Classification of anatomical variants of maxillary sinus shapes and symmetry using computerized tomographic imaging

Full text

Classification of anatomical variants of maxillary sinus
shapes and symmetry using computerized tomographic
imaging
ABSTRACT
Background: The maxillary sinus is characterized by a considerable variation in sizes and shapes and between the right and left sides.
Due to easy access to all its walls and surfaces, imaging via computerized tomography (CT) has enhanced the quality and quantity of
information obtainable from the assessment of the maxillary sinus. Aim: To determine normal variations in shapes and symmetry of the
maxillary sinus using CT. Methods: A total of 130 subjects comprising 79 males and 51 females, between the ages of 20 and 80 years,
with normal maxillary sinus CT anatomy, who had head CT scans carried out at the Radiology Department of the Usmanu Danfodiyo
University Teaching Hospital (UDUTH) Sokoto, over a period of five years, were used for this study. Images were taken with a GE Bright Speed
Multidetector Helical CT (GE Healthcare, USA, 2005) Scanner, while films were viewed on the computer monitor. Variations in shapes of the
maxillary sinus were identified on axial images and classified based on their resemblance to known shapes of solids. Data were analyzed
using Minitab 16.0 statistical package (Minitab inc. USA). Results: Five distinct shapes of the maxillary sinus were identified. These were:
irregular in two subjects (0.77%) (right =1 and left =1); oval in three subjects (1.15%) (right =2 and left =1); quadrangular in three
subjects (1.15%) (right =2 and left =1); spherical in 61 subjects (23.46%) (right =30 and left =31); and triangular 191 (73.46%)
(right =95 and left =96). Shapes were symmetrical in 85.38% and asymmetrical in 14.62% of subjects. Conclusion: Five normal but
distinct shapes of the maxillary sinus were identified, with the predominant shape, being the triangular type, and sinuses of individuals were
frequently symmetrical in shape.
Keywords: Anatomical variations, computerized tomography, maxillary sinus, shapes, symmetry
INTRODUCTION
The maxillary sinus occupies the cavity of the maxilla; it is the
largest of the paranasal sinuses and represents a complex
anatomical structure with a significant intra and inter-
individual variation.
[1,2]
It is characterized by a considerable
variation in size and shape and between the right and left
sides.
[3,4,5,6]
The maxillary sinus reaches its matured size at the
age of 20 years,when the permanent teeth fully develops. This
development is associated with changes in the extent of
pneumatisation,
[7]
and as a result, its shapes and sizes.
[8]
Genetic and environmental factors, in addition to adjacent
cartilages and bony facial structures may influence this
developmental process,
[9,10]
as such, a detailed knowledge
of the anatomy of the sinuses is critical in performing
procedures such as functional endoscopic sinus surgery.
[9,6]
Computerized tomography (CT) has improved the quality and
quantity of available information, derivable from the
assessment of the maxillary sinus, which are not directly
visible using other radiologic procedures like the
ABDULHAMEED ALIU
1
,MA'AJI S. MOHAMMAD
2
,BELLO S.
SIRAJO
1
,AHMAD M. ABRAHIM
1
,ZAGGA D. ABDULLAHI
1
1
Department of Anatomy, College of Health Sciences Usmanu
Danfodiyo University, Sokoto,
2
Department of Radiology,
Usmanu Danfodiyo University Teaching Hospital, Sokoto, Nigeria
Address for correspondence: Dr. Aliu Abdul-Hameed, Department of
Anatomy, Faculty of Basic Medical Sciences College of Health
Sciences, Usmanu Danfodiyo University, PMB. 2346, Sokoto,
Nigeria. GSM: +234(0)8062372824.
E-mail: aliu.abdulhameed@udusok.edu.ng, anastomosis74@gmail.com
Submission: 29 July 2019 Revision: 4 November 2019
Acceptance: 17 December 2019 Published: 5 February 2020
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How to cite this article: Aliu A, Mohammad MS, Sirajo BS, Abrahim AM,
Abdullahi ZD. Classification of anatomical variants of maxillary sinus shapes and
symmetry using computerized tomographic imaging. Sub-Saharan Afr J Med
2019;6:143-7.
