Christian Alexander Yataco-Wilcas, Alberto Salazar-Ascurra, Bruno Eduardo Diaz-Llanes, Yosimar Salomón Coasaca-Tito, Luis Alberto Lengua-Vega, Cristian Eugenio Salazar-Campos
  1. Department of Neurosurgery, Neurozone 3D Research Center, Lima, Peru.

Correspondence Address:
Cristian Eugenio Salazar Campos, Department of Neurosurgery, Neurozone 3D Research Center, Lima, Peru.


Copyright: © 2024 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Christian Alexander Yataco-Wilcas, Alberto Salazar-Ascurra, Bruno Eduardo Diaz-Llanes, Yosimar Salomón Coasaca-Tito, Luis Alberto Lengua-Vega, Cristian Eugenio Salazar-Campos. Morphometric analysis of the foramen magnum in the Peruvian population. 12-Jan-2024;15:9

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Background: The foramen magnum, as an anatomical structure, holds clinical and functional significance due to its strategic location in the craniovertebral transition. A detailed understanding of its dimensions and shapes is crucial for better comprehension of related pathologies and for enhancing neurosurgical techniques within a specific population. The objective is to measure precise morphometric reference points of the foramen magnum in individuals of Peruvian ancestry, aiming to establish specific anatomical patterns and potential variations within this population.

Methods: The study was conducted on 17 unidentified skulls donated to the NeuroZone3D Research Center, utilizing an inelastic and soft measuring tape as the tool. Our report considered direct anthropometric measurement techniques with data collection performed by a single researcher.

Results: Distinct morphometric characteristics were observed in the foramen magnum of the Peruvian population compared to other studies. The average measurements of the skull base revealed a foramen magnum with a mean length of 33.80 mm and a width of 28.70 mm, along with right condyles measuring 25 mm in length and 14.10 mm in width, and left condyles measuring 23.80 mm in length and 13.90 mm in width.

Conclusion: The morphometric analysis of the foramen magnum in the Peruvian population provides valuable insights into specific anatomical features within this ethnic group. These findings could have significant implications across various medical and surgical disciplines, from interpreting diagnostic images to designing more precise therapeutic interventions tailored to this population.

Keywords: Anatomical variations, Anthropometric measurements, Foramen magnum, Morphometric analysis, Neurosurgical techniques


The foramen magnum, an anatomical structure located at the base of the skull, has sparked notable multidisciplinary interest across various academic fields, ranging from forensic anthropology to neurosurgery and evolutionary biology.[ 20 , 29 , 30 ] This interest has been manifested through a series of morphometric and morphological investigations that have delved into the significance of the foramen magnum for a detailed understanding of human anatomy.

The foramen magnum is a fundamental anatomical region that serves as a critical point of connection between the spinal column and the central nervous system.[ 39 ] Its relevance lies in its close relationship with vital human body structures, such as the brainstem and the spinal cord, enabling the safe and protected passage of essential neural structures between the skull and the spinal column.[ 37 ]

A detailed understanding of the dimensions and morphological variations of the foramen magnum is crucial in medical practice, especially in neurology and neurosurgery.[ 6 , 35 ] Moreover, variations in its size, shape, or associated pathologies can have significant clinical implications.[ 40 ] Cases have been documented where abnormalities in the foramen magnum are associated with neurological disorders, congenital malformations, or conditions affecting the circulation of cerebrospinal fluid, underscoring its clinical relevance in diagnosis and treatment.[ 1 - 3 , 10 ]

Variability in the dimensions and characteristics of the foramen magnum in different ethnic populations has been documented,[ 13 , 14 ] emphasizing the importance of investigating and understanding specific anatomical features within a population. The purpose of this present study is to establish the morphometric profile of the foramen magnum in the Peruvian population, aiming to contribute to medical and surgical knowledge significantly and allow a better understanding of craniovertebral morphology within the Peruvian ethnic context.


Study sample

The study sample comprises 17 cadaveric specimens from institutional osteological collections in Peru. These specimens, mostly donated to the NeuroZone3D Research Center, represent various geographical origins.

Classification methods

For study purposes, the 17 specimens were classified by the NeuroZone3D Research Center and its collaborators without considering age or sex. This decision was made due to the complexity of tracking and the lack of evidence supporting these characteristics.

Data collection

Measurements were conducted using conventional measurement techniques with a soft, inelastic measuring tape (Perfect Measuring Tape Company, USA). A single researcher assessed each skull, determining six cranial measurements according to widely recognized nomenclature[ 4 , 12 , 15 , 21 , 41 ] with assistance from other authors.

Statistical analysis

The collected data were tabulated and analyzed using Microsoft Excel. The results of cranial measurements are presented as mean, median, standard deviation, minimum, and maximum values.

