The Journal of Laryngology and Otology December 1991, Vol. 105, pp. 990-994
The value of CT scanning in chronic suppurative otitis media B. J.
O'REILLY*,
E. B.
CHEVRETTON*,
I. WYLiEf, C.
THAKKAR-J-,
P. BUTLERI", N.
SATHANATHANI-,
G. A. MORRISON*, G. S. KENYON* (London)
Abstract High definition CT has been advocated for the evaluation of chronic suppurative otitis media (CSOM) either generally or in selected cases. It is said to be capable of producing the fine detail needed to detect lateral canal fistulae, exposed dura and facial canal dehiscences, and to demonstrate the ossicular chain. At present there is no agreement on either the indications for CT scanning in CSOM or the most appropriate scanning plane. To determine the value of high definition CT in CSOM and to decide a unit policy for its application, 36 cases of CSOM underwent pre-operative CT scanning and their scans were compared with the operative findings. Our results show CT to be highly sensitive to the presence of soft tissue disease and bone erosion, moderately sensitive to the presence of lateral canal fistulae but less sensitive to the presence of small areas of exposed dura, ossicular continuity and facial canal dehiscence. Axial scans were better able to demonstrate the lateral canal but otherwise coronal scans were superior; ideally patients should be scanned in both planes. The principle value of CT in CSOM is its ability to demonstrate disease which is not clinically apparent.
3. Has the dura been exposed? 4. Is the ossicular chain disrupted? 5. Is there a lateral canal fistula? 6. Is the facial canal dehiscent?
Introduction High definition CT has now largely replaced conventional polytomography for the imaging of the temporal bone and is capable of producing bony detail of outstanding quality. Potentially the most extensive use of temporal bone CT is in the evaluation of patients with chronic suppurative otitis media, however the indications for its use in this field are unclear. It has been variously argued that CT should be used to evaluate all suspected cholesteatomas (Johnson etal., 1983; Mafee etal., 1983) or in selected cases, such as closed mastoid cavities (O'Donoghue et al., 1987) and congenital cholesteatomas (Phelps and Wright, 1990). High definition CT has been proposed as a means of diagnosing cholesteatoma (Mafee etal., 1983; Jackler etal., 1984), demonstrating the ossicular chain (Swartz, 1983), and detecting labyrinthine fistulae (Bates etal., 1988; Johnson etal., 1983) and bony defects in the facial canal (Johnson etal., 1983; Mafee etal., 1983). To determine a policy on the use of CT scanning in cases of CSOM, a series of 36 cases were submitted for scanning prior to mastoid surgery. The films were then submitted to a panel of three neuroradiologists (I.W., C.T., P.B.) who were asked to provide a collective answer to each of the following questions without the benefit of the operative findings:
Their answers were then compared with the operative findings. Cases in which the operative notes were inadequate were discarded as was a case in which a proposed mastoidectomy was cancelled in favour of an aural polypectomy when the CT demonstrated no mastoid disease.
Methods CT scanning was performed on a Philips Tomoscan 350 Scanner using High Resolution mode and Bone Algorithm, viewed on wide window settings. Preferably, coronal scans are performed first before the patient becomes fatigued. 1.5 mm sections were used with 1.5 mm increments. Occasionally 1 mm increments were used, for example through the ossicular chain to minimize partial volume effects. Coronal scans run from the anterior cochlea to the descending portion of the facial canal. By a combination of head extension and gantry tilt we try to scan in the coronal plane. Axial sections are performed with orbito-meatal line parallel to the table top. 1.5 mm sections are used with 1.5 mm intervals. Sections are required from the floor of the external meatus to the first genu of the facial canal but in practice, four additional sections are taken below
1. Is there a soft tissue mass in the middle ear or mastoid? 2. Is there bone erosion?
Departments of Otolaryngology* and Neuroradiologyt, The Royal London Hospital, Whitechapel, London El 1RB. Accepted for publication: 29 August 1991. 990
991
CT SCANNING IN CHRONIC SUPPURATIVE OTITIS MEDIA
CT in detecting exposed dura in CSOM. O'Donoghue et al. (1987) detected one of their two cases of tegmen erosion on CT but did not report their incidence of false positives. Jackler etal. (1984) detected all four of their cases but also had eight false positives. Mafee etal. (1988a) missed three out of six cases but had no false positives. Using mainly axial scans, we could detect only five out of 11 cases and had six false positives. It is not possible to reliably demonstrate a dehiscence in the tegmen on axial cuts alone but even using coronal cuts we found the effect of partial volume averaging could give the false impression of a defect (Fig. 1).