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DOI:
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x-ray, and this is increasingly becoming important, especially
among anthropologists and paleopathologists.
[11,12]
The shapes of the maxillary sinus were classified into
triangular, oval, curved, rectangular and square shapes,
according to Lerno,
[13]
while Szilvassy
[14]
classified the
shapes of its base into; triangular, leaf, scapular and renal
shapes. In the report of Donal et al.
[3]
, ten out of twelve
models of cadaveric specimens showed a 3-walled pyramid,
different from the classical 4-sided pyramid, whereas, the
triangular sinuses were the most common among Turkish
population.
[15]
Maryam et al.
[16]
reported 17% sinus
asymmetry, and 83% of symmetric morphology with small
differences at some levels in the sinus outline,
[16]
whereas
sinus asymmetry was 100%, among Southwestern Nigerians,
using dry adult crania.
[17]
There is paucity of data on the
classification of normal anatomical shapes of the maxillary
sinus using CT among Nigerians (Africans), majority of the
studies mentioned above, were conducted among Caucasian
subjects. Information on the shape classification and
symmetry of the maxillary sinus will be useful to
maxillofacial surgeons and otolaryngologists, who, during
certain procedures employ the use of endoscopes in the
presence of limited sinus visibility. The aim of this study was
therefore, to compliment these few studies and to establish
baseline data for values in our environment.
MATERIALS AND METHODS
This retrospective study was carried out at the Radiology
Department of the Usmanu Danfodiyo University Teaching
Hospital (UDUTH) Sokoto, with the approval of the
institutional ethical committee. This study was conducted
on head CT scans of 130 subjects (79 males and 51 females),
between the ages of 20 and 80 years, with normal maxillary
sinus CTanatomy, over a five-year period, from April 2013, to
March 2018. Images were taken with a GE Bright Speed
Multidetector Helical CT (GE Healthcare, USA) scanner,
(2005 model, 15 cm FOV, 200 mA, 120 kV, scanning at high
resolution bone algorithm at 1 second and slice thickness of
5 mm). CT scans that demonstrated maxillary sinus disease,
subject ages of less than 20 years, craniofacial abnormalities,
mid-facial traumatic injuries, and tumors were excluded. The
CT images were viewed on the computer monitor, and
screened to assess if subjects were properly positioned
prior to scanning, to ensure sinus symmetry. This was
checked on the scout image by ensuring that, both rami
and angles of the mandible were aligned, the tips of the
mastoid processes and the alveolar margin of the maxilla,
were on the same plane, while, the upper margin of the
zygomatic bone, and the inferior orbital rim, are on the
same horizontal plane. Only axial films were used because
coronal imageshad a disadvantage of being distorted by metal
artefacts from tooth filling, and the fact that sinus outline on
this plane appearbasically the same.
[18]
Variations in shapes of
the maxillary sinus were identified at mid-sinus planes
corresponding to the lower border of the zygomatic arch,
roots of the pterygoid plates and floor of the sphenoid sinus.
These shapes were subsequently classified on the basis of
their resemblances to shapes of known solids into Irregular,
Oval, Quadrangular, Spherical, and Triangular.
[13]
Symmetry of
the maxillary sinus was resolved on the basis of the similarity
in shapes between the right and left sinuses. Data was
manually sorted out, tabulated, then, entered into
computer using Microsoft Excel, data analysis was done
using Minitab 16.0 statistical package (Minitab inc. USA),
while comparison was done using chi square tests [Figs 1–6].
RESULTS
The variations in normal anatomical shapes of the maxillary
sinus on axial CT slides seen in this study were five distinct
Figure 1: Axial CT of a 27 year old female showing the spherical shape
(arrows) of the maxillary sinus. R =Right side, L =Left side, A =Anterior,
P=Posterior.
Figure 2: Axial CT section of a 38 years old female showing asymmetry of
the maxillary sinus. The right side is oval (long arrow) while the left side is
quadrangular (short arrow). R =Right side, L =Left side, A =Anterior,
P=Posterior.
