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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 28  |  Issue : 2  |  Page : 112-116

Variant neurovascular relations of the sphenoid sinus in adult Nigerians


Department of Human Anatomy and Cell Biology, Delta State University, Abraka, Nigeria

Date of Submission24-Mar-2021
Date of Decision19-Jul-2021
Date of Acceptance26-Jul-2021
Date of Web Publication03-Sep-2021

Correspondence Address:
Dr. Beryl Shitandi Ominde
Department of Human Anatomy and Cell Biology, Delta State University, Abraka
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/npmj.npmj_505_21

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  Abstract 


Background: With the advent of endoscopic sinus surgery, the variant neurovascular relations of the sphenoid sinus are important to surgeons to minimise the iatrogenic complications. This study elucidates the variant neurovascular relations of the sphenoid sinus in adult Nigerians. Materials and Methods: This study was conducted at the Radiology Department of Delta State University Teaching Hospital after institutional approval. Brain computed tomography images of 336 patients, aged ≥20 years and spanning over 5 years' duration were utilised. We evaluated the sphenoid sinus for protrusion and dehiscence of neurovascular structures bilaterally. The position of the optic nerve in relation to the sinus was classified from Type 0–4. The Statistical Package for the Social Sciences software version 23 was used for the data analysis. The Chi-square test was used to probe for the association between the variants with regard to side and gender. P < 0.05 was considered statistically significant. Results: Dehiscence and protrusion of the internal carotid artery (ICA) occurred in 34, 10.1% and 83, 24.7% patients correspondingly. The dehiscence of optic, maxillary and Vidian nerves was (26, 7.7%), (60, 17.9%), and (53, 15.8%), whereas the frequency of their protrusion was (50, 14.9%), (76, 22.6%) and (87, 25.9%), respectively. All these variants except the ICA and maxillary nerve dehiscence showed a significant association with the side of occurrence (P = 0.001). Out of the 672 optic canals evaluated bilaterally, a preponderance of Type I (534, 79.5%) was observed followed by II (96, 14.3%), IV (35,5.2%), III (7, 1.0%) and Type 0 (0, 0%). Conclusion: Our study has shown that the neurovascular relations of the sphenoid sinus vary from previously documented reports, thus confirming the need for pre-operative evaluation.

Keywords: Internal carotid artery, maxillary nerve, optic nerve, sphenoid sinus, vidian nerve


How to cite this article:
Ominde BS, Igbigbi PS. Variant neurovascular relations of the sphenoid sinus in adult Nigerians. Niger Postgrad Med J 2021;28:112-6

How to cite this URL:
Ominde BS, Igbigbi PS. Variant neurovascular relations of the sphenoid sinus in adult Nigerians. Niger Postgrad Med J [serial online] 2021 [cited 2022 Sep 27];28:112-6. Available from: https://www.npmj.org/text.asp?2021/28/2/112/325556




  Introduction Top


The sphenoid sinus has a highly variable and complex anatomy and is the most difficult paranasal sinus to approach surgically.[1] Its variant pneumatisation is responsible for the inconsistent location of the adjacent neurovascular canals, namely the carotid canal, optic canal, foramen rotundum and Vidian canal for internal carotid artery (ICA), optic nerve, maxillary and Vidian nerves, respectively.[2],[3] The bone separating these canals from the sinus may be thin or altogether absent leading to dehiscence or protrusion of the nerves and ICA.[4] The prevalence of dehiscence and protrusion of the neurovascular structures into the sphenoid sinus varies in different populations.[1],[5],[6] Sphenoid pathology such as mucoceles and sinusitis may involve the neurovascular structures that abut its wall leading to a wide range of symptoms such as blindness due to optic neuritis.[7] These structures may also be injured during transsphenoidal surgery and Functional Endoscopic Sinus Surgery (FESS).[6] Computed tomography (CT) is the imaging modality of choice for precise evaluation of the variant pneumatisation patterns of the paranasal sinuses.[8] It is mandatory for neurosurgeons and otorhinolaryngologists to preoperatively evaluate the structures abutting the sphenoid sinus wall to provide intraoperative guidance and curtail iatrogenic complications.[1] This study, therefore, aimed at determining the variant neurovascular relations of the sphenoid sinus in adult Nigerians.


