10.14639/0392-100X-N2462
Objective. This study aims to determine the prevalence and types of Onodi cells through computed tomography and investigate the relationship between Onodi cell and the surrounding structures, paying particular attention to the risky proximity to the optic nerve canal. Methods. In this study, 430 computed tomography scans of paranasal sinuses were analysed to establish the prevalence and different types of Onodi cells. Furthermore, the relationship between Onodi cell and different patterns of sphenoid sinus pneumatisation and surrounding structures were investigated. Special attention was paid to the relationship between Onodi cell and the optic nerve canal, particularly in cases when the optic nerve canal was bulging by more than 50% into the Onodi cell (Type IV). Results. The Onodi cell was detected in 21.6% of cases, with the most common being Type I (48.5% right, 54.3% left). Type IV bulging of the optic nerve canal into the Onodi cell was observed in 47.1% of cases on the right side, 41.2% on the left side and bilateral in 11.7% of cases. Conclusions. In our series, we observed a high prevalence of Type IV optic nerve bulging into the Onodi cell. For this reason, we suggest that clinicians should always try to identify it in a pre-operative setting with computed tomography to avoid catastrophic consequences during endoscopic sinus surgery approaching the sphenoid area.
text/xml
1827-675X
2462
en
Giovanni Cavallo
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
computed  tomography
Type IV optic nerve and Onodi cell:  is there a risk of injury during sphenoid sinus surgery?
Text.Serial.Journal
https://www.actaitalica.it/
44
Rhinology
2023-12-29
2023-01-07
2024-02-28
2024-02-28
36-41
1
Giovanni Cavallo
2024
10.14639/0392-100X-N2462
36
Department of Otorhinolaryngology, University of Turin, “San Luigi Gonzaga” Hospital, Orbassano (TO), Italy
1827-675X
computed  tomography
en
41
Type IV optic nerve and Onodi cell:  is there a risk of injury during sphenoid sinus surgery?
https://www.actaitalica.it/article/download/2462/1065
44
ACTA OTORHINOLARYNGOLOGICA ITALICA 2024;44:36-41; doi: 10.14639/0392-100X-N2462




Rhinology


Type IV optic nerve and Onodi cell:
is there a risk of injury during sphenoid sinus surgery?
Gian Luca Fadda1, Anastasia Urbanelli1, Alessio Petrelli2, Marta Trossarello1, Letizia Nitro3, Alberto Maria Saibene3,
Eugenio De Corso4, Dario Gned5, Marco Panfili6, Giovanni Cavallo1
1
  Department of Otorhinolaryngology, University of Turin, “San Luigi Gonzaga” Hospital, Orbassano (TO), Italy; 2 National Institute
for Health, Migration and Poverty (INMP), Rome, Italy; 3 Otolaryngology Unit, “Santi Paolo e Carlo” Hospital, Department of Health
Sciences, University of Milan, Milan, Italy; 4 Otorhinolaryngology, “A. Gemelli” Unversitary Hospital IRCCS, Rome, Italy; 5 Department
of Diagnostic Imaging, University of Turin, “San Luigi Gonzaga” Hospital, Orbassano (TO), Italy; 6 Unit of Radiology, “A. Gemelli”
University Hospital Foundation IRCCS, Rome, Italy



