The term "connective tissue diseases" (CTDs) refers to a heterogeneous group of autoimmune disorders, including systemic sclerosis, rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, polymyositis, dermatomyositis, antisynthetase syndrome, and mixed connective tissue disease. Chest high-resolution computed tomography (HRCT) is the imaging method of choice for evaluating patients with known or suspected CTD-related interstitial lung disease (CTD-ILD), a complication accounting for substantial morbidity and mortality. While specific HRCT patterns and signs of CTD-ILD have been extensively described (hence the designation "the usual suspects"), the knowledge of various, less frequent conditions involving the lungs in patients with CTD would help the radiologist produce a clinically valuable report, thus potentially influencing patient management. This paper aims to provide an up-to-date review of various unusual pulmonary CTD-related conditions the radiologist should be aware of; namely, acute exacerbation of CTD-ILD, CTD-related interstitial lung abnormalities, lung amyloidosis, MALT lymphoma, antisynthetase syndrome, pleuroparenchymal fibroelastosis-like lesion, drug-induced ILD, combined pulmonary fibrosis and emphysema, and pulmonary hypertension. For each condition, the chest HRCT appearance and the key histopathological and clinical features are resumed, helping the radiologist participate actively in the multidisciplinary discussion of complex clinical cases.