  Materials and Methods Top


This was a descriptive, cross-sectional, retrospective study conducted at the Radiology Department of Delta State University Teaching Hospital in Nigeria. The purposive sampling technique was adopted in this study. Brain CT images taken using a 64 slice CT scanner (Toshiba Aquilon, Japan) at 120 kV and 300 mA were retrieved from the Picture Archiving Communications Systems. We used images taken between 1st June 2015 and 30th June 2020 for various reasons such as space-occupying lesions and stroke. Institutional approval was obtained, and the study was carried out based on the ethical standards set by the hospital (EREC/PAN/2020/030/0371). The inclusion criteria entailed: CT images of male and female patients aged 20 years and above besides quality and clear images. The study excluded the images of patients below 20 years, with sinonasal pathology, craniofacial trauma, history of surgery and poor quality images; for instance, those with motion artifacts and patient rotation. Therefore, brain CT images of 336 patients comprising 199 males and 137 females were reviewed in this study.

Three-millimetre-thick axial slices and coronal reformatted images were used to assess for the protrusion and dehiscence of the ICA, optic, Vidian and maxillary nerves based on the criteria described by Prabu et al.[2] and Gungor and Okur.[9] The position of the optic nerve in relation to the sphenoid sinus was categorised as follows: Type 0 – the nerve that does not border the wall of the sinus, Type 1 – the optic nerve is adjacent to the sinus, Type 2 – the nerve creates an indentation on the wall of the sinus, Type 3 – <50% of the nerve is exposed in the sinus and Type 4 – the nerve traverses the sphenoid sinus next to the posterior ethmoid sinus.[10] Statistical analysis was performed using the Statistical Package for the Social Sciences software version 23 IBM® Armonk, New York, USA. The Chi-square test was used to probe for the association between the neurovascular variants with side and gender. We chose P < 0.05 as the statistically significant value.


  Results Top


Brain CT images of 336 patients comprising 199 males (59.2%) and 137 (40.8%) females were evaluated in this study. These patients had an average age of 53.29 ± 18.18 years ranging from 20 years to 99 years. Dehiscence of the ICA occurred unilaterally with a prevalence of 34, 10.1%. We did not observe bilateral ICA dehiscence. ICA protrusion was recognised in 83 patients (24.7%) and with higher unilateral occurrence (48, 14.3%) than bilateral occurrence (35, 10.4%) [Figure 1]a and [Figure 1]c. Optic nerve dehiscence had a frequency of 26, 7.7% with higher bilateral 15, 4.5% than unilateral (11, 3.3%) existence while its protrusion was observed in 50 patients (14.9%), more commonly bilaterally (33, 9.8%) than unilaterally (17, 5.1%) [Figure 2]c and [Figure 2]d. Dehiscence and protrusion of the maxillary nerve had a prevalence of 60, 17.9% and 76, 22.6%, respectively with a more frequent unilateral (56, 16.7%; 57, 17%) than bilateral (4, 1.2%; 19, 5.7%) occurrence [Figure 1]b and [Figure 1]c. Vidian nerve dehiscence and protrusion were observed in 53, 15.8% and 87, 25.9% patients, respectively and showed a predominant unilateral existence (45, 13.4%; 70, 20.8%) compared to their low bilateral occurrence (8, 2.4%; 17, 5.1%) [Figure 1]b.
Figure 1: Computed tomography images showing (a) Protrusion of the right internal carotid artery (b) Protrusion of maxillary (yellow) and Vidian (green) nerves bilaterally (c) Dehiscence of maxillary nerves bilaterally (arrow heads) with dehiscence of the left internal carotid artery (arrow)

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Figure 2: Coronal reformatted images showing the Types of optic nerve (a) Type I bilaterally (b) Type II bilaterally (c) Type III with protrusion bilaterally (d) Type IV right (dehiscent optic nerve) with concomitant pneumatization of the anterior clinoid process

