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European Archives of Oto-Rhino-Laryngologyand Head & Neck ISSN 0937-4477 Eur Arch OtorhinolaryngolDOI 10.1007/s00405-012-2325-8
Co-existence of the Onodi cell with thevariation of perisphenoidal structures
Orhan Ozturan, Alper Yenigun, NazanDegirmenci, Fadlullah Aksoy & BayramVeyseller
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RHINOLOGY
Co-existence of the Onodi cell with the variationof perisphenoidal structures
Orhan Ozturan • Alper Yenigun • Nazan Degirmenci •
Fadlullah Aksoy • Bayram Veyseller
Received: 30 August 2012 / Accepted: 11 December 2012
� Springer-Verlag Berlin Heidelberg 2012
Abstract The presence of the Onodi cell (OC) may be
accompanied by morphological variations of the neigh-
boring anatomic structures. Such variations carry signifi-
cant surgical implications and challenges. Pneumatization
of the sphenoid sinus induces anterior clinoid pneumati-
zation (ACP), affects the type of the Vidian nerve (VN)
canal or alters the courses of the internal carotid artery
(ICA), and the optic nerves (ONs) are strongly depending
on it. Onodi cell pneumatization may reach and surround
the optic nerve in various extension. Our aim in the study
was to investigate the effect of Onodi cell’s potential
co-existence on these structures. This study was planned as
a retrospective and cross-sectional study. This study per-
formed in a tertiary referral center. Coronal computerized
tomography images of 999 patients were examined. Using
an 64 slices tomography machine, images taken at 3-mm
sections were reconstructed using a bone algorithm and
evaluated. OCs were present at 212 of the total 320 sides in
160 patients. Type-2 was found to be the most prevalent
type of VN canal configuration (Type-2: VN canal partially
protrudes into the sphenoid sinus or into the floor of the
sphenoid) among all patients (66.5 %) and among those
with OCs (71.2 %). The presence or absence of the OC did
not cause a statistically significant alteration of the int-
rasphenoidal course of the VN. The presence of OCs was
found to be significant (p \ 0.01) in accompanying pneu-
matization of the anterior clinoid process (34.4 %, 73/212),
protrusion (80.1 %, 170/212) and dehiscence (36.3 %,
77/212) of the optic nerve, and protrusion (59 %, 125/212)
and dehiscence (20.8 %, 44/212) of the ICA. In 108/320
sides where OCs were absent, no significant correlations
existed. This study shows that in the co-existence of an OC,
ACP, protrusion and dehiscence of the optic nerve and ICA
are encountered at significantly higher rates, while the
course of the VN is not necessarily altered.
Keywords Onodi cell � Vidian nerve � Optic nerve �Anterior clinoid process � Internal carotid artery �Paranasal sinuses � Computer tomography
Introduction
The Onodi cell (OC), also called the sphenoethmoidal cell,
is an ethmoidal air cell located at the most posterior end of
the ethmoid bone which pneumatizes into the sphenoid
sinus. It was first described in the 1900s by Adolf Onodi
(1857–1920), and was named after him [1]. Most authors
report the incidence of the OC as 8–14 % [2]. Due to its
intimate relationship with the optic nerve (ON) and the
internal carotid artery (ICA), assessing its presence before
surgery will help reduce the potential risk of injury to those
structures [3].
The Vidian nerve (VN) canal runs along the anterior
border of the foramen lacerum, over the floor of the
sphenoid sinus, extending into the pterygopalatine fossa.
VN enters the pterygopalatine fossa and joins the spheno-
palatine ganglion at its posterior side [4]. The protrusion or
dehiscence of VN canal may render VN vulnerable in
endoscopic manipulations of the sphenoid sinus area, and
in sinus diseases [5]. According to CT findings, VN con-
figuration is classified into three types [6]. Those three
O. Ozturan � N. Degirmenci � F. Aksoy � B. Veyseller
Department of Otorhinolaryngology, Bezmialem Vakif
University, Istanbul, Turkey
A. Yenigun (&)
Karaman State Hospital, Otorhinolaryngology Clinic,
Turgut Ozal Street No:1, Karaman, Turkey
e-mail: [email protected]
123
Eur Arch Otorhinolaryngol
DOI 10.1007/s00405-012-2325-8
Author's personal copy
types, as defined by Lee et al. are Type-1: VN canal
completely protrudes into the sphenoid sinus (Fig. 1),
Type-2: VN canal partially protrudes into the sphenoid
sinus or into the floor of the sphenoid (Fig. 2), and Type-3:
VN canal is completely embedded in the sphenoid corpus
(Fig. 3). Computerized tomography (CT) is considered as
the best tool for visualizing paranasal sinuses [7]. Before
any endoscopic operation to sphenoid sinus, important
structures adjacent to this sinus should be detected by CT
investigation.
