Risky anatomic variations of sphenoid sinus for surgery

We searched for the surgically risky anatomic variations of sphenoid sinus and aimed to compare axial and coronal tomography in detection of these variations. Fifty-six paranasal tomography images (112 sides) were evaluated for coronal, axial and both coronal and axial images. Tomographic findings including bony septum extending to optic canal or internal carotid artery; protrusions and dehiscences of the walls of internal carotid artery, optic nerve, maxillary nerve and vidian nerve; extreme medial course of internal carotid artery; patterns of aeration of the anterior clinoid process; and Onodi cells were evaluated. The results were classified as "present, absent, suspicious-thin (only for dehiscence) or no-consensus". The results of each plane were compared with that of the result of the both planes together. Kappa coefficient and Chi-square tests were used to compare both planes. Twelve cadaveric dissections were performed to reveal the proximity of sphenoid sinus to surgically risky anatomic structures. Endoscopy was applied to five cadavers. 18 evaluations were classified as 'no-consensus'. We detected 34, 35, 34 and 40 protrusions of internal carotid artery, optic nerve, maxillary nerve, vidian nerve, respectively. Dehiscences were present in 6, 9, 4 and 8, and suspicious-thin in 8, 10, 16 and 25 in canals of internal carotid artery, optic nerve, maxillary nerve and vidian nerve, respectively. Bony septum to internal carotid artery and optic nerve was observed in 30 and 22 cases. We observed 9 extreme medial courses of internal carotid artery, 27 aerated clinoid process and 9 Onodi cells. Axial images were superior in detection of bony septum to internal carotid artery and Onodi cells; while the coronal images were more successful in detection of protrusion of optic nerve and vidian nerve, and dehiscense of maxillary nerve and vidian nerve (P<0.05). In cadaveric dissections, the septa were inserted into the bony covering of the carotid arteries in two sinuses (8.3%). Detailed preoperative analysis of the anatomy of the sphenoid sinus and its boundaries is crucial in facilitating entry to the pituitary fossa and reducing intraoperative complications. Coronal tomography more successfully detects the sphenoid sinus anatomic variations.