Variations in the shape of foramen magnum at the base of human skulls among Indians in Rajasthan

Variations in the shape of foramen magnum can affect the normal anatomy of vital structures passing through it. Therefore, it is of interest to evaluate the various shapes of foramen magnum by using CT scans performed in patients of Indian population to establish clinical correlation. A total of 314 CT images of human skull base obtained from the Department of Radio-diagnosis, Geetanjali Medical College and Hospital, Udaipur, Rajasthan were used in the present study. All the patients’ CT scans were observed to determine the shape of foramen magnum. They were classified into one of the following shapes: Oval, round, tetragonal, egg shaped, hexagonal, pentagonal and irregular. The shapes of the foramen magnum in CT scans were oval in 39.09%, round in 22.61%, tetragonal in 12.10%, hexagonal in 10.51%, irregular in 7.96%, pentagonal in 5.41% and egg shaped in 1.59% CT images. Data shows that it is easy to operate at the base of skull in case of round, oval and hexagonal shape foramen magnum, as the working space is more in these shapes.

correlation. A total of 314 CT images of human skull base obtained from the Department of Radio-diagnosis, Geetanjali Medical College and Hospital, Udaipur, Rajasthan were used in the present study. All the patients' CT scans were observed to determine the shape of foramen magnum. They were classified into one of the following shapes: Oval, round, tetragonal, egg shaped, hexagonal, pentagonal and irregular. The shapes of the foramen magnum in CT scans were oval in 39.09%, round in 22.61%, tetragonal in 12.10%, hexagonal in 10.51%, irregular in 7.96%, pentagonal in 5.41% and egg shaped in 1.59% CT images. Data shows that it is easy to operate at the base of skull in case of round, oval and hexagonal shape foramen magnum, as the working space is more in these shapes.

Background:
In modern era of clinical medicine, CT scan has evolved as a powerful and widely used diagnostic imaging tool.

Materials and Methods:
Present study was done in the Department of Anatomy, Geetanjali Medical College and Hospital, Udaipur, Rajasthan after obtaining institutional ethical approval. Total 314 patients' CT images of human skull base obtained from the Department of Radiodiagnosis, Geetanjali Medical College and Hospital, Udaipur, Rajasthan were used in the present study. The CT images belong to the patients who had undergone CT scan evaluation for head and neck region for different clinical indications between the year of 2013 and 2018. All the patients' CT scans were visually assessed to determine the shape of FM and was classified into one of the following seven shapes -oval, round, tetragonal, egg shaped, hexagonal, pentagonal and irregular ( Figure 1). The findings of the present study were statistically analyzed by using Microsoft Office Excel 2019.

Results & Discussion:
The various shapes of the foramen magnum in CT images found in current study are oval in 39.09%, round in 22.61%, tetragonal in 12.10%, hexagonal in 10.51%, irregular in 7.96%, pentagonal in 5.41% and egg shaped in 1.59% cases. (Table 1, Figure 2) Evaluation of the different shape of skull base foramina by using computed tomography scans of patients has gained importance in clinical medicine. Most common shape of foramen magnum observed in the present study was oval, which was present in 39.09% cases. This value is lower as compared to the observations by Ganapathy et al.
[5] (2014) ( (2013) in 9.5% CT images observed egg shape of foramen magnum in their study, which is higher than the present value. The difference in percentages of various shapes of foramen magnum could be due to study done on different population or interobserver variation or genetic variation. Anatomical values obtained by different authors are nearly the same, which is not correct with regards to the values of the radiologic study [9][10][11][12][13][14].

Conclusion:
Data shows that the oval shape is the most common, round is the second most common and egg shape is the least most common shape of foramen magnum in CT images of Indian population. Data also shows that it is easy to operate at the base of skull in case of round, oval and hexagonal shape foramen magnum, as the working space is more in these shapes.