SUMMARY
Objective. This study aims to determine the prevalence and types of Onodi cells through com-
puted tomography and investigate the relationship between Onodi cell and the surrounding
structures, paying particular attention to the risky proximity to the optic nerve canal.
Methods. In this study, 430 computed tomography scans of paranasal sinuses were ana-
lysed to establish the prevalence and different types of Onodi cells. Furthermore, the rela-
tionship between Onodi cell and different patterns of sphenoid sinus pneumatisation and
surrounding structures were investigated. Special attention was paid to the relationship be-
tween Onodi cell and the optic nerve canal, particularly in cases when the optic nerve canal
was bulging by more than 50% into the Onodi cell (Type IV).
Results. The Onodi cell was detected in 21.6% of cases, with the most common being Type I
(48.5% right, 54.3% left). Type IV bulging of the optic nerve canal into the Onodi cell was ob-
served in 47.1% of cases on the right side, 41.2% on the left side and bilateral in 11.7% of cases.
Conclusions. In our series, we observed a high prevalence of Type IV optic nerve bulging
into the Onodi cell. For this reason, we suggest that clinicians should always try to identify
it in a pre-operative setting with computed tomography to avoid catastrophic consequences
during endoscopic sinus surgery approaching the sphenoid area.
KEY WORDS: Onodi cell, optic nerve, endoscopic sinus surgery, sphenoid sinus, computed                Received: January 7, 2023
tomography                                                                                            Accepted: June 13, 2023
                                                                                                      Published online: December 29, 2023

Introduction                                                                                          Correspondence
                                                                                                      Gian Luca Fadda
Adolf Ónodi (1857­-1919), professor of rhinolaryngology, described cellula                            E-mail: dott.fadda@gmail.com
sphenoethmoidalis (after that, known as “Onodi cell”) in 1903 as a condition
in which the most posterior or lateral ethmoid air cell extends posteriorly to lie                      How to cite this article: Fadda GL, Urbanel-
lateral and/or superior to the sphenoid sinus (SS) 1.                                                   li A, Petrelli A, et al. Type IV optic nerve
Onodi cell (OC) is of particular interest during endoscopic sinus surgery (ESS)                         and Onodi cell: is there a risk of injury dur-
                                                                                                        ing sphenoid sinus surgery? Acta Otorhi-
because of its close relationship with the optic nerve canal (ONC) and the                              nolaryngol Ital 2024;44:36-41. https://doi.
internal carotid artery (ICA), making it crucial to examine computed tomogra-                           org/10.14639/0392-100X-N2462
phy (CT) scans pre-operatively to avoid serious injuries 2-4.
                                                                                                      © Società Italiana di Otorinolaringoiatria
Another reason why OC must be detected prior to surgery is because an OC                              e Chirurgia Cervico-Facciale
often causes the natural ostium of the sphenoid sinus to be located more supe-
riorly, and it is necessary for the surgeon to be aware of this anatomical variant                                   OPEN ACCESS
when operating.                                                                                       This is an open access article distributed in accordance with
Multiple studies have demonstrated an increased prevalence of OC identifica-                          the CC-BY-NC-ND (Creative Commons Attribution-Non-
                                                                                                      Commercial-NoDerivatives 4.0 International) license. The
tion when examining CT scans on two to three axial planes 4-7.                                        article can be used by giving appropriate credit and mentio-
                                                                                                      ning the license, but only for non-commercial purposes and
Our study aims to investigate, through the analysis of 430 CT scans (860 sides),                      only in the original version. For further information: https://
the prevalence and the patterns of OC and sphenoid sinus pneumatisation                               creativecommons.org/licenses/by-nc-nd/4.0/deed.en




36
                                                                  Risk of iatrogenic injury in the presence of Type IV optic nerve and Onodi cell




(SSP) and the relationship between OC and the ONC, with
particular attention to its bulging into the OC as it repre-
sents a relevant risk factor for critical and potentially ir-
reversible consequences during ESS.

