Epidermoid and dermoid sequestrations occur infrequently in bone, are confined to the calvarium and tuft of terminal finger phalanges and present a characteristic roentgenographic appearance.
Misplaced epithelial rests early in embryonic life account for the origin of most epidermoid tumours.
The usual history is that of a lump on the surface of the skull that has been present for long time but recently increased in size.
The typical appearance of an intradiploic dermoid is that of a radiolucent defect, well marginated by a dense sometimes a scalloped border. As the cyst enlarges , there is widening and ballooning of the diploic space with erosion and destruction of the inner and outer tables