Mastoid obliteration with hydroxyapatite--the value of high resolution CT scanning in detecting recurrent cholesteatoma.

Mastoid obliteration carries a risk of enclosing cholesteatoma within the mastoid cavity. Using temporal bones obliterated with either muscle or hydroxyapatite granules, the value of high resolution CT scanning in the early detection of 'epithelial pearls' was studied. The results showed that scanning was effective in detecting small epithelial pearls within the cavity obliterated with hydroxyapatite, but not so effective when muscle was used. This is explained by the difference in the CT density between epidermoid cysts and hydroxyapatite allowing the cysts (dark shadows) to be identified easily within a white background. The authors also studied scans performed on 31 ears following mastoid obliteration with hydroxyapatite. There was no residual cholesteatoma in the obliterated area but there was an area of abnormality identified within the obliterated area in one patient due to a cholesterol granuloma.