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CC BY 4.0 · Indian Journal of Neurotrauma 2025; 22(02): 168-172
DOI: 10.1055/s-0044-1801779
Original Article

Morphometric Analysis of Tentorial Orifice and its Anatomical Variations as Relevant to Transtentorial Herniation: A Preliminary Cadaveric Study

Diksha Sharma 
1   Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
,
Rakshay Kaul
1   Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
,
Deepak Agrawal 
1   Department of Neurosurgery, All India Institute of Medical Sciences, New Delhi, India
› Author Affiliations

Funding None.
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Abstract

Background

The tentorial orifice is a space in the tentorium cerebelli that lies toward the center and anteriorly related to the brainstem, cranial nerves, cerebrum, and cerebellum. The tentorium cerebelli is a fold of the dura mater that separates the supratentorial and infratentorial chambers. The anatomy of the tentorial orifice is complex in morphology, and it has a great significance in the neurosurgical field. Detailed understanding of the anatomical variations in the tentorial notch may help find the progression and clinical aspects of transtentorial herniation.

Objective

The aim of the study was to investigate the morphometric characteristics of the tentorial notch and its anatomical variations in human cadavers.

Materials and Methods

The study was conducted on 20 human cadavers, aged 20 to 74 years, after the conventional autopsy procedure within 24 hours after death, followed by sectioning of the midbrain at the level of the tentorial edge to note the respective observations, which were the following: (1) maximum notch length (MNL), the length between the apex of the notch and the posterosuperior edge of the dorsum sellae; (2) maximum notch width (MNW) and maximum width of the tentorial notch; (3) interpedunculoclival distance, the distance between the posterosuperior edge of the dorsum sellae and the interpeduncular fossa; (4) apicotectal distance, the distance from the apex of the notch to the tectum of midbrain; and (5) anterior notch width, the width of the tentorial notch in the axial plane through the dorsum sellae posterior aspect. The tentorial notch is classified into eight types by using two variables, which are MNL and MNW. The data obtained were analyzed.

Results

Twenty autopsy cases, comprising 18 males and 2 females, were included in the study. The groups defined by MNW (mean: 29.12 ± 1.88 mm [range: 24.4–34.3]) were labeled as narrow, midrange, and wide. Other groups defined by MNL (mean: 52.13 ± 5.01 mm [range: 44.2–59.92 mm]) were labeled as short, midrange, and long.

Conclusion

Anatomical variability in the morphology of the tentorial aperture may be associated in various clinical scenarios related to transtentorial herniation and other traumatic brain injuries. This preliminary study provides a guideline to plan the trajectory during neurosurgical procedures to be performed in the vicinity of the tentorial aperture.


 

Keywords

transtentorial herniation - tentorium cerebelli - brainstem herniation - notch classification - cadaveric study

Introduction

The tentorium cerebelli is one of the four dural folds that separate the cranial cavity into two compartments containing the forebrain and hindbrain. This dural fold is deficient toward the center and anteriorly to produce a gap, the tentorial aperture.[1] The midbrain traverses through the tentorial orifice and this space provides the only communication between the two chambers, supratentorial and infratentorial. The space between the brainstem and the free edge of the tentorium cerebelli is divided into three spaces, which are anterior, middle, and posterior. The anterior one lies anterior to the brainstem and the third nerve is related to this space; the middle space lies on each side of the brainstem and the hippocampus is related to this area; and the posterior space is in posterior relation to the midbrain and in relation with the region of the pineal gland and the vein of Galen.[2]

Transtentorial herniation ensues in a wide variety of neurosurgical disorders, including traumatic brain injury, tumors, and cerebral edema. However, if it remains untreated, transtentorial herniation steps forward swiftly to death. In the absence of direct neuroradiological imaging invention, the lethal consequences of brainstem compression due to uncal herniation were recognized and first described by Meyer in 1920.[3] Corsellis and Sunderland studied the anatomical variations of the tentorial notch, which acted as a milestone for neurosurgeons.[4] [5] After this, modern neuroimaging techniques had also emerged.[6] The tentorial aperture varies morphologically in dimensions and has a great importance in the neurosurgical field. However, this aperture is defined by the free edge of the tentorial fold, yet it remains anatomically indefinable because of its complicated and variable anatomy in three dimensions, absence of blood vessels along its free edge, and only infrequent calcification.[7]

Therefore, the present preliminary study was done with the objective of explicating the morphology of the tentorial aperture in the Indian population in unfixed human cadavers. This article provides a reference anatomical data for determination of dimensions and type of notch on magnetic resonance imaging and computed tomography scan, which may facilitate neurosurgical decision-making.