FIG. 1 Coronal scan demonstrating an apparent breech in the integrity of the tegmen tympani (arrowed).
and above these limits to allow for adequate reformation in the sagittal plane should that be required. The scans were interpreted retrospectively and without clinical information by three Consultant Neuroradiologists. (I.G.W., C.H.T., P.B.). A consensus of opinion was obtained if there was any disagreement.
FIG. 2a Axial scan depicting an intact lateral semi-circular canal (arrowed).
Discussion
Cholesteatoma Our scans were able to detect soft tissue masses in the mastoid and middle ear in every case where it was present and this reflects the experience of most other authors (Mafee etal., 1986; O'Donoghue etal., 1987; Shaffer etal., 1980). However, we could not distinguish cholesteatoma from other soft tissue disease and this again is the experience of most authors (Jackler etal., 1984; Phelps and Wright, 1990), although Mafee etal. (1983) believed it was possible to identify cholesteatoma by its characteristically low attenuation value and Johnson etal. (1983) found that the presence of a well-defined edge to the mass was a sure indication of cholesteatoma. Cholesteatoma characteristically causes bone erosion and when this feature was present in association with a soft tissue mass on CT both Jackler. etal. (1984) and O'Donoghue etal. (1987) found cholesteatoma to be present in 80 per cent of cases explored. Using the same criteria, we detected 23 out of 29 cases of cholesteatoma (79 per cent), a false negative rate of 21 per cent. In most instances cholesteatoma is visible otoscopically but CT could be valuable in diagnosing cholesteatoma behind an intact tympanic membrane (as in congenital cholesteatoma or after combined approach tympanoplasty) and residual disease in the sinus tympani and the facial recess.
FIG. 2b Axial scan depicting an eroded lateral semi-circular canal (arrowed).
Exposed dura There have been few assessments of the accuracy of
Coronal scan depicting an eroded lateral semi-circular canal (arrowed). The patient had undergone previous mastoid surgery.
FIG. 2C
992
B. J. O'REILLY ET AL.
Lateral canal fistulae Lateral canal fistulae occur in about 10 per cent of cases of CSOM [Sheehy et al., 1977) and their pre-operative recognition may reduce the chances of a 'dead ear' (O'Donoghue etal., 1987; Bates etal., 1988), favouring coronal scans, detected four out of five lateral canal fistulae but do not reveal their false positive rate. Jackler et al. (1984) also used coronal scans but had a high incidence of false positives and suggested that the axial scan was better suited for this investigation. Phelps and Wright (1990) advocated scanning in both planes when vestibular symptoms were present. In our own series, we detected six out of eight lateral canal fistulae and had a false positive rate of 3.5 per cent. The axial scans were the more satisfactory because they depicted the canal in its entirety (Fig. 2a, b) and were less likely to produce false positives, but useful information could also be gained from coronal scans (Fig. 2c) and we believe both planes should be employed.
FIG. 3a and b Coronal and axial scans showing erosion of the second portion of the facial canal in the anterior part of its course (arrowed).
