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Role of high resolution computed tomography of temporal bone in preoperative evaluation of chronic suppurative otitis media

Chronic suppurative otitis media (CSOM) is a common condition seen in patients attending ENT department. Cholesteatoma is potentially serious condition as it can progressively enlarge and erode into neighbouring structures. It can be associated with lot of complications, since temporal bone is surrounded by many vital structures [meninges, brain, internal carotid artery, jugular bulb, facial nerve, etc.] and its’ gross anatomical variations makes the surgery difficult at times. The diagnosis of aural cholesteatoma is made with both otoscopic, as well as microscopic examination. Imaging procedures, such as high-resolution computed tomography (HRCT) and magnetic resonance imaging (MRI), may suggest presence of cholesteatoma within temporal bone, and may be used to complement clinical examination.


INTRODUCTION
Chronic suppurative otitis media (CSOM) is a common condition seen in patients attending ENT department. Cholesteatoma is potentially serious condition as it can progressively enlarge and erode into neighbouring structures. 1 It can be associated with lot of complications, since temporal bone is surrounded by many vital structures [meninges, brain, internal carotid artery, jugular bulb, facial nerve, etc.] and its' gross anatomical variations makes the surgery difficult at times. 2 The diagnosis of aural cholesteatoma is made with both otoscopic, as well as microscopic examination. Imaging procedures, such as high-resolution computed tomography (HRCT) and magnetic resonance imaging (MRI), may suggest presence of cholesteatoma within temporal bone, and may be used to complement clinical examination. 3 (fallopian canal) erosion, middle ear and mastoid (tegmen) dehiscence, mastoid destruction (automastoidectomy), sigmoid plate dehiscence, and bony external auditory canal erosion. 4 Prior knowledge of the extension and the complications of cholesteatoma will alert the clinician and guide in surgical approach and treatment plan. So this study was undertaken with purpose to evaluate pre-operative HRCT temporal bone and to determine its' usefulness in patients with chronic suppurative otitis media (CSOM) undergoing surgery.

METHODS
This prospective study was conducted at Sri Venkateshwara ENT institute, BMCRI, Bangalore over a period of 3 months (1 Oct 2017 to 31 Dec 2017). Total 30 patients of clinically suspected CSOM with cholestaetoma were enrolled for this study. Written informed consent from all patients was taken before enrollment in the study.

Inclusion criteria
Inclusion criteria were patients with clinically suspected atticoantral type of chronic suppurative otitis media of all age groups and either sex; patients willing to give consent.

Exclusion criteria
Exclusion criteria were patients with previous ear surgeries; patients with history of trauma to temporal bone; patients with neoplastic growth involving middle ear; patients not willing to give consent.
A detailed history with regard to ear discharge, deafness, tinnitus, earache, vertigo, headache and fever was taken, and recorded in a systematic order, with special consideration of associated symptomatology suggestive of any impending or already established complication of chronic otitis media. All patients' ears were examined under microscope before surgery. A thorough clinical evaluation of patients was performed. Hearing status was assessed by pure tone audiometry (PTA). High-resolution CT images for all patients were obtained in axial plane with thin sections (0.6 mm). Scanning commenced from the lower margin of the external auditory meatus and extended upward to the arcuate eminence of the superior semicircular canal. Coronal and sagittal reconstructions were made and images were analysed. All patients underwent surgical exploration of middle ear cleft and the type of surgery was determined by the clinical diagnosis, HRCT findings and per-operative findings. All intra-operative findings were recorded. For each of the above mentioned areas, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) were calculated for HRCT findings comparing with intraoperative findings.
Detection of facial canal erosion on HRCT had sensitivity of 80%, specificity of 100%, positive predictive value 100% and negative predictive value 96.1%. This means HRCT has limited role for catching facial canal erosion but it excludes absence of erosion very accurately. Erosion of bony EAC was seen in 16.6% cases (sensitivity and specificity of 100%). Jugular bulb dehiscence was found in 1 case (100% sensitivity and specificity).
Erosion of the lateral semicircular canal was seen in 10% cases (sensitivity 75% and specificity of 100%). None of patients had intracranial complications. In our study, findings of HRCT guided us in planning the surgical procedure in individual patient. 6 patients were planned for inside out mastoidectomy because of limited disease present in epitympanum, 21 patients for modified radical mastoidectomy because of extensive disease in middle ear cleft and 3 patients who were having limited to moderate disease in middle ear cleft were planned for cortical mastoidectomy with tympanoplasty (Table 4).

