Differential diagnosis method for lung cancer

Clinical manifestations: The clinical manifestations of lung cancer are closely related to the location, size, compression, invasion of adjacent organs, and metastasis of the tumor. Tumors grow in larger bronchi, often causing irritating coughs. The enlargement of the tumor affects bronchial drainage, and secondary lung infection may cause purulent sputum. Another common symptom is bloody sputum, usually with blood spots, blood streaks, or intermittent hemoptysis; for some patients, even one or two bloody sputums are of great reference value for diagnosis. Some patients may experience chest tightness, shortness of breath, fever, and chest pain due to large bronchial obstruction caused by tumors.

When advanced lung cancer compresses adjacent organs and tissues or metastasizes to distant sites, it may cause: ① compression or invasion of the phrenic nerve, causing paralysis of the ipsilateral diaphragm. ② compression or invasion of the recurrent laryngeal nerve, causing vocal cord paralysis and hoarseness. ③ compression of the superior vena cava, causing venous distension in the face, neck, upper limbs and upper chest, subcutaneous tissue edema, and increased venous pressure in the upper limbs. ④ invasion of the pleura, which may cause pleural effusion, mostly bloody. ⑤ cancer invades the mediastinum, compresses the esophagus, and may cause dysphagia. ⑥ upper lobe apex lung cancer, also known as Pancoast tumor or superior pulmonary sulcus tumor, may invade and compress organs or tissues located at the upper opening of the thorax, such as the first rib, supraclavicular artery and vein, brachial plexus, cervical sympathetic nerve, etc., causing chest pain, venous distension of the jugular vein or upper limb, edema, arm pain and upper limb movement disorders, ptosis of the upper eyelid on the same side, pupil constriction, enophthalmos, anhidrosis on the face, and other cervical sympathetic syndromes.

A small number of lung cancers, due to the production of endocrine substances by the tumor, clinically present non-metastatic systemic symptoms, such as osteoarthritis (clubbed fingers, joint pain, periosteal hyperplasia, etc.), Cushing syndrome, myasthenia gravis, male breast enlargement, multiple muscular neuralgia and other extrapulmonary symptoms. These symptoms may disappear after the removal of lung cancer.

Diagnosis: Early diagnosis is of great significance. Regular chest X-ray screening should be conducted for people over 40 years old. For middle-aged people with persistent cough or bloody sputum or lung masses found in X-ray examination, the possibility of lung cancer should be considered and further thorough examination should be conducted.

Main methods of diagnosing lung cancer

1. X-ray examination: It is the main means of diagnosing lung cancer. In the early stage, there may be no abnormal signs in the X-ray manifestations of central lung cancer. When the tumor blocks the bronchus, the distal lung tissue becomes infected, and the affected lung segment or lobe shows signs of pneumonia. When the bronchial lumen is completely blocked by the tumor, the corresponding lobe or one side of the lung may become deflated.

The tomographic X-ray film may show the shadow of the mass protruding into the bronchial cavity, irregular and thickened tube walls, or narrowing and obstruction of the lumen. When the tumor invades the adjacent lung tissue and metastasizes to the hilar mediastinal lymph nodes, a mass in the hilar region may be seen, or the mediastinal shadow may widen with a wavy outline, irregular mass shape, uneven edges, and sometimes lobed. When the mediastinal lymph nodes compress the phrenic nerve, the diaphragm may be seen to be elevated, and paradoxical movement of the diaphragm may be seen on fluoroscopy. Enlarged metastatic lymph nodes under the tracheal carina may increase the tracheal bifurcation angle, and the adjacent anterior esophageal wall may also be compressed. In advanced cases, pleural effusion or rib destruction may also be seen.

The most common X-ray manifestation of peripheral lung cancer is a solitary circular or oval mass around the lung field, with a diameter ranging from 1 to 2 cm to 5 to 6 cm or larger. The mass has an irregular outline, often showing small lobes or notches, with fuzzy and rough edges, often with short and thin burrs. In a few cases, calcification points are occasionally seen in the mass. When peripheral lung cancer grows and blocks the bronchial lumen, segmental pneumonia or atelectasis may occur. The central part of the tumor is necrotic and liquefied, and thick-walled eccentric cavities can be seen. The inner wall is uneven, and there is rarely an obvious liquid level.