Cranial reference points: Neurozone3D skull base protocol

The NeuroZone3D protocol represents a cranial reference system used to measure human skull dimensions. Based on recognized literature in neurosurgery, its primary objective is to unify consistent definitions that contribute to consensus in broad discussions about neuroanatomy, thus providing a supportive tool for the scientific community.

Within this protocol, six cranial measurements were prioritized at the skull base, including the length and width of the foramen magnum, as well as the condyle of the occipital bone. Detailed information on cranial measurements, their abbreviations, and specimen identification are provided in Tables 1 and 2 and Figure 1 .

Table 1:

Definitions of neuroanatomical cranial structures at the skull base (*).


Table 2:

Description of cranial measurements from the NeuroZone3D skull base protocol.


Figure 1:

Inferior view of the skull with anatomical landmarks and measurements between the average distances of cranial points. (a) Skull base in an inferior view: cranial reference points are highlighted in green, red dashed lines indicate length measurements (ba, basion; o, opisthion; i, inion; y op, opisthocranion), and a yellow line measures the width of the occipital condyles (oc) and the foramen magnum. The shaded orange color delineates the articular facet of the left occipital condyle (fac), while a light blue tone outlines the pharyngeal tubercle (tf) on the occipital bone. Additionally, a red shading marks the right condylar fosase (fo), and a dark blue hue highlights the external occipital crest (crt)of the occipital bone. (b) The left occipital condyle is shown with approximate measurements of length (red dashed line) and width (yellow line). (c) The right occipital condyle is depicted with approximate measurements of length (red dashed line) and width (yellow line) of the structure.



Cranial measurements from 17 skulls revealed significant variations in the dimensions of the foramen magnum and the condyles. For the foramen magnum, lengths ranged from 30.00 mm to 38.00 mm, with widths varying between 25.00 mm and 33.00 mm. Regarding the condyles, the average length of the right condyle was 25.00 mm, ranging from 21.00 mm to 30.00 mm, while the left condyle showed an average length of 23.80 mm, varying between 18.00 mm and 33.00 mm. Concerning width, the right condyle had a mean of 14.10 mm, fluctuating between 12.00 mm and 17.00 mm, whereas the left condyle averaged a width of 13.90 mm, ranging from 11.00 mm to 17.00 mm [ Table 3 ].

Table 3:

Cranial measurements of the foramen magnum in millimeters from Peruvian specimens.


When evaluating the skull base, the foramen magnum exhibited an average length of 33.80 ± 2.28 mm and a width of 28.70 ± 2.21 mm. Regarding the condyles, the right condyle showed a length of 25.00 ± 2.29 mm and a width of 14.10 ± 1.57 mm, while the left condyle recorded an average length of 23.80 ± 3.46 mm and a width of 13.90 ± 1.48 mm. The overall average length measurements for both condyles yielded a value of 19.68 ± 2.90 mm, while the average width was 11.18 ± 1.54 mm [ Table 4 ].

Table 4:

Cranial Measurement: Quartile, median, mean±standard deviation, minimum, and maximum values in millimeters from Peruvian specimens.



For the first time, the collection at the NeuroZone3D Research Center in Peru provides detailed measurements of the foramen magnum and condyles in cadaveric specimens [ Table 5 ]. In comparison, studies from Colombia and Brazil[ 15 , 19 , 33 ] revealed similar measurements for the foramen magnum; however, they did not detail condyle measurements, limiting the comprehensive comparison between these anatomical samples. The NeuroZone3D Research Center collection stands out for its specific focus on both measurements, contributing to a more comprehensive understanding of craniovertebral morphology compared to studies from Colombia and Brazil.

Table 5:

Measurements of the foramen magnum and occipital condyles in cadaveric specimens by geographical location.


Anatomical studies of the foramen magnum in Nigeria revealed significant measurements in African specimens. Osunwoke and Oladipo[ 27 ] analyzed a broader group of 120 specimens, obtaining an average length of 36.11 ± 2.60 mm and a width of 29.56 ± 2.60 mm. On the other hand, Ukoha et al.,[ 36 ] with a smaller number of samples, 90 males and ten females, revealed slightly greater lengths in men with an average of 36.26 ± 2.30 mm in length and 30.09 ± 2.50 mm in width, while women showed slightly smaller measurements with an average length of 34.39 ± 3.88 mm and a width of 28.16 ± 1.90 mm. Both studies provide valuable information, but the breadth of the sample studied by Osunwoke and Oladipo provides a more generalized view of these measurements, although specific data on the condyles were not presented.