Ossicular disruption It is relatively easy to visualize the bodies of the malleus and the incus on CT but this has little clinical value unless the integrity of the whole ossicular chain can be demonstrated. The long processes of the malleus and incus, and the stapes superstructure are the components most at risk in CSOM but are also the most difficult to demonstrate on CT. Mafee etal. (1988b) were able to define the state of the ossicular chain in 89 per cent of cases scanned and O'Donoghue etal. (1987) reported that they had detected erosion of the long process of the incus in 67 per cent and absence of the stapes superstructure in 86 per cent of cases scanned. On the other hand, Jackler et al. (1984) were able to predict the state of the ossicular chain in only seven per cent of their cases and Phelps and Wright (1990) doubted that CT could demonstrate the ossicular chain reliably because of the combination of partial volume averaging and tissue silhouetting. Our own series shows an ability to correctly predict an intact ossicular chain in only 50 per cent of cases, the error in all cases being a failure to identify the long process of the incus or the stapes superstructure.
Facial canal dehiscences Demonstrating both the second and third parts of the facial canal requires two-plane scanning (Jackler et al., 1984; Mafee etal., 1988) so we concentrated on the second part where most dehiscences are found. This was generally clearly shown on our coronal scans (Fig. 3a) and on some axial scans (Fig. 3b) but in many cases soft tissue overlying the canal caused a loss of contrast gradient obscuring a small dehiscence, a problem also encountered by Jackler etal. (1984) and Mafee etal. (1988). Our detection rate for facial canal dehiscence (four out of nine cases) is poor but comparable to those of Freng et al. (1988) (one in four cases) and Mafee et al. (1988) (none in six cases). O'Donoghue etal. (1987) appear to have detected all (nine) of their facial canal dehiscences but also had six false positives. The majority of our patients had no facial weakness and it is possible that an erosion causing a facial palsy would be more readily apparent on CT. Conclusions Our results show CT to be extremely sensitive to the presence of soft tissue disease and bone erosion and
FIG. 4 External auditory canal obstructed by an aural polyp (arrowed). No disease deep to the tympanic membrane.
993
CT SCANNING IN CHRONIC SUPPURATIVE OTITIS MEDIA
RESULTS Feature ME mass Mastoid mass Bone erosion Dura exposure Ossicular disruption Canal fistula VII n. fistula
ME mass Mastoid mass Bone erosion Dura exposure Ossicular disruption Lateral canal fistula VII n. fistula
Present at operation
OnCT
False negative rate
False positive rate
Agreement
31 30 20 11 26 8 9
31 29 18 5 19 6 4
0% 3% 10% 55% 27% 25% 56%
40% 33% 62.5% 16% 30% 3.5% 15%
94.5% 92% 67% 72% 72% 92% 75%
Sensitivity 100% 97% 90% 46% 73% 75% 44%
Specificity 60% 67% 38% 84% 70% 96% 85%
Positive predictive value 94% 94% 64% — 86% —
Negative predictive value 99% 80% 75% — 50% —
The positive predictive value is the probability of the condition being present given a positive scan. The negative predictive value is the probability of the condition being absent given a negative scan. Figures are not given where the data is too sparse to give a reasonable confidence interval.
acceptably so to the presence of lateral canal fistulae, however we were disappointed by the lack of sensitivity to the more subtle features of dura exposure, ossicular disruption and facial canal dehiscences. Possible reasons for this include: (a) Our method of statistical analysis. A number of authors use the rate of agreement between the scans and the operative findings as a measure of success. This can be very misleading; using this yardstick we had a 75 per cent success rate in assessing the facial canal yet we missed five out of nine dehiscences! Most papers do not give all their false positive and negative rates and we found none which gave predictive values for their scans although this is the best measure of their worth. (b) The small number of lateral canal fistulae and facial dehiscences in all papers make comparisons difficult. (c) For the purposes of the study, our radiologists were given no