An anatomical description of the vermian fossa: The reappraisal of an overlooked entity

Jeshika S Luckrajh; J Naidoo; L Lazarus

doi:10.4103/JASI.JASI_131_19

ORIGINAL ARTICLE

Year : 2020 | Volume : 69 | Issue : 4 | Page : 233-236

An anatomical description of the vermian fossa: The reappraisal of an overlooked entity

Jeshika S Luckrajh, J Naidoo, L Lazarus
Department of Clinical Anatomy, School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of Kwazulu-Natal, Westville Campus, Durban, South Africa

Date of Submission	17-Sep-2019
Date of Acceptance	14-Sep-2020
Date of Web Publication	29-Dec-2020

Correspondence Address:
Dr. L Lazarus
Department of Clinical Anatomy, School of Laboratory Medicine and Medical Sciences, College of Health Sciences, University of Kwazulu-Natal, Westville Campus, Private Bag X54001, Durban 4000
South Africa

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JASI.JASI_131_19

Abstract

Introduction: The vermian fossa (VF) is a shallow depression at the inferior end of the internal occipital crest, which lodges the inferior part of the cerebellar vermis. Published literature describes the VF as having a highly variable incidence and morphology. The present study is aimed to investigate the incidence, morphology, and morphometry of the VF within a select South African population and to conduct a review of the literature regarding this structure. Material and Methods: A total of 100 dry, adult skulls of South African origin were analyzed to determine the morphological and morphometric parameters of the VF. Results: The VF was found to be present in 62% of cases. The shape of the VF was classified as triangular (27%), quadrangular (8%), and atypical (27%). The average length of the VF was 13.78 mm, and the average width was 11.62 mm. The morphometric findings of this study correlate with that of previous studies; however, the incidence of atypical shaped VF (27%) is higher in comparison to previous studies (9.7%). Discussion and Conclusion: The detailed anatomical description of the VF may aid in the study of diseases which cause alterations in the size and morphology of the vermis of the cerebellum as well as in transvermian approaches to tumors within the fourth ventricle. Furthermore, due to the paucity of anatomical descriptions of the VF, a reappraisal of this structure is warranted as it is of prime importance to clinicians operating in or interpreting radiological images of the posterior cranial fossa.

Keywords: Cerebellar vermis, posterior cranial fossa, vermian fossa

How to cite this article:
Luckrajh JS, Naidoo J, Lazarus L. An anatomical description of the vermian fossa: The reappraisal of an overlooked entity. J Anat Soc India 2020;69:233-6

How to cite this URL:
Luckrajh JS, Naidoo J, Lazarus L. An anatomical description of the vermian fossa: The reappraisal of an overlooked entity. J Anat Soc India [serial online] 2020 [cited 2023 Mar 26];69:233-6. Available from: https://www.jasi.org.in/text.asp?2020/69/4/233/305372

Introduction

The vermian fossa (VF) is a shallow endocranial depression located between the inferior end of the internal occipital crest and the posterior border of the foramen magnum.^[1] The function of the VF and the reason for its development in the posterior cranial fossa has been a mystery to anatomists and anthropologists for centuries.^[2],[3] Lombroso, known as the father of criminology, who proposed the atavistic tendencies of criminals, had identified the VF as one of the anatomical features of a criminal.^[2] This author, who referred to the VF as the median occipital fossa, had made this conclusion after identifying an enlarged vermis and VF during the postmortem of one who had committed “atrocious crimes.”^[2] In 1926, East had attributed an enlarged VF to intracranial pressure as the result of hydrocephaly in a 4-month-old infant.^[3] These seemingly strange attributions of the VF are not acknowledged in current times and literature regarding the VF is quite brief in standard anatomical texts. According to Grays Anatomy (41^st edition), the VF “may exist” which alludes to the variability of this structure, and this may account for the absence of VF literature in other anatomical textbooks.^[1] However, there is a necessity for anatomists and medical educators to have a thorough knowledge of all structures, which may lead to a higher quality of medical education. Furthermore, in the present era of radiological imaging, structures of the skull may serve as an important role in diagnostic medicine. Berge and Bergman stated that knowledge of the size and incidence of structures and variations of the skull may aid in the diagnostic evaluation of radiologic images and acknowledged that the absence of essential anatomic data on normal variations is a severe deficiency of modern anatomy textbooks.^[4] The VF has been identified as one such structure which has been sparsely described from an anatomical perspective.

