Computed tomography

High resolution computed tomography, contrast-enhanced, computed tomography (CT) and pulmonary angiography

High-resolution CT

High-resolution CT provides detailed views of the lung parenchyma and facilitates the diagnosis of interstitial lung disease and emphysema. Chest CT is further useful in the detection of mediastinal and hilar pathology suggesting rare causes of pulmonary hypertension such as sarcoidosis or fibrosing mediastinitis.

A main pulmonary artery diameter of 29 mm or greater (fig. 1) has a sensitivity and specificity of 84 % and 75 % for predicting pulmonary hypertension. The corresponding values for presence of an artery-to-bronchus ratio of 1 or greater in at least 3 lobes (fig. 2) are 65 % and 78 %. The presence of both conditions has a specificity of 100 %.

High-resolution CT has an accuracy of about 90 % for the diagnosis of sarcoidosis and almost 100 % for the diagnosis of Langerhans-cell histiocytosis, which both can manifest as severe pulmonary hypertension, the latter almost invariably.

High-resolution CT may be very helpful where there is a clinical suspicion of PVOD. Characteristic changes of interstitial oedema with diffuse central ground-glass opacification and thickening of interlobular septa suggest PVOD (fig. 3); additional findings may include lymphadenopathy and pleural effusion [2].  

Pulmonary capillary haemangiomatosis is suggested by diffuse bilateral thickening of the interlobular septa and the presence of small, centrilobular, poorly circumscribed nodular opacities.

A feature suggestive of CTEPH, but also occurring in IPAH, is a mosaic perfusion of the lung parenchyma (fig. 4) often erroneously interpreted as ground-glass opacities of infiltrative lung diseases or obliterative bronchiolitis. The latter can be distinguished from pulmonary hypertension by the presence of air-trapping in expiratory images.

       

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fig. 1

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fig.2

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fig. 3

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fig. 4


Contrast CT angiography

Contrast CT angiography of the PA is helpful in determining whether there is evidence of surgically accessible CTEPH if multidetector CTs with a very high resolution are available. It can delineate the typical angiographic findings in CTEPH such as complete obstruction, bands and webs, and intimal irregularities as accurately and reliably as digital subtraction angiography [3,4]. With this technique, collaterals from bronchial arteries can be identified and CT angiographic evidence of extensive central vessel disease and limited small vessel involvement indicates a favorable surgical outcome.

Traditional pulmonary angiography is still required in many centres for the work-up of CTEPH to identify patients who may benefit from surgical pulmonary endarterectomy. Angiography can be performed safely by experienced staff in patients with severe PH using modern contrast media and selective injections. Angiography may also be useful in the evaluation of possible vasculitis or pulmonary arteriovenous malformations.