DISCUSSION
The advent of HRCT has made a significant impact on surgical management of individuals with middle ear pathologies. It confirms and expands upon otoscopic findings, resolves clinical doubts, and plays a significant role in planning surgery.
In this study, male: female ratio was 1.14:1 which is in accordance with the study by Kemppainen et al. 5 The most common presenting symptom was otorrhoea followed by hearing loss which is in accordance with a study by Yorgancilar et al. 6 In our study, CT was 100% sensitive for diagnosing cholesteatoma by HRCT images which is in correlation with the studies by Sirigiri et al and Bathla et al. 7,8 It was 100% specific for diagnosing cholesteatoma in epitympanum, mesotympanum and hypotympanum but was less specific for cholesteatoma in antrum and aditus. In our study, HRCT was found to have less sensitivity in differentiating cholesteatoma from granulations which is in consonance with other studies. [8][9][10][11] HRCT was found to be helpful in correctly picking out extent of the disease which is in agreement with studies by Donoghue et al and Mafee et al. 12,13 Early radiological sign of cholesteatoma is bone erosion. In our study, all cases (90%) reported in CT were confirmed at surgery. Hence, HRCT is 100% sensitive and specific to detect scutum erosion as per this study. This is in accordance to study by Juveria  In this study, ossicles erosion was seen in 80% of patients with CSOM with cholesteatoma ( Figure 1). This is comparable to findings by Suat Keskin et al who found it in 76.78% of their patients. 15 Incus was the commonest ossicle to be involved in 80% which is accordance to 86.1% seen by Mohammadi et al. 4 HRCT temporal bone was found to be 95.8% sensitive and 100% specific for incus. This is almost similar to findings by Tak et al who found 91% sensitivity and 100% specificity. 9 Malleus was second most common seen in 60% with 89.4% sensitivity and 90.9% specificity. Garg   In our study, 86.6% cases showed poorly cellular or sclerotic. CT scan was found to have 100% sensitivity and specificity to know the type of mastoid pneumatisation. Mastoid cortex erosion was seen in 16.6% of patients with 100% sensitivity and 100% specificity ( Figure 2). Similar results were also noted in study by Niveditha  The dural plate is best observed in the coronal plane and as a thin bone plaque covering the epitympanum and the mastoid (Figure 3). 11 In our study, HRCT temporal bone was found to be 100% sensitive and specific in identifying tegmen tympani erosion which is in consonance with studies by Tak et al and Chatterjee et al. 9,16 Sinus plate erosion was seen in 20% of cases with 85.7% sensitivity and 100% specificity (Figure 4)   In our study, facial canal erosion was observed on HRCT with moderate sensitivity (80%) but high specificity (100%) ( Figure 5). This is in consonance with other studies. 7,8,[18][19][20][21][22] The reason of low to moderate sensitivity is that, in the area of tympanic portion of the facial nerve canal, the bony floor is very thin and may not be visualized on coronal and axial CT images. 23 In our study, Erosion of the lateral semicircular canal was seen in 10% cases with sensitivity 75% ( Figure 5) which is similar to study by Rogha et al and specificity 100% which is in correlation with the study by Gul et al. 24,25 HRCT had 100% sensitivity and 100% specificity for erosion of bony EAC which isn't in correlation with study by Vanita et al who reported 0% sensitivity and 100% specificity. 26 In Our study, Jugular bulb dehiscence was present in 1 case ( Figure 6). It is an important anatomic variation which was observed that can result in catastrophic outcomes during middle ear surgery. 27 There was significant correspondence between HRCT and clinical findings, which lead to better diagnosis of probable problems before surgery, and improved the success rate of cholesteatoma surgeries.

CONCLUSION
HRCT temporal bone can provide fairly detailed information about anatomy of the middle ear cleft, the extension and the complications of cholesteatoma but misinterpretations are possible.
We believe that it is necessary to routinely evaluate most atticoantral CSOM patients with HRCT temporal bone pre-operative because HRCT is important in surgery decision process and for collecting information on special anatomic structures by which possible complications due to anatomic differences can be prevented during surgery.

ACKNOWLEDGMENTS
I am thankful to Dr Srinivas M R, Associate professor, department of radiology, BMCRI, Bangalore for his guidance. I also thank Dr Kaushal Brahmaroutu and Dr Geetha priyadarshini, post graduates, department of radiology, BMCRI, Bangalore for their valuable support and guidance.