RESUMO
Background: Foramen magnum (FM) is an important landmark of the skull base and is of particular interest foranthropology, anatomy, forensic medicine and other medical field. It is one of several oval or circular aperturesin the base of the skull, through which medulla oblongata is transmitted. Variations of the shape of FM have gotdiagnostic clinical and radiological importance. The dimensions of FM have clinical importance because thevital structures that pass through it may suffer compression as in cases of FM achondroplasia and FM brainherniation, so this study aimed to access its diameter and determining its various shape.Materials and Methods: Study sample consisted of 75 dry adult human skull of unknown sex, free from anypathology and collected from Department of Anatomy, P.D.U. Medical College, Rajkot, Gujarat and Americaninternational institute of medical sciences, Udaipur, Rajasthan, India.Results: The FM was observed to have round shape in 8%, egg shape in 9.33% tetragonal in 25.33%, oval in33.33%, irregular in 2.67%, hexagonal in 8% and pentagonal in13.33% of the cases. The mean antero-posteriorand transverse diameter of the FM was recorded as 34.00+/- 2.38 mm and 28.68+/-1.88 mm respectively. TheMaximum diameter of antero-posterior and transverse diameter was recorded 39.53mm and 32.14mmrespectively. The Minimum diameter of antero-posterior and transverse diameter was recorded 28.72 mm and23.54 mm respectively.Conclusion: Though the present study has a limitation as the exact age and sexes of skull were not determined,this study may provide an important reference and the measurements may be used as a data for the descriptionof normal morphological variants of FM. The present study will be of useful to the neurosurgeons and is alsohelpful to the anthropologists and clinical anatomists.