Risky anatomic variations of sphenoid sinus for surgery

Abstract

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.

Assessment of the Relation of the Optic Nerve to the Posterior Ethmoid and Sphenoid Sinuses by Computed Tomography

“…The opticocarotid recess is presumed to concur with ipsilateral optic nerve protrusion into the sphenoid sinus 8 . Sirikci et al 1 , Ünal et al 4 and Hewaidi et al 8 reported a significant relationship between protrusion of the ON into SS and the pneumatization of ACP. We observed 23.5 % patients on the right side and 14.7 % patients on the left side with both pneumatization of ACP and protrusion of ON.…”

“…Protrusion of optic nerve and bony dehiscence of the wall of optic nerve was evaluated according to the criteria of Sirikci et al 1 and Ünal et al 4 . In coronal section, protrusion was defined as the presence of more than half the circumference of the concerned structures into the sinus cavity with or without defects in their bony margins.…”

Study of the relationship between sphenoid sinus volume and protrusions in the sphenoid sinus

“…Firstly, the presence of the ICA and ON protrusions was identified and assessed on the axial plane according to Unal's method [6]. Briefly, the protrusion of the ICA was determined as finding for placement of ICA with 50% of its diameter in SS and obvious or light protrusions was determined as finding for placement of ICA with more than 50% or 10% -50% of its diameter.…”

“…However, the protrusions don't appear in all cases. The prevalence of the protrusions is quite variable, which may affect the success of transsphenoidal endoscopic surgery [6,[8][9][10][11][12][13]. The prevalence of protrusion of ICA is not conclusive, ranging from 5.2% [14] -32.8% [15], 48.5% [16] and 67.7% [8], depending on the degree of individual pneumatization and the definition used in each study.…”

“…Anatomical and radiological studies dealt with the sphenoid sinus and its surrounding structures based on cadavers or CT studies in these years. Several literatures have documented the dimensions, septation, pattern of SS pneumatization, SS surrounding structures [3][4][5], prevalence of protrusions [6] and the relation between pneumatization and protrusions [7]. These studies provided important information for surgeries in this area and promoted advancement of the surgery as well.…”