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144 Sub-Saharan African Journal of Medicine | Volume 6 | Issue 3 | July-September 2019
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shapes. These were; Irregular in 2 subjects (0.77%); (right =1
and left =1), Oval in 3 subjects (1.15%); (right =2 and
left =1), Quadrangular in 3 subjects, (1.15%); (right =2
and left =1), Spherical in 61 subjects (23.46%); (right =30
and left =31), and Triangular 191, (73.46%); (right =95 and
left =96). There was no significant relationship between
males and females, in the number of subjects who had a
particular sinus shape [Table 1, Table 2]. The predominant
Figure 4: Axial CT of a 65 years old male with an irregular type (short
arrow) of sinus shape on the right maxillary sinus and triangular type (long
arrow) on the left. R =Right side, L =Left side, A =Anterior, P =Posterior.
Figure 3: Axial CT of 44 years old male showing the quadrangular type
(arrows) of maxillary sinus shape. R =Right side, L =Left side,
A=Anterior, P=Posterior.
Figure 5: Axial CT of a 42 year old female showing a triangular shaped
maxillary sinus (arrows). R =Right side, L =Left side, A =Anterior,
P=Posterior.
Figure 6: A pie chart showing the frequency of the observed shapes of the maxillary sinus.
Table 1: The relationship between observed anatomical shapes
of the maxillary sinus and sinus location with respect to right or
left sides
Shapes Proportions Total
Right Left
Irregular 1 (0.77%) 1 (0.77%) 2 (0.77%)
Oval 2 (1.54%) 1 (0.77%) 3 (1.15%)
Quadrangular 2 (1.54%) 1 (0.77%) 3 (1.15%)
Spherical 30 (23.08%) 31 (23.85%) 61 (23.46%)
Triangular 95 (73.08%) 96 (73.85%) 191 (73.46%)
a
χ
2
=0.585,df =3. Data areexpressed as number (%) of the classesof sinus shapes betweenthe
right and left sides. Therewas no statistically significant relationship between sinus shapes and
sinus location in terms of rightor left (P>0.05).
a
The triangular sinus shape was predominant.
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shape of the maxillary sinus in the studied population was
triangular.
With respect to the incidence of symmetry and asymmetry
between the right and the left sides, in the shapes of
subjects’maxillary sinus, this study found that, 111
subjects (85.38%), accounting for 64 males, (49.23%) and
47 females, (36.15%), had symmetrical sinus shapes, while
sinus asymmetry was found in 19 subjects (14.62%), in which
15 (11.54%) were males and 4 (3.08%) were females. There
was a statistically significant relationship between sinus
shapes and gender, P<0.05 [Table 2].
DISCUSSION
The several findings regarding the complex nature of
maxillary sinus anatomy emanating from different studies
is a reflection of the influential effects of human variability
and the different degrees of pneumatisation.
[19,20]
In this
study, five distinct shapes of normal human maxillary sinus
were observed on axial CT scans with the predominant
shape being triangular. This favorably agrees with the
report of Gunay et al.
[15]
, although, in another report,
shape classification of the maxillary sinus was
unsuccessful
[21]
, possibly because, they aimed at
classifying only the medial wall of the sinus using dried
crania. The reasons for these differences are unknown,
however, these may be due to the influence of
environmental, genetic, ethnic or racial factors.Several
other authors have classified the shapes of the maxillary
sinus into other natural shapes like the leaf, scapular, renal
and solids of evolution, for comparison and
resemblances.
[13,14,22]
In this study, the occurrence of shape symmetry or
asymmetry, between the right and left sides, showed
that, the maxillary sinus among Northwestern Nigerians
were frequently symmetrical (85.38%). This result is in
agreement with the findings of Maryam.
[16]
However,
Amusa et al.
[17]
reported sinus asymmetry in 100% of the
24 dried human skulls from Southwestern Nigeria. These
differences could also possibly have resulted from the
differences in the methods that were applied,
environmental, ethnic, or genetic factors.
Clinically, this information is valuable, and could be applied
in preoperative assessment to determine a safer and easy
access to the pterygopalatine fossa through the maxillary
sinus.
CONCLUSION
CT examination of the maxillary sinus is valuable, and
supportive in investigating variations of the maxillary sinus
for a wide range of surgical, clinical and anthropological
significance. From this study, five normal, but distinct
shapes of the maxillary sinus were identified, the triangular
type was predominant, while these sinus shapes were
frequently symmetrical between the right and left sides.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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a
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