 

Materials and Methods

The preliminary study was conducted on unfixed human cadavers after getting an approval from the ethical committee. It was performed during autopsies of cadavers, aged 20 to 74 years, performed within 24 hours of death to prevent any alteration in tentorial notch morphology due to decomposition or putrefaction.[8]

Dissection Steps

The unfixed heads of the human cadavers were placed using a block to keep the head at an angle of 45 to 60 degrees above the horizontal plane. Make a coronal incision with the help of a scalpel from mastoid to mastoid and separate the subcutaneous attachments. Retract the scalp anteriorly toward the eye and nose and posteriorly beyond the occipital protuberance. Dissect the temporalis muscle and reflect it inferiorly. Evert the scalp and cut the skull circumferentially just above the superciliary ridges and above the inion with the help of an electric saw and remove the skull cap followed by cutting the dura. Lift the frontal lobes in a gentle way with the help of the fingers and cut the anterior falx. Dissect the diencephalon axially above the level of the optic chiasma, through the third ventricle to the apex of the tentorial notch. The cerebrum is removed, leaving intact a little part of the diencephalon, posterior part of the falx, and tentorium cerebelli. Cut the optic nerve rostral to the pituitary fossa. Follow with the contour of the tentorial edge to the point of the notch apex and the midbrain was cut in the axial plane. Field was cleared with help of water and gauze.


 

 

Measurements

The following measurements were made during the autopsy with the help of a geometry compass and vernier caliper to determine the morphometric variations of the tentorial aperture ([Figs. 1] and [2]):

Zoom
Fig. 1 Schematic diagram showing the measurements of the tentorial notch. ANW, anterior notch width; AT, apicotectal distance; IC, interpedunculoclival distance; NL, notch length; MNW, maximum notch width; PTL, posterior tentorial length.
Zoom
Fig. 2 Measurements of the tentorial notch. AT, apicotectal distance; IC, interpedunculoclival distance; MNW, maximum notch width.

  • Maximum notch length (MNL), the length between the apex of the notch to the posterosuperior edge of the dorsum sellae.

  • Maximum notch width (MNW), maximum width of the tentorial notch.

  • Interpedunculoclival distance (IC), the distance between the posterosuperior edge of the dorsum sellae and the interpeduncular fossa.

  • Apicotectal distance (AT), the distance from the apex of the notch to the tectum of the midbrain.

  • Anterior notch width (ANW), the width of the tentorial notch in the axial plane through the dorsum sellae posterior aspect.


 

Results

Out of 20 cadavers, 18 cadavers were males and 2 were females. The majority of the cadavers were males. The mean MNL measured 52.13 ± 5.01 mm (range: 44.2–59.92 mm) and the mean AT distance measured 19.09 ± 6.91 mm (range: 9.09–39.57 mm; [Table 1]). The correlation between these two values was significant (r = 0.66). However, the quantification of the cerebellar tissue located in the tentorial aperture has not been done, but there was a positive correlation between cerebellar tissue and the AT distance.

Table 1

Summary data for morphometric measurements of the anatomy of the tentorial notch

Value

Age at the time of death (y)

MNL (mm)

MNW (mm)

IC (mm)

AT (mm)

ANW (mm)

Minimum

20

44.2

24.4

7.32

9.09

22.4

1st quartile

24

47.3

28.11

11.30

14.22

24.39

Mean ± SD

36.3 ± 16.36

52.13 ± 5.01

29.12 ± 1.88

13.59 ± 4.35

19.09 ± 6.91

26.16 ± 2.45

Median

28

51.8

29.09

3rd quartile

54

56.26

29.7

14.27

24.71

27.29

Maximum

74

59.92

34.5

25.58

39.57

31.15

Abbreviations: ANW, anterior notch width; AT, apicotectal distance; IC, interpedunculoclival distance; MNL, maximum notch length; MNW, maximum notch width; SD, standard deviation.


