Primary bronchogenic carcinoma, also known as lung cancer, is malignant tumor originating from the bronchial, bronchiolar, and alveolar epithelium and glandular epithelium. Its mortality is high, and its incidence is increasing year by year. It is the most common malignant tumor in human body. In the past, most lung cancers found in clinical practice were in the middle and late stages. Now, with the widespread application of CT and the improvement of health awareness, more and more early lung cancers are detected. Cigarette smoking is still the main pathogenic factor, and other factors include air pollution and genetics.
Clinical presentation and pathology
According to different biological behaviors, lung cancer is divided into small cell lung cancer and non-small cell lung cancer. The former accounts for 15% - 20%; the latter mainly includes squamous cell carcinoma, adenocarcinoma, adenosquamous carcinoma, and large cell carcinoma.
According to the location of lesion, lung cancer can be divided into central lung cancer, peripheral lung cancer, and diffuse lung cancer. In central lung cancer, the tumor occurs in the lung segment and bronchi, mostly squamous cell carcinoma. In peripheral lung cancer, the tumor occurs in the bronchioles, mainly adenocarcinoma. In diffuse lung cancer, the tumor occurs in the terminal bronchioles or alveolar walls.
Lung cancer in the early stage often has no clinical symptoms and is often discovered accidentally during physical examination. Lung cancer in the middle and late stages mainly presents with cough, expectoration, hemoptysis, thoracodynia, and fever. Its clinical symptoms and signs are closely related to the location, size, peripheral invasion, location of metastases, and the presence or absence of paraneoplastic syndrome of the tumor.
Imaging manifestations
Central lung cancer
Early central lung cancer is tumor confined to the bronchial lumen or infiltrating along the wall, the peripheral lung parenchyma is not involved, and there is no distant metastasis.
X-ray
There are often no abnormal manifestations on the chest film, and occasionally there may be localized emphysema or obstructive pneumonia.
CT
CT can clearly show irregular thickening of the bronchial wall, stenosis of the lumen, or intraluminal nodule.
Figure 1 Early central lung cancer
Contrast-enhanced CT shows local irregular thickening of the wall of the right intermediate bronchus and lumen stenosis (↗).
Middle and late central lung cancer often has apparent manifestations on chest x-ray and CT examinations.
X-ray
The main manifestation on the chest film is hilar mass, lobulated or with irregular edges, and is often accompanied by obstructive pneumonia or atelectasis.
CT
CT can clearly show mass inside the bronchial lumen or on the wall, irregular bronchial wall, rat tail narrowing, and conical or annular truncation of the lumen. Obstructive pneumonia is manifested by consolidation of lung tissue distal to the affected bronchus, mostly scattered. When atelectasis occurs, the homogeneous density of the lung lobe or segment increases and the volume decreases. In addition, contrast-enhanced CT can clearly show whether central lung cancer invades the mediastinal structure or is accompanied by hilar and mediastinal lymph node metastasis, whether the blood vessels are invaded or compressed and displaced, and whether the lumen is narrowed or occluded and the wall is irregular.
Figure 2 Middle and late central lung cancer
a, b. In the same case. a. Chest x-ray film shows a mass in the right hilum accompanied by atelectasis in the right upper lung, and the mass in combination with the lower edge of the atelectatic lung form Golden S sign (white ↗); b. Coronal CT shows a conical truncation at the origin of the bronchus in the right upper lobe (black ↗), accompanied by atelectasis of the right upper lobe.
MRI
Through axial, coronal, and sagittal examinations, the relationship between the hilar mass and the bronchus and the involvement of the mediastinal blood vessels can be determined. Lung cancer mass is isointense and homogeneous on T1WI and hyperintense on T2WI. Large mediastinal blood vessels show flow voids on MRI, which is easy to distinguish from tumor. Mass is predominantly hyperintense on DWI and predominantly hypointense on ADC, which is helpful for diagnosis and differential diagnosis.
Peripheral lung cancer
Early peripheral lung cancer is tumor ≤ 2. 0cm in diameter, without distant metastasis.
