[Epidermoid formation in the developing middle ear and its relationship to congenital cholesteatoma].

Forty-nine fetuses, ranging from 12 weeks to full term of fetal age, were collected to study the epidermoid formation(EF) in the middle ear. The results showed that: 1) Sixteen of 49 fetuses had EFs in the middle ear aged 14 to 38 weeks of gestation. The structure always appeared between the anterosuperior edge of the eardrum and the anterior limb of the tympanic ring. The width and height of the EFs were 60.82 +/- 5.68 microns and 45.87 +/- 6.82 microns respectively. 2) The EFs might be classified into two types: simple EF and hyperplastic EF. Most of the simple EFs would degenerate and disappear in the late fetal stage, but a few of them might transform into hyperplastic ones. The hyperplastic EF showed more active appearance and multilayered structure, so it seemed to grow continuously, and might develop into congenital cholesteatoma.