Diagnostic significance and possible pitfalls of nuclear grooves in extrathyroid cytology

The diagnostic significance of grooved nuclei in the cytology of extrathyroid lesions is not well-described in the literature. Isolated cases of metastatic adult granulosa cell tumor, reactive mesothelial hyperplasia, Langerhans' cell histiocytosis, recurrent renal cell carcinoma, and round cell liposarcoma were reviewed, and their cytologic features were discussed. While nuclear grooving can be present to a different extent in all these conditions, the significance of this feature in diagnostic cytology varies. The integration of clinical information, radiologic findings, different morphologic features, and immunohistochemistry is necessary before a final conclusion is reached.