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The right-sided protrusion of ICA, dehiscence of the carotid canal and protrusion of the optic nerve were more prevalent. Conversely, the protrusion of maxillary and vidian nerves besides the dehiscence of optic, maxillary and vidian nerves showed a left-sided preponderance. Apart from ICA dehiscence and maxillary nerve dehiscence, all the other neurovascular variants showed a statistically significant association with the side of occurrence (P = 0.001 for each) [Table 1]. However, all the neurovascular variants observed showed no significant association with gender on both sides (P > 0.05) [Table 2]. The classification of the optic nerve revealed that out of all the 672 sides evaluated, the predominant type was Type I (534, 79.5%) followed by Type II (96, 14.3%), Type IV (35, 5.2%) and finally Type III (7, 1.0%). There was no Type 0 optic nerve observed. All the types did not show any association with gender [Table 3]. The prevalence of bilateral symmetry in the Type I, II, III and IV was 247, 73.5%; 38, 11.3%; 3, 0.9%, and 17, 5.1% respectively. Asymmetry in the Type of optic nerve was seen in 31 patients (9.2%) [Figure 2]a,[Figure 2]b,[Figure 2]c,[Figure 2]d. [Table 4] shows the prevalence of the neurovascular variants in relation to the sphenoid sinus in different populations, whereas [Table 5] shows a comparison of data regarding the types of optic nerves in different studies.
Table 1: Laterality of neurovascular variants in relation to the sphenoid sinus

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Table 2: Gender distribution of the variant neurovascular relations of the sphenoid sinus

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Table 3: Classification of the optic nerve

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Table 4: Variations of the neurovascular relations of the sphenoid sinus in literature

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Table 5: Classification of the optic nerve

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  Discussion Top


The prevalence of ICA dehiscence was 10.1% and this was slightly lower than the reports by Fasunla et al.[10] and Yekpe et al.[5] in Nigeria and Benin, respectively. Our finding was within the range documented in India.[2],[4] In Turkey, Dasar and Gokce[11] and Kaya et al.[12] documented lower frequencies, whereas higher frequencies were reported in Libya, Sudan and Saudi Arabia.[7],[13],[14] The prevalence of ICA protrusion was 24.7%, slightly lower than 27.3% and 25.4% documented by Fasunla et al.[10] and Kajoak et al.[13] in Nigeria and Sudan, respectively. Conflicting with our reports, other African studies documented higher frequencies.[5],[7] Our finding was within the range reported in Turkey and lower than the prevalence in Iran and India.[1],[6],[11],[12] Contrary to the findings of Jaworek-Troć et al.,[15] the ICA protrusion in this study was predominantly observed on the right and showed no significant association with gender. The protruded part of ICA may be covered by mucosa and misdiagnosed as soft-tissue pathology.[2],[9] In addition, infectious diseases involving the sphenoid sinus increase the risk of protrusion of the artery.[15] Either protrusion of the ICA or dehiscence of its canal increases the vulnerability to arterial damage by sinus disease or iatrogenic injury during endoscopic intranasal transphenoidal skull base surgery causing bleeding within the closed and narrow sphenoid sinus with inevitable neurological sequelae. The bleeding is more challenging to control and may therefore be fatal.[9]

Dehiscence of the optic canal was observed in 7.7% of the patients and this was lower than the findings by Fasunla et al.,[10] Hewaidi and Omami[7] and Kajoak et al.[13] in Africa. It was also within the range documented in India.[1],[3] Our finding was higher than the observations in Turkey and lower than the frequency in Saudi Arabia.[12],[14] The frequency of optic nerve protrusion was 14.9% which on comparison with other African studies was higher than the prevalence documented by Kajoak et al.[13] and Yekpe et al.[5] and lower than the findings by Hewaidi and Omami[7] and Fasunla et al.[10] Our frequency was within the range documented in India and Turkey [Table 3].[1],[3],[11],[12] The protrusion of the optic nerve and dehiscence of its canal makes it vulnerable to iatrogenic injury during endoscopic sphenoidectomy or intranasal transphenoid pituitary surgery.[4] Moreover, the optic nerve may be involved in sphenoid sinus disease such as sinusitis or mucoceles and this leads to rhinogenic optic neuritis.[1] Furthermore, sinus diseases may compress the nerve leading to venous congestion with subsequent nerve ischemia leading to visual defects.[9] The canalicular part of the optic nerve is highly susceptible to injury due to its poor vascularisation.[2]

