Unclassifable Fibrosing Lung Disease

Patients with unclassi able FLD may constitute up to 15% of brosing lung disease cohorts [47]. These patients either do not have an obvious diagnosis that can be made with over 50% certainty based on all available information or refect patients in whom a clear diagnosis cannot be determined even following surgical lung biopsy [48]. Patients with an indeterminate UIP pattern where disease distribution is not lower zone predominant could be labelled as unclassi able FLD or managed with a working diagnosis whilst disease behaviour is monitored, and the patient re-evaluated at a future date.

Other Fibrosing Lung Diseases

Non-specifc Interstitial Pneumonia Pattern

HRCT features traditionally associated with a non-speci c interstitial pneumonia pattern include a more central distribution of traction bronchiectasis than is typically seen in UIP-IPF [49], and the presence of subpleural sparing [50] (Fig. 29.13). Following the publication of the 2011 guidelines for UIP [7], there has been a reduction in the number of idiopathic NSIP cases diagnosed by multidisciplinary teams. As the focus of diagnosis has moved towards identifying UIP-IPF, many cases that would have previously been assigned NSIP on HRCT were labelled as possible UIP from 2011 and probable UIP from 2018 onwards. An NSIP pattern is common in connective tissue disease-related interstitial lung disease (CTD-ILD), and if idiopathic pneumonia with

a

autoimmune features (IPAF) [51] gains consensus as a disease entity, idiopathic NSIP might indeed become a rare diagnosis.

Fibrosing Sarcoidosis

The upper lobe predominance of sarcoidosis typically distinguishes it from UIP-IPF, but distinguishing brosing sarcoidosis from CHP can be challenging. In brosing sarcoidosis architectural distortion and brosis originate at the lung hilum and extend to the posterior segments of the upper lobes [52]. In addition to volume loss and traction bronchiectasis, brobullous apical destruction can also be seen [53]. Perilymphatic and peri ssural nodularity with calci ed or non-calci ed mediastinal and hilar lymph nodes can aid CT diagnosis. Of note, sarcoidosis may very rarely present with typical UIP-IPF features on HRCT [54].

CTD-ILD and Drug-Induced FLD

As the diagnosis of CTD-ILD requires serological con rmation, diagnosis in an MDT setting is less problematic than for other brosing lung diseases. However, this is not to underplay the wide variety of radiological appearances that CTD-­ ILD may manifest, including airways disease [55], lungbrosis, organising pneumonia, pleural disease and pulmonary hypertension disproportionate to the severity of lungbrosis [56, 57]. Recognising drug-induced FLD requires an appropriate clinical history, but typical HRCT patterns are those of organising pneumonia and/or NSIP [58].

b

Fig. 29.13  Imaging features associated with non-speci c interstitial pneumonia include central bronchiectasis (a) which contrasts with the predominantly peripheral bronchiectasis seen in idiopathic pulmonary

brosis. Subpleural sparing (b) can also be seen and is often most marked in the lower lobes