Materials and methods
This is a retrospective study including the analyses of para-      Figure 1. Onodi cell (*) Type I pattern of pneumatisation is above and medial
nasal sinus CT images of 430 patients, analysing a total of        to the horizontal line. (1a) Coronal, (1b) Axial and (1c) Sagittal, paranasal CT
860 SS), collected at a 1.5 mm slice thickness as part of the      scan. A horizontal line was drawn at the uppermost part of the sphenoid sinus
pre-surgical assessment for patients undergoing ESS for            (s) in the coronal image (1a). Optic canals (white arrows) with bulging > 5 mm
                                                                   (Type IV) are shown.
chronic rhinosinusitis. Patients were enrolled between No-
vember 2017 and December 2022 at “San Luigi Gonzaga”
University Hospital. Inclusion criteria were individuals older     • the relationship between OC and different patterns of
than 18 years with sinonasal symptoms (nasal obstruction,            SSP (sellar, presellar, conchal and postsellar type) was
chronic sinusitis, rhinorrhoea) undergoing sinus surgery             evaluated considering the location of posterior sinus
for the first time. Patients with sinonasal malignancies, fa-        wall concerning the position of the sella turcica on the
cial bone fractures, previous head trauma and massive nasal          sagittal plane 9.
polyposis that could modify normal anatomy were excluded.
High-resolution CT images were performed in three axial            Statistical analysis
planes and without contrast medium, as is normally done in         The associations between variables of interest were eval-
pre-operative assessment protocols. Images were reviewed           uated using the Chi-square test. If the expected frequen-
and analysed independently by three sinus surgeons and             cies were less than 5 for more than 25% of the cells in the
two radiologists with extensive and long-lasting sinus sur-        contingency tables, Fisher’s exact test was performed. The
gery experience using a commercially available software            analyses were conducted using SAS System 9.4 (SAS Inc,
viewer (window OsiriX).                                            Cary, NC, USA).
Based on CT scans, the following variables were assessed:
• sagittal, coronal, and axial planes of all analysed CT
   were used to identify the presence of OC and its locali-
                                                                   Results
   sation (right, left, or bilateral). OC was identified as an     CT scans of 430 patients were analysed retrospectively
   ethmoidal cells extending posteriorly or laterally to the       (mean age, 53 ± 18.9 years; range, 18-92). 57% of patients
   anterior wall of the SS;                                        were male (n = 245) and 43% female (n = 185). OC was
• according to Thimmaiah et al. 8, three patterns of OC            identified in 93 of 430 scans (21.6%). Of these, 35.5% were
   pneumatisation were assessed: Type I (superior) if the          detected on the right side, 37.6% on the left side, and 26.9%
   sphenoethmoidal cell was located above and medial to            were bilateral. Type I was the most prevalent, accounting for
   the sphenoid sinus (Fig. 1), Type II (superolateral) if the     16 scans (48.5%) on the right side, 19 (54.3%) on the left
   air cell was located both above and below to a horizontal       side, and 35 scans considering the totality of OC detected
   line drawn at the uppermost part of SS in a coronal plane       simultaneously on the right and left sides (Tab. I); 18.3% of
   (Fig. 2), and Type III (lateral) if sphenoethmoidal cell
   was located below the horizontal line (Fig. 3);
• the relationship between ONC and OC wall was eval-
   uated according to the studies of Ozdemir et al. 2 and
   Chmielik et al. 2,4. The grade of protrusion of ONC was
   calculated by measuring the diameter of the ONC on the
   axial and sagittal plane, focusing specifically on Type IV
   which defines ONC bulging into the OC by more than 5
   mm or more than 50% of the circumference of the ONC
   in two planes (axial or sagittal plane). It is worth to note    Figure 2. Onodi cell (*) Type II is above and below the horizontal line. Axial
                                                                   (2b) CT image showing protrusion of ICA (double arrow). (2a) Coronal, (2b)
   that this classification of types of ONC are defined only
                                                                   Axial and (2c) Sagittal, paranasal CT scan. A horizontal line was drawn at the
   in relation to an OC, and not to any other cells or the SS;     uppermost part of the sphenoid sinus (s) in the coronal image (2a). Optic ca-
• the presence of the ICA bulging into an OC;                      nals (white arrows) with bulging > 5 mm (Type IV) are shown.



