Where to Look for AFB in FNA Smears from Tuberculous Lymph Nodes.

Demonstration of acid fast bacilli (AFB) is essential for the definitive cytodiagnosis of tuberculosis. However, it is not seen in all cases of tuberculosis, being more commonly observed in necrotic lesions. Tuberculosis shows a spectrum of lesions that form a continuum extending from good immunity end with purely granulomatous lesions to poor immunity end with purely necrotic lesions. Each stage has distinctive microscopic picture and determines the chance of finding AFB. AFB yield was the highest (92.7%) in necrotic lesions containing eosinophilic structures (ES).