European Journal of Molecular & Clinical Medicine

Background: Foramen magnum (FM) is the largest foramen in the skull. It lies in an antero-median position and leads into the posterior cranial fossa. The present study was conducted to assess different shapes of foramen magnum.
Materials & Methods: 56 dry adult human skulls of either gender obtained in Anatomy department will be selected and the shape of foramen magnum will be determined.
Results: Out of 56 dry skull, 26 were of males and 30 were of females. Shape found was round in 26, oval in 14, irregular in 5, hexagonal in 3, pentagonal in 4, pentagonal in 4, tetragonal in 2 and egg shaped in 2 cases. The difference was significant (P< 0.05).
Conclusion: The analysis of various shapes of foramen magnum is utmost important. This study provides guidance to the surgeons, radiologists, orthopedics, anthropologists as well as forensic experts.

Introduction
The foramen magnum is a wide communication between posterior cranial fossa and the vertebral canal. The narrow anterior part of the foramen magnum has apical ligament of dens, upper fasciculus of the cruciate ligament and membrana tectoria, both are attached to the upper surface of basioccipital bone infront of the foramen magnum. Its wide posterior part contains the medulla oblongata and its meninges. In subarachnoid space spinal rami of the accessory nerve and vertebral arteries, with their sympathetic plexus, ascend into the cranium; the posterior spinal arteries descend posterolateral to the brain stem.
 
Materials and Methods
This is a prospective and observational study conducted in the Department of Anatomy, Index Medical College. Maximum anteroposterior diameter of the Foramen Magnum: Maximum distance between anterior and posterior margins measured along the midsagittal plane of the Foramen Magnum. Maximum transverse diameter of the Foramen Magnum: Maximum distance between the lateral margins measured along the transverse plane of the Foramen Magnum. Length of the occipital condyle: Maximum length of the Occipital Condyle taken along the articular surface and the parameter is recorded bilaterally. Maximum width of the occipital condyle: Maximum width of the Occipital Condyle taken along the articular surface perpendicular to the Occipital Condyle length and the parameter is recorded bilaterally
 
Results
100 subjects were studied (80 males and 20 females) with an overall mean age of 38.92 ± 10.95 years. The mean and standard deviation for all the five measurements were obtained to derive the FM dimensions in the study population, which showed that except LD all other parameters were noted higher in males, highlighting sexual dimorphism in FM dimensions. Gender accuracy formula: [(‑0.263 x LD) +0.156 x TD) + (0.437 x C) + (0.659 x A)] – 102.17 By applying the data to the derived equation, canonical variables were derived for all the parameters of FM dimensions. Also, an attempt was made to assess the efficiency of all five parameters of FM in sex determination. The overall accuracy of 72.5% was got when 120 subjects were considered. The maximum accuracy was got for C and the least for LD.
 
Conclusion
The study recommends the use of SMV radiographs in elucidating FM morphometric variations for the identification of unknown individuals and may act as a guide to the anatomists, neurosurgeons, and in other medical fields as well. These findings would be interrogated as reliable indicators in sex determination of unknown skulls. Data should be only used as a corroborative finding in predicting sex in case of fragmented cranial bases and not recommended as sole indicators for sexing complete skulls.