                                                                                                                                               37
G.L. Fadda et al.




                                                                                   sults demonstrated a significant association between the
                                                                                   Type IV-ONC and all OC sub-types (p value < 0.01) for both
                                                                                   sides, except for Type III-OC on the left (p value = 0.59).
                                                                                   Analysis of SSP associated to the presence of OC identi-
                                                                                   fied a predominance of the sellar type (60.6% on the right
                                                                                   side, 65.7% on the left side), followed by the postsellar
                                                                                   type (27.3% right and 20% left) and presellar type (12.1%
Figure 3. Onodi cell (*) Type III is below the horizontal line. (3d) Endoscopic    right and 11% left) (Tab. II). Type I-OC was more repre-
right sphenoid sinus, Onodi cell and optic canal are shown. (3a) Coronal, (3b)     sented among cases associated with the sellar type of SSP,
Axial and (3c) Sagittal, paranasal CT scan. A horizontal line was drawn at the     both on the right side (9 cases) and on the contralateral side
uppermost part of the sphenoid sinus (s) in the coronal image (3a). Optic ca-
nals (white arrows) with bulging > 5 mm (Type IV) are shown.                       (14 cases). Only one case of Type I-OC was associated with
                                                                                   the presence of the conchal type of SSP (left-sided).

cases presented a bulging of the ONC into the OC by more                           Discussion
than 50% of the circumference (Type IV). Of these, 47.1%
occurred on the right side, 41.2% on the left side and 11.7%                       In the present investigation, we reported an incidence of
                                                                                   OC of 21.6%. Similar percentages were described by Oz-
(only 2 cases) on both left and right side. ICA protruded into
                                                                                   turan et al. (16.6%) 10, while many previous studies showed
the OC in 8 scans (8.6%) (Tab. I). The presence of OC was
                                                                                   extremely variable percentages ranging between 8% and
significantly associated with the presence of a Type IV-ONC                        65% 3,11-19. This inconsistency in the prevalence of OC
for both sides (p value < 0.0001). The presence of bilateral                       may be due to the different methods used for its identifi-
OCs also showed a statistically significant association with                       cation (radiological vs anatomical). Tanaviratananich et
Type IV-ONC coexistence (p value < 0.0001).                                        al. 17 found a prevalence of 60% during studies conducted
The association between the presence of Type IV-ONC and                            on cadavers, and similar results were reported in the works
all the different types of OC was also investigated. Our re-                       by Kantarci et al. (60%) 13 and Tomovic et al. (65.3%) 12.


Table I. Relation between side and type of Onodi cell and bulging Type IV of the optic nerve canal on 430 paranasal sinus CT scans.
                                                                Men               Women                        Bulging                Protrusion ICA
                                                 N (%)            N (%)              N (%)                 ONC (type IV)
 R-Onodi cell                                  33 (35.5)         18 (29)           15 (48.4)                   8 (47.1)                  3 (37.5)
                                                                                                        (p value < 0.0001)
     Type I                                       16 (48.5)        9 (50.0)           7 (46.7)                   5 (62.5)                  2 (66.7)
                                                                                                           (p value < 0.0001)
     Type II                                      11 (33.3)        6 (33.3)           5 (33.3)                   2 (25.0)                  1 (33.3)
                                                                                                           (p value < 0.0001)
     Type III                                      6 (18.2)        3 (16.7)           3 (20.0)                   1 (12.5)                     -
                                                                                                            (p value < 0.001)
 L-Onodi cell                                  35 (37.6)        27 (43.5)           8 (25.8)                   7 (41.2)                  3 (37.5)
                                                                                                        (p value < 0.0001)
     Type I                                       19 (54.3)       14 (51.9)           5 (62.5)                   4 (57.1)                  2 (66.7)
                                                                                                           (p value < 0.0001)
     Type II                                       9 (25.7)        7 (25.9)            2 (25)                    3 (42.9)                  1 (33.3)
                                                                                                           (p value < 0.0001)
     Type III                                      7 (20.0)        6 (22.2)           1 (12.5)                       -                        -
                                                                                                             (p value = 0.59)
 B-Onodi cell                                  25 (26.9)        17 (27.5)           8 (25.8)                   2 (11.7)                  2 (25.0)
                                                                                                        (p value < 0.0001)
 Total                                      93/430 (21.6)     62/93 (66.7)        31/93 (33.3)              17/93 (18.3)                8/93 (8.6)
ONC: optic nerve canal; R: right; L: left; B: bilateral.




