3.7 Radiology

3.7.1 X-rays

Chest X-ray is a non-specific investigation for TB. In many national programmes, it is not routinely indicated in sputum smear-positive patients because of limited resources.

Chest X-ray is considered as an additional diagnostic tool given its limitations of nonspecificity. Indeed, several comparative studies have shown that the error rate of under- or over-reading the film by specialists is around 20%. It is often difficult to detect the difference between old healed lesions of fibrosis and active TB. They are rarely conclusive and can only complete the clinical presentation and history to constitute a body of arguments suggestive of TB.

Chest X-ray is however recommended when the smear microscopy results are negative or when TB is suspected in children24. It is particularly useful where the proportion of bacteriologically unconfirmed TB (i.e. smear microscopy or Xpert MTB/RIF negative) is likely to be high; for example, in populations with a high incidence of HIV.

In HIV co-infection, infiltrates (especially in advanced immunodeficiency) tend to be more diffuse and located in the lower lung zones; the X-ray may even appear normal in 10% of the cases. Cavitary disease is seen less in those infected with HIV, and in one study, only 33% of HIV-infected patients with PTB had cavities on X-ray when compared to 78% of HIV-negative patients with PTB25.

Chest X-rays are valuable tools for the diagnosis of pleural and pericardial effusions, especially at the early stages of the disease when the clinical signs are minimal. The X-ray showing an enlarged heart is a key element for diagnosis of pericardial TB26.

Chest X-ray is essential in the diagnosis of miliary TB. It shows small characteristic nodulary infiltrations disseminated in both pulmonary fields26.

Another use of radiography includes examination of the joints and bones when TB is suspected. Radiography, including the use of computerized tomography scans (CT scans), can be useful for Pott’s disease.

3.7.2 Ultrasound

Ultrasound is useful in confirming pleural effusions27.

Ultrasound is extremely useful in pericardial TB as it can document that an effusion is the cause of an enlarged heart seen on chest X-ray.

It is moderately useful in diagnosing abdominal TB, whereby documenting multiple enlarged lymph nodes on an abdominal ultrasound is consistent with TB, however, multiple enlarged lymph nodes can be seen in other diseases, especially in HIV. Bowel wall thickening (ileocaecal region) is also suggestive of abdominal TB.