Rare pulmonary tumours: a histological and radiological overview

Adenocarcinoma, squamous cell carcinoma, and small cell carcinoma represent about 95% of lung tumours. However, the lung is the site of numerous types of tumours that may have an epithelial, mesenchymal, neuroendocrine, or lymphohematopoietic origin. With minor exceptions, both the clinical manifestations and the imaging characteristics are non-specific; many of the low-incidence tumours have common features with the high-incidence tumours. This article presents a group of low-incidence pulmonary tumours that pose multiple difficulties in terms of diagnosis due to non-specific symptomatology and non-specific imaging aspect. This article aims to correlate the histological data with imaging aspects to facilitate diagnostics. Because these tumours are rare and because they present in a variety of forms, problems may occur when establishing a diagnosis and trying to predict their behaviour. It is challenging to differentiate common lung tumours from rare ones based on clinical, radiological, or histological features. Only the presence of the imaging particularities, such as the location of the lesion, the association with certain patterns (appearance of ground glass, the “halo” sign, the presence of calcifications), and the histological/immunohisto-chemical profile can lead to the establishment of a correct diagnosis.