EVALUATION OF FORAMEN MAGNUM IN DRY HUMAN SKULLS OF DAKSHINA KANNADA DISTRICT

Address for Correspondence: Dr Pretty Rathnakar, Associate Professor, Department of Anatomy, K.S. Hegde Medical Academy, Deralakatte, Mangalore, Karnataka, India. E-Mail: prettyshrinath@gmail.com Background: Foramen magnum is situated in the posterior cranial fossa in anteromedian position. It is of great importance in anthropology, forensic medicine and skull base surgeries. Objective: Calculate anteroposterior (AP), transverse diameter(TD), area of foramen magnum and to observe its various shapes. Materials and Methods: 50 dry human skull bones of unknown sex was obtained from anatomy department. Measurements were taken by vernier calipers .SPSS 16 was used to calculate mean and standard deviation. Results: Mean AP diameter was found to be 33.64±0.228 mm, mean TD was 27.040±0.214 mm and Mean area was 714.99±0.844 mm2. Oval shaped foramen magnum was the most common variety (46%). 20% was tetrahedral,16% round ,14% egg shaped 2% hexagonal and 2% irregular . Conclusion: Present study focuses on morphometric and morphological variation in foramen magnum. This will be useful for anatomists , forensic experts , radiologists and neurosurgeons .

Transcondylar approach is being used frequently to access lesions of cervicomedullary junction and those ventral to brainstem [4].Vital structures that pass through foramen magnum can

EVALUATION OF FORAMEN MAGNUM IN DRY HUMAN SKULLS OF DAKSHINA KANNADA DISTRICT
Foramen magnum is situated in the posterior cranial fossa in anteromedian position .It is oval, being wider behind having anteroposterior diameter as its greatest [1].It is encroached anterolaterally by occipital condyles and its posterior part is thin and semicircular [2].
It contains the lower end of medulla oblongata, meninges , vertebral arteries, spinal accessory undergo compression such as in cases of achondroplasia [5] and brain herniation [6].Thus variations in dimensions and shape of foramen magnum is of great clinical significance.
The study was conducted on 50 dry skulls of unknown sex and age obtained from department of anatomy and students studying in K.S Hedge Medical Academy, Mangalore, Karnataka, India.Area of foramen magnum was calculated by the formula [7].

MATERIALS AND METHODS
Mean AP ,TD ,area was calculated .
Mean and standard deviation were calculated using SPSS 16.
The various shapes of foramen magnum was observed by naked eye and were classified as oval ,round tetrahedral, egg shaped.

The parameters measured included: Anteroposterior(AP) diameter of Foramen magnum: Distance between basion and opisthion.
Transverse diameter (TD) of foramen magnum: Maximum diameter at the lateral margins.
All measurements were recorded using vernier callipers to an accuracy of 0.1mm.Two measurements were taken and average of two values were considered as final .

RESULTS
Dimensions of foramen magnum in the present study is mentioned in Table 1.In the present study we found oval shaped foramen magnum to be the most common variety (46%).20% was tetrahedral ,16% round ,14% egg shaped 2% hexagonal and 2% irregular.

DISCUSSION
Due to protected position of foramen magnum and relative more thickness of base of skull it is well preserved in most specimen [8].Also it is least likely to undergo morphological changes Hence it is used frequently in anthropometry.
Foramen magnum presents many important structures passing through it.Variations in shape and size of foramen magnum is thus important for surgeons incase they have to approach this region .Also foramen magnum compressions are noted in conditions such as achondroplasia and cerebral herniation [19].
Various types of shape of foramen magnum is quoted in literature .Various studies show disparity in the frequency of occurrence of different types of shape of foramen magnum.The various shapes described are oval, round, tetragonal, pentagonal, biconvex, hexagonal.Irregular etc. [20].
In the present study we found oval shape of foramen magnum to be the most commonest variety(46%).20% was tetrahedral ,16% round, 14% egg shaped 2% hexagonal and 2% irregular.We did not come across pentagonal and biconvex varieties.Comparison between present study and other studies regarding commonest variety of shape of foramen magnum is shown in Table 2.
Present study focuses on morphometric and morphological variation in foramen magnum.This will be useful for anatomists, forensic experts, radiologists and neurosurgeons.Further studies on the same can be done using CT scan and Magnetic resonance imaging technique using more samples.
ABBREVIATIONS AP -Anteroposterior TD -Transverse diameter A -Area Mm -Millimetre

Table 2 :
Comparison between present study and other studies regarding commonest variety of shape of foramen magnum.