38
                                                                                                Risk of iatrogenic injury in the presence of Type IV optic nerve and Onodi cell




Furthermore, many of the studies were carried out analys-                                         On the other hand, Yeoh et al. 20 found a prevalence of 51%
ing only one 12 or two CT planes (axial and/or coronal). In                                       of ONC protruding into the OC and concluded that the
our study, the identification of OC was performed on all                                          most dangerous type of ONC was the one with no bulging,
three CT scan planes (coronal, axial and sagittal) to obtain                                      because of the extremely thin wall separating the spheno-
a more accurate evaluation of this anatomical variant.                                            ethmoidal air cell and the ONC itself.
Regarding the prevalence of sub-types of OC, Thimmaiah                                            Another risk of injury during sphenoid sinus surgery is rep-
et al. 8 described three main patterns of pneumatisation,                                         resented by the proximity of OC to the ICA. In this study, 8
with Type II being the most common, followed by Type I                                            cases were found (8.6%) where the ICA protruded into the
and Type III. In our study, Type I was the most common                                            OC, thus exposing the endoscopic procedure to the risk of a
followed by Type II. Our percentages correlate with those                                         catastrophic haemorrhage. Ozturan et al. 10 reported an ICA
found in the previous literature: in the study by Ali et al. 3,                                   protrusion rate of 2.8% in absence of an OC, but a preva-
Type I was the most prevalent, while Chmielik et al. 4 re-                                        lence of protruding ICA of 59% when the OC was present.
ported that Type II was the most common pattern (Tab. III).                                       They also concluded that increased dimension of OC sig-
The improvement of systematic pre-operative CT analysis to                                        nificantly correlated with higher rates of protrusion of ICA.
detect the presence of OC and their pattern of pneumatisa-                                        The relationship between different types of OC and differ-
tion can decrease the risk of ONC injury during ESS, thus                                         ent patterns of SSP were also evaluated. According to the
avoiding catastrophic consequences such as blindness 8. Öz-                                       Güldner classification 9, four types (sellar, presellar, conchal,
demir et al. 2 reported four types of relationships between                                       and postsellar types) of SSP were considered. The sellar type
the ONC and OC, using the classification first described by                                       was most commonly associated with the presence of OC,
Chmielik et al. in their study 4. Type IV-ONC in relation-                                        followed by the postsellar type. We did not find any similar
ship with the OC was described by some authors as the most                                        correspondence in all previous analysed studies.
dangerous pattern, as the potential risk during ESS is greater                                    It is important to analyse CT scans before sinus surgery
when more than 50% of the circumference of ONC is bulg-                                           on all three axial planes, as stated before and based on
ing into the OC 20. We found 17 cases (18.3%) of ONC pre-                                         evidence in the literature. The sagittal plane is the most
senting a bulging into the OC for more than 50% (Type IV),                                        important for OC identification, since it provides informa-
representing a relevant risk factor for injury during ESS.                                        tion on the antero-posterior extension of the most posterior
The dangerous relationship between OC and ONC has been                                            ethmoidal cell in relation to the sphenoid sinus.
pointed out previously by several authors 2,4,11,12,21, but most                                  Regarding complications during ESS in the presence of
considered the totality of ONC bulging, without differentiat-                                     OC, in addition to accurate pre-operative review of the pa-
ing those that protruded more than 50% (Type IV).                                                 tient’s surgical anatomy, the surgeon’s experience and care-