Anatomical studies conducted across various regions of Asia have unveiled intriguing patterns in the measurements of the foramen magnum and condyles, particularly when examining differences between men and women in these measurements. In the study conducted in Oman by Kumar et al.[ 14 ] in 2015, a significant disparity between sexes was evident: men exhibited significantly larger dimensions in the foramen magnum (36.78 ± 1.52 mm in length and 30.05 ± 2.36 mm in width) compared to women (33.22 ± 2.00 mm in length and 29.49 ± 1.66 mm in width). This discrepancy points to a distinctive anatomical difference between genders in this Asian region.

Conversely, multiple investigations in India[ 24 , 28 , 31 , 32 ] have shown a similar trend where, generally, men tend to have larger measurements in both length and width of the foramen magnum and condyles compared to women. Although variability in the data is observed, this persistent discrepancy between sexes is a notable finding. It possibly suggests gender-based anatomical differences within the Indian population based on their region of origin.

A recent study conducted in Thailand demonstrated similar results, showing a clear disparity between men and women in measurements.[ 34 ] Men exhibited considerably larger dimensions in the foramen magnum and condyles compared to women, aligning with trends observed in other Asian studies. Even in Saudi Arabia, the same trend is observed in terms of the length and width of the foramen magnum, as well as the dimensions of the condyles.[ 18 ] These collective data from various Asian countries suggest consistency in anatomical differences between genders in the region, which could have significant implications not only in neurosurgery but also in various medical and research fields related to anatomy and medicine.

The anatomical analysis of the foramen magnum and condyles has been the subject of numerous studies in Europe, revealing significant variability in the measurements obtained. In Olivier’s work,[ 26 ] average measurements of the foramen magnum were found to be 35.70 ± 2.72 in length and 30.84 ± 2.15 in width. Detailed condyle measurements were also presented with values of 23.75 ± 2.74 in length and 11.50 ± 1.20 in width. A subsequent study conducted by Catalina-Herrera at the University of Seville broke down measurements by gender.[ 5 ] In men, the average measurements of the foramen magnum were 36.2 ± 2.60 in length and 31.1 ± 2.60 in width, while in women, these measurements were slightly smaller, with values of 34.30 ± 2.04 in length and 29.6 ± 1.53 in width. Years later, analyses of the foramen magnum were expanded considering gender differences,[ 8 , 11 , 16 , 17 , 25 , 38 ] showing significant variations, while other studies specifically focused on condyle measurements,[ 9 , 23 , 25 ] providing a detailed but more limited perspective of these anatomical structures.

The addition of this present study conducted in Peru provides specific data on the foramen magnum and condyles in this region of America. The obtained values rank on the lower average compared to other previously mentioned studies, both in America and other regions. This observation emphasizes the need to consider anatomical variability not only among different geographical locations but also within the same region, highlighting the importance of future research to understand morphological diversity in craniovertebral morphology.

The significance of craniotomy varies considerably depending on the geographical region and specific anatomical characteristics of each population. Detailed anatomical studies in different countries have revealed significant variations in the dimensions of the foramen magnum and condyles, emphasizing the need to consider local anatomical peculiarities in neurosurgical interventions.[ 7 ] For instance, analyses in Europe have highlighted variations between genders in foramen magnum measurements,[ 5 , 8 , 9 , 11 , 16 , 23 , 25 , 26 , 38 ] while in Asia, distinct differences between men and women in various cranial measurements have been observed.[ 14 , 18 , 24 , 28 , 31 , 32 , 34 ] These anatomical discrepancies can influence surgical techniques, emphasizing the relevance of an approach tailored to the region and/or geographical area to enhance the outcomes of craniotomies.

The creation of indices tailored to each type of skull based on the region or country emerges as an innovative and crucial strategy in the field of neurosurgery. These indices could establish specific parameters for each region, considering the anatomical differences found in detailed anatomical studies.[ 7 , 22 ] By developing customized indices according to geography, surgical techniques could be enhanced, allowing for more precise planning adapted to the unique anatomical characteristics of each population. This personalized approach could reduce risks during cranial interventions, optimizing the effectiveness of procedures and improving postoperative outcomes in neurosurgical surgeries.


The morphometric analysis of the foramen magnum and condyles in a sample of the Peruvian population revealed distinctive anatomical characteristics compared to studies conducted in other regions of the world. Significant variations were observed in the dimensions of the foramen magnum and condyles, showing slightly smaller average measurements in this population. These findings highlight the importance of considering anatomical diversity within a specific region when planning neurosurgical interventions and clinical diagnoses. The development of indices tailored to the craniovertebral morphology of each population could be crucial to enhancing the precision and effectiveness of surgical techniques, reducing risks, and optimizing postoperative outcomes in neurosurgical procedures.

Ethical approval

The Institutional Review Board approval is not required.

Declaration of patient consent

Patients’ consent not required as patients’ identities were not disclosed or compromised.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.


The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.


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