Tuberculosis overview:

Tuberculosis (TB) remains a worldwide cause of morbidity and mortality. Patients from endemic areas (such as South East Asia and Africa), and those with impaired immunity, are at higher risk. TB is caused by Mycobacerium tuberculosis and is spread through inhalation of aerosolised droplets containing the bacteria, which results in pulmonary infection in the majority of cases.  Disease usually manifests as a result of a hypersensitivity response to the bacteria resulting in granuloma formation. Nodal disease usually occurs first, which can subsequently lead to pulmonary and/or multisystem involvement through haematogenous dissemination (1).

Predictable radiological patterns have been recognised for most potential sites of disease involvement.

Thoracic manifestations:

In the lungs the disease can either manifest as primary TB which results from a response to initial infection, or as post primary TB. The latter occurs when the hypersensitivity response results in granuloma formation with incomplete clearance of bacteria, which can remain dormant for a period of time. Subsequently, reactivation of latent bacteria leads to post primary tuberculosis. The radiological manifestations of primary TB are usually consolidation and nodal enlargement (the so-called Ranke’s complex). Primary TB does not demonstrate a lobar predilection and can affect any lobe. Pleural effusions on the same side as the initial infection are common. Post primary TB usually has a different pattern of disease: upper lobe predominant mass-like granulomata, which often cavitate, are typical. Endobronchial TB with centrilobular nodules or a tree-in-bud type pattern are also typical (2).

Extra-thoracic manifestations:

Although thoracic manifestations are more common, the incidence of extrathoracic TB continues to increase. It is more common in patients with a background of immunocompromise (3). As with thoracic TB, predictable patterns can also arise with other sites of involvement. This poster describes the usual patterns of osseous/spinal TB and nodal disease (and not other extrathoracic sites) because the cases described manifest unusual patterns involving these systems. Tuberculous adenopathy on CT typically demonstrates low attenuation central necrosis with peripheral hyperenhancement. Whilst these findings are often considered pathognomonic, they are actually non-specific and can be encountered in other pathologies, in particular malignancy. Osseous TB most often involves the spine and presents as a spondylitis. It frequently occurs as multifocal disease, but often starts as non-specific osteolysis. Eventually this is associated with an extraosseous inflammatory phlegmon. In the spine, this often leads to subligamentous spread to involve discs and vertebrae at other levels. Vertebral osteolysis can also lead to vertebral collapse and kyphotic/gibbus deformities (4).

Tuberculosis as a cancer mimic:

Given that TB often presents with vague symptoms, can be multifocal, and can involve multiple systems, it can easily mimic malignancy. Imaging findings can be non-specific.  Sophisticated modern imaging techniques, such as PET CT, often demonstrate increased metabolic activity in tuberculous lesions which also leads to difficulty in differentiating between the two entities. Ultimately pathological sampling is required definitively to differentiate between the two.