The mean values of the ANW and MNW measured 26.16 ± 2.45 mm and the mean distance measured 29.12 ± 1.88 mm ([Table 1]). A strong correlation was found between these two values (r = 0.69). A mean IC distance of 13.59 ± 4.35 mm was found.

Notch Classification

The tentorial notches were classified into eight types by using two variables, MNL and MNW ([Table 2]). The matrix formation used for tentorial notch classification is shown [Table 3] and the tentorial notch has been classified into eight types ([Table 2]).

Table 2

Various types of tentorial notches and the criteria used for typing

Type of notch

Dimension

Range (mm)

Percentage

Wide

MNW (wide)

29.80–34.30

20

MNL (midrange)

47.4–56.26

Narrow

MNW (narrow)

24.74–28.11

0

MNL (midrange)

47.4–56.26

Long

MNW (midrange)

28.20–29.70

5

MNL (long)

56.4–59.92

Short

MNW (midrange)

28.20–29.70

0

MNL (short)

44.20–47.30

Typical

MNW (midrange)

28.20–29.70

30

MNL (midrange)

47.4–56.26

Large

MNW (wide)

29.80–34.30

0

MNL (long)

56.4–59.92

Small

MNW (narrow)

24.74–28.11

15

MNL (short)

44.20–47.30

Mixed

MNW (narrow)

24.74–28.11

0

MNL (long)

56.4–59.92

MNW (wide)

29.80–34.30

MNL (short)

44.20–47.30

Abbreviations: MNL, maximum notch length; MNW, maximum notch width.


Table 3

Matrix preparation for classification of the tentorial notch

Type of notch (total number of cases), n = 20

MNW

Short MNL

Midrange MNL

Long MNL

Narrow

Small (3)

Narrow (0)

Mixed (1)

Midrange

Short (0)

Typical (6)

Long (1)

Wide

Mixed (0)

Wide (4)

Large (0)

Abbreviations: MNL, maximum notch length; MNW, maximum notch width.


The first quartile of the MNW ranging from 24.74 to 28.11 mm was labeled as narrow, and the middle two quartiles ranging from 28.2 to 29.7 and 29.8 to 34.3 mm were labeled as midrange and the wider type, respectively. Out of 20 cases, 5 (25%) were narrow, 10 (50%) was midrange, and 5 (25%) were wide. The first quartile of the MNL ranging from 44.2 to 47.3 mm was labeled as short, the middle two quartiles ranging from 47.4 to 56.26 and 56.4 to 59.92 mm were labeled as midrange and long type, respectively. Out of 20 cases, 5 (25%) were short, 10 (50%) were midrange, and 5 (25%) were long ([Table 3]).

The tentorial notch having a long MNL and a midrange MNW was classified as long (5%). The tentorial notch having a midrange MNL and a wide MNW was classified as wide (20%) as shown in [Fig. 3]. The tentorial notch having a midrange MNL and a narrow MNW was classified as narrow (0%). The tentorial notch having a short MNL and a midrange MNW was classified as short (0%). The tentorial notch having a long MNL and a wide MNW was classified as large (0%). The tentorial notch having a midrange MNL and a midrange MNW was classified as typical (30%), as shown in [Fig. 4]. The tentorial notch having a short MNL and a narrow MNW was classified as small (15%). Some notches were seen to be distributed under both wide and short or long and narrow. Both types of notches were classified as mixed (30%).

Zoom
Fig. 3 The wide type of notch (wide maximum notch width and midrange maximum notch length).
Zoom
Fig. 4 The typical type of notch (midrange maximum notch width and midrange maximum notch length).

