Negative images in the fine needle aspiration cytologic diagnosis of mycobacterial infections.

Cytologic diagnosis of mycobacterial infection has conventionally depended on the recognition of granulomatous inflammation with caseous necrosis and the identification of acid-fast bacilli with special stains. Immunocompromised patients however may not mount the expected response. Mycobacteria can be seen as negative images in fine needle aspiration cytologic smears from patients with acquired immunodeficiency syndrome. We report the cytologic findings of lymphnode aspiration from four patients where the mycobacteria were seen in the routine May Grunwald Giemsa-stained smear as unstained rod-shaped structures in the background and within histiocytes. These were confirmed to be acid-fast bacilli with the Ziehl-Neelsen stain.