A histopathologic study of epidermoid cysts in Korea: comparison between ruptured and unruptured epidermal cyst

Background: An epidermoid cyst is a common epithelial-lined cyst. There have been many studies on epidermoid cysts, but few focused on ruptured epidermoid cyst and its histopathologic characteristics. Objective: We evaluated the histopathologic differences between ruptured and unruptured epidermoid cysts, and their relationships. Methods: We retrospectively examined 359 excision biopsy specimen diagnosed as epidermoid cyst from 1991 to 2011 at Department of dermatology at Daegu Catholic University Hospital. Results: The mean cyst area was 38.89 mm(2) and the mean cyst area of the unruptured group was larger than that of the ruptured group. The mean wall thickness was 90.15 mu m and was thicker in ruptured group than in unruptured group. The correlation between cyst diameter and wall thickness had statistically negative correlation in unruptured and in ruptured group. In ruptured group, the cystic size of the cases with rete ridge was smaller than that of without rete ridge. The cyst wall thickness of the cases with rete ridge was thicker than that of the cases without rete ridge. Limitations: For comparative evaluation of sizes, randomly shaped cysts are assumed to be perfectly elliptic. And only those with more than 3/4 cystic wall remaining were included in the subject. Conclusion: When comparing the ruptured and the unruptured cyst, the rupture of cyst had significant relationship with increased cyst diameter and area, increased wall thickness, more cyst contents, and more wall changes. Moreover, the presence of rete ridge in ruptured cystic wall is a valuable variable to recognize the duration of the rupture.