Fine Needle Aspiration Cytology of Kikuchi's Lymphadenitis: with Emphasis on Differential Diagnosis with Tuberculosis

Background: Although Kikuchi's lymphadenitis (KL) has been known to have characteristic cytological features, pathologists encounter difficulties in making a diagnosis with fine needle aspiration cytology (FNAC). The objective of this study was to assess the diagnostic pitfalls of KL with FNAC, particularly with emphasis on differential diagnosis with tuberculosis. Methods: FNAC of 10 patients with a histological diagnosis of KL and tuberculosis was reviewed. Results: Acidophilic cells were observed in all the 10 KL cases, even if the smears were insufficient. Crescentic histiocytes were seen in 8, granular background in 7, and karyorrhectic debris in 3 cases. Epithelioid histiocytes or neutrophils were not seen in any of the KL cases. Of the 10 cases of tuberculosis, acidophilic cells were observed in 6 cases, crescentic histiocytes in none of them, cheese-like background in 9, karyorrhectic debris in 8, epithelioid histiocytes in 4, and neutrophils in 8 cases. Conclusions: The acidophilic cell could be the most sensitive but not the specific marker of KL with FNAC. The crescentic histiocytes might be the sensitive and considerably specific marker of KL. The cytological features distinguishing tuberculosis from KL may be cheese-like necrosis admixed with neutrophils and epithelioid histiocytes.