clinical information. (d) For reasons of cost and pressure on scanning facilities, most patients underwent only axial scans and the number of sections had to be limited, but this may be closer to the normal clinical situation than some other studies in which two plane scanning and multiple sections were routinely employed. (e) There was undoubtedly a learning curve for both the radiologists and radiographers involved in the study and it is likely that our results would have improved if the study had continued. Despite these reservations we feel that some conclusions can be drawn from our study: 1. Ideally all cases should be scanned in both axial and coronal planes but, when considerations of time or cost prohibit this, coronal scans are preferable to axial scans, except when a lateral canal fistula is suspected. 2. CT is so sensitive to the presence of soft tissue disease within the middle ear and mastoid that a negative scan effectively excludes the possibility of CSOM. 3. Fistulae in the lateral semicircular canal can be
demonstrated with an acceptable degree of accuracy using a combination of axial and coronal scans. 4. Despite our poor results to date, we believe it is possible to detect most acquired facial canal dehiscences. 5. We do not believe it is possible to demonstrate small defects in the tegmen tympani or the ossicular chain in its entirety. 6. Given the limitations of the medium, it is hard to justify scanning all patients with CSOM prior to surgery. Instead it may be better to select those patients in whom the diagnosis or the extent of the disease is in doubt: eg closed cavities and congenital cholesteatomas, cases where the drum cannot be examined due to atresia or obstruction (Fig. 4), and those with neurpotological complications. 7. These scans and their reports should be subject to regular clinical audit. References Bates, G. J., O'Donoghue, G. M., Anslow, P., Houlding.T. (1988) Can CT Detect Labyrinthine Fistulae Preoperatively? Ada Otolaryngologica, 106: 40-45. Freng, A., Larsen, P. L., Nordhus, T. (1988) Cholesteatomas of the Temporal Bone. Preoperative CT Versus Peroperative Findings. Scandinavian Audiology Supplement, 30: 185—188. Jackler, K. R., Dillon, W. P., Schindler, R. A. (1984) Computed Tomography in Suppurative Ear Disease: A Correlation of Surgical and Radiographic Findings. Laryngoscope, 94, 746-752. Johnson, D. W., Voorhees, R. L., Lufkin, R. B., Hanafee, W., Canalis, R. (1983) Cholesteatomas of the Temporal Bone: Role of Computed Tomography. Radiology, 148: 733-737. Mafee, F. M., Kumar, A., Yannias, A., Valvassori, G. E., Applebaum, E. L. (1983) Computed Tomography of the Middle Ear in the Evaluation of Cholesteatomas and other Soft-Tissue Masses: Comparison with Pluridirectional Tomograpahy. Radiology, 148: 465-472. Mafee, M. F., Aimi, K., Kahen, H. L., Valvassori, G. E., Capek, V. (1986) Chronic Otomastoiditis: A Conceptual Understanding of CT Findings. Radiology, 160: 193-200. Mafee, M. F., Levin, B. C., Applebaum, E. L., Campos, M., James, C. F. (1988) Cholesteatoma of the Middle Ear and Mastoid: A Comparison of the CT Scan and Operative Findings. Otolaryngologic Clinics of North America, 21(2): 265-293. O'Donoghue, G. M. (1987) Imaging the Temporal Bone (editorial). Clinical Otolaryngology, 12: 157-160.
994 O'Donoghue, G. M., Bates, G. J., Anslow, P., Rothera, M. P. (1987) The Predictive Value of High Resolution Computerized Tomography in Chronic Suppurative Ear Disease. Clinical Otolaryngology, 12: 89-96. Phelps, P. D., Wright, A. (1990) Imaging Cholesteatoma. Clinical Radiology, 41: 156-162. Shaffer, K. A., Haughton, V. M., Wilson, C. R. (1980). High Resolution Computed Tomography of the Temporal Bone. Radiology, 134: 409-414. Sheehy, J. L., Brackmann, D. E., Graham, M. D. (1977) Complications of Cholesteatoma: a Report on 1024 Cases. In First Inter-
B. J. O'REILLY ET AL.
national Conference on Cholesteatoma (McCabe, B. F., Sade, J., Abramson, M., eds.), Aesculapius Press, Birmingham, Alabama, 420-429. Swartz, J. D. (1983) High Resolution Computed Tomography of the Middle Ear and Mastoid. Radiology, 148: 449-454. Address for correspondence: Sqn. Ldr. B. J. O'Reilly, F.R.C.S.Ed., E.N.T. Department, Princess Mary's Hospital, Halton, Aylesbury, Bucks HP22 5PS.