X-ray
Chest film shows irregular intrapulmonary nodule, with lobulation sign, spiculation sign, and pleural indentation sign.
CT
CT can clearly show the internal characteristics, edges, and peripheral signs of the tumor. Small peripheral lung cancer presents ground glass nodule (GGN) or solid nodule. Usually, GGN can be divided into pure ground glass nodule (pGGN) and mixed ground glass nodule (mGCN), and the latter has higher malignancy. pGGN is often difficult to show on chest x-ray and is often missed in diagnosis, but it can be easily seen on CT. Pathologically, tumor cells growing along the alveolar wall in an adherent or infiltrative manner can be seen, and air can still be seen in the incompletely collapsed alveolar cavity, so the lesion shows ground glass opacity, and CT value is often negative.
Figure 3 Early peripheral lung cancer
a. CT lung window shows a nodule in the right lung (↗), with spiculation sign; b. CT mediastinal window shows a lobulated nodule in the right lung with internal vacuole sign and external pleural indentation sign (↗).
Middle and late peripheral lung cancer often has large nodule or mass in the lung.
X-ray
Chest film shows mostly spherical mass in the lung, with lobulation sign, spiculation sign, and pleural indentation sign. When necrotizing tumor is drained through the bronchus, thick-walled eccentric cavity can be formed. Calcification in the mass is less common.
CT
CT, especially HRCT, can show the details of nodule and mass more sensitively and clearly than chest x-ray, including changes in the morphology, edges, cavity, and peritumoral signs. Contrast-enhanced CT can show significantly homogeneous or inhomogeneous enhancement, which is helpful for the diagnosis of lung cancer.
Figure 4 Middle and late peripheral lung cancer
a. CT lung window shows a thick-walled cavity of the irregular mass in the right upper lung, with lobulation sign, spiculation sign, and pleural indentation sign at the edge; b. CT mediastinal window shows rough inner wall of the thick-walled cavity and mural nodules, and surgical pathology confirms it is squamous cell carcinoma.
MRI
Lung cancer mass is homogeneous and isointense on T1WI and hyperintense on T2WI. When tumor is necrotizing, mass is usually inhomogeneous; the material part of the mass is often predominantly hyperintense on DWI.
Diffuse lung cancer
X-ray
Diffuse lung cancer on chest radiograph often presents small nodules widely distributed in both lungs, or massive pneumonia-like changes. The lesions are progressive and tend to fuse; the fused lesions are massive, and even develop into consolidation of the entire lung lobe; and sometimes air bronchogram sign can be seen.
CT
CT shows diffusely distributed nodules in both lungs, with or without enlarged hilar and mediastinal lymph nodes. When the lesions fuse into massive consolidation, air bronchogram sign can be seen, but there are rigid running and leafless tree sign, and this consolidation is different from that in lobar pneumonia in manifestations. On contrast-enhanced CT, since this type of tumor cells can secrete some mucus, the consolidated area is hypodense, and sometimes hyperdense vessels can be seen and is termed CT angiogram sign, which is one of the important diagnostic features.
Diagnosis and differential diagnosis
Central lung cancer needs to be differentiated from endobronchial tuberculosis and bronchial adenoma. Endobronchial tuberculosis has thickened bronchial walls with irregular inner edges and smooth outer edges; sometimes stenosis and dilation coexist; generally, no wall mass is formed; and obstructive pneumonia or atelectasis may occur. Bronchial adenoma has a smooth surface, the adjacent bronchial walls are not invaded or thickened, and definite diagnosis requires transbronchial biopsy.
Peripheral lung cancer needs to be differentiated from inflammatory myofibroblastic tumor (IMT), tuberculoma, and pulmonary hamartoma. Inflammatory myofibroblastic tumor generally has smooth edges, with no or occasional lobes, and is often significantly enhanced on contrast-enhanced CT. Tuberculoma has clear edges, may have annular or patchy calcification, and is often accompanied by peripheral satellite lesions. Pulmonary hamartoma has smooth and sharp edges, without spicules, and may have lobes; if there is popcorn calcification or fat component, the diagnosis can be confirmed.