Annals of Case Reports (ISSN: 2574-7754)

review article

  PDF Download

The Sphenoid Sinus Revisited

Geerinck K, Dockx M, Eloy Ph*

CHU UCL Namur, site of Godinne, Avenue Therasse, 5530, Yvoir, Belgium

*Corresponding author: Pr Eloy, ENT department, CHU UCL Namur, site of Godinne, Avenue Therasse, 5530, Yvoir, Belgium

Received Date: 19 August 2022

Accepted Date: 23 August 2022

Published Date: 26 August 2022

Citation: Geerinck K, Dockx M, Eloy Ph (2022) The Sphenoid Sinus Revisited. Review Article. Ann Case Report 7: 922. DOI:https://doi.org/10.29011/2574-7754.100922

Abstract

In the past, the sphenoid sinus has often been overlooked. It was considered as an inaccessible paranasal sinus cavity due to its specific anatomical location, making it difficult to diagnose diseases.

Today, the sphenoid sinus is regarded as equal to any other paranasal sinus cavity, and thus home to various diseases. Over the years, the assessment of these diseases has improved. Indeed, nasal endoscopy and qualitative head imaging (CT-scan and MRI) have been developed. These technologies provide information about the nature of disease, about the state of the walls of the sphenoid sinus and about extension of a lesion to adjacent structures. The endoscopic endonasal approach has improved safety and efficacy of sphenoid sinus surgery. Moreover, the sphenoid sinus acts as a gateway to the skull base. In fact, it enables removal of sellar and parasellar lesions. This endoscopic endonasal transsphenoidal approach (EETA) has lower morbidity rates than transcranial approaches.

The authors propose an overview of the sphenoid sinus from an ENT point of view.

Introduction

The sphenoid sinuses are the most posterior and medial paranasal sinus cavities, located deep inside the head. Different important neurovascular structures surround them. Embryologically, they originate from the cartilaginous nasal capsule (1). They result from the pneumatization of the sphenoid bone. There is no sphenoid sinus in newborns. Pneumatization starts at the age of 3, initially in posterior, inferior and lateral directions. At the age of 7 the pneumatization goes up to the sella turcica. At 18 the development is completed (2).

In adults, 4 different degrees of pneumatization have been described: the conchal, presellar, sellar and postsellar pattern.

In the conchal type, the posterior wall of the sinus is located anteriorly to the sella turcica. Among Caucasians, this type of pneumatization is the least common one. Its incidence varies from 0% to 5% (3,4).

Because of the thickness of bone present between the anterior sphenoid wall and the sella turcica, a transsphenoidal approach is not recommended in case of sellar surgery. In the presellar type, the posterior limit of the sinus extends into the anterior portion of the sella. Its incidence varies from 24% to 28% in Caucasians.

 Finally, the sellar and postsellar types of pneumatization are most prevalent. Together, their incidence varies from 67% to 80%. These are the preferred types when performing endonasal surgery of the sphenoid sinus and surgery of the pituitary gland (3,5,6).

Figure 1: The 4 types of pneumatization of the sphenoid sinus. (A) In conchal pneumatization, the sinus cavity is almost virtual. (C, D) The most appropriate patterns for endoscopic endonasal transsphenoidal surgery are the sellar and post-sellar types.

Relevant anatomy

Generally, the sphenoid sinuses are separated by at least one intersinus septum. This septum is a thin sagittal bony plate, rarely median, which should always be identified on preoperative imaging. Indeed, it might be inserted onto the carotid or the optic nerve canal instead of the sellar floor. Some sphenoid sinuses have no intersinus septum, others have an accessory septum or even multiple ones (6).

The Onodi cell (OC) is the most posterior and lateral ethmoidal cell. It has important relationships with the optic nerve, which is lateral and superior to it. The sphenoid sinus is situated more medially, inferiorly and posteriorly (3,7).

Each sphenoid sinus communicates with the nasal cavity by means of an aperture in the upper part of the anterior wall. This aperture, also called an ostium, is situated at the junction of the superior third and the two inferior thirds of the anterior wall of the sphenoid sinus. The superior turbinate is the best surgical landmark to identify the natural ostium. It separates the sphenoethmoidal recess and the posterior ethmoid (8). In 85% of cases the ostium is situated medially to the posterior end of the superior turbinate (ST), in the sphenoethmoidal recess. In 15% of cases, it is situated lateral to the tail of the ST (9-11).

The lateral sinus wall contains noble structures. Often, the internal carotid artery (ICA) and the optic nerve (ON) can be identified bulging in the sphenoid cavity. In between there is the optico-carotid recess (OCR). In some cases, the maxillary nerve or the second branch of the trigeminal nerve (V2) and the Vidian nerve (V) may be recognized. The more pneumatized the sphenoid sinus, the more these structures are protruding. Therefore, they may be at risk during surgery, in case the surgeon is too posterior and lateral in the sphenoid cavity (3,12).

After removal of the bone covering the sella and the planum sphenoidale, access to the dura mater is gained. When the dura is opened, the following structures can be seen: The optical chiasma, the pituitary stalk, the sella, the basilar artery and the genu of the internal carotid artery (which might be close to the pituitary gland).