Aspiration cytology of neuroendocrine tumors below the diaphragm

In a series of 630 transabdominal fine-needle aspirates, 24 neuroendocrine tumors (NETs) presenting below the diaphragm were encountered. Of these, 10 were classic small-cell undifferentiated carcinomas (SCUCs). Recognition of SCUC in abdominal aspirates has major directive value, pointing to bronchogenic origin, possibly unsuspected, in most cases (eight of 10 in this series). The other 14 NETs were 10 pancreatic islet-cell tumors and four intestinal carcinoids, both diagnosed more frequently in metastatic than in primary sites (10 of 14 in the liver in this series). The cytologic presentation of these non-SCUC neoplasms has received little literature attention, and it is described and illustrated here, with discussion of cytologic pitfalls and differential diagnoses. Diagnostic specificity was 100%, and sensitivity was also 100%, exclusive of two sampling errors. The purpose of this article is to establish a broader view of the range of morphological features of the extended neuroendocrine group of tumors in aspiration cytology.