Sphenoid bone is placed between the frontal, temporal and occipital bones in the middle cranial fossa at the base of the skull. Certain parts of sphenoid bone are connected by ligaments, which occasionally ossify such as, pterygospinous (between the spine and the upper part of the lateral pterygoid plate), the sella turcica bridge (between the anterior and posterior clinoid processes) and the carotico-clinoid (between the anterior and the middle clinoid processes). They can be developed unilaterally or bilaterally and vary in frequency [1-8]. This paper reports the morphometric characteristics and the morphological analysis of a dry skull with complete ossification of interclinoid ligaments causing formation of carotico-clinoid foramen as well as sella turcica bridge.

During teaching medical students, it was noticed in one dry skull that ossification not only reaches anterior and middle clinoid processes, forming Carotico-clinoid Foramen (CCF), but also includes the anterior and posterior clinoid processes forming Sella Turcica Bridges (STB) bilaterally (Figures 1-3).

Figure 1: View form top of ossified interclinoid processes.

Figure 2: View of left ossified interclinoid processes.

Figure 3: View of right ossified interclinoid processes.

The age and the sex of the skull is not known but probably it may be male as the superciliary arches and glabella are prominent and probably the age may be between 30 yrs and 40 yrs as sagittal suture is fused internally, but not externally.

The morphologic analysis and morphometric description are described in (Table 1). All measurements are taken by Vernier caliper.

Table 1: Morphometric description of ossified interclinoid ligaments in our specimen.

The CCF was first described by Henle in 1855, as an osseous bridge between the tip of the anterior and middle clinoid processes. The CCF can be incomplete or complete and unilateral or bilateral. The incidence of incomplete unilateral foramen varies from 8-35% while a bilateral and complete foramina are very rare found in 0.2-4% of population. A racial variation also been reported regarding CCF. A high incidence has been noted in Turkish (35-67%), Caucasian Americans (34.84%), Alaskan Eskimos (17%), Sardinians (23.4%), Koreans (15.7%), Portuguese, Nepalese, whereas low incidence was found in Japanese (9.9%), Brazilians (2.5%) [3-7]. Regarding the sexual variations, contradictory results have been reported by different authors. While Freire et al. [8], found it to be more common in females, Lee et al. [9], found it otherwise more common in males. When unilateral, it is more common in right side [10].

Ozdogmus et al. [11] demonstrated that, due to caliber of the internal carotid artery (ICA) in the area of the skull being larger than the diameter of the CCF, it was reported that there is a high possibility of headache caused by compression of ICA in the presence of CCF. The sella turcica region is circumscribed within the anterior and posterior clinoid processes. The sella turcica bridge can be partial or complete ossification of the interclinoid ligaments, which has been reported by many authors Tebo, [12]. The incidence of the sella turcica bridge ranges from 1.54 to 5.9%. The only way of diagnosing the calcification of sella turcica is with a lateral skull cephalometric radiography by Das and Paul [13].

STB may influence structures like the ICA, ophthalmic artery, optic nerve, Trochlear nerve, Oculomotor nerve and pituitary gland by Skratz et al. [14], but when there is no clinical sign and symptoms, it is considered a normal variant. A greater frequency of STB has been described in patients with severe craniofacial deviation and tooth anomalies by Cedeberg et al. [15]. Radiographically seller bridges were demonstrated to a 25% in idiots, to 20% in criminals, to 15% in epileptics and to 38% in other cases of mental disorders [16].

CCF and STB have a great clinical significance and anatomical knowledge of these foramina may be helpful for neurosurgeons, neurophysicians, endocrinologist, radiologist, anatomists and biological anthropologist.

Neurosurgeons have to approach the parasellar region in case of aneurysm of the intracavernous and clinoid segment of the ICA, carotico-clinoid fistula and tuberculum sella meningiomas. In these cases removal of anterior clinoid process is mandatory for proper visualization of the structures. Presence of an osseous bridge between clinoid processes makes removal of anterior clinoid process more difficult and enhances the risk of hemorrhage, especially if an aneurysm is present. ICA in clinoid segment and Oculomotor nerve may be damaged through the removal of anterior clinoid process. Drilling of anterior clinoid process may also cause inadvertent injury to the optic nerve [17].

Neurophysicians must consider the presence of Type I interclinoid bar or carotico-clinoid foramen which may cause compression, tightening or stretching of the ICA leading to different types of transient ischemic attacks and headache [18].

A CCF may confuse radiologist while doing carotid arteriogram and pneumatization or marrow density assessment of anterior clinoid process. It is important for anatomists/embryologist to know about this variant and to explain the same on ontogenic basis. Physical anthropologists are interested in the factors which are responsible for causation of such variants like age, sex, race, regional variation and hereditary influences [19].

The presence of ossified interclinoid ligaments is not rare, but the incidence of sella turcica bridge is lesser than carotico clinoid foramen. The thorough knowledge of its occurrence will help not only physicians, but also radiologists, neurosurgeons for preoperative scanning and precautions to be taken to prevent the fatal complications during surgery. As the regular anatomy text books are not providing the detail descriptions of the different interclinoid ligaments of foramens, the present report and discussion may help to the clinicians as well as anatomists.