Comparative study of findings of preoperative computerised tomography of mastoids with intraoperative findings in cases with CSOM.
Patients with chronic suppurative otitis media are very common and frequent OPD visitors in medical colleges and other hospitals across India. It is also very common in Barpeta district of Assam because of poor socio-economic status, overcrowding, poor hygiene, lack of specialist care and habit of bathing specially in ponds and rivers. Diagnosis of CSOM is mainly made by history, otoscopy and examination under microscope. The X-ray mastoid is done to know mastoid pneumatisation and the level of sinus and dural plates. Other investigations are audiometry to know the degree of hearing loss and pus for culture and sensitivity for microorganisms and choice of antibiotic therapy. Surgical treatment is required for those cases which are not improved with conservative managements, cases of CSOM associated with cholesteatoma and also those cases with extracranial or intracranial complications. Previously mastoid surgery was based on clinical examinations, otoscopy and microscopic examinations. Imaging of the temporal bone by HRCT scan and MRI scan plays an important role in diagnosing cases, selection of surgical procedures and also follow-up. Evidence of location and extension of disease and of asymptomatic complications secondary to bony erosion influence the management and selection of surgical procedures.(1) Computerised tomography provides reliable details of temporal bone anatomy, congenital malformations, levels of sinus and dural plates and pneumatisation of mastoids. HRCT can show subtle details of cholesteatoma and its extension, involvement of hidden areas, e.g. sinus tympani and facial recess.
Information regarding ossicular chain erosion, erosion of LSSC and fallopian canal can also be appreciated by HRCT. However, there are concerns that CT scan cannot differentiate between cholesteatoma and granulation tissue and it lacks guaranteed sensitivity for erosive complications!1) Such concerns have raised doubts on its value as routine investigation.
The aim of the study is to evaluate the findings of preoperative HRCT mastoids and to determine the accuracy and the usefulness of these imaging methods in patients with CSOM undergoing surgery by comparing with intraoperative findings. Intraoperative findings are considered as final findings.
MATERIALS AND METHODS
This prospective study was carried out at Department of ENT and Department of Radiology of Fakhruddin Ali Ahmed Medical College and Hospital between 2012 and 2015. A total no. of 50 patients with atticoantral variety of CSOM are included in the study. Patients with chronic comorbid condition like granulomatous disease and residual or recurrent disease after previous operation are excluded.
The diagnoses of atticoantral variety of CSOM are made from history, clinical examination, otoscopy and Examination Under Microscope (EUM). Preoperative HRCT mastoid done in all cases planned for mastoid exploration. HRCT scans are done in 16 slice Philips multiplanar machine and consists of less than 1 mm cut in axial and coronal sections. CT findings are evaluated by a single radiologist. The preoperative CT scan findings are noted and tabulated. Thereafter patients are subjected to either canal wall down or canal wall up mastoidectomy depending on the disease extension. Following areas of interest are noted in preoperative HRCT Scan.
1. Soft tissue mass.
2. Aeration of mastoid.
3. Extension of disease.
4. Sinus plate erosion.
5. Dural plate erosion.
6. Lateral semicircular canal dehiscence.
7. Facial canal dehiscence.
8. Status of incus, malleus and stapes.
9. Extension beyond mastoid.
32 out of 50 patients were males and remaining 18 were females. On examination under microscope 31 cases had attic perforation with cholesteatoma flakes, 14 cases with posterosuperior retraction pocket and 3 patients had attic retraction pocket and 2 patients were with posterosuperior retraction with central perforations.
In the literature, it is shown wide variation in the reported sensitivity and specificity of HRCT of the temporal bone. In general, our findings are similar to those reported, Table 2.
