Sphenoid sinus types, dimensions and relationship with surrounding structures
Introduction
Sphenoid sinus is considered to be the most variable cavity in the human body (Teatini et al., 1987) and is of great relevance pertaining to optimal surgical access to the pituitary gland. Transsphenoidal surgery, first applied in 1907, became a standard procedure for treatment of intrasellar lesions (Perondi et al., 2013). Compared to the alternative transcranial approach, transsphenoidal approach is more efficient and associated with lower morbidity and mortality (Aydin et al., 2007). Moreover, sphenoid sinus pneumatization may provide access to other parts of the skull base (Wang et al., 2010). Therefore, the degree and direction of sphenoid sinus pneumatization play a crucial role in the planning of surgical procedures. Awareness of the sphenoid sinus anatomical variations is essential for both avoiding iatrogenic lesions and understanding pathogenesis of the processes, which can occur in the sinus cavity.
The sphenoid sinus originates from the posterior divisions of the nasal cavity. Sinuses have been classified into four types according to the extension of pneumatization: conchal, presellar, sellar and postsellar (Fig. 1A–D). This classification is based on the location of the posterior sinus wall in respect to sella turcica. Conchal type sinuses are very small and situated behind the superior turbinate, concha nasalis superior. The sinus cavity can be restricted to the sphenoid body, but pneumatization can also extend into the greater wing and/or pterygoid process of the sphenoid, and into the basal part of the occipital bone. If the pneumatization reaches planum sphenoidale or clivus, only a thin wall separates the sinus cavity and dura mater of the anterior and posterior cranial fossa, respectively. Additionally, the sinus cavity may be in a close relationship to the canals and grooves of the sphenoid – foramen rotundum, pterygoid canal, optic canal, carotid groove and foramen ovale; i.e., with the transversing neurovascular structures: maxillary nerve, pterygoid nerve, optic nerve, internal carotid artery and mandibular nerve, respectively.
The existing analyses of the sphenoid anatomy have been focused primarily on the extensions of the sinus cavity (Kayalioglu et al., 2005, Hamid et al., 2008, Idowu et al., 2009) or on protrusions of the adjacent neurovascular structures (Omami et al., 2011, Sirikci et al., 2000, Hewaidi and Omami, 2008). Typically, they have considered the right and the left sinus as a single cavity (Güldner et al., 2012, Kayalioglu et al., 2005, Hamid et al., 2008, Idowu et al., 2009) and have suffered from a lack of uniform criteria for protrusion classification, particularly in a quantitative sense (“extent of protrusion”). We aimed to relate sphenoid sinus types and dimensions simultaneously to their interactions (protrusions) with the surrounding neurovascular structures and extensions into other parts of the sphenoid. In doing so, we considered the left and the right sinuses as separate cavities (Fig. 1E) and have proposed a novel system of quantitative classification of protrusions of the neurovascular structures. We believe that such a system, by providing uniform criteria, could improve comparability of reports by different authors. Furthermore, we believe that quantification of the extent of protrusions could be of practical relevance, as it appears plausible to assume that more prominent protrusions might convey a higher risk (incidence, severity) of iatrogenic surgical complications.
Section snippets
Skulls
A total of 51 skulls (Whites of European descent) were randomly selected from the skull collection at the Institute of Anatomy “Drago Perović” (University of Zagreb, School of Medicine) (Dumić-Čule et al., 2014). We assumed that the growth of the sphenoid sinus is completed by the end of puberty (Budu et al., 2013) and that age (after puberty) and gender have no relevant impact on the studied parameters (Tomovic et al., 2013). We therefore set the lower age limit for inclusion at 20 years, and
Description of the skulls and sinuses
Of the 51 skulls (age 20–86 years, median 60), 33 were male (age 20–80 years, median 60) and 18 were female skulls (age 21–86 years, median 63.5). As shown in Table 2, 28 skulls (54.9%) had the same type of sphenoid sinus on both sides (most commonly sellar, 25.5%), whereas the rest had different types of sinuses on the two sides, with postsellar-sellar as the most common combination (21.6%). Out of 102 sinuses, the most prevalent type was sellar (41.2%), whereas only two conchal (2%) sinuses
Discussion
Considering the importance of the sphenoid sinus in surgical management of the pituitary gland and the fact that it may provide access to other parts of the skull base (Aydin et al., 2007, Perondi et al., 2013, Wang et al., 2010), awareness of its anatomical variations is of considerable practical relevance. Among diversity of the described variations, the most important are differences in sinus type, size and shape. The sinus is also highly variable regarding its extensions outside the body of
Conclusions
In conclusion, considering the common sphenoid sinus anatomical variations, a detailed preoperative radiological evaluation is needed to ascertain a successful transsphenoidal surgical procedure (Meyers and Valvassori, 1998). However, the standard clinical radiological techniques might not be able to visualize all elements that may increase the risk of iatrogenic injury. The present analysis suggests that the regularly evaluable elements, such as sinus type and elementary dimensions (i.e.,
References (22)
- et al.
Study of the relationship between sphenoid sinus volume and protrusions in the sphenoid sinus
Forensic Med. Anat. Res.
(2014) - et al.
The endoscopic endonasal trans-sphenoidal approach to the sellar and suprasellar area. Anatomic study
J. Neurosurg. Sci.
(2007) - et al.
Risky anatomic variations of sphenoid sinus for surgery
Surg. Radiol. Anat.
(2006) - et al.
The anatomical relations of the sphenoid sinus and their implications in sphenoid endoscopic surgery
Rom. J. Morphol. Embryol.
(2013) - et al.
Imaging the sphenoid sinus
Austrlas. Radiol.
(1994) - et al.
Variations on the standard transsphenoidal approach to the sellar region, with emphasis on the extended approaches and parasellar approaches: surgical experience in 105 cases
Neurosurgery
(2004) - et al.
Dynamics of optic canal and orbital cavity development revealed by microCT
Surg. Radiol. Anat.
(2014) - et al.
Analysis of pneumatization and neurovascular structures of the sphenoid sinus using cone-beam tomography (CBT)
Acta Radiol.
(2012) - et al.
Anatomic variations of the sphenoid sinus and their impact on trans-sphenoid pituitary surgery
Skull Base
(2008) - et al.
Anatomic variation of sphenoid sinus and related structures in Libyan population: CT scan study
LJM
(2008)