UIP in Other Fibrosing Lung Diseases

As mentioned previously, a UIP pattern of brosis in IPF suggests a progressive form of lung disease. Whilst the consensus diagnostic guidelines on which CT evaluation is predicated revolve around the diagnosis of IPF, it must be remembered that honeycombing is not infrequently seen in other brosing lung diseases including CHP [20, 30] (Fig. 29.9a–c), rheumatoid arthritis-related interstitial lung disease (RAILD) (Fig. 29.9d–f) and sarcoidosis. Though the distribution of brosis and honeycombing may be different from UIP-IPF, studies have shown that patients with CHP [31] and RAILD [32, 33] with a UIP pattern have comparable mortality to IPF patients, independent of their disease severity.

Pleuroparenchymal Fibroelastosis (PPFE)

PPFE was originally described as an upper lobe predominant condition that was idiopathic [34], familial [35] or occurring in patients undergoing organ transplantation [36]. However, it has been increasingly recognised in several brosing lung diseases including IPF (Fig. 29.10a–c), CHP (Fig. 29.10d–f) and systemic sclerosis (Fig. 29.10g–i). In IPF [37] and CHP [38] PPFE has been shown to predict mortality independent of patient age, gender and baseline disease severity. PPFE has also been linked to worsening forced vital capacity (FVC) decline in patients with IPF [37].

The CT characteristics of PPFE include peripherally distributed triangular foci of dense consolidation (pleural broelastosis) with well-de ned centrally placed foci of dense aggregated tissue (parenchymal broelastosis). Patients often have a narrowing of the antero-posterior diameter of the chest wall which is associated with a depression in the contour of the suprasternal chest wall (Fig. 29.10). PPFE

invariably involves the upper lobes but can extend to involve the middle and lower lobes and is associated with an increased risk of pneumothoraces. The 2018 IPF diagnostic guidelines [6] speci ed that whilst the presence of PPFE should be noted, the patient’s radiological description should focus on the underlying brosing lung disease. Therefore, in the case of Fig. 29.10a–c, the patient would be described as having a UIP pattern with PPFE.

Combined Pulmonary Fibrosis and Emphysema

The co-occurrence of lung brosis and emphysema is a relatively frequent nding in several brosing lung diseases such as IPF [39] and RAILD [40] given the high proportion of heavy smokers often seen in both patient groups. The importance of CPFE relates to the observation that extensive emphysema can elevate lung volumes thereby potentially masking the severity of a patient’s lung brosis when severity is evaluated using forced vital capacity measurements. In CPFE disproportionate reductions in the transfer factor for carbon monoxide (DLco) are often present. Furthermore, extensive co-existing emphysema has been shown to affect the rate of FVC decline in IPF [41]. Though CPFE is not a formal diagnosis, patients have been noted to have an increased risk of developing pulmonary hypertension [42] and lung cancer [43], necessitating careful scrutiny of CT imaging for evidence of a dilated main pulmonary artery and new pulmonary nodules. A characteristic appearance noted in areas where emphysema and brosis co-exist in that of conglomerate cystic airspaces which can increase in size over time (Fig. 29.11). Intriguingly there is also increasing evidence that emphysema may develop in patients with FLD who have never smoked [40] suggesting potential autoimmune mechanisms responsible for lung damage [44].

Fig. 29.9  Axial computed tomography images in two patients with diagnoses other than idiopathic pulmonary brosis where a usual interstitial pneumonia (UIP) pattern can be observed. A patient with hypersensitivity pneumonitis (a–c) demonstrates a lower zone predominant distribution of brosis and low attenuation lobules within normal

regions of the lung. In the left lower lobe honeycomb cysts are visible signifying a UIP pattern. In a patient with rheumatoid arthritis-related interstitial lung disease (d–f), there is a lower zone predominance to thebrosis where honeycomb cysts are visible bilaterally signifying a UIP pattern

Fig. 29.10  Three patients with a computed tomography pattern of pleuroparenchymal broelastosis (PPFE) and lung brosis. In patients with idiopathic pulmonary brosis (a–c), hypersensitivity pneumonitis (d–f) and systemic sclerosis (g–i) there is evidence of a suprasternal depression in the anterior chest wall contour. Triangular foci of

dense consolidation are visible originating from the pleural surfaces (black arrows), extending down to the lower lobes. A pneumothorax (white arrow), which not uncommonly complicates PPFE is visible in the mid-­zone of the patient diagnosed with idiopathic pulmonarybrosis (b)

Fig. 29.11  Combined pulmonary brosis and emphysema in a patient diagnosed with idiopathic pulmonary brosis (a–c) and hypersensitivity pneumonitis (d–f). Traction bronchiectasis in a lower zone predomi-

nant distribution was seen in both cases. Emphysema co-located amongst areas of brosis is evident in the right lower lobe (c) and left lower lobe (f) as conglomerative thick-walled cystic lesions

Chronic Hypersensitivity Pneumonitis

Differentiating CHP from IPF is one of the most common challenges faced by a multidisciplinary team. Although typically considered an upper and mid-zone predominant disease [45,

46], CHP can be lower lobe predominant in a third of cases [20]. Ancillary features in addition to the presence of low attenuation lobules that may suggest CHP include a bronchocentric distribution to lung brosis, poorly de ned centrilobular nodules (indicating subacute disease) and cysts [20, 24] (Fig. 29.12).