Key words: C.T. scanning; Otitis media, suppurative; Cholesteatoma.
The value of CT scanning in chronic suppurative otitis media B. J.
O'REILLY*,
E. B.
CHEVRETTON*,
I. WYLiEf, C.
THAKKAR-J-,
P. BUTLERI", N.
SATHANATHANI-,
G. A. MORRISON*, G. S. KENYON* (London)
Abstract High definition CT has been advocated for the evaluation of chronic suppurative otitis media (CSOM) either generally or in selected cases. It is said to be capable of producing the fine detail needed to detect lateral canal fistulae, exposed dura and facial canal dehiscences, and to demonstrate the ossicular chain. At present there is no agreement on either the indications for CT scanning in CSOM or the most appropriate scanning plane. To determine the value of high definition CT in CSOM and to decide a unit policy for its application, 36 cases of CSOM underwent pre-operative CT scanning and their scans were compared with the operative findings. Our results show CT to be highly sensitive to the presence of soft tissue disease and bone erosion, moderately sensitive to the presence of lateral canal fistulae but less sensitive to the presence of small areas of exposed dura, ossicular continuity and facial canal dehiscence. Axial scans were better able to demonstrate the lateral canal but otherwise coronal scans were superior; ideally patients should be scanned in both planes. The principle value of CT in CSOM is its ability to demonstrate disease which is not clinically apparent.
3. Has the dura been exposed? 4. Is the ossicular chain disrupted? 5. Is there a lateral canal fistula? 6. Is the facial canal dehiscent?
Introduction High definition CT has now largely replaced conventional polytomography for the imaging of the temporal bone and is capable of producing bony detail of outstanding quality. Potentially the most extensive use of temporal bone CT is in the evaluation of patients with chronic suppurative otitis media, however the indications for its use in this field are unclear. It has been variously argued that CT should be used to evaluate all suspected cholesteatomas (Johnson etal., 1983; Mafee etal., 1983) or in selected cases, such as closed mastoid cavities (O'Donoghue et al., 1987) and congenital cholesteatomas (Phelps and Wright, 1990). High definition CT has been proposed as a means of diagnosing cholesteatoma (Mafee etal., 1983; Jackler etal., 1984), demonstrating the ossicular chain (Swartz, 1983), and detecting labyrinthine fistulae (Bates etal., 1988; Johnson etal., 1983) and bony defects in the facial canal (Johnson etal., 1983; Mafee etal., 1983). To determine a policy on the use of CT scanning in cases of CSOM, a series of 36 cases were submitted for scanning prior to mastoid surgery. The films were then submitted to a panel of three neuroradiologists (I.W., C.T., P.B.) who were asked to provide a collective answer to each of the following questions without the benefit of the operative findings:
Their answers were then compared with the operative findings. Cases in which the operative notes were inadequate were discarded as was a case in which a proposed mastoidectomy was cancelled in favour of an aural polypectomy when the CT demonstrated no mastoid disease.
Methods CT scanning was performed on a Philips Tomoscan 350 Scanner using High Resolution mode and Bone Algorithm, viewed on wide window settings. Preferably, coronal scans are performed first before the patient becomes fatigued. 1.5 mm sections were used with 1.5 mm increments. Occasionally 1 mm increments were used, for example through the ossicular chain to minimize partial volume effects. Coronal scans run from the anterior cochlea to the descending portion of the facial canal. By a combination of head extension and gantry tilt we try to scan in the coronal plane. Axial sections are performed with orbito-meatal line parallel to the table top. 1.5 mm sections are used with 1.5 mm intervals. Sections are required from the floor of the external meatus to the first genu of the facial canal but in practice, four additional sections are taken below
1. Is there a soft tissue mass in the middle ear or mastoid? 2. Is there bone erosion?
Departments of Otolaryngology* and Neuroradiologyt, The Royal London Hospital, Whitechapel, London El 1RB. Accepted for publication: 29 August 1991. 990
991
CT SCANNING IN CHRONIC SUPPURATIVE OTITIS MEDIA
CT in detecting exposed dura in CSOM. O'Donoghue et al. (1987) detected one of their two cases of tegmen erosion on CT but did not report their incidence of false positives. Jackler etal. (1984) detected all four of their cases but also had eight false positives. Mafee etal. (1988a) missed three out of six cases but had no false positives. Using mainly axial scans, we could detect only five out of 11 cases and had six false positives. It is not possible to reliably demonstrate a dehiscence in the tegmen on axial cuts alone but even using coronal cuts we found the effect of partial volume averaging could give the false impression of a defect (Fig. 1).
