Introduction:
Sinusitis is the most common condition in
routine medical and ENT practice.  Sinusitis
significantly impacts quality of life, worse than chronic debilitating diseases
like diabetes and congestive heart failure 1. However all patients of
sinusitis/ PNS disease does not require to undergo surgical intervention like FESS.

            Plain
radiography is the most common imaging modality used for evaluating sinonasal
pathology. CT scan is considered gold standard for the imaging of  PNS disease 
despite the ionizing radiation exposure involved in the CT scan 2, 3.

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The advent of FESS has led
to greater demand for coronal CT scan of the paranasal sinuses because of the
precise anatomical details elicited by CT scan. Role of MRI was evaluated in
various previous studies and concluded that it has the potential to replace
plain radiograph and CT scan as a screening modality 4, 5. MRI has shown promising
results in detecting and differentiating inflammatory and neoplastic pathologies.
MRI is also superior to CT scan in detecting intracranial/ intraorbital complications
of sinonasal disease 2, 6. MRI
of the paranasal sinuses is capable in differentiating mucosal thickening from
sinus secretions 4. Hence, there is need to evaluate the efficacy of MRI as
pre FESS work up as an alternative to CT scan.

 

 

Aims
and Objectives:

To compare the sensitivity and specificity of
MRI with CT scan in Pre FESS evaluation for mucosal sinonasal pathology with
the aim of replacing CT scan as the screening modality.

 

Material
and methods:

This prospective comparative study was
carried out in 100 consecutive patients who were referred for CT scan from
department of ENT for evaluation of PNS disease during a period of two years from
December 2012 to December 2014 in setting of a tertiary care hospital. Written
clearance was obtained from institutional ethical committee. Informed consent
was taken from all the patients for both CT scan and MRI . MRI was done for all
the volunteer patients on the same day. MRI was done using both T1 and T2 weighted
sequences (As mentioned in Table 1). There was no patient having known contraindication
to MRI such as electromagnetic /ferromagnetic implant/ cochlear implant, claustrophobia,
first trimester pregnancy.

All the patients underwent CT
scan on 16 slice CT scanner (Philips brilliance 16 slice helical Multidetector CT)
equipment. Scans were performed in axial plane for all the patients with the
plane of acquisition parallel to the hard palate and coronal reformatting was
done. Images with slice thickness of 0.8 mm were acquired from the anterior
walls of the frontal sinuses to the posterior wall of the sphenoid sinus.  The exposure settings used were 120 to 130
kVp and 80 to 100 mAs with Automatic exposure control (AEC). Analysis of
anatomical variants was performed using both PNS window and soft tissue windows
on CT viewer.

Subsequently, MRI was done
on the same day using 1.5 Tesla (1.5T) MRI Machine (Siemens 1.5T Somatom). Patient
were placed head first supine position with head and neck coil. Laser beam
localizer was placed over the Glabella. Three plane localizer was taken in the
beginning to plan the sequences. T2 TSE and T1 FLASH sequences with 3 mm slice
width and zero interslice gap were performed with a total acquisition time of 3
minutes and 30 seconds. (Tab 1)

The sensitivity, specificity were calculated for each of the
objective parameter as in the reporting checklist for  pre FESS evaluation, considering the CT scan
findings as the gold standard.

 

Observations and Results:

The
study group comprised of individuals between 7 to 77 years of age. All these cases
were evaluated by NCCT and MRI. The study group consists of 68 male and 32
female Fig-1

Bony anatomic variations of
the paranasal sinuses were evaluated in addition to sinonasal mucosal pathology.
Bony variations mainly included deviated nasal septum (DNS), pneumatization of Crista
Galli, type of Frontal cells, Agger Nasi cell, Haller`s cells, Posterior
ethmoid air cells, type of Ethmoid roof, type of optic nerve, pressure
deossification of ethmoid air cells and pathology of middle turbinate, lamina
papyracea, ethmoid bulla, hiatus semilunaris, uncinate process, sinus
lateralis, inferior turbinate, spheno-ethmoidal recess. The results are summarized
in Table- 2.

