As a rule of thumb, neoplastic lesions in the lung are similar to malignancies elsewhere, that is, they present as solitary or multiple discrete nodules. Metastases often have random distribution and different size. Please also refer to hematogenous metastases in the chapter “Nodula Diseases”.

This modality of growth along the bronchovascular bundles, in the interlobular septa, and within the pleura is called carcinomatous lymphangitis (CL). Please also refer to carcinomatous lymphangitis in the chapter “Septal Diseases”.

A peculiar pattern of presentation frequently responsible for the so-called ground-glass opacity (GGO) in CT is due to a lepidic growth of the neoplasm along alveolar septa. Please also refer to Adenocarcinoma in the chapter “Alveolar Diseases”.

In the context of a malignancy, this can be due to the presence of mucus as in pneumonia-like pattern of invasive mucinous adenocarcinoma, formerly mucinous BAC, or to the presence of neoplastic cells. In these cases, ground-glass opacity (GGO) and consolidations are the radiological expression of the disease, and more often a mixed pattern, where the two aspects coexist, is present. Please also refer to Adenocarcinoma in the chapter “Alveolar Diseases”.

Some tumors preferentially grow along bronchial and bronchiolar walls eventually invading their lumen. Also, preinvasive conditions such as DIPNECH (diffuse idiopathic pulmonary neuroendocrine cell hyperplasia) can exhibit this pattern of growth (). Expiratory HRCT shows patchy areas of black and white aspect due to air trapping. Some small solid nodules, consisting of tumorlets or typical carcinoids, also coexist (). Please also refer to DIPNECH in the chapter “Dark Lung Diseases”.

Characteristic of the exudative phase of a diffuse alveolar damage (DAD), they consist of proteinaceous exudate which adheres to the inner surface of the alveoli (Figure A ▶).

During the subsequent proliferative phase, the membranes are incorporated within the alveolar septa, which become thick (Figure B ).

Pulmonary alveolar proteinosis (PAP) consists of amorphous, lipid-rich, eosinophilic material with small globules and cholesterol clefts, within the alveolar spaces, with a rim of retraction at the edge (Figure A ).

Diffuse alveolar hemorrhage (DAH) is characterized by fibrin and hemosiderin-laden macrophages, which can be appreciated both on cytology in BAL fluid and at histology (Figure B). Capillaritis is often part of the picture; nevertheless, it represents a transient phenomenon and therefore it is not constantly seen.

Amyloid, whether nodular or interstitial, isolated finding or associated to chronic inflammation or low-grade lymphomas consists of the deposition of a homogeneous, acellular, pink material which can calcify or ossify (Figure A).

Microlitiasis appears as tiny, calcified micronodules filling the alveolar spaces (Figure B).

Lymphangioleiomyomatosis (LAM) is characterized by the presence of cysts with thin wall containing smooth muscle bundles (Figure A). LAM cells are spindle shaped and plump, with vacuolated cytoplasm.

Necrosis refers to the premature death of cells in living tissues; this is a detrimental event as opposed to apoptosis, which is actually the programmed cell death. It mostly appears as amorphous material with or without inflammatory cells (Figure B). Histologically, viable tissue cells and lung architecture (including vessels) are no longer appreciable in any kind of necrosis; so, the necrotic portion of a process results avascular in a computed tomography performed after the administration of contrast medium. Cavitation of the necrotic areas is also possible and frequent.