Can an omentum fine needle biopsy (FNB) diagnose tuberculosis (TB)?

From the Guidelines

Yes, an omentum fine needle biopsy (FNB) can diagnose tuberculosis (TB). This procedure involves using a thin needle to extract tissue samples from the omentum, which can then be examined for TB bacteria or characteristic histopathological features. Omental FNB is particularly useful when TB presents with abdominal involvement, which occurs in about 5-10% of extrapulmonary TB cases. The collected sample should be sent for acid-fast bacilli (AFB) staining, TB culture, and PCR testing for Mycobacterium tuberculosis, as well as histopathological examination to look for granulomas with caseous necrosis.

The sensitivity of omental FNB for TB diagnosis ranges from 60-85%, depending on the laboratory techniques used 1. If TB is confirmed, standard treatment involves a four-drug regimen (isoniazid, rifampin, ethambutol, and pyrazinamide) for 2 months, followed by isoniazid and rifampin for an additional 4 months. Omental FNB is valuable because it is minimally invasive compared to surgical biopsy, has fewer complications, and can provide definitive diagnosis in cases where other diagnostic methods have failed or are not feasible.

Some key points to consider when using omental FNB for TB diagnosis include:

• The importance of sending the collected sample for multiple tests, including AFB staining, TB culture, and PCR testing, to increase the chances of detecting TB bacteria or characteristic histopathological features.
• The need to consider the patient's clinical and radiographic findings, as well as the results of other diagnostic tests, when interpreting the results of omental FNB.
• The potential for omental FNB to provide a definitive diagnosis in cases where other diagnostic methods have failed or are not feasible, which can help guide treatment decisions and improve patient outcomes. It's also important to note that, according to the guidelines, a negative culture result is obtained in approximately 14% of patients with confirmed pulmonary TB disease 1, and a culture of sputum or other clinical specimen that contains M. tuberculosis provides a definitive diagnosis of TB disease.

In terms of treatment, the guidelines recommend that patients who are suspected of having pulmonary tuberculosis should have treatment initiated with INH, RIF, PZA, and EMB even when the initial sputum smears are negative 1. If M. tuberculosis is isolated in culture, treatment for active disease should be continued. Patients who have negative cultures but who still are presumed to have pulmonary tuberculosis should have a thorough follow-up clinical and radiographic evaluation at the time 2 months of therapy has been completed to determine whether there has been a response that can be attributed to antituberculosis treatment.

Overall, omental FNB is a valuable diagnostic tool for TB, particularly in cases with abdominal involvement, and can provide a definitive diagnosis and guide treatment decisions.

From the Research

Omentum Fine Needle Biopsy for TB Diagnosis

• The use of fine needle biopsy for diagnosing tuberculosis (TB) has been explored in various studies 2, 3, 4.
• Specifically, the diagnosis of omental tuberculosis using fine needle aspiration biopsy has been reported in a case study, where the patient was diagnosed with omental TB after a USS guided tissue biopsy revealed granuloma with central caseous necrosis 5.
• A study on the role of ultrasound-guided fine-needle aspiration cytology of the omentum in diagnosing abdominal tuberculosis found that the procedure was helpful in diagnosing abdominal TB in patients with omental thickening with or without other abnormal findings 6.
• The study found that granulomatous inflammation was reported in 89.5% of patients and acid-fast bacilli in 57.6% of patients, indicating the effectiveness of the procedure in diagnosing TB 6.

Diagnostic Accuracy

• The diagnostic sensitivity of fine needle aspiration biopsy for tuberculous lymphadenitis was found to be high, with a sensitivity of 86% for mycobacterial cultures from FNA specimens 4.
• However, the sensitivity of microscopy and cytology was found to be lower, at 18% and 38% respectively 4.
• The use of ultrasound-guided fine-needle aspiration cytology of the omentum was found to be effective in diagnosing abdominal TB, with a positive result reported in 70.4% of patients 6.

Clinical Utility

• Fine needle aspiration biopsy is a simple and safe outpatient procedure that can be performed by nurses in resource-limited settings, making it a valuable tool for diagnosing TB in areas where resources are limited 3.
• The procedure can provide material for direct microscopy, culture, and susceptibility testing, making it a useful diagnostic modality for TB 3, 4.
• The use of ultrasound-guided fine-needle aspiration cytology of the omentum can help diagnose abdominal TB in patients with omental thickening with or without other abnormal findings, making it a valuable diagnostic tool in certain clinical scenarios 6.