Morphometry and Intracranial Relations of the Sphenoid Sinus in Context to Endoscopic Transnasal Transsphenoidal Surgery

Abstract

Introduction Due to the variable degree of pneumatization, the shape and size of the sphenoid sinus are irregular. An endoscopic intranasal transsphenoidal approach is made in sphenoid sinus pathologies, sphenoid sinusitis, and sellar and parasellar diseases. A diagnostic approach to the sphenoid sinus is also done to get a better MRI scan of the pituitary. The present study aims to describe the variant types of sphenoid sinus, morphometry, anatomy, and relations of sphenoid sinus, which will be helpful to surgeons during an endoscopic approach to the sphenoid sinus. Materials and methods We studied 76 cadaveric sphenoid sinuses that were exposed by taking a sagittal section of 38 formalin-fixed cadaveric heads. After examining the inter-sphenoidal septum, it was removed to observe the inside aspect of the sphenoid sinus. Different dimensions of the sinus were noted down. The bulges inside the sinus due to neurovascular structures in relation to the sinus were observed. Results The most prominent type found was the sellar in 68.4% of cases preceded by the postsellar in 23.7% of cases. Presellar type of pneumatization was seen only in 7.9% of cases and the conchal type was absent. Intersphenoid septum was seen in 92,1% of cases, out of which 11.4% of septums were deficient on the posterior aspect. An internal carotid artery bulge in the sphenoid sinus was seen in 46% of cases. In 27.6% and 19.7% of sphenoid sinuses, bulging of the optic and vidian nerves, respectively, were seen. Some of these structures were dehiscent in the sphenoid sinus. Conclusions To get more space in the sphenoid sinus, the septa in the sinus are removed by surgeons, which may damage the walls of the sphenoid sinus. Knowledge of the relations of neurovascular structures with the sphenoid sinus will be helpful to surgeons during the transsphenoidal endoscopic approach to avoid any injury to these structures.

Keywords: endoscopy; internal carotid artery; maxillary nerve; optic nerve; pituitary gland; sphenoid sinus; vidian nerve.

Figure 1. The septa of SS

A: ISS having an oval opening in the posterior part. B: Small size CS. C: Well-developed CS having a concave margin, directed anteromedially. CS, crescent-shaped septum; H, hypophysis cerebri; ISS, intersphenoid sinus septum; SS, sphenoid sinus A horizontal red arrow is directed in the anterior direction and the upward red arrow shows the superior aspect of the specimen.

Figure 2. The bulges of the IC and optic nerve in the sphenoid sinus

A & C: showing the lateral wall of the right SS. B & D: showing the lateral wall of the left SS. The optic nerve is marked by a black colored star '★'. A horizontal red arrow is directed in the anterior direction and the upward red arrow shows the superior aspect of the specimen. H, hypophysis cerebri; IC, internal carotid artery; IOF, infraoptic fossa; SS, sphenoid sinus.

Figure 3. OC in the anterosuperior aspect of the SS

A: Left SS, B: Right SS. A horizontal red arrow is directed in the anterior direction and the upward red arrow shows the superior aspect of the specimen. H, hypophysis cerebri; OC, Onodi cells; SS, sphenoid sinus.

Figure 4. A: MN bulge and VN bulge in the anterior part of the sphenoid sinus. B: Anterior aspect of a dry sphenoid bone in which the dotted line indicates the direction of the SS recess between the FR and VC so that the bulges of MN and VN become prominent.

A horizontal red arrow is directed in the anterior direction and the upward red arrow shows the superior aspect of the specimen. FR, foramen rotundum; MN, maxillary nerve; SO, sphenoid ostium; SS, sphenoid sinus; VC, vidian canal; VN, vidian nerve.