A study authored by Simmen et al. [8] showed that the
existence of pneumatized supraorbital ethmoid cells sig-
nificantly altered the course of the anterior ethmoidal
artery. This finding may as well be paralleled by the
co-existence of the OC, may alter the morphological
changes in the floor and/or the lateral wall of the sphenoid
sinus. Pneumatization of the sphenoid sinus induces ACP,
affects the type of the VN canal or alters the courses of the
ICA and the optic nerves are strongly depending on it.
Onodi cell pneumatization may reach and surround the
optic nerve in various extension. Our study was aimed to
investigate the effect of Onodi cell’s potential co-existence
on these structures.
Methods
This is a retrospective study, approved by the local Clinical
Research Ethics Committee, evaluating coronal paranasal
sinus CT (Philips Brilliance 64-slice CT scanner, Philips
Medical Imaging, The Netherlands) images. The images
were taken at 3-mm sections and reconstructed using a
bone algorithm and evaluated. CT images were taken in
three planes (coronal, axial, sagittal). Coronal images
perpendicular to hard plate were investigated. The
vomerine crest was accepted as midline. Vidian canal was
demonstrated with CT imaging and its localization and
bony structures were studied. The relationships of the
Vidian canal to the sphenoid sinus, including whether it
was embedded in the bone, protruded into the bone, or was
linked to bone lamella in the sinus were examined.
All CT images were ordered for sinonasal, otologic and
maxillofacial injuiries, between January and June 2011.
Fig. 1 Coronal CT image showing protrusion of bilateral ON
(arrowhead), bilateral ACP (point star), protrusion of Vidian canal
(type-1) (triangle), pneumatization of bilateral PP (square) associated
with protrusion and dehiscence of left maxillary nerve (circle)
Fig. 2 Coronal CT image showing protrusion and dehiscence of
right ON (arrowhead), pneumatization of right PP (square), Vidian
canal type-2 (triangle) and right OC
Fig. 3 Coronal CT image showing protrusion of bilateral ON
(arrowhead), Vidian canal type-3 (triangle) and right OC
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Patients with nasal poliposis or sinus anomalies, and those
who had previous sinus surgery were excluded from the
study. In the evaluation of coronal sinus CTs, the perpen-
dicular lamina and the hard palate were preferably posi-
toned in right angles. OCs and the courses of VN canals
were noted in a total of 1,998 sphenoid sinuses in 999
patients. The presence of Onodi cell was determined fol-
lowing Stammberger et al. in that the optic nerve bulging
into a posterior ethmoid cell qualifies for an Onodi cell.
The radiological criteria for definition of the OC was to be
a posterior etmoid cell that invaded the superior portion of
the sphenoid to partially surround the optic canal.
According to CT findings, VN configuration is classified
into three types using classification introduced by Lee et al.
Those three types are Type-1: VN canal completely pro-
trudes into the sphenoid sinus, Type-2: VN canal partially
protrudes into the sphenoid sinus or into the floor of the
sphenoid, and Type-3: VN canal is completely embedded
in the sphenoid corpus. Evaluations of CT scans were
carried out by two otolaringologists and all of the films
read by two of them. The sections where the OC was seen
obviously were taken for evaluation. VN canals, ACPs,
ICAs and ONs were meticulously examined in CTs
showing unilateral and bilateral OCs. Configuration types
of the VN canal, and protrusion and dehiscence of ICA and
ON were classified according to the above mentioned cri-
teria. The categorical data were evaluated by the Chi
square analyses. Differences at the level of p \ 0.05 were
accepted to be statistically significant.
Results
The 999 patients examined by coronal paranasal sinus CTs
consisted of 537 males and 462 women, with an age range
of 13–91 years and a mean age of 36.4 years. Onehundred-
sixty of the 999 patients had the OC. The incidence of OC
is 16.6 %. Those 160 patients consisted of 93 males and 67
women, with an age range of 13–91, and a mean age of
40.8.
In a total of 160 patients, 66.3 % sides had the OC (212/
320 sides). 32.5 % of the patients had bilateral OCs,
36.3 % had OCs on the right side, and 31.3 % had OCs on
the left. The heights of the OC images seen in the coronal
section CTs were measured. The mean height was found to
be 0.84 cm (minimum 0.3 cm and maximum 1.6 cm).
