This study was undertaken to observe the frequency of mastoid canals and grooves in dry human skulls in north Karnataka. 100 dry human skulls from the Department of Anatomy of Shri B M Patil Medical College, BLDE University, Bijapur, India which were of unknown age and sex, were selected and observed in the present study. The mastoid regions of dry skulls were observed for the presence of mastoid canals and grooves, if any. A metallic wire was passed through the canal for its confirmation and then the length of mastoid canal and groove was measured. In some of the skulls, grooves led to the openings of the canals.

Only those skulls which had canals patent to metal wire were considered as possessing mastoid canals. The length of the canal was measured with the help of a thread by passing a metal wire. The diameter of the mastoid canal could be measured in only few skulls where mastoid canal was larger, but in most of the skulls, it was not possible to measure the diameter. Length of the mastoid grooves was measured with the help of a thread.

Mastoid canals of varying lengths were present in 53(53%) of the total 100 skulls which were observed, either bilaterally or unilaterally [Table/Fig-1 and 2]. Among the mastoid canals which were found in 53 skulls, 14(14%) were bilateral, 36(36%) were unilateral, 02(2%) were both mastoid canals and grooves together [Table/Fig-3] and 01(01%) was a double mastoid canal [Table/Fig-4]. Among the 36(36%) unilateral canals, 20(20%) were on the left side and 16(16%) on the right side. Mastoid grooves were present in 18(18%) of the total skulls (100) which were observed. Among the mastoid grooves which were found in 18 skulls, 03(3%) were bilateral 15(15%) were unilateral. Among the 15 unilateral grooves, 06(6%) were on the right side and 09(9%) were on left side [Table/Fig-5].The distances between the 2 openings of mastoid canal ranged from 1 to 31 mm. The lengths of mastoid grooves ranged from 9 to 21 mm. The diameter of the mastoid canal was measured; diameter was less than 5 mm in most of the skulls.

[Table/Fig-1]:

Shortest Mastoid Canal

[Table/Fig-2]:

Longest Mastoid Canal, Metal wire in the canal

[Table/Fig-3]:

Both Mastoid Canal & Groove, Aero shows mastoid groove, metal wire shows mastoid canal

[Table/Fig-4]:

Double Mastoid Canal, metal wire shows 1st mastoid canal, Aero’s showing both the ends of second mastoid canal

Knowledge on mastoid canals and grooves is very important for otolaryngologists and neurosurgeons, because they contain an arterial branch of occipital artery with its accompanying vein, which is liable to injuries which can result in severe bleeding.

In an earlier study which was done by Choudary et al., it has already been proved that mastoid canals were present in Indian human skulls [3]. Singh M proved the presence of mastoid canals and mastoid grooves in Japanese skulls. The percentage frequency of mastoid canals in Japanese population was observed to be higher than that in Indian population [4]. Another study which was done by Hussain et al., showed the presence of mastoid canals and mastoid grooves in south Indian skulls [5]. Present study revealed that percentage frequency of mastoid canals in north Karnataka population was observed to be higher than that in Japanese population.

Warwick et al., reported two occipital branches of the occipital artery at this site [6]. In the present study, the presence of double mastoid canals in one region and presence of a mastoid canal and a groove together on one side were also reported; this indicated presence of two branches of occipital artery at this site, this supported the findings of Warwick et al.

Percentage frequency of mastoid grooves in north Karnataka population was observed to be higher than that in Japanese population [Table/Fig-6].

Mastoid canals which contain vessels may be attributable to the mode of development of this part of the temporal bone. In the embryo, the bone develops from two components. The squamous part arises in mesenchyme in the 8^th week of foetal life and it forms the anterosuperior part. The petro mastoid part develops from the cartilaginous epiotic centre at 5-6^th months of foetal life and it forms the posteroinferior part by 1 year of age [1]. These are demarcated on the external surface as the petrosquamous suture and are directed downwards and forwards into the mastoid process. In the adult skull, these may barely be distinguishable or are seen as series of irregular depressions or well marked fissures. The squamous plate grows posterior and it covers a large area of the lateral surface of the petro mastoid bone. The ‘junction’ between these two components of the temporal bone is often separated by a heavy plate of bone in many adults, which is referred to as Korner’s septum or a ‘false bottom’ and is a remnant of the suture [7]. The ascending branch of the occipital artery, which lies on the developing petro mastoid in foetal life, is likely to be buried by the ossifying squamotemporal bone. In other words, this ascending branch of the artery in some skulls is ‘trapped’ between two growing bones.

Since the presence of this artery and its accompanying vein in this region is liable to injury, as it may be undetected, it is necessary for surgeons who operate this area, to be aware of this vascular arrangement, to avoid troublesome bleeding. The importance of structures in the mastoid area has increased due to the increasing use of the transtemporal route for surgical procedures which are performed by neurosurgeons and otolaryngologists, which involve access to structures in the posterior fossa and the mastoid air system.