Table II. Relation between the type of Onodi cell and type of sphenoid sinus on 430 paranasal sinus CT scans.
                           Sellar                         Presellar                      Conchal                                         Postsellar                 Total
                            N (%)                           N (%)                         N (%)                                            N (%)
 R-Onodi cell                20/33 (60.6)                            4/33 (12.1)                              -                          9/33 (27.3)            33/93 (35.5)
   Type I                      9/20 (45.0)                              2/4 (50.0)                                                          5/9 (55.6)
   Type II                     8/20 (40.0)                              2/4 (50.0)                                                          1/9 (11.1)
   Type III                    3/20 (15.0)                                   -                                                              3/9 (33.3)
 L-Onodi cell                23/35 (65.7)                            4/35 (11.4)                          1/35 (2.9)                     7/35 (20.0)            35/93 (37.6)
   Type I                      14/23 (60.9)                             3/4 (75.0)                         1/1 (100.0)                      1/7 (14.3)
   Type II                      4/23 (17.4)                             1/4 (25.0)                              -                           4/7 (57.1)
   Type III                     5/23 (21.7)                                  -                                  -                           2/7 (28.6)
 B-Onodi cell            R                L                     R                  L                  R              L               R               L
                    13/25* (52.0) 14/25* (56.0)            3/25* (12.0)        2/25* (8.0)       3/25* (12.0) 5/25* (20.0)      6/25* (24.0)    4/25* (16.0)    25*/93 (26.9)
   Type I            11/13 (84.6) 12/14 (85.7)               2/3 (66.7)         1/2 (50.0)         2/3 (66.7)     1/5 (20.0)      4/6 (66.7)      2/4 (50.0)
   Type II            2/13 (15.4)           -                1/3 (33.3)         1/2 (50.0)              -         4/5 (80.0)           -          2/4 (50.0)
   Type III                -           2/14 (14.3)              -                  -               1/3 (33.3)        -            2/6 (33.3)         -
 Total                                                                                                                                                          93/430 (21.6)
R: right; L: left; B: bilateral.
* (25*) This refers to the total number of patients with bilateral OC (in total 50 OC in this group).




                                                                                                                                                                            39
G.L. Fadda et al.




Table III. Comparison of Onodi cell indicence in the literature.
                         No. PNSCT           No. PNSCT                     No. OC (%)             No. R-side (%)   No. L-side (%)   No. Bilateral (%)   Bulging ONC (%)
                                                 sides
 Kasemsiri, 2011 16                187                   374                92 (49.7)*                  -                -                 -                  -
 Shin, 2011 14                     162                   324                54 (33.3)               16 (29.6)        15 (27.8)         23 (42.6)              -
 Tomovic, 2012 12                 170                    340               117 (68.8)               45 (38.5)        28 (23.9)        44 (37.6)               -
 Ozturan, 2013 10                 999                   1998               160 (16.6)               58 (36.3)        50 (31.2)        52 (32.5)             80.1%
 Wada, 2015 18                    261                    522               132 (50.6)*                  -                -                 -                34.8%
 Senturk, 2017 19                 618                   1236               326 (52.7)               94 (28.8)        78 (23.9)        154 (47.3)              -
 Chmielik, 2017 4                 196                    392                78 (39.8)                   -                -                 -                 25%
 Özdemir, 2019 2                  508                   1016               108 (21.2)               44 (40.7)        28 (25.9)        36 (33.4)            5.3%**
 Thimmaiah, 2017 8                1080                  2160               260 (24.1)                   -                -                 -                  -
 Ali, 2020 3                      201                    402                86 (42.8)                   -                -                 -                  -
 Fadda, 2022 22                   430                    860                93 (21.6)               33 (35.5)        35 (37.6)        25 (26.9)            18.3%**
PNSCT: paranasal CT; OC: Onodi cell; ONC: optic nerve canal. * sides; ** only Type IV bulging.



