Utility of fine needle aspiration cytology to comprehend the pathogenesis of extrapulmonary tuberculosis

Fine needle aspiration cytology (FNAC) is a precise, cost-effective, and minimal invasive technique for diagnosis of extrapulmonary tuberculosis (EPTB). This study was aimed to analyze clinical and cytological characteristics of EPTB with particular emphasis on pathogenesis.

This was a retrospective study analyzing 237 cases of EPTB diagnosed on FNAC. Depending on the presence of necrosis and granulomas, cases were divided into three classes. Association of cytomorphology with positivity for acid-fast bacilli was analyzed by Chi-square test to demonstrate any specific pattern.

Majority of our patients diagnosed as EPTB (73.8%) were young with male-to-female ratio of 1:1.3. The mean age was 23.2 years (age range 9 months to 81 years). The most frequent site involved was lymph node (89.5%) with predilection for cervical lymph nodes (81.4%). The extranodal sites affected were breast, abdominal wall, chest wall, salivary glands, soft tissue, bone, and genitourinary tract. Detailed cytological examination revealed necrotizing granulomatous inflammation as most common pattern (43%). Acid-fast bacilli were detected only in 43.5% of the cases and bacilli detection was more frequently associated with necrotizing lesions (64.9%). Non-necrotizing lesions showed AFB positivity only in 7.4% of the cases.

To achieve the goal of tuberculosis eradication, it is essential to understand its different forms of clinical presentation and detailed pathogenesis including host factors, host-pathogen interaction, and molecular mechanisms. Cytomorphological features of the representative lesions might be valuable in providing clues regarding possible pathogenetic mechanisms.