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Morphometric Study of Foramen Magnum and Variation in Its Shape

Introduction: Foramen magnum plays an important role as a landmark in the region of skull and spine because it transmits key structures like the lower end of the medulla oblongata, meninges, vertebral arteries and the spinal accessory nerve. Aims and objectives: Our aim was to provide basic osteometric data of anteroposterior and transverse diameters of foramen magnum and to observe its different shapes. Materials and methods: Thirty Four (34) adult human skulls of unknown sex were obtained from Department of Anatomy, RIMS, Ranchi. Foramen magnum diameters were calculated using sliding vernier calipers and shapes were visually assessed. Observations and results: Maximum anteroposterior diameter of foramen magnum was found to be 41.5mm and minimum was 28.5mm with the mean of 34.06mm whereas Maximum transverse diameter was 35mm and minimum was 22mm with the mean of 27.83mm. Percentage of foramen magnum shapes were as follows: oval 58.8%, Tetragonal 17.6%, hexagonal 11.8%, circular 8.82% and irregular 2.94% cases. Conclusion: Knowledge of dimensions of foramen magnum is important for radiologist, orthopaedicians and neurosurgeons, while planning and performing cranio-vertebral junction surgeries.