Impact of Window Computed Tomography (CT) Parameters on Measurement of Inflammatory Changes in Paranasal Sinuses

Abstract

Background
In accordance with the European guidelines on rhinosinusitis and nasal polyps (EPOS 2012), CT is used as the main imaging modality for the assessment intensity of inflammatory lesions.
The aim of this study was to measure the differences in the assessment of inflammatory changes in the paranasal sinuses due to different parameters of width (W) and length (L) of the CT window.

Material/Methods
A retrospective analysis included 44 CT scans of the paranasal sinuses that were performed in adults. All studies were characterized by the presence of inflammatory changes in at least one of the sinuses.
Measurements of the same inflammatory lesions were performed sequentially with different CT windows. The results were statistically analyzed.

Results
A statistically significant difference was observed between the average measurements that were performed with the use CT windows dedicated for the sinuses and head. A downward trend in the measured values and a shift towards soft tissue values was observed with decreasing window parameters.

Conclusions
A major cause of inaccurate examinations of pathological changes in the paranasal sinuses may be due to selection of unsuitable CT windows. Therefore, in order to avoid missing inflammatory lesions in the paranasal sinuses, it is reasonable to use CT windows dedicated for the sinuses or bones.

Full text

Impact of Window Computed Tomography (CT)
Parameters on Measurement of Inflammatory Changes
in Paranasal Sinuses
Maciej CebulaABCDEF, Monika Danielak-NowakABF, Sandra ModlińskaABEF
Department of Radiodiagnostics and Invasive Radiology, School of Medicine in Katowice, Medical University of Silesia,
Katowice, Poland
Author’s address: Maciej Cebula, Department of Radiodiagnostics and Invasive Radiology, School of Medicine in Katowice,
Medical University of Silesia, 16 Medyków Str., 40-752 Katowice, Poland, e-mail: mcebula@sum.edu.pl
Summary
Background:
In accordance with the European guidelines on rhinosinusitis and nasal polyps (EPOS 2012), CT is
used as the main imaging modality for the assessment intensity of inflammatory lesions.
The aim of this study was to measure the differences in the assessment of inflammatory changes in
the paranasal sinuses due to different parameters of width (W) and length (L) of the CT window.
Material/Methods:
A retrospective analysis included 44 CT scans of the paranasal sinuses that were performed in
adults. All studies were characterized by the presence of inflammatory changes in at least one of
the sinuses.
Measurements of the same inflammatory lesions were performed sequentially with different CT
windows. The results were statistically analyzed.
Results:
A statistically significant difference was observed between the average measurements that were
performed with the use CT windows dedicated for the sinuses and head. A downward trend in
the measured values and a shift towards soft tissue values was observed with decreasing window
parameters.
Conclusions:
A major cause of inaccurate examinations of pathological changes in the paranasal sinuses may
be due to selection of unsuitable CT windows. Therefore, in order to avoid missing inflammatory
lesions in the paranasal sinuses, it is reasonable to use CT windows dedicated for the sinuses or
bones.
MeSH
Keywords:
Dimensional Measurement Accuracy • Sinusitis • Tomography Scanners, X-Ray Computed
PDF fi le: http://www.polradiol.com/abstract/index/idArt/901939
Received: 2016.10.13
Accepted: 2016.12.21
Published: 2017.10.20
Background
The European guidelines on rhinosinusitis and nasal pol-
yps (EPOS 2012) recommends endoscopy of the nasal
cavities and CT of the paranasal sinuses as the stand-
ard methods for diagnosing inflammation of the parana-
sal sinuses. Visualization of inflammatory changes in at
least one of the sinuses is necessary for diagnosis. This
approach applies to both children and adults. In accord-
ance with the above-mentioned guidelines, CT is used as
the main imaging modality for the assessment of intensity
of inflammatory lesions. It is also important for clinical
decision-making and planning of functional endoscopic
sinus surgery [1].
Given the crucial diagnostic role of CT, a proper technique
of this examination and precise measurements of inflam-
matory changes are extremely important.
The aim of this retrospective study was to measure differ-
ences in the assessment of inflammatory changes in the
paranasal sinuses due to different parameters of width (W)
and length (L) of the CT window. The secondary aim was to
analyze reproducibility of measurements of inflammatory
Authors’ Contribution:
A Study Design
B Data Collection
C Statistical Analysis
D Data Interpretation
E Manuscript Preparation
F Literature Search
G Funds Collection
Signature: © Pol J Radiol, 2017; 82: 567-570
DOI: 10.12659/PJR.901939
ORIGINAL ARTICLE
567