The presence of the OC was 11 % on the right side,
10.2 % on the left side, with a total of 10.6 % on both
sides. The anatomical variations of the 999 patients (1998
VN canals) were evaluated according to the method
described above. The prevalence of Type-1 was 7 % on the
right side, 7.8 % on the left, with a total prevalence of
7.4 % on both sides. Type-2 had a prevalence of 65.1 % on
the right, 67.8 % on the left, and 66.5 % when both sides
were taken together. Type-3 had a prevalence of 27.8 % on
the right, 24.3 % on the left, and 26 % on both sides.
The types of VN canal, ACP, protrusion and dehiscence
of ICA and of ON were examined of the 160 patients (320
sides). At the right side, the configuration of VN canal was
Type-2 in 66.4 % of the patients with OCs, 84 % in
patients without the OC. At the left, Vidian canal Type-2
was seen in 76.5 % of the patients with OCs, 63.8 % in
patients without the OC. The correlation of the presence of
the OC with the type of VN canal configuration was
evaluated by the Chi square test. No statistically significant
correlation was found (p = 0.67 on the right, p = 0.19 on
the left) (Table 1).
The types of VN canal configurations were also exam-
ined in the overall patient population, and Type-2 was
found to be the most common type (66.5 %). The most
prevalent type of VN canal in patients with OCs was also
found to be Type-2 (71.2 %) (Fig. 4). The presence of the
OC and the type of VN canal did not have a significant
statistical correlation (p = 0.92 on the right side, p = 0.83
on the left). Statistically, the presence of the OC did not
significantly alter the intrasphenoidal course of VN.
On the right, 32.7 % of the patients with an OC had
ACP; that rate was 4 % in patients without an OC
(p \ 0.01). On the left, 36.3 % of the patients with an
OC had ACP; the rate was 5.2 % in those without an OC
(p \ 0.01). The overall co-existence of the OC and ACP
was found to be 34.4 %, while the presence of ACP
without the presence of an OC was 4.6 %. The co-exis-
tence of ACP and the OC had a significant correlation on
both sides (p \ 0.01) (Table 2).
On the right side, the co-existence of ON protrusion and
the OC was found to be 76.4 %, while ON protrusion was
24 % in patients without an OC (p \ 0.01). On the left
side, the co-existence of ON protrusion and the OC was
found to be 84.3 %, while ON protrusion was only 7 % in
patients without an OC (p \ 0.01). The overall rate of the
co-existence of ON protrusion and the OC was 80.1 %, and
the presence of ON protrusion in the absence of an OC was
17.6 %. The co-existence of ON protrusion and the OC was
found to be statistically significant on both sides (p \ 0.01)
(Table 1).
On the right, the co-existence of ON dehiscence and the
OC was 30.9 %, while the prevalence of ON dehiscence
was 0 % in those patients without an OC (p \ 0.01). On
the left, the co-existence of ON dehiscence and the OC was
42.2 %, while the prevalence of ON dehiscence was 0 % in
those patients without an OC (p \ 0.01).
The total occurence of ON dehiscence in the presence of
the OC was 36.3, and 0 % (0/108) in the absence of an OC.
The co-existence of ON dehiscence with the OC was sta-
tistically significant on both sides (p \ 0.01) (Table 1).
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On the right side, the co-existence of ICA protrusion and
the OC was seen in 59.1 % of the patients, while only 6 %
of those without an OC had ICA protrusion (p \ 0.01). On
the left, the co-existence of ICA protrusion and the OC was
seen in 58.8 %, while the rate of ICA protrusion was 5.2 %
in those without an OC (p \ 0.01). The overall prevalence
of ICA protrusion was found to be 59 % in the presence of
the OC, and 5.6 % without the OC (p \ 0.01). The corre-
lation between ICA protrusion and the presence of the OC
was found to be statistically significant on both sides
(Table 1).
On the right side, the co-existence of ICA dehiscence
and the OC was present in 19.1 % of the patients, while
ICA dehiscence was present in 6 % of those without an OC
(p \ 0.01). On the right side, the co-existence of ICA
dehiscence and the OC was present in 21.8 % of the
patients, while no ICA dehiscence was seen in those
without an OC: 0 % (p \ 0.01). The overall rate of prev-
alence of ICA dehiscence was found to be 20.8 % in the
presence of the OC, and 5.6 % without a coexisting OC
(p \ 0.01). The correlation between ICA dehiscence and
the presence of the OC was found to be statistically sig-
nificant on both sides (Table 1).
