APPLICATION OF COMPUTED TOMOGRAPHY SCAN FUSION WITH DIFFUSION-WEIGHTED ECHO-PLANNER MAGNETIC RESONANCE IMAGING FOR CHOLESTEATOMA IN CHILDREN
Otitis media with discharge refractory to medical treatment is occasionally encountered, even in this era of broadly active antibiotics. Aural discharge can be caused by congenital or acquired cholesteatoma, which is difficult to diagnose at the first visit. The incidence of cholesteatoma is < 5% in such children.
In this study, we applied high-resolution CT and DWI (diffusion-weighted image) MRI to identify choles-teatoma in those children with acute otitis media and otitis media with effusion.
DWI-MRI relies on the signal produced by the motion of water molecules and it is one of the T2-weighted image and T2-related shine-through effects.
Limitations of DWI are retraction pocket auto-evacuate keratin debris resulting in a ‘dry cholestatoma’, which produces no restricted diffusion signal on the DWI-MRI sequence. In addition, air-bone susceptibility artifacts produced with echo-planner imaging (EPI) sequences makes interpretation more difficult.
In this study, a conventional 1.5 Tesla MRI scanner was used. Diagnosis of cholesteatoma was based on the presence of high-intensity signals in the middle ear or mastoid cavity on the DWI-EPI. DWI-MRI and high-resolution CT image were stored on a Ziostation workstation.
Cases presented are pediatric cholesteatoma in patients who visited our outpatient clinic complaining of protracted ear discharge.
We applied DWI-MRI and CT fusion imagery in these cases. Many benefits can be realized by combining these techniques. It can clarify relationships between temporal bone structures and pathology, be of help in diagnosis and precise localization of cholesteatoma, provide useful information for surgical planning, is easy to use in pediatric cases, and when the images are registered, several things can be determined at once. In clinical routine, the CT scan plane is tilted compared with the MRI scan plane to minimize radiation on the eyes, and when we register both images, angle adjustments are needed. Unlike other MRI sequences like T2-WI, anatomical structures such as the facial nerve are unapparent as anatomical index.
Limitations of these images are due to the air-bone susceptibility artifact around the skull base and its blur image; the evaluation of the lesions in supratubal recessus and epitympanic spaces are difficult. In addition, due to the T2-shine-through effect, distinguishing between cholesteatoma and inflammatory water retention lesion can be difficult.
In conclusion, DWI-CT fusion imagery can provide complementary information about temporal bone structures and pathologies. Due to the limitations of DWI which include air-bone susceptibility, blurred images, and difficulties in distinguishing cholesteatoma from inflammatory water retention lesions, evaluation of the extent of the disease can be difficult depending on the site of the lesions.
Address for correspondence: Hiroko Monobe, Department of Otolaryngology, Japanese Red Cross MedicalCenter, 4–1-22 Hiroo, Shibuya-ku, Tokyo, Japan. h-monobe@chime.ocn.ne.jp
Cholesteatoma and Ear Surgery – An Update, p. 241
Edited by Haruo Takahashi
2013 © Kugler Publications, Amsterdam, The Netherlands