In the course of routine roentgenologic examinations of the chest I have observed a number of cases of intrathoracic dermoids, and the information gained in this series of cases will probably be of interest.
The term dermoid is used in the title rather than teratoma, because the majority of the cases observed have been benign. However, in spite of the fact that the dermoids were benign, they became dangerous to life in some cases on account of their size.
In some instances the tumors, closely associated with the mediastinum, offered considerable difficulty in differential diagnosis, especially in differentiation from aneurysm. In this connection I would state that the usually accepted statement in the textbooks that on fluoroscopic examination the determination of visible pulsation in a mediastinal tumor is a simple matter of observation and a positive means of diagnosis between aneurysm and tumor is by no means always true. This