changes in paranasal sinuses performed with different CT
windows and by different raters.
Material and Methods
This retrospective study included 44 CT scans of parana-
sal sinuses performed in the year 2015 in the Department
of Radiodiagnostics and Interventional Radiology, School
of Medicine, Medical University of Silesia, Katowice with
the LightSpeed Pro 32 (GE) scanner. The studied group con-
sisted of 28 women aged 50.89±14.08 years, and 16 men
aged 51.25±17.21 years. In all patients, the presence of
inflammatory changes in at least one of the sinuses was
noted. All scans were acquired with a standard protocol for
the paranasal sinuses, in accordance with the procedures
of calibrating [2]. The examinations were performed with
0.625mm slice thickness, in the supine position, without
gantry tilt, and scanner settings were adjusted to the range
of the scanned area (250–300 mA, 120kV).
Using a dedicated station (AW General Electric), three
raters performed measurements of the same inflammatory
lesions independently and at different times. The meas-
urements were made on axial images in the following CT
windows:
• Sinuses (W: 3000, L 500).
• Bone (In 2000, L 350).
• Soft tissue (W: 400, L: 40).
• Head (W: 100 L: 35).
In order to minimize measurement errors, the values of
individual raters were averaged for the analysis of meas-
urement differences between different CT windows.
The database was created in Microsoft Excel (Microsoft),
and statistical calculations were performed with Statistica
12.5 software (StatSoft).
The Shapiro-Wilk test was used to assess normality of dis-
tribution. In order to assess the significance of differences
in the averaged measurements of changes between differ-
ent CT windows, the Kruskal-Wallis and Dunn’s tests were
used. An accurate evaluation of measurement reproduc-
ibility with the R&R analysis was not possible due to sin-
gle measurements of each of the inflammatory lesions that
were made by each rater. In order to compare the measure-
ments of different raters that were made in particular CT
windows, we used the Kruskal-Wallis test.
Results
Inflammatory changes were most commonly observed
in the maxillary sinuses (n=36). They were also present
within the frontal sinus (n=4), ethmoid sinus (n=3), and
sphenoid sinus (n=1). There was no significant correlation
between sex, age, size, and location of the inflammation
(p>0.05 for all tests).
The distribution of average measurements of inflammatory
lesions within the sinuses in each CT window is shown in
Figure 1 and Table 1.
A statistically significant difference was observed in the
average measurements between CT windows dedicated for
sinuses and head (p<0.05). Based on the average measure-
ments that were performed in each of the CT windows,
a downward trend in the measured values and a shift
towards the values assigned to soft tissues can be observed
with decreasing window parameters.
The differences in measurements made by all raters in all
CT windows are presented in Figure 2.
The differences between measurements performed by
respective raters were not statistically significant in any of
the tested windows (p>0.05).
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Sinus Bone Head
CT window level
Mean length of inflammatory changes grouped by CT window level
Soft tissue
Lenght (mm)
Kruskal-Wallis test:
p=0.0192
Figure 1. The mean and standard deviation of measurements of
inflammatory lesions (mm) in all CT windows. Based on the
Kruskal-Wallis test, the differences between the windows
are statistically significant.
Table 1. Results of Dunn test between CT windows (p value).
Sinus
R: 101.52
Bone
R: 98.000
Soft tissue
R:83.250
Head R:
71.227
Sinus – 1.000 0.555 0.032
Bone 1.000 – 1.000 0.082
Soft tissue 0.555 1.000 – 1.000
Head 0.032 0.082 1.000 –
Kruskal-Wallis test result p=0.019.
Original Article © Pol J Radi ol, 2017; 82: 567-570
568

