Abstract
A 47-year-old man had been sufferring from the pain and swelling in his left thumb for a month.
Roentgenograms revealed the enlarged terminal phalanx with distended and thinned cortex.
By the surgical operation, the radial portion of the cortex was perforated. The content of this cyst was a semisolid, cheesy one as seen in the atheroma. The inner surface of the cyst-wall was lined by the thinn and soft membrane, which was consist of the stratified squamous epithelium and sud surrounding connective tissue without hair, sebaceous gland and sweat duct.
For these reason this cyst was diagnosed as epidermoid cyst.
Although a small portion of the attenuated cortex seemed to be destroyed roentogenologically, judging from surgical finding, the cyst was not suposed to occure outside the phalangeal bone, but inside the bone.
Therefore, if the epidermoid cyst is originated from the deeply buried skin, the trauma should be serious one in this case. In spite of this, the patient remembers no traumatic lesion in his thumb.