 

 

Discussion

A wide spectrum of morphometric variability seen in the tentorial notch anatomy raises a fundamental question of its relevance in the human body. Sunderland classified notches into two groups, that is, broad and narrow; however, Corsellis gave a proposal that patterns of herniation must be affected by the size and shape of the tentorial aperture. Both authors clearly showed the orifice's anatomical variations and its relation with the brainstem, but there was failure of the well-defined classification system.[4] [5] There are few studies that have attempted to analyze the significance of variability in tentorial notch anatomy and its association with herniation. They have demonstrated a correlation between the radiological and autopsy findings, simply strengthening the need for further research to validate this corroboration.[9] [10] Klintworth proposed that the tentorium cerebelli and the tentorial aperture vary considerably in positioning, size, and shape in different animal species. In some animals like fish, reptiles, and amphibians, the tentorium cerebelli is absent, whereas in some mammals like rats and guinea pigs, this tentorial partition is not complete. But in humans and monkeys, this tentorial dural fold becomes a crescent-shaped fold that acts as a partition and divides the cranial cavity into two compartments separating the cerebral and cerebellar hemispheres.[11]

The various parameters of dimensions of the tentorial notch are compared with different populations in [Table 4]. The MNL in our study (52.13 ± 5.01 mm) is less as compared with the studies by Sunderland[5] who examined the Australian population (54.9 ± 6.93 mm) and Ono et al[2] who reported an MNL of 52 mm. The values of IC reported in our study are higher than those observed by Ono et al,[2] which was 12.1 mm ([Table 4]). The range of AT distance in our study was found more (9.09–39.57) than that reported by Adler and Milhorat[12] (4–32 mm) and Ono et al[2] (13–27 mm). This shows that there is greater AT distance in the Asian population as compared with that of the western population.

Table 4

Comparison of data of tentorial notch with U.S., Australian, and Indian population

Parameters

Our study (Indian population)

Ono et al[2] (in U.S. population)

Sunderland[5] (in Australian population)

Mean ± SD (mm)

Range (mm)

Mean ± SD (mm)

Range (mm)

Mean ± SD (mm)

Range (mm)

MNL

52.13 ± 5.01

44.2–59.92

52

46–67

54.9 ± 6.93

44–75

MNW

29.12 ± 1.88

24.4–34.3

29.6

26–35

30.16 ± 3.21

23–39

IC

13.59 ± 4.35

7.32–25.58

12.1

7.8–15.6

AT

19.09 ± 6.91

9.09–39.57

19.8

13–27

ANW

26.16 ± 2.45

22.4–31.15

27.06 ± 3.53

19–35

Abbreviations: ANW, anterior notch width; AT, apicotectal distance; IC, interpedunculoclival distance; MNL, maximum notch length; MNW, maximum notch width; SD, standard deviation.



 

Conclusion

This study provides the baseline data for the neurosurgeons about the anatomical variations of the tentorial aperture. Moreover, this morphometric analysis elucidates its clinical relevance in neurosurgery. The dimensions of the tentorial aperture may determine the clinical sequelae and prognosis of many neurosurgical conditions.


 

 

Conflict of Interest

None declared.


Address for correspondence

Deepak Agrawal, MBBS, MS, MCh
Department of Neurosurgery, All India Institute of Medical Sciences
New Delhi 110029
India   

Publication History

Article published online:
25 March 2025

© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution License, permitting unrestricted use, distribution, and reproduction so long as the original work is properly cited. (https://creativecommons.org/licenses/by/4.0/)

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Zoom
Fig. 1 Schematic diagram showing the measurements of the tentorial notch. ANW, anterior notch width; AT, apicotectal distance; IC, interpedunculoclival distance; NL, notch length; MNW, maximum notch width; PTL, posterior tentorial length.
Zoom
Fig. 2 Measurements of the tentorial notch. AT, apicotectal distance; IC, interpedunculoclival distance; MNW, maximum notch width.
Zoom
Fig. 3 The wide type of notch (wide maximum notch width and midrange maximum notch length).
Zoom
Fig. 4 The typical type of notch (midrange maximum notch width and midrange maximum notch length).