HRCT mastoid is better than conventional radiograph in preoperative assessment of cholesteatoma. It gives a detailed anatomical picture of temporal bone and possible variations of anatomy in re-do cases. In our study, we found soft tissue density in mesotympanum, attic and mastoid with a sensitivity and specificity of 100%. Our results are similar to study made by Sandeep Sreedhar et al (2) But studies by Sirigiri and Dwaraknath, (3) Mafee et al, (4) O'Reilly et al (5) and Shaffer et al (6) found sensitivity of 90 to 94% and specificity of 60 to 70%. Though Jackler et al (7) and Garber and Dort (8) found it to be less sensitive and specific.
However, HRCT is less sensitive in differentiating the type of soft tissue disease whether it is cholesteatoma or granulation tissue or fluid collection in middle ear and mastoid. Previous studies have shown it to be a poor diagnostic tool in this area.[8-11] The author will be agreeing with other authors that active squamous variety of CSOM is a condition, which is mostly diagnosed clinically.
In our study, the decision of operation was made on the basis of clinical findings mainly on pre-operative examination under microscope (EUM). The scan was used as an adjunct to provide additional information for surgical planning and to aid informed consent preoperatively. This is supported by Sethi N et al [i2] and Banerjee et ali"]
In our study, we found that HRCT has high sensitivity and specificity for detecting malleus and incus erosion as compared to stapes erosion. This is in agreement with studies by Sreedhar et al  Mafee et al,  Shaffer et al,  Jackler et al  and Garber et al  Using HRCT, Mafee et al  was able to diagnose state of ossicular erosion in 89% cases and Jackler et al  in 83% cases. In contrast, O'Reilly  could detect ossicular erosion in 50% cases. Sethi N et al  shows a sensitivity of 35% and specificity of 43% of HRCT for ossicular erosion. Our study has high sensitivity and specificity for malleus and incus erosion as compared to stapes erosion because of presence of soft tissue density around it make difficult to identify erosion. In this regard, we got the same result as Sreedhar et al.  According to Sethi N et al,  there is no clear radiological definition of what is a bony defect/dehiscence (i.e. what is minimum size detectable by HRCT). This lack of clarity may contribute to the low sensitivity and variable specificity.
Sirigiri and Dwaraknath,  O'Reilly et al,  Jackler et al  and Garber and Dort  were able to diagnose dehiscence in horizontal part of facial canal with 60% sensitivity and 90% specificity. In our study we got a sensitivity of 100% and specificity of 94%, which is comparable to the study made by Sreedhar et al  and Jackler et al.  The variable results can be explained by the small number of cases of facial canal dehiscence and statement made by Mafee et al  and Garg P et al. 
They stated that visualisation of thin bony structures like facial canal may be misleading due to error in computer reconstruction of their images. These structures may be appearing eroded due to the fact that computer averages their density with adjacent soft tissue and air. 
Sheehy et al  states that lateral semicircular canal fistula are seen in 10% cases of unsafe CSOM. Their preoperative recognition might reduce the chances of dead ear. O'Donoghue et al  and Bates et al  had detected 4 out of 5 lateral canal fistula using HRCT. In our study HRCT shows LSSC fistula in 3 cases, but intraoperatively we found fistula in one case. Therefore, we got sensitivity of 100% and specificity of 96%. Our findings are comparable to the study made by Sreedhar et al  and Sirigiri and Dwaraknath et al. 
In our study, we got sensitivity and specificity for tegmen plates erosion were 83% and 84% and sinus plate was 100% and 97% respectively. There is wide variation in sensitivity and specificity of tegmen and sinus plate erosion in literature. The difference of specificity and sensitivity can be again attributed to less numbers of cases in the study and computed tomography averages their density with adjacent soft tissue and air. 
This study shows HRCT is a good preoperative tool, which can determine disease extension in middle ear, attic and mastoid region. There is a good correlation between erosion of malleus and body of incus with intraoperative findings, although long process of incus and stapes could not reliably be detected by HRCT. The disease extension into sinus tympani and involvement of facial canal, lateral semicircular canal, tegmen plates and sinus plate are unpredictable by HRCT.