DNS
was reported in 56 patients on CT scan. All of these cases were identified
accurately by MRI. In addition bony spur was also identified accurately by MRI.
Hence sensitivity of 100% (CI: 0.88 to 1) and specificity of 100 % (CI:  0.85 to 1) was detected.

 

Four cases of pneumatised Crista Galli were detected on CT scan whereas
MRI failed to detect pneumatization in one of these patients which corresponds
to sensitivity of 50% (CI: 0.0945 to 0.9055) and specificity of 100% (CI:
0.9259 to 1).

Frontal sinus pathology (mostly
frontal sinusitis) was reported in 48 out of the 100 patients who underwent CT
scan. MRI detected 60 cases (12 false positive) with a sensitivity of 100% (CI:
0.862 to 1.0) and specificity of 76.9 % (CI: 0.5795 to 0.8897) Fig-2.

In addition MRI were able to
detect the type of frontal cell correctly in 32 cases and failed to detect in 4
cases, hence sensitivity of 89% (CI:  
0.672 to 0.969) and specificity of 100 %. (CI: 0.8928 to 1) Fig -3.

Agger
nasi pathology was present in 10 patients on CT scan. MRI detected 4 of these
cases and two false positive case with a sensitivity of 20% (CI: 0.01053
to   0.7012) and specificity of 97.8 %
(CI: 0.9213 to 1).

 

74
% of the patients had type II ethmoid roof, whereas 24% cases had type I
ethmoid roof and 2% have type III ethmoid roof. MRI detected all these
variations with a sensitivity of 100% (CI: 0.90 to 1) and specificity of 100%
(CI: 0.77 to 1).

 

52 of the 100 patients were
detected to have maxillary sinus pathology on CT scan. MRI detected 54 of these
cases (02 false positive) with sensitivity of 100% (CI: 0.8713 to 1) and specificity
of 95.83% (CI:   0.7976 to 0.9926) Fig-4.

16 of the 100 patients had uncinate
process pathology on CT scan, MRI detected 6 of these cases. Sensitivity was 37.5%
(CI: 0.1368 to 0.6943) and specificity was reported 100% (CI: 0.9162 to 1). 38
of the 100 patients were detected to have middle turbinate pathology on CT
scan. MRI detected 36 of these cases with sensitivity of 94.7 % (CI: 0.7536 to
0.9906), and specificity of 100% (CI: 
0.9143 to 1).

14 of the 100 patients were
detected to have ethmoid bulla pathology on CT scan, MRI detected 12 of these
cases correctly with sensitivity of 85.7 % (CI: 0.4869 to 0.9743) and specificity
of 100% (CI: 0.918 to 1).

34 of the 100 patients were
detected to have hiatus semilunaris pathology on CT scan. MRI detected 30 of
these cases with sensitivity of 88.24% (CI: 0.6566 to 0.9671), and specificity
of 100% (CI: 0.8957 to 1). 10 of the 100 patients were detected to have lamina
papyracea pathology on CT scan. MRI detected none of these cases. 8 of the 100
patients were detected to have Haller`s cells pathology on CT scan. MRI
detected 4 of these cases with sensitivity of 50% (CI: 0.15 to 0.85) and
specificity of 100% (CI:  0.9229 to 1) Fig
-5.

22 of the 100 patients were
detected to have sinus lateralis pathology on CT scan, MRI detected 10 of these
cases (02 false positive) with sensitivity of 36.36% (CI: 0.1236 to 0.6838) and
specificity of 97.44% (CI: 0.8682 to 0.9955).

16 of the 100 patients were
detected to have inferior turbinate pathology on CT scan. MRI detected all
these cases with sensitivity of 100% (CI: 0.6756 to 1) and specificity of 100%
(CI: 0.9162 to 1).

2
of the 100 patients were detected to have posterior ethmoid air cell pathology
on CT scan and MRI failed to detect these cases. 10 of the 100 patients were
detected to have spheno-ethmoidal recess pathology on CT scan. MRI detected
none of these cases.

 

12
of the 100 patients were detected to have sphenoid sinus pathology on CT scan.
MRI detected 10 of these cases with sensitivity of 83.33% (CI: 0.4365 to
0.9699) and specificity of 100% (CI: 0.9197 to 1).