FIG. 1 Coronal scan demonstrating an apparent breech in the integrity of the tegmen tympani (arrowed).
and above these limits to allow for adequate reformation in the sagittal plane should that be required. The scans were interpreted retrospectively and without clinical information by three Consultant Neuroradiologists. (I.G.W., C.H.T., P.B.). A consensus of opinion was obtained if there was any disagreement.
FIG. 2a Axial scan depicting an intact lateral semi-circular canal (arrowed).
Discussion
Cholesteatoma Our scans were able to detect soft tissue masses in the mastoid and middle ear in every case where it was present and this reflects the experience of most other authors (Mafee etal., 1986; O'Donoghue etal., 1987; Shaffer etal., 1980). However, we could not distinguish cholesteatoma from other soft tissue disease and this again is the experience of most authors (Jackler etal., 1984; Phelps and Wright, 1990), although Mafee etal. (1983) believed it was possible to identify cholesteatoma by its characteristically low attenuation value and Johnson etal. (1983) found that the presence of a well-defined edge to the mass was a sure indication of cholesteatoma. Cholesteatoma characteristically causes bone erosion and when this feature was present in association with a soft tissue mass on CT both Jackler. etal. (1984) and O'Donoghue etal. (1987) found cholesteatoma to be present in 80 per cent of cases explored. Using the same criteria, we detected 23 out of 29 cases of cholesteatoma (79 per cent), a false negative rate of 21 per cent. In most instances cholesteatoma is visible otoscopically but CT could be valuable in diagnosing cholesteatoma behind an intact tympanic membrane (as in congenital cholesteatoma or after combined approach tympanoplasty) and residual disease in the sinus tympani and the facial recess.
FIG. 2b Axial scan depicting an eroded lateral semi-circular canal (arrowed).
Exposed dura There have been few assessments of the accuracy of
Coronal scan depicting an eroded lateral semi-circular canal (arrowed). The patient had undergone previous mastoid surgery.
FIG. 2C
992
B. J. O'REILLY ET AL.
Lateral canal fistulae Lateral canal fistulae occur in about 10 per cent of cases of CSOM [Sheehy et al., 1977) and their pre-operative recognition may reduce the chances of a 'dead ear' (O'Donoghue etal., 1987; Bates etal., 1988), favouring coronal scans, detected four out of five lateral canal fistulae but do not reveal their false positive rate. Jackler et al. (1984) also used coronal scans but had a high incidence of false positives and suggested that the axial scan was better suited for this investigation. Phelps and Wright (1990) advocated scanning in both planes when vestibular symptoms were present. In our own series, we detected six out of eight lateral canal fistulae and had a false positive rate of 3.5 per cent. The axial scans were the more satisfactory because they depicted the canal in its entirety (Fig. 2a, b) and were less likely to produce false positives, but useful information could also be gained from coronal scans (Fig. 2c) and we believe both planes should be employed.
FIG. 3a and b Coronal and axial scans showing erosion of the second portion of the facial canal in the anterior part of its course (arrowed).
