Lung cancer cases present a variety of clinical symptoms and X-ray signs depending on the tumor site, pathological type and early and late stages of the disease, and are easily confused with other lung diseases. Therefore, the differential diagnosis of lung cancer, especially for early stage cases, is important for early diagnosis and treatment.
(A) Tuberculosis
1.Tuberculosis bulb Easily confused with peripheral type lung cancer. Tuberculosis bulbs are mostly seen in young patients. The lesions are often located in the apical and posterior segments of the upper lobe or the dorsal segment of the lower lobe, and generally grow inconspicuously with a long duration of disease. On the X-ray film, the density of the mass shadow is not uniform, and sparse translucent areas can be seen, often with calcified spots, smooth margins and clear demarcation, and there are often other scattered tuberculosis foci in the lung.
2. The x-ray signs of cornified pulmonary tuberculosis are similar to those of diffuse bronchoalveolar carcinoma. The fever, night sweats and other symptoms of systemic toxicity are obvious, and anti-tuberculosis drug treatment can improve the symptoms and the lesions are gradually absorbed.
3.Pulmonary hilar lymph node tuberculosis The hilar mass shadow on X-ray may be misdiagnosed as central type lung cancer. Tuberculosis of hilar lymph nodes is mostly seen in young and young adults, often with symptoms of tuberculosis infection, rarely with hemoptysis, often with positive tuberculin test, and with good effect of anti-tuberculosis drug treatment.
It is worth mentioning that lung cancer can coexist with tuberculosis in a few patients. Since there is no special clinical manifestation and the X-ray signs are easily ignored, clinicians are often satisfied with the diagnosis of tuberculosis and ignore the co-existing cancerous lesions, which often delays the early diagnosis of lung cancer. Therefore, for middle-aged or older patients with pulmonary tuberculosis, if the lump-like shadow is present in the focal area of tuberculosis or other lung fields, and the lump shadow does not improve after anti-tuberculosis drug treatment, but increases in size or is accompanied by lung segment or lobe atelectasis and widening of the shadow in one lung door, the coexistence of tuberculosis and lung cancer should be highly suspected, and further sputum cytology and bronchoscopy must be performed.
(B) Inflammation of the lung
1. Bronchopneumonia Obstructive pneumonia arising from early lung cancer is easily misdiagnosed as bronchopneumonia. Bronchopneumonia generally has an acute onset, with obvious symptoms of infection such as fever and chills, and the symptoms disappear rapidly after antibacterial drug treatment, and the lung lesions are absorbed more quickly. If the inflammation is slowly absorbed or recurring, further in-depth examination should be conducted.
2.Lung abscess When the central part of lung cancer is necrotic and liquefied to form cancerous cavity, the X-ray signs are easily confused with lung abscess. Cases of lung abscess often have a history of aspiration pneumonia. In the acute stage, there are obvious symptoms of infection, and the sputum is large, purulent and smelly; on X-ray, the cavity wall is thin, the inner wall is smooth and there are fluid planes, and the lung tissue or pleura around the abscess often has inflammatory lesions. The contrast agent can enter the cavity during bronchography, and is often accompanied by bronchial dilatation.
(C) Other thoracic tumors
Benign tumors of the lung Sometimes benign tumors of the lung must be distinguished from peripheral type lung cancer. Benign lung tumors generally do not show clinical symptoms, grow slowly and have a long course. On the X-ray film, it shows a nearly round block shadow, which may have calcification points, neat outline, clear boundary and no lobar shape.
2.Isolated metastatic carcinoma of the lung Isolated metastatic carcinoma of the lung is difficult to be distinguished from primary peripheral type lung cancer. The differential diagnosis mainly relies on detailed medical history and symptoms and signs of the primary carcinoma. Metastatic carcinoma of the lung generally presents less respiratory symptoms and sputum blood, and sputum cytology examination is not easy to find cancer cells.