 

10 of the 100 patients were
detected to have pressure deossification on CT scan, MRI detected 4 of these
cases with sensitivity of 40% (CI: 0.1176 to 0.7693) and specificity of 100%
(CI: 0.9213 to 1) Fig-6.

In certain parameters, the
calculations are yielding sensitivity and specificity of 100% which is
attributable to low sample size.

 

DISCUSSION

Our prospective study which was conducted at
tertiary care hospital, evaluated the role of CT and MR for sinonasal mucosal disease.
CT is the present gold standard for evaluation of PNS disease and pre FESS workup
in sinonasal disease 7. Surgical intervention/ FESS is performed only for a
small fraction of the patients undergoing CT scan.  

Antero lateral wall structures collectively
make the drainage pathway for frontal, maxillary sinuses and anterior ethmoid
air cells and are called OMU (Osteo Meatal Unit). The main components of OMU
are hiatus semilunaris, maxillary infundibulum, maxillary ostia, ethmoid
infundibulum and frontal recess.

 

The patterned reporting
checklist based protocol for pre FESS evaluation provides road map for surgeon
allowing tailored approach on individual basis. It is very important to visualize the anatomic
details and their relationship with other structures in order to avoid surgical
catastrophe. In our study identification of bony landmarks along with its variation
specially type of ethmoid roof, uncinate process variations, pathologies of hiatus
semilunaris, lamina papyracea, sinus lateralis, posterior ethmoid air cell and pressure
deossification on MRI were correlating with CT scan  to a great extent. It is corresponding with
the findings of Mafee et al (7) and Zinreich (10). Air and bone both show low signal on MRI and hence appear as dark
areas on MRI images. Therefore it is very difficult to detect bony variation on
MRI imaging unless  adjacent structure have mucosal thickening or
secretions. The kind and the extent of the mucosal disease was evaluated with almost
equal sensitivity and specificity in both the modalities.

Though CT is superior for
evaluation of the bony details of the paranasal sinuses, the inherently
superior soft-tissue resolution and multiplanar capabilities makes MRI better
for characterisation of soft-tissue lesion and extension of disease processes
beyond the paranasal sinuses.

CT scan involves
ionizing radiation exposure especially to the thyroid and lens of the eyes which
is of concern in young patients and avoidable by performing MRI 4.

Routine MRI
sequences for PNS involving T1 and T2 weighted images involve longer scan
duration (about 10-15 minutes) and it was considered to be a limiting factor as
a routine investigation for PNS. However with the advent of faster MRI
sequences, it is possible to reduce the scan duration. With the use of faster
MRI sequences (T1 FLASH and T2 sequences with 3mm slice width and zero interslice
gap) utilized in our study, the total scan duration was reduced to 5 minutes
and 30 seconds.

Our study
suffers limitation of small sample size, yielding erroneous specificity at few
parameters.  Further large scale studies
are recommended to establish concrete values.

CONCLUSION

CT scan is presently the modality
of choice for evaluation of PNS pathology for both diagnostic evaluation and surgical
planning. Radiograph PNS Water`s view which is presently the most commonly
requisitioned imaging modality for PNS disease has very poor sensitivity and
specificity and is mostly inconclusive.  Patients therefore eventually have to undergo
CT scan of the PNS in the absence of alternative options of cross sectional
imaging. Whereas only a small fraction of patients undergoing CT scan need
surgery. MRI with the development of fast imaging sequences (3 mm slice width
with zero distance factor T1 FLASH and T2 TSE sequences) provide excellent results
in detection of mucosal pathologies.  

MRI offers a radiation free
alternative imaging tool for screening and diagnosis of PNS pathology especially
in cases where diagnosis is the principal concern and radiation hazard is to be
avoided.

            Although
MRI has relatively poor sensitivity and specificity in delineation of bony
landmarks and anatomical variants, it provides excellent contrast resolution
for mucosal pathologies and offers a radiation free alternative for pre FESS
evaluation. Also it is of significance in public institutions where cost of MRI
investigation is not a factor for the patient.

 

CONFLICTS
OF INTEREST

 All
authors have none to declare.