Ossicular disruption It is relatively easy to visualize the bodies of the malleus and the incus on CT but this has little clinical value unless the integrity of the whole ossicular chain can be demonstrated. The long processes of the malleus and incus, and the stapes superstructure are the components most at risk in CSOM but are also the most difficult to demonstrate on CT. Mafee etal. (1988b) were able to define the state of the ossicular chain in 89 per cent of cases scanned and O'Donoghue etal. (1987) reported that they had detected erosion of the long process of the incus in 67 per cent and absence of the stapes superstructure in 86 per cent of cases scanned. On the other hand, Jackler et al. (1984) were able to predict the state of the ossicular chain in only seven per cent of their cases and Phelps and Wright (1990) doubted that CT could demonstrate the ossicular chain reliably because of the combination of partial volume averaging and tissue silhouetting. Our own series shows an ability to correctly predict an intact ossicular chain in only 50 per cent of cases, the error in all cases being a failure to identify the long process of the incus or the stapes superstructure.
Facial canal dehiscences Demonstrating both the second and third parts of the facial canal requires two-plane scanning (Jackler et al., 1984; Mafee etal., 1988) so we concentrated on the second part where most dehiscences are found. This was generally clearly shown on our coronal scans (Fig. 3a) and on some axial scans (Fig. 3b) but in many cases soft tissue overlying the canal caused a loss of contrast gradient obscuring a small dehiscence, a problem also encountered by Jackler etal. (1984) and Mafee etal. (1988). Our detection rate for facial canal dehiscence (four out of nine cases) is poor but comparable to those of Freng et al. (1988) (one in four cases) and Mafee et al. (1988) (none in six cases). O'Donoghue etal. (1987) appear to have detected all (nine) of their facial canal dehiscences but also had six false positives. The majority of our patients had no facial weakness and it is possible that an erosion causing a facial palsy would be more readily apparent on CT. Conclusions Our results show CT to be extremely sensitive to the presence of soft tissue disease and bone erosion and
FIG. 4 External auditory canal obstructed by an aural polyp (arrowed). No disease deep to the tympanic membrane.
993
CT SCANNING IN CHRONIC SUPPURATIVE OTITIS MEDIA
RESULTS Feature ME mass Mastoid mass Bone erosion Dura exposure Ossicular disruption Canal fistula VII n. fistula
ME mass Mastoid mass Bone erosion Dura exposure Ossicular disruption Lateral canal fistula VII n. fistula
Present at operation
OnCT
False negative rate
False positive rate
Agreement
31 30 20 11 26 8 9
31 29 18 5 19 6 4
0% 3% 10% 55% 27% 25% 56%
40% 33% 62.5% 16% 30% 3.5% 15%
94.5% 92% 67% 72% 72% 92% 75%
Sensitivity 100% 97% 90% 46% 73% 75% 44%
Specificity 60% 67% 38% 84% 70% 96% 85%
Positive predictive value 94% 94% 64% — 86% —
Negative predictive value 99% 80% 75% — 50% —
The positive predictive value is the probability of the condition being present given a positive scan. The negative predictive value is the probability of the condition being absent given a negative scan. Figures are not given where the data is too sparse to give a reasonable confidence interval.
acceptably so to the presence of lateral canal fistulae, however we were disappointed by the lack of sensitivity to the more subtle features of dura exposure, ossicular disruption and facial canal dehiscences. Possible reasons for this include: (a) Our method of statistical analysis. A number of authors use the rate of agreement between the scans and the operative findings as a measure of success. This can be very misleading; using this yardstick we had a 75 per cent success rate in assessing the facial canal yet we missed five out of nine dehiscences! Most papers do not give all their false positive and negative rates and we found none which gave predictive values for their scans although this is the best measure of their worth. (b) The small number of lateral canal fistulae and facial dehiscences in all papers make comparisons difficult. (c) For the purposes of the study, our radiologists were given no clinical information. (d) For reasons of cost and