Discussion
Sphenoid sinus is one of the most difficult sinuses in par-
anasal sinuses for surgery and is surrounded with important
structures. These structures include ON, ICA, VN, and they
Table 1 Vidian nerve canal
types in different conditionsAll patients Right Left Total
VN canal type 1 7.0 % (70/999) 7.8 % (78/999) 7.4 % (148/1998)
VN canal type 2 65.1 % (651/999) 67.8 % (678/999) 66.5 % (1329/1998)
VN canal type 3 27.8 % (278/999) 24.3 % (243/999) 26.0 % (521/1998)
In the presence of the OC
VN canal type 1 6.4 % (7/110) 3.9 % (4/102) 5.1 % (11/212)
VN canal type 2 66.4 % (73/110) 79.5 % (78/102) 71.2 % (151/212)
VN canal type 3 27.3 % (30/110) 19.6 % (20/102) 23.5 % (50/212)
Fig. 4 Typing the Vidian nerve canal in subject with and without
OC population
Table 2 ACP protrusion and
dehiscence of the OC and ICA
ACP anterior clinoid
pneumatization, ICA internal
carotid artery, OC Onodi cell,
ON optic nerve, PP pterygoid
process, VN Vidian nerve
Right Left Total
In the presence of the OC
PACP 32.7 % (36/110) 36.3 % (37/102) 34.4 % (73/212)
ON protrusion 76.4 % (84/110) 84.3 % (86/102) 80.1 % (170/212)
ON dehiscence 30.9 % (34/110) 42.2 % (43/102) 36.3 % (77/212)
ICA protrusion 59.1 % (65/110) 58.8 % (60/102) 58.9 % (125/212)
ICA dehiscence 19.1 % (21/110) 21.8 % (23/102) 20.8 % (44/212)
In the abscence of the OC
PACP 4 % (2/50) 5.2 % (3/58) 4.6 % (5/108)
ON protrusion 24 % (12/50) 7 % (7/58) 17.6 % (19/108)
ON dehiscence 0 % (0/50) 0 % (0/58) 0 % (0/108)
ICA protrusion 6 % (3/50) 5.2 % (3/58) 5.6 % (6/108)
ICA dehiscence 6 % (3/50) 0 % (0/58) 2.8 % (3/108)
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are separated from sphenoid sinus by very thin bony lam-
elle. Dehiscence would occur on these bone lamelles
occasionally and the risk of damage on these structures gets
higher during any operation to this site. Before any endo-
scopic operation on this site, variations of these important
structures should be detected by CT investigation.
Most authors report the incidence of the OC as 8–14 %
[2]. In our study we found 9.42 % compatible with the
relevant literature.
The relationship of ON with the posterior paranasal
sinus is classified in terms of protrusion and dehiscence
(Figs. 1, 2, 3, 5) [9, 10]. When more than a half ([50 %) of
the nerve protruded into the sinus cavity as seen in coronal
CT sections, protrusion was confirmed. Dehiscence of the
bone was acknowledged when no bone density separating
ON from the sinus was present in CT images.
In another study conducted in 1996 with 150 patients
classifies ON in four types according to its relationship
with posterior paranasal sinuses [11].
Type-1: ON runs a course adjacent to the sphenoid
sinus, but makes no indentation on the wall of the sinus,
Type-2: ON runs a course adjacent to the sphenoid
sinus, and makes some indentation on the wall,
Type-3: ON runs a course through the sphenoid sinus,
Type-4: ON runs a course adjacent to the sphenoid sinus
and posterior ethmoidal cells.
Injuries of the ON are encountered as complications of
sinus diseases and also accompanying surgical traumas,
especially in the presence of protrusion and dehiscence. If
the nerve is surgically injured while still inside the sinus,
the risk of blindness is considerably high [12]. Infections of
the sphenoid sinus or a mucocele compressing the optic
canal or the ON may also lead to visual impairment.
Compression of the ON may lead to ischemia of the nerve
or to venous congestion. It is reported that development
of an OC may be accompanied by protrusion of the ON
[9, 10]. Studies conducted in the years of 2000, 2006, 2008
and 2009 reported significant correlations between protru-
sion of the ON inside the sphenoid sinus and ACP [9, 10,
13, 14].
