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ORIGINAL ARTICLE
Year : 2020  |  Volume : 69  |  Issue : 3  |  Page : 133-136

Morphometry of sphenoid air sinus and its ostium for surgical relevance: A cadaveric study


Department of Anatomy, Vinayaka Mission's Kirupananda Variyar Medical College and Hospital, Vinayaka Mission's Research Foundation (Deemed to be University), Salem, Tamil Nadu, India

Date of Submission22-Aug-2019
Date of Acceptance04-Aug-2020
Date of Web Publication30-Sep-2020

Correspondence Address:
Dr. B Senthil Kumar
Department of Anatomy, Vinayaka Mission's Kirupananda Variyar Medical College and Hospital, Vinayaka Mission's Research Foundation (Deemed to be University), Salem - 636 308, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JASI.JASI_110_19

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  Abstract 


Introduction: The sphenoid air sinuses and their ostia are highly variable structures. The ostia are located on either side of the midline. The exact location of the sphenoid ostium is very much essential in endoscopic sinus surgeries as well as for the transsphenoidal hypophyseal approach. The present study was done to determine the anatomical location of the sphenoid sinus ostium in relation to the surrounding landmarks. It is a descriptive study. Material and Methods: The study was carried out in the Department of Anatomy, VMKV Medical College and Hospital, Salem, on forty sagittal head and neck sections of adult formalin-fixed cadavers. The length and width of the sinus were measured. The shape and type of the sphenoid sinus ostia were also noted. The distance of the sinus ostium from various landmarks was measured using Vernier calipers. The morphometric parameters were compared by Student's t-test on both sides. Results: Most of the specimens showed sellar variety than presellar variety on both right and left sides. The shape of the sphenoid sinus ostia was predominantly round shape, followed by oval and slit shape. The length and width of the sinus on the right side were less when compared to the left side. The distance between the sphenoidal ostia and several landmarks showed no significant difference except the distance from ostium to superior concha. Discussion and Conclusion: During the endoscopic approach of the sphenoid sinus ostium, it is not always easy to locate the ostium. The present morphometric study will serve as a guideline for the endoscopic surgical approach of the sphenoid sinus ostium using the various anatomical landmarks.

Keywords: Concha, sphenoid ostium, transsphenoidal hypophyseal approach


How to cite this article:
Kumar B S, Selvi G P. Morphometry of sphenoid air sinus and its ostium for surgical relevance: A cadaveric study. J Anat Soc India 2020;69:133-6

How to cite this URL:
Kumar B S, Selvi G P. Morphometry of sphenoid air sinus and its ostium for surgical relevance: A cadaveric study. J Anat Soc India [serial online] 2020 [cited 2020 Dec 1];69:133-6. Available from: https://www.jasi.org.in/text.asp?2020/69/3/133/296903




  Introduction Top


The advancement in endoscopic sinus surgery (ESS) had facilitated a clear cut idea about anatomy and pathophysiology of paranasal air sinuses for surgeons. The surgeon aims to aerate the sinuses and restore the mucociliary clearance so that the paranasal air sinuses are retained back to normal function.[1] ESS helps the surgeons for the diagnosis and treatment of sinusitis.[2] The anatomy of sinuses can be visualized clearly by high-resolution computed tomography (CT) which also helps to diagnose the mucosal disease.[3] The normal anatomy along with any variations of sinus structure, its pathologic appearances in disease condition, has to be well understood by the surgeons and radiologists to provide appropriate patient care.[4] Anatomic variation of the sphenoid sinus is not so common, but if it is present, then it may complicate the surgery, and henceforth, the knowledge of these variations should be known precisely to surgeons. Accurate evaluation of the variations is possible with preoperative CT scans of the sinuses.[5] A comprehensive knowledge of the variable regional anatomy of the sphenoid sinus will reduce the surgical complications that occur during the transsphenoidal approach and functional ESS.[6],[7],[8],[9] The anatomic variations of the sphenoid sinus predispose to recurrent or chronic sinusitis.[10]