pressure on scanning facilities, most patients underwent only axial scans and the number of sections had to be limited, but this may be closer to the normal clinical situation than some other studies in which two plane scanning and multiple sections were routinely employed. (e) There was undoubtedly a learning curve for both the radiologists and radiographers involved in the study and it is likely that our results would have improved if the study had continued. Despite these reservations we feel that some conclusions can be drawn from our study: 1. Ideally all cases should be scanned in both axial and coronal planes but, when considerations of time or cost prohibit this, coronal scans are preferable to axial scans, except when a lateral canal fistula is suspected. 2. CT is so sensitive to the presence of soft tissue disease within the middle ear and mastoid that a negative scan effectively excludes the possibility of CSOM. 3. Fistulae in the lateral semicircular canal can be
demonstrated with an acceptable degree of accuracy using a combination of axial and coronal scans. 4. Despite our poor results to date, we believe it is possible to detect most acquired facial canal dehiscences. 5. We do not believe it is possible to demonstrate small defects in the tegmen tympani or the ossicular chain in its entirety. 6. Given the limitations of the medium, it is hard to justify scanning all patients with CSOM prior to surgery. Instead it may be better to select those patients in whom the diagnosis or the extent of the disease is in doubt: eg closed cavities and congenital cholesteatomas, cases where the drum cannot be examined due to atresia or obstruction (Fig. 4), and those with neurpotological complications. 7. These scans and their reports should be subject to regular clinical audit. References Bates, G. J., O'Donoghue, G. M., Anslow, P., Houlding.T. (1988) Can CT Detect Labyrinthine Fistulae Preoperatively? Ada Otolaryngologica, 106: 40-45. Freng, A., Larsen, P. L., Nordhus, T. (1988) Cholesteatomas of the Temporal Bone. Preoperative CT Versus Peroperative Findings. Scandinavian Audiology Supplement, 30: 185—188. Jackler, K. R., Dillon, W. P., Schindler, R. A. (1984) Computed Tomography in Suppurative Ear Disease: A Correlation of Surgical and Radiographic Findings. Laryngoscope, 94, 746-752. Johnson, D. W., Voorhees, R. L., Lufkin, R. B., Hanafee, W., Canalis, R. (1983) Cholesteatomas of the Temporal Bone: Role of Computed Tomography. Radiology, 148: 733-737. Mafee, F. M., Kumar, A., Yannias, A., Valvassori, G. E., Applebaum, E. L. (1983) Computed Tomography of the Middle Ear in the Evaluation of Cholesteatomas and other Soft-Tissue Masses: Comparison with Pluridirectional Tomograpahy. Radiology, 148: 465-472. Mafee, M. F., Aimi, K., Kahen, H. L., Valvassori, G. E., Capek, V. (1986) Chronic Otomastoiditis: A Conceptual Understanding of CT Findings. Radiology, 160: 193-200. Mafee, M. F., Levin, B. C., Applebaum, E. L., Campos, M., James, C. F. (1988) Cholesteatoma of the Middle Ear and Mastoid: A Comparison of the CT Scan and Operative Findings. Otolaryngologic Clinics of North America, 21(2): 265-293. O'Donoghue, G. M. (1987) Imaging the Temporal Bone (editorial). Clinical Otolaryngology, 12: 157-160.
994 O'Donoghue, G. M., Bates, G. J., Anslow, P., Rothera, M. P. (1987) The Predictive Value of High Resolution Computerized Tomography in Chronic Suppurative Ear Disease. Clinical Otolaryngology, 12: 89-96. Phelps, P. D., Wright, A. (1990) Imaging Cholesteatoma. Clinical Radiology, 41: 156-162. Shaffer, K. A., Haughton, V. M., Wilson, C. R. (1980). High Resolution Computed Tomography of the Temporal Bone. Radiology, 134: 409-414. Sheehy, J. L., Brackmann, D. E., Graham, M. D. (1977) Complications of Cholesteatoma: a Report on 1024 Cases. In First Inter-
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national Conference on Cholesteatoma (McCabe, B. F., Sade, J., Abramson, M., eds.), Aesculapius Press, Birmingham, Alabama, 420-429. Swartz, J. D. (1983) High Resolution Computed Tomography of the Middle Ear and Mastoid. Radiology, 148: 449-454. Address for correspondence: Sqn. Ldr. B. J. O'Reilly, F.R.C.S.Ed., E.N.T. Department, Princess Mary's Hospital, Halton, Aylesbury, Bucks HP22 5PS.
Key words: C.T. scanning; Otitis media, suppurative; Cholesteatoma.
