The origin of the pseudoglandular spaces in metastatic smooth muscle neoplasm of uterine origin. Report of a case with ultrastructure and review of previous cases studied by electron microscopy.

The entity known as "leiomyomatous hamartoma," a term that has been used in reference to metastatic smooth muscle neoplasms of uterine origin (MSMNUO), is uncommon. Several articles have dealt with clinical and light microscopic aspects of this lesion. Four reports on the ultrastructure of this type of neoplasm have been published, but they have been primarily concerned with its smooth muscle component. Much controversy exists as to whether the glandular elements are part of the neoplastic process or preexisting pulmonary elements. This ultrastructural study confirms that the gland-like spaces represent entrapped alveoli and terminal respiratory bronchioles.