Discussion
Acute sinusitis occurs in around 1–2% of the general pop-
ulation, and chronic sinusitis may affect even 10% of the
population in Europe [3]. Not only do these diseases affect
the quality of life of patients, but they also cause an eco-
nomic problem [4]. In the USA, sinusitis is responsible for
over two million patient visits and medical costs of over
two billion dollars annually [5]. In Poland, family doctors
issue sick leaves in 95% of patients with sinusitis, and
the average duration of such a leave is 7.5 days [6]. Given
such a large scale of the problem, all radiologists deal with
examinations of patients with sinusitis.
There is no correlation between the severity sinusitis that
can be assessed in computed tomography and the intensity
of symptoms. However, the usefulness of various imaging
methods in diagnosing sinusitis has been proven [7].
The current guidelines for the diagnosis and treatment of
sinusitis do not specify in detail what parameters should
be evaluated on CT [1]. Radiological textbooks deliberate
in great detail about the pathological changes that can
be observed within the paranasal sinuses, but very rare-
ly do they explain the measurement methodology. Since
thickening of the mucous membrane greater than 3mm is
considered to be pathological, accuracy of measurement
plays a vital role [8]. It is possible to overlook inflamma-
tory changes, while analyzing CT examination of sinuses in
the windows dedicated for soft tissues or head, instead of
measuring the width of the mucous membrane in the bone
or sinus window. We showed that the measurements are
reproducible between different raters (Figure 2) and should
correspond to the real size of the lesions. Notwithstanding
technical factors such as the quality of the workstation
screen and measurement reproducibility, the choice of CT
window parameters is the only variable that should be con-
sidered as a possible source of misjudgment.
As regards X-rays that are performed for diagnosing sinusi-
tis, they are routinely performed in the Waters projec-
tion (occipitomental, with open mouth) [5,9]. However, CT
scans in the frontal plane are much more precise and more
effective than X-ray images for the evaluation of complex
pathologies involving the opening of maxillary sinuses,
especially before potential endoscopic treatment [10].
In case of doubt as to the nature of lesions that are detected
on CT, MRI of the paranasal sinuses is frequently able to
narrow down the diagnosis. Strongly T2-weighted sequenc-
es are particularly useful, as they distinguish secretions in
the paranasal sinuses from focal lesions [10]. Determination
of the pathogen responsible for sinusitis is possible on CT,
however, MRI has better sensitivity and specificity [11].
Conclusions
Due to an increasing number of cases of paranasal sinusitis,
an accurate description of lesions in this region is impor-
tant for making the diagnosis and planning treatment.
Given a good reproducibility of measurement between
independent raters, CT minimizes the risk of operator-
dependent errors. A major cause of inaccurate evaluations
of pathological changes in the paranasal sinuses may be
due to selection of unsuitable CT windows. Therefore, in
order to avoid missing inflammatory lesions in the parana-
sal sinuses, it is reasonable to use CT windows dedicated
for the sinuses or bones.
Acknowledgements
We would like to thank Professor Jan Baron, Head of
Department of Radiodiagnostics and Invasive Radiology
of Medical University of Silesia for his constant support,
invaluable insight, and substantial guidance.
Conflict of interests
The authors do not have any disclosures or conflict of
interests that they would like to declare in relation to their
paper.
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Observer
Differences in measurement between observes grouped by CT window level
3
Lenght (mm)
Kruskal-Wallis test:
Sinus: p=0.8407
Bone: p=0.8083
Soft tissue: p=0.9666
Head: p=0.8740
Sinus
Bone
Soft tissue
Head
Figure 2. The mean and standard deviation of measurements of
inflammatory lesions (mm) in all CT windows, for each
of rater. Based on the Kruskal-Wallis test, the differences
between observers are not statistically significant.
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