In addition, the anatomy of the VF and its variations may be of relevance to the surgeon employing a transventricular and supracerebellar infratentorial approach to remove midline tumors of the posterior cranial fossa or a transvermian approach to remove tumors within the fourth ventricle.^[5],[6] A detailed description of the VF may also aid in the study of diseases that cause alterations in the size and morphology of the vermis of the cerebellum, as it has been reported that certain cases of cerebellar cortical dysplasia are associated with VF variations.^[5]

Therefore, the present study is aimed to investigate the anatomical parameters of the VF by determining its incidence, morphology, and morphometry.

Material and Methods

A total of one hundred adults, dry skulls were obtained from the Department of Clinical Anatomy, University of KwaZulu-Natal, South Africa. Ethical approval was obtained from the Institutional Ethics Committee (BREC Ref No: 256/19). The specimens were of South African origin; however, the gender of each specimen was unknown.

The incidence, shape, length, and width of the VF were recorded. A digital Vernier caliper (Linear Tools, 2012, 0–150 mm, LIN 86500963) was employed to measure the morphometric parameters. The shape of the VF was classified as Type 1 (Triangular), Type 2 (Quadrangular), and Type 3 (Atypical), according to the classification system used by Kale and Öztürk.^[7] In cases of quadrangular and atypically shaped VF, the length and width were taken at the longest and widest part of the VF, respectively.

Descriptive statistics (incidences) were used to describe the results of this study.

All specimens with macroscopic damage or lesions of the posterior cranial fossa were excluded from this study, and only specimens without macroscopic damage or lesions of the posterior cranial fossa were included.

Results

The VF was found to be present in 62% of cases [Table 1]. The shape of the VF was classified as Triangular in 27% of cases, Quadrangular in 8% of cases, and Atypical in 27% of cases [Figure 1] and [Table 1]. The average length of the VF was 13.78 mm, and the average width was 11.62 mm [Table 2].

Figure 1: Morphological presentation of the Vermian fossa. (a) Type 1 - triangular; (b) Type 2 - quadrangular; (c) Type 3 – atypical

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Table 1: Incidence and morphological presentation of the Vermian fossa

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Table 2: Morphometry of the Vermian fossa

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Discussion

The term “Vermian” is related to the cerebellar vermis, which is commonly known to be the primary structure found within the VF. The Latin term vermis is translated worm and this may refer to the shape of the cerebellar vermis, which includes the tuber, pyramid, uvula, and nodule.^[1] However, Kunc et al. highlighted that there is no true contact of the occipital bone with the vermis of the cerebellum and therefore suggested that the term “Vermian Fossa” should be replaced with “triangular eminence” (eminentia triangularis) and defined as flat triangular prominence at the inferior end of the internal occipital crest, formed by the attached margins of the falx cerebelli.^[13] The descriptions of the VF in anatomical textbooks are either brief or absent altogether. There are several studies in the literature which describe the VF; however, these studies represent data largely from Asian populations. Murlimanju et al. suggested that VF morphology may be influenced by racial differences; it is therefore of value to analyze this structure within different population groups.^[5] The results of this study represent data from a select South African population to add to the global body of knowledge.