The HRCT gives a relatively rough guide to surgical anatomy of temporal bone rather than a definitive study. However, it would be mutually beneficial for both surgeon and radiologist to interpret the CT results and comparing them with the intraoperative findings. For the surgeon, a good meticulous anticipatory surgical technique with wide exposure is the key for safe surgery rather than a preoperative CT scan. HRCT can be used as an adjunct to preoperative assessment and counselling of the patients regarding surgical outcomes.
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[3.] Sirigiri RR, Dwaraknath K. Correlative study of HRCT in attico- antral disease. Inaian J Otolaryngol Head Neck Surg 2011;63(2):155-8.
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[6.] Shaffer KA, Haughton VM, Wilson CR. High resolution computed tomography of the temporal bone. Radiology 1980;134(2):409-14.
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[11.] Sheehy JL, Brackmann DE, Graham MD. Complications of cholesteatoma. A report 0n 1024 cases. In: McCabe BF, Sade J, Abranson M, eds. First international conference on cholesteatoma. Birmingham, Alabama: Aesculapius press 1977:420-9.
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Ranjan Kumar Nath (1), Biraj Kumar Das (2), Madhurjya KR Thakur (3), Mrinmoy Mayur Choudhury (4)
(1) Assistant Professor, Department of ENT, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta, Assam.
(2) Professor and HOD, Department of ENT, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta, Assam.
(3) Professor and HOD, Department of Radiodiagnosis, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta, Assam.
(4) Registrar, Department of ENT, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta, Assam.
Financial or Other, Competing Interest: None. Submission 26-08-2016, Peer Review 17-09-2016, Acceptance 26-09-2016, Published 01-10-2016.
Corresponding Author: Dr. Ranjan Kumar Nath, Assistant Professor, Department of ENT, Fakhruddin Ali Ahmed Medical College & Hospital, Barpeta, Assam-781301.
Table 1: Study Results CT Per False False Scan Operative Positive Negative Scutum erosion 40 38 2 0 Tegmen erosion 12 5 8 1 Sinus plate erosion 5 4 1 0 Lateral canal erosion 3 1 2 0 Facial Canal Dehiscence 5 2 3 0 Malleus erosion 38 34 6 2 Incus erosion 41 38 5 2 Stapes erosion 18 9 12 3 Mesotympanum involvement 25 25 0 0 Attic involvement 40 40 0 0 Mastoid involvement 31 31 0 0 Aditus widening 31 28 4 1 Sensitivity Specificity Scutum erosion 100% 85% Tegmen erosion 83% 84% Sinus plate erosion 100% 97% Lateral canal erosion 100% 96% Facial Canal Dehiscence 100% 94% Malleus erosion 100% 80% Incus erosion 95% 70% Stapes erosion 75% 77% Mesotympanum involvement 100% 100% Attic involvement 100% 100% Mastoid involvement 100% 100% Aditus widening 96% 84% Table 2: Comparison of Sensitivity and Specificity to those Reported in Literature Our Study Literature Soft tissue mass Sensitivity 100% 89%-100% Specificity 100% 100% Sinus plate erosion Sensitivity 100% 67-98% Specificity 97% 66.7-93% Ossicular erosion Sensitivity 75-100% 56-100% Specificity 70-80% 54%-89% LSCC dehiscence Sensitivity 100% 0-97% Specificity 96% 83%-96% Tegmen plate dehiscence Sensitivity 83% 6-100% Specificity 84% 74-96% Facial canal dehiscence Sensitivity 100% 0-100% Specificity 94% 86-95%
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|Title Annotation:||Original Research Article; chronic suppurative otitis media|
|Author:||Nath, Ranjan Kumar; Das, Biraj Kumar; Thakur, Madhurjya KR; Choudhury, Mrinmoy Mayur|
|Publication:||Journal of Evolution of Medical and Dental Sciences|
|Date:||Oct 3, 2016|
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