INCIDENCE OF OSSIFIED INTERCLINOID BARS IN DRY HUMAN SKULLS OF GUJARAT STATE

A group of intrinsic ligaments of the sphenoid bone which connect the anterior, middle & posterior clinoid processes occasionally get ossified and give rise to various types of ossified interclinoid bars. In present study the incidence of various types of ossified interclinoid bars were observed in 200 dry human skulls of unknown age & sex belonging to department of Anatomy of various Medical Colleges of Gujarat region. The interclinoid bars are classified on the basis of two classifications, proposed by Rani Archana et al and Keyers. Rani Archana et al, classified interclinoid bars into four types : Type I (caroticoclinoid foramen) bridge present between anterior and middle clinoid process, Type II bridge between anterior, middle and posterior clinoid process, Type III bridge between anterior and posterior clinoid process and Type IV bridge between the middle and posterior clinoid process. Each interclinoid bar was classified into contact, incomplete, complete types based on the classification of Keyers. In present study total incidence of interclinoid bars was 18%. Type I were present in 10.5%, out of which 8% were complete and 2.5% were incomplete. Types II in 3.5%, amongst them 2% were complete and 1.5% was mixed. Type III in 4%, out of which 2% were complete and 2% were incomplete. Total incidence of caroticoclinoid foramens was 14.5%, out of which 11.5% were complete and 3% were incomplete. Total incidence of sellar bridge was 7.5%, out of which 4.5% were complete and 3% were incomplete. Presence of osseous interclinoid bars may cause compression of surrounding structures like the cavernous sinus and its content, sphenoid sinus and pituitary gland. Therefore, detailed anatomical knowledge of various types of interclinoid bars can increase the success of diagnostic evaluation and surgical approaches to the region.


Introduction:
The ossification of ligamentous structures in various parts of the body may result in a clinical problem such as compression of neighbouring structures and complications in regional surgery. Williams et al 1 describes that there are three clinoid processes present on either side of sella turcica which is saddle shaped depression on intracranial surface of body of sphenoid bone. The anterior clinoid processes are formed by the medial and anterior prolongations of the lesser wing of the sphenoid bone, the posterior clinoid processes are present at the end of the dorsum sellae and the middle clinoid processes are present on either side of tuberculum sellae. The carotico-clinoid ligament connecting anterior and middle clinoid processes sometime get ossified forming the carotico-clinoid foramen which transmits one of the segment of internal carotid artery. Ossification of interclinoid ligament that connecting anterior and posterior clinoid processes is termed as interclinoid osseous bridge or sella Turcica Bridge. Thus ossification of the ligaments connecting the clinoid processes of the sphenoid bone may give rise to bony bridges. Du Boulay mentioned that this ligamentous ossification occurs in the early age and is possibly an extension of the normal ossification of the anterior and posterior clinoid processes 2 . Bridge formation occur either between the anterior and the middle (carotico-clinoid bridge; carotico-clinoid foramen of Henle), the anterior and the posterior (sella turcica bridge), or between the middle and posterior clinoid processes. In rare instances, the three processes fuse with each other 3,4 . According to Basmajian 5 and Breathnach 6 these bridges are related to the cavernous sinus, internal carotid artery, and pituitary gland. In surgical procedures such as exposure of the cavernous sinus through superior approach and in the management of paraclinoid aneurysm, excision of anterior clinoid process becomes mandatory. The presence of important neurovascular structures in the vicinity of anterior clinoid process makes this procedure very difficult. Presence of ossified interclinoid bars not only poses difficulty in removal of anterior clinoid process but also enhances the risk of damage to the adjacent important structures. IJBAR (2012) 03 (12) www.ssjournals.com Various authors have reported that several endocrinological and neurological disorders are associated with such variations 7,8 . Sella bridges were demonstrated roentgenologically to a 25% extent in idiots, to 20% in criminals, to 15% in epileptics, and to 38% in other cases with mental disorders 9 . The present study is conducted to determine incidence and types of the ossified interclinoid bars in dry skulls of Gujarat population. The obtained results were compared with those of other studies on different populations.

Material and Method:
This study was performed on 200 dry human skulls with removed calvaria of unknown age & sex belonging to department of Anatomy of various Medical Colleges of Gujarat region. In all cases, the anterior, middle, and posterior clinoid processes were examined on both right and left sides to reveal their relationship and the incidence of ossified interclinoid bars. For the classification of the interclinoid bars, the method proposed by Rani Archana et al 10 and the method proposed by Keyers 11 were used.

Rani Archana et al, classified interclinoid bars into four types 10 :
Type I: -Bridge present between anterior and middle clinoid process(caroticoclinoidforamen). Type II: -Bridge between anterior, middle and posterior clinoid process.
Type III (sella turcica bridge):-Bridge between anterior and posterior clinoid process. Type IV: -Bridge between the middle and posterior clinoid process.

