Table 2.

Imaging findings for each form of PTB.

Form of PTB	Imaging Findings	Comments
Primary TB	Lymphadenopathy CXR: Lobulated hilar/paratracheal opacity. Potential for airway attenuation or deviation. Doughnut sign on lateral radiograph. US: Well defined round/oval hypoechoic (to thymic tissue and fat) nodes within the anterior and superior mediastinum. CT: Typically, low attenuation centrally with peripheral rim enhancement of node post contrast administration. Alternatively, matted conglomerate with ‘ghost-like’ rim enhancement. MRI: Low T2/STIR signal intensity nodes. Post gadolinium T1 images may demonstrate rim enhancement.	Right sided lymphadenopathy more common than left. CXR typically normal during incubation period. US unable to assess hilar region. CT detects nodes in a significant proportion of patients with normal CXR. Central low attenuation with peripheral enhancement helps distinguish from non-TB adenopathy. MRI comparable to CT in node detection over 3 mm.
Primary progressive TB	Progressive adenopathy CXR: Airway compression or displacement most reliable finding. Attenuation can result in distal ipsilateral hyperinflation, atelectasis or consolidation. US: Unable to assess airway compression but may detect distal complications. CT: Smooth luminal narrowing indicates extrinsic compression. Irregular narrowing may indicate erosion into lumen. Excellent for identifying complications, planning treatment and monitoring treatment response. MRI: Detection of compressive nodes and distal complications comparable to CT. Poorer resolution (in comparison with CT) makes airway lumen assessment and exact nodal location identification difficult. Airspace disease CXR: Opacification of lung parenchyma silhouetting adjacent structures. May display air bronchograms. US: Comparable detection rates to CXR with peripheral consolidation. Able to identify <0.5cm consolidation (usually undetectable on CXR). CT: Classic ‘tree-in-bud’ pattern. Central low attenuation non-enhancing regions represent caseous necrosis. MRI: Able to characterize TB consolidation. Consolidation in viable lung tissue demonstrates intermediate-to-high STIR signal. Low signal on STIR sequence indicates necrotic lung tissue. Miliary TB	Younger children more likely to develop nodal airway compression due to inherently narrower airways and weaker cartilaginous support structures. Airway attenuation is the most reliable CXR sign. Distal complications of airway compression include atelectasis, air-trapping, consolidation, necrosis and breakdown. Airway attenuation and characterization of complications better characterized by CT and MRI. Miliary TB best identified by presence of diffuse small nodules and thickened septal lines. CT is the superior imaging technique.
	CXR: Often normal. Diffuse small non-calcified nodules. Thickened interlobular septal lines. US: No sensitive findings in children yet described. CT: Miliary nodules visualized well before visible on CXR. Small (<3 mm) randomly distributed nodules with thickened interlobular septa. MRI: Unable to detect <3 mm nodules. Useful in detecting lesions in solid organs (liver/spleen)
Post primary TB	Cavitation CXR: Often difficult to distinguish small cavity from consolidation. Airspace opacification surrounding an area of cavitation represents central caseous necrosis and liquefaction. Air-fluid level may represent secondary infection. CT: Central low-attenuating cavity. Cavity wall variable in size. Cavity surrounded by consolidation. MRI: Low signal cavity with surrounding consolidation.	Cavity formation is the hallmark of post-primary TB. Small cavities easily missed on CXR. CT and MRI superior to CXR in the detection of cavities. Usually predominate in upper lobes or apical segments of lower lobes. More common in adolescents. CT is useful in assessing cavity wall thickness.