Gross and Endoscopic Anatomy of Sphenoid Air Sinus in Cadavers and Adults Of North Karnataka - A cross Sectional Study

Abstract

Introduction – ABSTRACT Sphenoid sinus is most inaccessible paranasal sinus. It has got importance due to trans-sphenoid approach to the pituitary gland. It is surrounded by internal carotid artery, optic nerve, maxillary nerve and vidian nerve. Injury to these structures gives rise to inevitable complications. Most of the complications are due to wide variation in anatomy of sphenoid sinus and its relations. This study is an attempt to know the percentage of variations in North Karnataka population, through cadaveric dissection and CT scan study. Objectives – To study variations in extent of pneumatization, termination of inter-sinus septa, accessory septae and its termination, dimensions of sphenoid sinus, presence of onodi cells and neuro-vascular relations of sphenoid sinus. Material and methods – Permission was taken from respective Heads of Department of Anatomy, ENT and Radiology and Principal, JNMC, Belgaum to conduct the study. Study was started with ethical clearance from Independent Ethics Committee. All cadavers available in the Anatomy Department of Jawaharlal Nehru Medical College were included in the study. Selected patients and adults ( age range - 18 to 85 years ) from KLE’s Dr. Prabhakar Kore Hospital and Research Center, Belgaum were included in the study. Consent was taken from all living subjects that were included in the study. vii Endoscopic examination and dissection of sphenoid sinus was carried out in 30 cadavers ( 3 female and 27 male ) using 0 0 , 30 0 , 70 0 rigid nasal endoscopes. Sections were then made in the sagittal plane to confirm the anatomical findings and to take the necessary measurements with millimeter strips. Gross and endoscopic study was done in cadavers. Dimensions and relations of sphenoid sinus were noted and tabulated. Findings from CT scan study were tabulated separately. Results – In 20% of cadavers the sphenoid sinus was pre-sellar, in 14% it was sellar and in 66% it was post-sellar. Conchal type of sphenoid sinus was absent. Bony septa or crests were seen in 13 cadavers, out of which in 4 cadavers ( 32% ) they were bilateral and in remaining 9 cadavers ( 69% ) they were unilateral. The septa terminated on bone covering internal carotid artery ( ICA ) in 7 cadavers while in 2 cadavers they terminated on the bone covering optic nerve ( ON) . Dimensions of the sphenoid sinus were antero-posterior ( 2.5 + 0.5 cm ) , transverse ( 2.4 + 0.4 cm ) and vertical ( 2.2 + 0.6 cm ) . The sphenoid ostium was oval or rounded in 28 and 32 cases respectively. The average size of sphenoid sinus was 5.7 ml. In 14 cadavers we found right dominance and in 8 cadavers left dominance. In 22 cadavers inter-sinus septum terminated on sites other than normal position. In 8 cadavers it terminated over bone covering internal carotid artery and in 3 cadavers it terminated on bone covering optic nerve. In rest of the cadavers it terminated away from the midline. Carotid prominence was found in 15 sinuses and optic nerve bulge was found in 6 sinuses. viii Our findings of CT scan study were as follows: Out of 60 sinuses, pre-sellar-8 ( 13.3% ) , sellar-14 ( 23.3% ) and post-sellar-37 ( 61.6% ) and in case of 1 subject, left side sinus was conchal. Pneumatization of greater wing of sphenoid was observed in 2 sinuses ( 2.2% ) , of pterygoid process it was in 4 sinuses ( 6.6% ) and of anterior clinoid process it was in 2 sinuses ( 2.2% ) . We also found onodi cell in 1 sinus ( 1.4% ) . Accessory septae were observed in 11 sinuses ( 18.2% ) , single in 7 sinuses ( 11.6% ) and multiple in 4 sinuses ( 6.6% ) . In 6 sinuses these septae terminated over lateral wall of sinuses ( 10% ) while in 4 sinuses they terminated over bony wall covering internal carotid artery ( 6.6% ) and in 1 sinus on bony wall covering optic nerve ( 1.4% ) . The mean, standard deviations of all dimensions for male and female subjects respectively were: right antero-posterior 2.7 ± 0.42 and 2.7 ± 0.53 cm, left antero-posterior 1.9 ± 0.76 and 2.7 ± 0.55 cm, right transverse 2.2 ± 0.53 and 2.1 ± 0.62 cm, left transverse 1.7 ± 0.56 and 2.1 ± 0.54 cm, right vertical 2.4 ± 0.33 and 2.3 ± 0.43 cm, left vertical 2.1 ± 0.61 and 2.2 ± 0.43 cm. We found statistically significant correlation for right antero-posterior dimension. Right dominance was observed in 20 persons while left dominance in 10 persons. Protrusion of ICA was observed in 9 sinuses ( 15% ) . Protrusion of optic nerve was observed in 2 sinuses ( 33% ) . Protrusion of maxillary nerve and vidian nerve were observed in 3 sinuses ( 5% ) . Dehiscent bony wall was not observed in any sinus. Onodi cell was observed in 1 sinus ( 13% ) . Endoscopic findings in live patients ( 18 male and 7 female ) were: in 14 patients sphenoid ostium was round and in 11 patients it was oval. Accessory septa were observed in 16 patients ( 64% ) . In 3 patients ( 12% ) accessory septa was inserted into the bony wall covering of the carotid arteries and only in 1 patient it inserted into the bony wall ix covering of the optic nerve. Optic nerve bulge was observed in 6 patients ( 24% ) . Bony wall covering optic nerve was intact in all patients. Internal carotid artery bulge was observed in 8 patients ( 32% ) . Dehiscent bony wall was observed in 2 patients ( 8% ) . Conclusion – The present study was done to know the gross anatomy of sphenoid sinus and its relations. Surgeries over sphenoid sinus and pituitary gland can cause iatrogenic injuries to important structures and at times fatal complications. With the advent of Endoscopes and newer imaging techniques, surgeries over sphenoid are now safer. Sphenoid sinus shows various types of pneumatization, and when pneumatization spreads outside the body of sphenoid sinus it creates various recesses. These place the sinus in close proximity to important neurovascular structures that are present around the sinus. Newer techniques are emerging for safety of patients due to complex and highly variable anatomy of the sphenoid sinus. Now intra-operative fluoroscopic imaging or intra-operative navigational devices are used to confirm surgical landmarks making these techniques very safe.