 10.1016/j.clineuro.2018.06.028. [Epub ahead of print] PubMed PMID: 29986205.
5)

Rhoton AL Jr. Tentorial incisura. Neurosurgery. 2000 Sep;47(3 Suppl):S131-53. PubMed PMID: 10983307.
6)

Hart MG, Santarius T, Kirollos RW. How I do it–pineal surgery: supracerebellar infratentorial versus occipital transtentorial. Acta Neurochir (Wien). 2013 Mar;155(3):463-7. doi: 10.1007/s00701-012-1589-5. Epub 2012 Dec 27. PubMed PMID: 23269352.
8)

Gu Y, Hu F, Zhang X. Purely endoscopic resection of pineal region tumors using infratentorial supracerebellar approach: How I do it. Acta Neurochir (Wien). 2016 Nov;158(11):2155-2158. Epub 2016 Aug 9. PubMed PMID: 27506850.
9)

Qi S, Fan J, Zhang XA, Zhang H, Qiu B, Fang L. Radical resection of nongerminomatous pineal region tumors via the occipital transtentorial approach based on arachnoidal consideration: experience on a series of 143 patients. Acta Neurochir (Wien). 2014 Dec;156(12):2253-62. doi: 10.1007/s00701-014-2224-4. Epub 2014 Sep 23. Erratum in: Acta Neurochir (Wien). 2015 Feb;157(2):349. PubMed PMID: 25246142

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