Morphological Analysis and Morphometric Study of the Foramen Magnum

The foramen magnum is the oval shape opening situated at the base of the skull. The transcondylar approach is being increasingly used to access lesions of the Craniovertebral junction. Understanding the anatomy of the foramen magnum is important for skull base surgery. The present study was aimed at analysing the foramen magnum morphologically and morphometrically.100 adult human dry skullsat the Institute of Anatomy, Madras Medical College and twenty cranial CT scans obtained from the archives of Barnard Institute of Radiology, Rajiv Gandhi Government General Hospital, Chennai were used for the study. In the present study it was found that the foramen magnum was oval in 40% of the skulls studied. The mean AP diameter of the foramen magnum in dry skulls and cranial computerized tomographicscans were measured as 35.12±2.65mm and 35.03±0.95mm respectively. The mean transverse diameter of the foramen magnum in dry skulls and cranial CT were measured as 29.03±2.15mm and 28.79±1.17mm respectively. The mean maximum length of the right and left occipital condyle were measured as 23.85±2.12mm and 23.77±2.29mm respectively. The maximum and minimum width of the right occipital condyle were measured as 13.2 ±1.36mm and 6.86±1.34mm respectively. The maximum and minimum width of the left occipital condyle were measured as 13.44±1.41mm and 7.04±1.26mm respectively. The mean length of right and left occipital condyle were measured as 23.11±0.73mm and 23.20±0.74mm respectively in cranial CT. The mean width of right and left occipital condyle were measured as 12.92±0.65mm to 12.88±0.69mm respectively in cranial CT. The bicondylar distance, anterior intercondylar distance and the posterior intercondylar distance were measured as 47.23±3.10mm, 20.81±2.40mm and 41.97±1.67mm respectively. The posterior condylar canal was present in 40 skulls on right side and 49 skulls on left side. The Hypoglossal canal septum was present in 24%. The mean distance between intracranial edge of right hypoglossal canal and anterior margin of right occipital condyle was measured as 11.02±1.29mm and from left hypoglossal canal and anterior margin of left occipital condyle was measured as10.93±1.3mm.The mean distance between intracranial edge of right hypoglossal canal and posterior margin of right occipital condyle was measured as 12.26±0.59mm and from left hypoglossal canal and posterior margin of left occipital condyle was measured as12.25±0.59mm. The data obtained will be useful for neurosurgeons in analyzing the anatomy of Craniovertebral junction for preoperative planning and management of skull base surgery. The findings will also be enlightening for Radiologists, Orthopedicians, Anthropologists, Morphologists and Clinical Anatomists