The literature revealed a weighted mean incidence of the VF in 32.9% of cases; however, the present study recorded the VF in 62% of cases [Table 1]. This finding is lower than that of recent literature, which records the incidence of the VF ranging from 66.7% to 80% [Table 1]. However, earlier studies by Cireli et al., Berge and Berman and Kale and Öztürk recorded significantly lower incidences of 11.4%, 4%, and 8.2%, respectively [Table 1].^[4],[7],[14] It is notable that the latter studies were done in the USA and Turkey, respectively, whereas the studies reflecting higher incidences were conducted in India. The significant difference in incidence between the studies as well as the consistency in results from the Indian studies, supports the hypothesis that racial and geographic distribution may contribute to the variation of the VF.^{[5],[7],[8],[12]} The incidence of the VF within a select South African population, as is recorded in this study, has not been previously reported and is of clinical relevance to surgeons during the preoperative planning of surgeries within the posterior cranial fossa.

The morphological characteristics of the VF are variable and have been described as Type 1–3, according to the classification system proposed by Kale and Öztürk.^[7] Type 1 represents a triangular fossa, Type 2 represents a quadrangular fossa, and Type 3 represents an atypically shaped fossa [Figure 1].^[7] Type 1 was found in 27% of cases in the present study. This is the most commonly found shape in the literature, and the weighted mean incidence of Type 1 in the literature was 54.2% (range: 4.4%–90.6%) [Table 1].

Type 2, quadrangular VF, was found in 8% of cases in this study. This correlates closely with the findings of Ranjan et al. and Pandey et al., who recorded Type 2 VF in 8% and 6.3%, respectively [Table 1].^[9],[12] The weighted mean incidence of Type 2, as depicted in the literature, was 8.1% (range 2.5%–20%), which correlates closely with the findings of the present study. Kale and Öztürk stated that a few authors termed the quadrangular VF as fossa occipitalis mediana since it was deeper than other cases.^[7] However, in developing the classification of VF morphology, Kale and Öztürk classified fossa occipitalis mediana as Type 2 VF since the locations of the two are the same, the only difference being the depth of the fossa.^[7] Furthermore, Kale and Öztürk hypothesized that the distinction in the depth of the VF may be attributed to the size and shape of the inferior cerebellar vermis and therefore concluded that this classification may be indicative of the size and shape of the inferior cerebellar vermis.^[7]

Type 3 VF described atypical cases which presented with a morphology which was neither triangular nor quadrangular but did display a fossa. In the present study, Type 3 was recorded in 27% of cases; this finding is higher than the weighted mean incidence of 9.2% (range: 1.3%–21.6%) in the literature [Table 1].

The average length of the VF in the present study was 13.8 mm. This finding was lower than the weighted mean length of the VF in the literature, which was 18.8 mm. The average width of the VF was 11.6 mm, in the present study. This finding is less than the weighted mean width recorded in the literature (14.7 mm) [Table 2].

Sanudo et al. stated that both diagnosis and therapeutic performance may be augmented by studies of morphological variations.^[15] Despite its high incidence, the VF is currently considered an anatomical variation and is an overlooked entity in many standard anatomical texts. Further to highlighting the VF as a distinguished structure of skull anatomy, the present study reported morphological and morphometric parameters of the VF. These results may aid the surgeon operating in the posterior cranial fossa during procedures such as the transventricular and supracerebellar infratentorial removal of midline tumors or the transvermian approach to tumors within the fourth ventricle.^[9]

The closest anatomical structures to the VF are the posterior cerebromedullary cistern from the superior aspect and the division of the occipital sinuses continuing into the marginal sinuses from the lateral aspect. Surgeons operating in this area may benefit from knowing the incidence of variations of the VF, which may influence surrounding structures such as a duplicated falx cerebelli.^[13],[16] Furthermore, the detailed knowledge of the anatomical parameters of the VF may aid in the study of diseases which cause alterations in the size and morphology of the cerebellar vermis as cerebellar cortical dysplasia are associated with VF variations.^[5]

Conclusion

Considering the paucity of literature regarding the VF in anatomical texts as well as the clinical relevance of this structure, this study highlights the need for a reappraisal of the VF. It is recommended that future studies include larger sample sizes, with biographical data for more comprehensive statistical analysis. Accurate knowledge of the anatomy and variations of the VF is of importance to anatomists, radiologists, and surgeons and may aid in mitigating iatrogenic injuries.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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