The body of the sphenoid bone is pneumatized to form the sphenoid air sinus. The pneumatization of bones of the skull base is most common. The sphenoid sinus and adjacent bony structures may show various degrees of pneumatization. Sometimes, a pneumatization can be so extensive that it reaches the anterior clinoid process (ACP), foramen rotundum, vidian canal, pterygoid process (PP), or maxilloethmoid recess. The ACP and PR are the frequent sites of pneumatization in the skull base. The clinical significance of the pneumatization requires clarification.[5]

The sphenoid sinus communicates with the nasal cavity through sphenoid ostia, which are located on each side of the midline. The sphenoid air sinus opens into the sphenoethmoidal recess. Sphenoid sinuses and their ostia are highly variable structures. The sinus is related to various structures such as optic nerve in its superolateral wall, carotid artery in the lateral wall, trigeminal nerve in the inferolateral wall, and the vidian nerve in the floor of the sinus.[11] The above structures are separated from the sinus only by a thin bony wall/septum of around 0.5 mm thickness, and even sometimes, the bony wall is replaced by bony dehiscence.[12] The pituitary gland lies on the roof of the sphenoidal air sinus which is separated only by a thin bony wall. The sphenoidal air sinus is related to the cavernous sinus and internal carotid artery laterally which may be accidently injured during the transsphenoidal approach of the pituitary gland. The extent of pneumatization of sphenoid air sinus is highly variable.[13] The exact location of the sphenoid ostium is very much essential in ESSs as well as the transsphenoidal hypophyseal approach. During the endoscopic approach of the sphenoid sinus ostium, it is not always easy to locate the ostium; only few studies were carried out in India on this perspective. The accessibility of the sphenoid sinus is most difficult as it is known for the most variable cavity of the human body.[14] The present study will serve as a guideline for identifying the location of sinus ostium during the endoscopic surgical approach using the various anatomical landmarks.


  Material and Methods Top


The present descriptive study was carried out in the Department of Anatomy, VMKV Medical College and Hospital, Salem, on forty sagittal head and neck sections of adult formalin-fixed cadavers after obtaining ethical clearance from the institution reference number (VMKVMC/IEC/18/51). The length of the sinus was measured from the lower margin of the sphenoid ostium to the midpoint of the posterior wall of the sphenoid sinus, whereas the width was measured from the midpoint of the roof to the midpoint of the floor of the sphenoid sinus. The shape and type of sphenoid sinus ostia were noted [Figure 1] and [Figure 2]. The distance of the ostium from the major anatomical landmarks was measured using Vernier calipers. The various surgical relevant anatomical landmarks used include midpoint of choana, nasion, anterior end of the superior concha, and midpoint of basisphenoid [Figure 1]. The extent of pneumatization toward the sella was also noted.
Figure 1: Anatomical landmarks for measurements and types of sphenoid air sinus

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Figure 2: Type of sphenoid air sinus

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  Results Top


Majority of specimens showed sellar variety (23, 57.5%) than presellar variety (17, 42.5%) on both right and left sides. The shape of the sphenoid sinus ostia was predominantly round shape (16, 40%), followed by oval (12, 30%) and slit shape (12, 30%). The morphometry of sphenoidal air sinus was measured and compared between the right and left sides by independent t-test [Table 1]. The length of the sinus on the right side was less when compared to the left side. The width of the sinus showed a significant difference among the sides and was found to be more on the left side when compared to the right side. When analyzed, the morphometric data of the sphenoid air sinus were found to be statistically significant (P < 0.01)[Table 1].
Table 1: Morphometry of sphenoidal air sinus

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The distance of the ostium from the various anatomical landmarks was measured and compared between the sides, and the distance from the ostium to superior concha was found to be significant, whereas other measurements were insignificant when compared [Table 2]. The various surgical relevant anatomical landmarks used include choana, nasion, anterior end of the superior concha, and basisphenoid.
Table 2: Measurement of sphenoidal ostium from various anatomical landmarks

