A convincing and large body of evidence for the benefit of much more aggressive treatment of neuroendocrine tumors (NETs) has accumulated in recent years (1–6). The interventional radiologist is frequently involved by this trend and hence must have a general knowledge of the many aspects of these tumors. In general, NETs are much slower growing than are the more commonly encountered malignancies. Furthermore, they are rare. Hence, they are usually diagnosed later in their course. Distant metastases are found in 12.9% of all carcinoids at the time of their diagnosis, and the majority of metastases are from small intestinal primary tumors, with the most frequent site of distant metastasis being the liver (7, 8). However, even when far advanced, these tumors usually are amenable to aggressive treatment that would not be undertaken for other, more common malignancies at an equally advanced stage.

NOMENCLATURE AND DESCRIPTION

NETs represent a heterogeneous group of lesions with widely varying natural histories. The term carcinoid was initially coined to describe a carcinoma-like tumor that was believed to be less aggressive than adenocarcinoma (9). It is now known, however, that although they tend to grow more slowly than most other malignancies, these lesions actually represent a wide array of biologic and clinical behavior.

There has been considerable confusion in the literature regarding the classification and nomenclature of NETs and carcinoids. Pathologists have historically referred to all NETs as carcinoids because of their similar histologic appearance.