ful use of appropriate surgical instrumentation also play a                                      difficulties in locating the skull base during trans-sphe-
key role in the successful management of potential iatro-                                        noid exposure.
genic injuries.                                                                                  In the most challenging cases, given the risk by Type IV
To minimise intra-operative injuries during sphenoid sur-                                        of ONC bulging into the OC, use of neuronavigation sys-
gery in the presence of Type IV optic nerve into the OC,                                         tems to assist the surgeon during ESS may be helpful to
Fadda et al. 22 recommend using a neuroinvestigation sys-                                        reduce the risk of complications; especially in cases where
tem and to not use drills and surgical chisels to avoid in-                                      the widely enunciated risky variants of ONC may place the
juries of vital structures, in particular in presence of pro-                                    surgeon in a dangerous intra-operative setting, exposing the
truded ICA or ONC.                                                                               patient to potentially catastrophic consequences. Finally, in
In addition, Humphreys et al. 23 reports use of through-cut-                                     such cases, traumatic surgical tools such as drill or chisel
ting forceps instead of traction-instruments to remove bony                                      should be avoided when approaching the OC if the ONC is
partitions to avoid possible damage of vital neurovascular                                       bulging into it (particularly in cases of Type IV-ONC).
structures, to preserve the mucosal layer, and to reduce the
risk of neo-osteogenesis and scarring. Shaver dissection                                         Conflict of interest statement
along the sphenoid area should be carefully used to mini-                                        The authors declare no conflict of interest.
mise the risk of dural violation and consequent brain injury.
Strength and level of wall suction should be well regulated.                                     Funding
Lastly, use of a neuroinvestigation system is also recom-                                        This research did not receive any specific grant from fund-
mended similar to Fadda et al. 22.                                                               ing agencies in the public, commercial, or not-for-profit
                                                                                                 sectors.
Conclusions
The identification of OC and its relationship with adja-                                         Author contributions
cent structures in pre-operative assessment represents a                                         GLF: substantial contributions to the work reported in this
prerogative of ESS because of its proximity to important                                         manuscript and surgeon, final approval of the version to be
anatomical structures such as the ONC and ICA. Its iden-                                         published; AU: substantial contributions to the conception or
tification is crucial to avoid potential complications dur-                                      design of the work, final approval of the version to be pub-
ing surgery 11. Furthermore, the presence of an OC, if not                                       lished; AP: substantial contribution to the statistical analysis
previously detected, can also be a source of a more diffi-                                       and interpretation of the data, final approval of the version to
cult approach to the sphenoid sinus for the surgeon, since                                       be published; MT, EdC, GC: substantial contributions to the
it may cause the natural ostium of the sphenoid sinus to                                         preparation of patients undergoing surgery, editing, revision
be located more superiorly, and the asymmetry between                                            and final approval of the version to be published; LN, AMS,
sides may steer the surgeon in the wrong direction while                                         MP, DG: substantial contributions to the analysis of the CT
opening the sinus. This anatomic variant can also cause                                          scans, final approval of the version to be published.



40
                                                                               Risk of iatrogenic injury in the presence of Type IV optic nerve and Onodi cell




Ethical consideration                                                                Otorhinolaryngol 2013;270:2057-2063. https://doi.org/10.1007/
This study was approved by the “San Luigi Gonzaga” Uni-                              s00405-012-2325-8
                                                                                11
                                                                                     Kim JY, Kim HJ, Kim CH, et al. Optic nerve injury secondary to
versity Hospital Ethics Committee (Date: 18.03.2022, pro-
                                                                                     endoscopic sinus surgery: an analysis of three cases. Yonsei Med J
tocol number: 4526). The research was conducted ethically,                           2005;46:300-304. https://doi.org/10.3349/ymj.2005.46.2.300
with all study procedures being performed in accordance                         12
                                                                                     Tomovic S, Esmaeili A, Chan NJ, et al. High-resolution computed
with the requirements of the World Medical Association’s                             tomography analysis of the prevalence of Onodi cells. Laryngoscope
Declaration of Helsinki.                                                             2012;122:1470-1473. https://doi.org/10.1002/lary.23346
Written informed consent was obtained from each partici-
                                                                                13
                                                                                     Kantarci M, Karasen RM, Alper F, et al. Remarkable anatomic vari-
                                                                                     ations in paranasal sinus region and their clinical importance. Eur J
pant for study participation and data publication.                                   Radiol 2004;50:296-302. https://doi.org/10.1016/j.ejrad.2003.08.012.
                                                                                14
                                                                                     Shin JH, Kim SW, Hong YK, et al. The Onodi cell: an obstacle to sellar
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