Colloid and pigmented histiocytes in lymph node aspirates as a clue to metastasis in patients with a history of papillary thyroid carcinoma

Introduction: Cystic changes, calcification, colloid material, and multinucleated giant cells are frequently associated with primary and metastatic papillary thyroid carcinoma (PTC). These features are sometimes present in negative lymph node fine-needle aspiration cytology (FNAC). This study aims to review nodal aspirates of PTC to elucidate the significance of these cytological features in aspirates without tumor cells.Methods: FNAC specimens from patients with PTC confirmed on thyroidectomy were reviewed for cystic changes, tumor-associated features, and lymphoid components. Histologic follow-up of the lymph nodes were retrieved for correlation.Results: A total of 113 aspirates were retrieved, of which 79 showed tumor cells on the FNAC specimen, and 95 were matched to a positive lymph node histology. At univariable analysis, calcification (n = 18/113, p = .044), colloid material (n = 40/113, p = .001), multinucleated giant cells (n = 29/113, p = .028), tumor cells (n = 79/133, p < .001), foamy histiocytes (n = 36/113, p = .002) and pigmented histiocytes (n = 62/113, p < .001) were associated with a positive histology. Presence of lymphoid fragments (n = 11/113, p < .001) and abundant background lymphocytes correlated with a negative histologic follow-up (n = 45/113, p = .005). In aspirates without tumor cells, multivariable analysis demonstrated colloid material (p < .001) and pigmented histiocytes (p = .003) to be independently predictive of metastatic PTC, whereas lymphoid fragments (p < .001) were independently associated with a negative histologic follow up.Conclusion: Colloid material and pigmented histiocytes, and to lesser degree calcification and multinucleated giant cells, when seen in an aspirate without tumor cells, raises suspicion metastatic disease. On the contrary, the lymphoid fragments can be regarded as supportive evidence of adequate sampling and a true negative result.