Abstract
Objective
CT temporal bone scans are often performed to aid in surgical planning and management of cholesteatomas. With improvements in the resolution of CT scans today, it is now possible to obtain more information from these scans than before. The aim of this study is to compare findings on high resolution CT (HRCT) temporal bone scans to intra-operative findings, so as to determine how well various middle ear structures are assessed by HRCT scanning.
Study design
Retrospective study.
Setting
Otology clinic of a tertiary otolaryngology centre.
Subjects and methods
32 mastoidectomies performed by a single otologist for clinically confirmed cholesteatoma were included. Correlation of CT and intra-operative findings on the status of structures including the ossicles, semicircular canals, facial canal and tegmen was analysed using kappa and AC 1 statistics.
Results
In all patients, a soft tissue mass with bony erosion in keeping with a cholesteatoma was seen on CT. Radiosurgical agreement was excellent for the presence of semicircular canal erosion (k = 0.89, AC 1 = 0.96), facial canal dehiscence (k = 0.74, AC 1 = 0.76), tegmen erosion (k = 0.76, AC 1 = 0.92) and malleus erosion (k = 0.76, AC 1 = 0.85). It was good for incus erosion (k = 0.71, AC 1 = 0.92) and stapes erosion (k = 0.63, AC 1 = 0.73).
Conclusion
There was good to excellent radiosurgical agreement in the assessment of the status of various middle ear structures. Improvement in radiosurgical agreement from existing studies in the literature was noted. This was especially true for features such as facial canal dehiscence. With technological advancements, CT temporal bone scans appear even more valuable for evaluation of patients prior to cholesteatoma surgery.
1
Introduction
The resolution of computed tomography (CT) scans of the temporal bone has improved over the last decade, making it possible for radiologists and clinicians to obtain more details from imaging. A high-resolution computed tomography (HRCT) of the temporal bone is an important preoperative investigation for cholesteatoma surgery. Prior knowledge about temporal bone anatomy and disease extent can help surgeons plan their surgical approach. Additionally, HRCT scans can also highlight the presence of potentially dangerous problems such as facial canal dehiscence, erosion of tegmen with dural exposure, or semicircular canal erosion, thus aiding surgeons in avoiding surgical complications .
However, while the HRCT has a valuable role in evaluating patients with cholesteatoma prior to mastoidectomy, it is also important to be cognizant of any limitations and pitfalls. Some studies have highlighted that CT scans may misleadingly suggest the presence of lateral semicircular canal fistulization, tegmen tympani erosion, and facial nerve involvement as these structures have thin bony covering that may be subject to volume averaging with adjacent soft tissues . This may in turn affect the surgical management of suppurative ear disease . Another study found that pre-operative CT scans contributed little to surgical management and is of questionable value . Most prior studies were performed using HRCT scanning with 1.0–1.5 mm thick cuts . Also, some studies done included all types of chronic suppurative ear disease , which may cause study results to be difficult to interpret as cholesteatomas, middle ear mucosal disease, and granulation are very different disease entities.
In our institution, temporal bone HRCT scans are performed with finer 0.5 mm cuts, which minimize problems due to volume averaging. The question then arises if clinicians can now obtain more accurate information pre-operatively than previously described.
The aim of this study is to correlate findings on 0.5 mm fine-cut HRCT temporal bone scans to intra-operative findings of patients with cholesteatoma, so as to determine the degree of radio-surgical agreement.
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