The prevalence of maxillary dehiscence (17.9%) was within the range documented in India and higher than the findings in Libya and Benin.[3],[4],[5],[7] The prevalence among the Sudanese was higher than in our population.[13] The protrusion of the maxillary nerve into the sphenoid sinus (22.6%) was slightly lower than the findings by Hewaidi and Omami,[7] Kajoak et al.,[13] Dasar and Gokce[11] and Singh et al.[1] Our prevalence was higher than the findings of Hiremath et al.,[3] Yekpe et al.[5] and Joghataei et al.[6] [Table 3]. The maxillary nerve protrusion and dehiscence are caused by the extension of sphenoid sinus pneumatisation onto the greater wing of sphenoid.[13] These variants predispose to iatrogenic nerve injury during FESS and trigeminal neuralgia when the nerve is inflamed in sphenoid sinusitis.[9]

The dehiscence of Vidian nerve (15.8%) was higher than the reports from Turkey, Iran and India and lower than in Sudan.[3],[4],[6],[12],[13] The prevalence of Vidian nerve protrusion (25.9%) was closely related to the findings in Libya and Iran and within the range documented in India and Turkey.[3],[4],[6],[7],[11],[12] A higher prevalence of the Vidian nerve protrusion was reported in Sudan while the frequency in Benin was lower than our finding [Table 3].[5],[13] The extensive pneumatisation of the sphenoid sinus into the pterygoid process is responsible for the variations of the Vidian canal.[13] These variants are associated with deep nasal pain often referred to as Vidian neuralgia.[1] Their radiologic prediction before endoscopic transphenoidal surgery and Vidian neurectomy will reduce injury to this nerve and improve the outcome of the surgery.[9] The discrepancies in the prevalence of the neurovascular dehiscence or protrusion have been ascribed to differences in ethnicity, sample size, methodology and definitions of the variants.[7],[13] For instance, some scholars define protrusion as the presence of any proportion of the canals into the sinus, while others define protrusion as the presence of at least one third or more than half of the circumference of the structure in the sinus cavity.[2],[9],[10]

According to our observations, the classification of the optic nerve with respect to the sphenoid sinus showed that Type I was the most predominant (79.5%) followed by Type II (14.3%), Type IV (5.2%), Type III (1.0%) and Type 0 (0%). In Oyo state Nigeria, Fasunla et al.[10] documented decreasing frequencies of Type I, 0, II, III and IV correspondingly. Their documented prevalence of Type I was lower while that of Type 3 was higher than our findings. On the other hand, the prevalence of Type IV was comparable to our findings. The frequencies of these types of the optic nerve in our study also varied from the reports in Saudi Arabia, Turkey and India [Table 5].[16],[17],[18] These discrepancies in the literature could possibly be ascribed to differences in genetics, race, geographical and environmental factors. Furthermore, the differences may also be attributed to the variations in the classification of the position of optic nerve. For instance, the classification system used by Abdalla[8] varied from the system we adopted in our study. They observed a preponderance of Type II followed by Types III, V, IV and lastly Type I. The prevalence of bilateral symmetry with Type I, II, III and IV optic nerve was 73.5%, 11.3%, 0.9% and 5.1%, respectively. This were different from 58.88%, 3.23%, 3.23% and 8.06% correspondingly as documented by Ravindra and Devika[18] in India. It is important for neurosurgeons and otorhinolaryngologists to preoperatively assess the location of the optic nerves adjacent to the sphenoid sinus for safe endoscopic surgery.


  Conclusion Top


The position of the neurovascular structures abutting the wall of the sphenoid sinus varied from previously documented reports. Comprehensive preoperative radiological evaluation is obligatory for proper surgical planning to abate iatrogenic complications.

Strength of study

CT images depict the detailed variant anatomy of the sphenoid sinus and the adjacent structures accurately.

Limitation of study

The study excluded images with sinus pathology; hence, the effect of these lesions on the location of the neurovascular structures in relation to the sphenoid sinus was not assessed.

