The cytologic features of sinonasal undifferentiated carcinoma and olfactory neuroblastoma.

Sinonasal undifferentiated carcinoma (SNUC) is a rare, aggressive malignancy of the sinonasal tract. Olfactory neuroblastoma (ONB) is an uncommon neuroectodermal tumor of the superior nasal cavity. Upon examining these lesions, a broad differential diagnosis of poorly differentiated round cell tumors must be considered. The cytologic features of SNUC and ONB have been rarely reported. We searched our cytology files for cases of SNUC and ONB and assessed the following: cellularity, architecture, cytoplasm, cell size, nuclear contours, nucleoli, chromatin, anisonucleosis/anisocytosis, mitotic activity, background, and nuclear crush. Seven cases of SNUC produced hypercellular smears with a single-cell-predominant pattern. Cells were intermediate-sized with irregular nuclear contours and small nucleoli. Nuclear crush and mitotic figures were noted. The background exhibited naked nuclei and karyorrhectic debris. Of 7 cases, 6 (86%) exhibited vacuoles or extracellular lumina. The 10 cases of ONB exhibited cellularity, cellular arrangement, and chromatin similar to SNUC. In contrast, ONBs demonstrated fibrillary cytoplasm and smooth nuclear contours; mitotic figures were generally absent. Homer Wright rosettes were encountered in 9 cases (90%). We believe that in the appropriate clinical context, a specific cytologic diagnosis should be possible.