Keyers 11 further classified each type of bridge into three subtypes depending upon the extent of fusion between the bony bars arising
from the respective clinoid process. a. Complete type: -A complete fusion between two bony bars b. Contact type : -Presence of a dividing line or suture between bony bars c. Incomplete type: -If a spicule of bone was extending from one clinoid process towards the other with a gap in between, In Type II variety of osseous bridge a fourth subtype of fusion was also observed where a combination of any of the above two subtypes was present between the adjacent clinoid process and this subtype was termed as mixed type 10 . The incidence of caroticoclinoid foramen (include type I & II) and sella turcica bridge (include type II & III) was also studied separately.

Result:
In the present study out of 200 skulls the total incidence of the various types of interclinoid bony bars was 18% (n = 36).
In present study no skulls showed contact type of interclinoid bony bars.

Discussion
The interclinoid ligament joins the anterior and posterior clinoid processes while the caroticoclinoid ligament connects the anterior and middle clinoid processes 1 . Frazer did not mention the caroticoclinoid ligament as a separate entity. According to Frazer, the anterior, middle and posterior clinoid processes are connected by interclinoid ligaments 12 . The ossified interclinoid ligament forms a bony bridge between the anterior, middle and posterior clinoid processes of the sphenoid bone. These bony bridges are known as sellar bridge 13 . In the present study the total incidence of type I bridges was 10.5% which is nearer to the incidence observed by Rani Archana(12%) but lower than incidence observed by Keyers(34.84%) & Erturk et al(35.67%). In the present study the incidence of bilateral type I bridges( 6%) was more as compared to unilateral (4.5%), and the complete subtype (8%) was more than the incomplete subtype (2.5%), while Rani Archana 14 observed that the incomplete subtype(6.8%) was more than complete subtype(3.6%) (Table 4a). In this study total incidence of type II Bridge (bilaterally) was 3.5% which is nearer to the incidence found by Rani Archana (5.6%) & Dyke (2-3%) but lower than incidence observed by Keyers (7.82%). The incidence of complete type II bridge was more common in present study whereas Rani Archana found that mixed type II bridge was more common (Table 4b).  (Table 4c). In present study no skull showed contact type of bridge.
Type IV interclinoid bridge is rarest which is present between middle and posterior clinoid process. Keyes 11 also described this type as rarest one.
IJBAR (2012) 03 (12) www.ssjournals.com   (Table 6). Various theories have been postulated to explain the formation of these interclinoid osseous bridges. Dyke 15 found the ossification in the dura between the anterior, middle and posterior clinoid processes in 2-3% of skulls. Schaeffer 32 stated that a bony bridge connecting the anterior and posterior clinoid processes is a persisting vestige of the primitive cranial wall. Kier 33 postulated that osseous interclinoid ligament was a developmental anomaly and showed the existence of the foramen that is formed by this ligament in fetus and infant skull. Lang 22 reported that sellar bridges are laid down in cartilage at an early stage of development and ossify in early childhood. It is a challenging task for neurosurgeons to approach the parasellar region of central skull base in cases of aneurysm of the intracavernous and clinoid segment of the internal carotid artery, carotico-cavernous fistula and tuberculum sella meningiomas. In these cases removal of the anterior clinoid process becomes mandatory for IJBAR (2012) 03 (12) www.ssjournals.com proper visualization of the structures. The research studies have also reported that the presence of an osseous bridge between the tip of the anterior clinoid process and either the middle or posterior clinoid process makes removal of the anterior clinoid process more difficult and increases the risk of its removal, especially if an aneurysm is present 34 . The segment of the internal carotid artery in the clinoid space-the clinoid segment-and the oculomotor nerve may be damaged during the removal of the anterior clinoid process 35 . Drilling of the anterior clinoid process may also cause inadvertent injury to the optic nerve 36 . From the ongoing discussion it is clear that Types I, II and III varieties of interclinoid osseous bars, if present, will enhance the risk of damage to the adjacent structures in any surgery involving the anterior clinoid process. Therefore preoperative imaging should always be advised, to obtain a satisfactory result from these surgeries. Kim et al. 37 suggested that if interclinoid bars are present extending from anterior clinoid process, then combined extra and intradural approach should be adopted for removal of anterior clinoid process. The existence of Type I interclinoid bony bar or carotico-clinoid foramen may cause compression, tightening or stretching of the internal carotid artery 23 .

Conclusion:
Among four types of interclinoid bars type I was more commonly found in present study. No skull showed contact subtype. The knowledge of interclinoid bars is important for neurosurgeons to provide information on the limited intraoperative view and reduce mortality and morbidity in surgical approaches.