Radiological Findings: 

The radiological patterns observed on CT can be as follows [5]: 

• Organising Pneumonia Pattern: This is the most common form of DI-ILD. It represents a type of acute pulmonary damage that is histopathologically characterised by interstitial inflammation and excessive proliferation of granulation tissue within the terminal bronchioles and alveoli. Bilateral, multifocal, peripheral ground-glass opacities and/or consolidation areas with a predominance in basal regions are observed. It may also present as ground-glass opacities with a peripheral consolidation halo (atoll sign), which can be migratory and variable over time.

• Non-Specific Interstitial Pneumonia Pattern: This is the second most frequent pattern and is often associated with mild symptoms and/or asymptomatic patients. Histopathologically, it is characterised by thickening of the lung interstitium due to inflammatory infiltrate (cellular NSIP) and/or fibrosis (fibrotic NSIP). The cellular form presents bilateral, peripheral, patchy or diffuse ground-glass opacities, with a predominance in the middle and basal zones. In the fibrotic form, a peripheral reticular pattern is seen, with a predominance in the lower lobes, and subpleural respect may be present in both forms.

• Hypersensitivity Pneumonitis Pattern: This is an infrequent form of DI-ILD, generally presenting in its non-fibrotic form with mild symptoms. Ground-glass opacities can be observed, with or without air trapping areas and centrilobular micronodules, with a predominance in the upper lobes.

• Acute Interstitial Pneumonia Pattern: A rare form of DI-ILD, associated with acute symptoms of dyspnoea and hypoxia, which histologically presents as diffuse alveolar damage with necrosis of type 2 pneumocytes, alveolar oedema, and necrosis of alveolar endothelial cells. It is characterised by the rapid development of bilateral diffuse pulmonary opacities, with ground-glass or confluent consolidations, affecting nearly the entire parenchyma. In some cases, a "crazy paving" pattern with interlobular septal thickening may also be observed. 

• Simple Pulmonary Eosinophilia Pattern: Typically asymptomatic, with patchy ground-glass opacities or unilateral or bilateral consolidations. It resolves spontaneously within a few weeks. It has been linked to treatment with checkpoint inhibitors (ICI), particularly Osimertinib.

Other less frequent entities that may be encountered, which do not have typical radiological features, include:

• Sarcoid-like granulomatosis: A very rare entity associated with ICI therapy, characterised by presenting histological and radiological features identical to those of sarcoidosis, with hilar and mediastinal lymphadenopathy and perilymphatic nodules. On PET-CT, these may show uptake and mimic metastatic disease, highlighting the importance of recognising this entity to avoid misinterpretation.

• Pneumonitis Flare: Associated with ICI therapy. It occurs as an exacerbation or flare of previously treated pneumonitis when corticosteroid dose reduction or withdrawal occurs without reintroducing ICI treatment.

• Radiation Recall: This refers to an acute inflammatory pneumonitis occurring after the administration of an inducer drug in a previously irradiated field.