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  Discussion Top


Type of sphenoid sinus pneumatization

The sphenoid pneumatization can be classified as three main types.[15] Type 1 is the conchal type or the fetal type which shows a small sinus separated from the sella turcica by a very thin layer of trabecular bone. Type 2 is the presellar type or juvenile type and is pneumatized up to the level of sella turcica. Type 3 is the sellar type or adult type and is pneumatized below the sella or further posteriorly.[10] In a study done by Sareen et al., the sellar type was found to be more frequent. It appears in 75%–86% of cases, followed by the presellar type which is found to be present in 10%–25%, followed by conchal type seen in only 2% of cases.[16] In a study done by Tan andOng,[17] the sellar type was found in 55% of sinuses, followed by conchal (28%) and presellar type (17%). In another study, the sellar pneumatization was most common. Sellar pneumatization is an ideal anatomical configuration for transsphenoidal hypophysectomy because the bulge of the sella turcica floor is easily visualized in the operative field.[18],[19] In the present study, the sellar variety was found in 23 (57.5%), whereas the presellar variety was found in 17 (42.5%) on both right and left sides together, whereas conchal type was not seen in any of the specimens as found by other authors Tan andOng and Sareen et al.[17],[18]

Shape of the sphenoid ostia

In a study done by D'Souza et al., the sphenoid sinus ostia were slit type in majority of the cases, followed by oval and round shape.[10] The round shape ostia were seen more on the left side compared to the right side. In another study, 70% of the ostia were found to be round in shape, whereas 28% were ovoid.[11] In the study, the sphenoid sinus ostia were predominantly round shape (16, 40%), followed by oval (12, 30%) and slit shape (12, 30%) irrespective of the sides.

Morphometry of sphenoid air sinus

Ariji et al. and Ikeda et al. reported that the volume of paranasal air sinuses increases up to 20 years and then decreases as age advances.[20],[21] Schatz andBecker observed that sphenoid sinus increases in size up to 15 years and thereafter maintains the same size and volume.[22] The sphenoid air sinus starts to develop rapidly after the age of 3 years and spreads back toward the sella turcica around the age of 7 years and reaches adult form at the age of 12 years. The maximum average of sphenoid sinus volume was 7.5 cm3 and 8.2 cm 3 reported by Schatz et al.[23] In another study, the sphenoid sinus volume increased in both sexes up to 25 years (8.71 ± 2.44 cm 3) and decreased after the age of 25.[2] In the present study, the sphenoidal air sinus was measured and compared between the right and left sides [Table 1]; the volume was not measured as the study was done on specimen of sagittal section and hence only length and width were measured. The length of the sinus on the right side was less when compared to the left side. The width of the sinus showed a significant difference among the sides. When analyzed, the morphometric data of sphenoid air sinus were found to be statistically significant (P < 0.01) [Table 1].

Sphenoid ostium from various anatomical landmarks

The sphenoid sinuses are the most inaccessible paranasal sinuses when compared to all other sinuses.[24] The distance of the sphenoid ostium from various anatomical landmarks in comparison with other studies is tabulated [Table 3].
Table 3: Comparison of distance of sphenoid ostium from various anatomical landmarks with previous studies

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In the present study, the distance from ostium to superior concha was found to be significant, whereas other measurements were insignificant when compared between right and left. Kim et al.[25] suggested that the best anatomical reference that enables identification of the sphenoid ostium is the posteroinferior end of the superior turbinate, where each ostium is located medially and superiorly. The sphenoid ostium was identified at an average distance of 1.49 cm superior to the choana by Abuzayed et al.[26] In another study, the distance was 1.37 cm on the right side and 1.5 cm on the left side [Table 3].[10] In the present study, the distance between sphenoid ostium and choana was 2.30 cm on the right side and 2.46 cm on the left side and was considered to be the most reliable landmark to approach sphenoid ostium. The knowledge of the anatomical relationships of the sphenoid sinus is needed for the success of ESSs and to avoid the various intraoperative surgical complications.[27]


  Conclusion Top


During the endoscopic approach of the sphenoid sinus ostium, it is not always easy to locate the ostium. The present study will serve as a guideline for the endoscopic surgical approach of sinus ostium using the various anatomical landmarks. The four landmarks include choana, nasion, anterior end of the superior concha, and basisphenoid which will be helping to approach the sphenoid ostium. The study will be further extended in humans using CT scan. Accurate evaluation of the distance of the sphenoid ostium from the above landmarks will be possible with preoperative CT scans of the sinuses.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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