Hybrid cysts: a clinicopathological study of seven cases.

Hybrid cysts develop from more than two components of the pilosebaceous unit. The pathogenesis of this unusual disease has not yet been elucidated. The aim of this study was to assess the clinical and histopathological features of hybrid cysts. Histological sections of seven cases indexed as hybrid cysts were reviewed from 1996-2009 at the Department of Dermatology, Eulji Medical Center, Seoul, Korea. Hospital charts and slides were retrospectively evaluated. All cases had a combination of an epidermal cyst and a pilomatricoma with sharp transitional zones. The epidermal cyst lining was composed of thickened stratified squamous epithelium with a granular layer. Basophilic cells, shadow cells and the contents of the pilomatricoma were present in all lesions. There were no differences in the clinical features between patients with hybrid cysts and others with single cystic lesions. There were five women and two men, ranging in age from 11 to 50 years (mean 27 years). The most common sites were the upper extremities. None of the patients had any sign of Gardner's syndrome. Hybrid cysts are an interesting pathological phenomenon. Further study is needed to analyze hybrid cysts to improve our understanding of their pathogenesis and development from tumours of the pilosebaceous unit.