ICA runs a critical course inside the sphenoid sinus,
located posterolaterally [9]. ICA can also be protruded or
dehiscent (Figs. 6, 7). If the surgeon is not aware of these
variations preoperatively, fatal complications may be
encountered. Controlling an intrasphenoidal ICA bleeding
is quite difficult. Even if the bleeding is successfully con-
trolled, irreversible neurologic sequels may entail [9]. In a
study involving 92 patients, Sirikci et al. [9] reported a
26.1 % prevalence of ICA protrusion and a 22.8 % prev-
alence of ICA dehiscence. Fuji et al. [15] noted that among
the 25 cadavers in their series, 8 % had ICA dehiscence in
the sphenoid sinus. Kennedy et al. [16] found that the rate
of ICA dehissence in sphenoid sinuses was 20–25 %. In
our study, ICA protrusion and dehissence were found as
2.8 % in the absence of an OC; when the OC was present,
these rates increased to 59 % for protrusion, and to 20.8 %
for dehissence of the ICA. Thus, with the presence of the
OC, ICA protrusion and dehissence rates increased very
significantly. Another finding in our study showed that
increased height of the OC correlated significantly with
higher rates of protrusion and dehissence of the ICA.
The configuration of the VN canal as seen in CT images
was classified by Lee et al. in three types, according to the
relationship of VN with the floor of the sphenoid sinus
[16]. Lang and Keller reported that 38 % of their 150 cases
exhibited VN canal configuration Type-3, 34 % had Type-
2, and 18 % had Type-1 [17]. Yazar et al. [18] again in a
series of 150 cases reported a 54 % prevalence of Type-2,
36 % of Type-1, and 10 % of Type-3 using a different
definition of VN canal classification; they also noted a
32 % dehiscence rate of the bony structure. Liu et al. [19]
examined 341 patients, where they also classified VN
canal, using Lee et al.’s definition, in three types according
to its relationship with the floor of the sphenoid, and
reported a 53.4 % prevalence of Type-3 (embedded in the
sphenoid corpus), 34.2 % of Type-2, and 12.5 % of Type-1
in their series. In our study, we noted that VN canal Type-2
was the most prevalent type (66.5 %) among our 999
patients, followed by Type-3 (26 %) and Type-1 (7.4 %).
With a coexistent OC, the course of VN canal was found to
be Type-2 in a great majority (71.2 %) of the patients. The
presence of an OC did not significantly alter the intrasph-
enoidal course of VN; also the height of the OC did not
cause a significant alteration on the course of VN canal.
Fig. 5 Coronal CT image showing protrusion and dehiscence of
bilateral ON (arrowhead), bilateral ACP (point star), pneumatization
of bilateral PP (square) and bilateral OC
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The results of our study showed significant correlations
between the presence of the OC and ACP 34.4 %, ON
protrusion 80.1 % and dehissence 36.3 %, and ICA pro-
trusion 59 % and dehissence 20.8 % (p \ 0.01). When the
OC was absent, those rates were much lower: 4.6 % for
ACP, 17.6 % for protrusion and 0 % for dehissence of the
ON, and 5.6 % for protrusion and 2.8 % for dehissence of
the ICA.
When the above study is adapted for classifying pro-
trusion of ON, Type-1 and Type-2 stand for \50 % pro-
trusion, and Types 3 and 4 stand for [50 % protrusion of
ON; Type-1 was found to be the most common type, with a
rate of 76 % [12]. Another study dating from 2004
evaluated ON in 100 patients, using the same classification,
and again Type-1 was the most common type, with a rate
of 64 % [11]. In our study, in the absence of an OC[50 %
protrusion of ON had a rate of 17.6 % (19/108) which was
compatible with the relevant literature [20]. When the OC
was present, [50 % protrusion rate of ON increased to
80.1 % (170/212), which showed a statistically significant
correlation between the presence of an OC and protrusion
of ON (p \ 0.01).
Eventhough pneumatization of bilateral pterygoid pro-
cess has not been observed in the past studies, it was
observed in three patients in our study (Figs. 1, 4, 5).
Conclusion
The results of this study demonstrated that the presence of
the OC did not cause a significant alteration in the int-
rasphenoidal course of VN, but its presence caused a sig-
nificant increase in ACP, and in protrusion and dehissence
of both ON and of the ICA. Increased height of the OC
correlated significantly with higher rates of protrusion and
dehissence of the ICA and ACP, on the contrary this sig-
nificance did not replicate for the course of VN canal and
protrusion and dehissence of the ON.
These observations point out the importance of careful
preoperative CT analyses in preparation for surgery of the
sphenoid sinus area, and of delineating a specific roadmap
for each patient. Preoperative discovery of the prevalance
of OC is an indispensible necessity in ensuring the safety of
sphenoid sinus surgery.
Acknowledgments The authors would like to thank to Ass. Prof.
Omer Uysal, PhD, from the Department of Biostatistics and Medical
informatics for his kind statistical assistance.
Conflict of interest None.
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Fig. 6 Coronal CT image showing protrusion and dehiscence of
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and bilateral OC
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