Acknowledgement

We would like to acknowledge Priscilla Ejiroghene and Emmanuel Akpoyibo who assisted with data collection and analysis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Singh BP, Metgudmath RB, Singh D, Saxena U. Anatomical variations of sphenoid sinus among patients undergoing computed tomography of paranasal sinus. Int J Otorhinolaryngol Head Neck Surg 2019;5:888-92.  Back to cited text no. 1
    
2.
Prabu SS, Veerapandian R, Prgadhees R, Pradeep S, Rajendran M. Neurovascular variations of sphenoid sinus: Impact on transsphenoidal surgery. Int J Sci Study 2018;6:5-9.  Back to cited text no. 2
    
3.
Hiremath R, Suligavi S, Pol M, Anegundi TJ, Rudrappa K. Computed tomographic study on the anatomic variations of the sphenoid sinus and its related structures in a North Karnataka population. J Clin Diagn Res 2012;6:1262-5.  Back to cited text no. 3
    
4.
Priyadarshini D, Prabhu LV, Kumar A, Pai MM, Kvn D. The anatomical variations in the neurovascular relations of the sphenoid sinus: An evaluation by coronal computed tomography. Turk Neurosurg 2015;25:289-93.  Back to cited text no. 4
    
5.
Yekpe P, Akanni D, de Souza CO, Adjadohoun S, Kiki M, de Tove KM, et al. Anatomic variants of sphenoid sinuses and adjacent structures: A study of 225 skull CT scans at CNHU-HKM in Benin, West Africa. Open J Radiol 2018;8:181-90.  Back to cited text no. 5
    
6.
Joghataei MT, Hosseini A, Ansari MJ, Golchini E, Namjoo Z, Mortezaee K, et al. Variations in the anatomy of sphenoid sinus: A computed tomography investigation. J Pharm Res Int 2019;26:1-7.  Back to cited text no. 6
    
7.
Hewaidi GH, Omami GM. The anatomic variation of the sphenoid sinus and its related structures in the Libyan population: A CT scans study. Libyan J Med 2008;3:128-33.  Back to cited text no. 7
    
8.
Abdalla MA. Pneumatization patterns of human sphenoid sinus associated with internal carotid artery and optic nerve by CT scan. Rom J Neuro 2020;19:244-51.  Back to cited text no. 8
    
9.
Gungor G, Okur N. Evaluation of paranasal sinus variations with computed tomography. Haydarpasa Numune Med J 2019;59:320-7.  Back to cited text no. 9
    
10.
Fasunla AJ, Ameye SA, Adebola OS, Ogbole G, Adeleye AO, Adekanmi AJ. Anatomical variations of the sphenoid sinus and nearby neurovascular structures seen on computed tomography of black Africans. East Cent Afr J Surg 2012;17:57-64.  Back to cited text no. 10
    
11.
Dasar U, Gokce E. Evaluation of variations in sinonasal region with computed tomography. World J Radiol 2016;8:98-108.  Back to cited text no. 11
    
12.
Kaya M, Çankal F, Gumusok M, Apaydin N, Tekdemir I. Role of anatomic variations of paranasal sinuses on the prevalence of sinusitis: Computed tomography findings of 350 patients. Niger J Clin Pract 2017;20:1481-8.  Back to cited text no. 12
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13.
Kajoak SA, Ayad CE, Najmeldeen M, Abdalla EA. Computerized tomography morphometric analysis of the sphenoid sinus and related structures in Sudanese population. Glob Adv Res J Med Med Scie 2014;3:160-7.  Back to cited text no. 13
    
14.
Sumaily I, Aldhabaan S, Hudise J. Anatomical variations of PNS. Gender and age impact. Glob J Otolaryngol 2018;14:007-14.  Back to cited text no. 14
    
15.
Jaworek-Troć J, Walocha JA, Chrzan R, Żmuda P, Zarzecki JJ, Pękala A, et al. Protrusion of the carotid canal into the sphenoid sinuses: Evaluation before endonasal endoscopic sinus surgery. Folia Morphol (Warsz) 2020. Published online:2020-08-07. Awaiting print publication DOI:10.5603/FM.a2020.0086. Pubmed:32789847.  Back to cited text no. 15
    
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Alrumaih RA, Ashoor MM, Obidan AA, Al-Khater KM, Al-Jubran SA. Radiological sinonasal anatomy. Exploring the Saudi population. Saudi Med J 2016;37:521-6.  Back to cited text no. 16
    
17.
Yazici D. Evaluation of anatomical variations on paranasal sinus CT. ENT Update 2018;8:175-9.  Back to cited text no. 17
    
18.
Ravindra BN, Devika C. Evaluation of optic nerve variations in relation to posterior paranasal sinuses among study population of Mandya district of Karnataka state. Int J Radiol Diagn Imaging 2020;3:16-20.  Back to cited text no. 18
    


    Figures

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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