3.Mediastinal tumor Central type lung cancer may sometimes be confused with mediastinal tumor. Diagnostic pneumothorax can help to clarify the location of the tumor. Mediastinal tumors are less likely to present with hemoptysis, and sputum cytology fails to find cancer cells. Bronchoscopy and bronchogram can help in the differential diagnosis. Mediastinal lymphoma is more often seen in young patients, often bilateral, and may have systemic symptoms such as fever.
Predicting primary tumor by X-ray features of lung metastasis
1.Primary tumor can be inferred from the shape and margin of metastases: ①sarcoma lung metastases are mostly spherical in shape, with the smoothest margin and higher density; ②pulmonary metastases of choriocarcinoma have slightly blurred margin and are distributed in both lungs in a cotton ball-like pattern. The margins are sharp before chemotherapy and often become irregular due to chemotherapy or bleeding in the marginal area. The thick lung texture with bead-like and corn-like changes can be seen in dynamic observation, which is often the early metastatic sign of choriocarcinoma. After the primary foci are removed and effective anti-cancer treatment is run for 2-3 weeks, the lung metastases shrink or disappear quickly. This phenomenon is also seen in testicular embryonic cell carcinoma, but rarely in other malignant tumors; ③ lung metastases of thyroid cancer are mostly corn-like, pinhead to rice-grain in size, scattered in both lungs with thickened lung texture; ④ metastases of gastric cancer are mostly of lung lymphatic infiltration type, showing an increase in hilar shadow, with more thin cord-like shadows spreading from both sides of the hilar to the lung field, and gradually thinning to the periphery of the lung. (5) The cancer nodules of lung metastasis of kidney cancer can be in the shape of “shell” shadows.
2.The primary tumor can be inferred from the multiplication time, cavity, pneumothorax, calcification and ossification of metastases: the multiplication time of sarcoma and choriocarcinoma is shorter, about 10~12d; that of seminoma is second, about 24~48d; that of squamous carcinoma is second, about 50~60d; that of adenocarcinoma is longer, about 75~90d; and that of thyroid carcinoma is longer, up to several years. About 4%-9% of the lung lesions can form cavities, especially in the upper lobes. Among them, squamous carcinoma is the most common, followed by female germline carcinoma. Lung metastases from adenocarcinoma are more common in colorectal carcinoma, which can also form multiple pulmonary cavities. The cavity is caused by necrosis in the center of the lesion, occasionally there can be liquid flat. The cavity can be caused by chemotherapy, there are two kinds of cavities, thick-walled and thin-walled, the former is more cancerous, the latter is more sarcoma, the cavity rupture can produce pneumothorax. In metastases near the subpleural area, tissue necrosis and formation of bronchopleural fistula are the causes of pneumothorax, and the appearance of pneumothorax is often the precursor of pulmonary metastasis from osteosarcoma. The cavities of pulmonary metastases in the head and neck are small and thin-walled, and those of metastases from germline cancers are large and thick-walled. Calcification or ossification is suggestive of sarcoidosis or malignant tumor. However, calcification has also been reported in metastases from chondrosarcoma, synovial sarcoma, giant cell tumor, colon cancer, ovarian cancer, breast cancer, and thyroid cancer.
Differentiation of primary lung tumors from metastatic lung tumors?
Isolated nodules in the lung following a history of extra-pulmonary tumor should be considered first for metastatic lung cancer. For solitary nodular pulmonary metastases, differentiation from multiple primary carcinomas in the lung, i.e., double or multiple primary carcinomas, should be emphasized. Among the isolated lesions in the lungs of malignant tumor cases, about 20%-60% can be primary lung cancer, while the true lung metastasis can be only 23%-46%.
(A) Exclusion rule
1.The primary tumor is sarcoma or malignant melanoma, and most of the intrapulmonary masses are metastatic.
2.The primary tumor is highly differentiated squamous cell carcinoma or breast cancer, and the intrapulmonary masses are more likely to be multiple primary carcinomas.
3.The primary tumor is adenocarcinoma or hypofractionated carcinoma, and intrapulmonary masses are more likely to be metastatic or have equal chance of primary and metastatic carcinoma.
4.If the multiplication time of single nodular shadow in the lung is <10d or >1 year, then most of the malignant tumors can be excluded, but the exceptions should still be alerted.