Morphological Analysis and Morphometry of the Foramen Magnum: An Anatomical Investigation

AIM: The objectives were to study the morphology of the foramen magnum in dry skulls and to evaluate its antero-posterior diameter, transverse diameter and the foramen magnum index. MATERIAL and METHODS: The foramen magna of 53 dry human cadaver skulls that were obtained from the neuroanatomy laboratory were examined. Different shapes of the foramen magnum were macroscopically noted and classified. The antero-posterior and transverse diameters were measured and the average foraminal index was calculated. RESULTS: The foramen magnum shapes were determined as a round shape in 22.6% of cases, egg shape in 18.9%, tetragonal in 18.9%, oval in 15.1%, irregular in 15.1%, hexagonal in 5.6% and pentagonal in 3.8% of the cases. In 20.7% of skulls, the occipital condyle was observed to protrude into the foramen. The mean antero-posterior and transverse diameter of the foramen magnum was determined as 31 +/- 2.4 mm and 25.2 +/- 2.4 mm respectively. The average foramen magnum index was 1.2 +/- 0.1. CONCLUSION: The present study has determined the various shapes of foramen magnum and its morphometry. The data obtained may be of useful to the neurosurgeon in analyzing the morphological anatomy of craniovertebral junction. The findings are also enlightening for the anthropologists, morphologists and clinical anatomists.