The X-ray manifestation of nodular bronchioloalveolar carcinoma is a solitary spherical shadow with clear outlines; the X-ray manifestation of diffuse bronchioloalveolar carcinoma is an invasive lesion with blurred outlines, ranging from a small piece to a lung segment or an entire lung lobe, similar to pneumonia.

Computerized tomography (CT) can display thin-section images to avoid overlap between lesions and normal lung tissue. It has high density resolution and can detect early lung cancer in areas hidden by general X-ray examinations (such as the apex of the lung, above the diaphragm, beside the spine, behind the heart, mediastinum, etc.). It is very valuable in determining whether there is mediastinal lymph node metastasis and helps to formulate treatment plans.

Magnetic resonance imaging (MRI): Also known as nuclear magnetic resonance imaging, its advantages are that it is easy to distinguish the mediastinum, hilar blood vessels from masses and lymph nodes, and multi-faceted imaging can better determine the tumor range and vascular involvement, and has good contrast resolution. However, due to the high air content in the lungs, the effect is not as good as CT, and it is expensive, so it is not widely used.

2. Sputum cytology: Cancer cells shed from the surface of lung cancer can be coughed up with sputum. Sputum cytology can confirm the diagnosis by finding cancer cells, with an accuracy rate of more than 80%. Especially in cases with bloody sputum, the chance of finding cancer cells in sputum is higher, and sputum should be sent for repeated examination for several times.

3. Bronchoscopy: For central lung cancer, the tumor can be directly seen in the bronchial cavity, and a small piece of tissue can be taken for pathological section examination. The surface tissue of the tumor can also be brushed through the bronchus or the bronchial secretions can be aspirated for cytological examination.

4. Transthoracic puncture biopsy: The positive rate of obtaining histological diagnosis for peripheral lung cancer can reach more than 90%, and the method is simple. However, in rare cases, complications such as pneumothorax, pleural cavity infection or bleeding, and cancer cell spread along the needle track may occur.

5. Pleural effusion examination: After the pleural effusion is extracted and centrifuged, the precipitate is taken for smear examination to look for cancer cells.

6. Mediastinoscopy: It can directly observe the lymph nodes under the anterior tracheal carina and on both sides of the bronchial area, and can take biopsy tissue for pathological examination to determine whether lung cancer has metastasized to the hilar and mediastinal lymph nodes. A positive result indicates that the lesion is extensive and is not suitable for surgical treatment. The positive rate of central lung cancer is higher.

7. Thoracoscopic examination: A small incision is made through the chest wall to insert a thoracoscope or fiber bronchoscope to directly observe the extent of the lesion or take living tissue for pathological section examination.

8. Radionuclide lung scan: Lung cancer and its metastatic lesions have an affinity for radionuclides such as gallium-67 and mercury-197 chloride. After intravenous injection, radionuclide deep concentration images are present at the cancerous site, and the positive rate can reach about 90%. However, pneumonia and some other non-cancerous lesions can also show positive phenomena, so a comprehensive analysis must be conducted in combination with clinical manifestations and other data.

9. Biopsy of metastatic lesions: For patients with advanced lung cancer who have metastasized to the supraclavicular, cervical, axillary lymph nodes or subcutaneous nodules, pathological sections of lesion tissue can be removed or tissue can be extracted by puncture for smear examination to confirm the diagnosis.

10. Thoracotomy: If the nature of the lesion cannot be determined after various examinations, and the possibility of lung cancer cannot be ruled out, thoracotomy should be performed if the patient's general condition permits. During the operation, a biopsy or corresponding treatment should be performed according to the lesion to avoid delaying the disease.

Differential Diagnosis

1. Tuberculosis

① Tuberculoma is easily confused with peripheral lung cancer. Tuberculoma is more common in young people, and the course of the disease is generally long and slow. The lesions are often located in the posterior segment of the upper lobe tip or the dorsal segment of the lower lobe. The density of the block shadows on the X-ray film is uneven, and sparse translucent areas and calcification points can be seen. There are often scattered tuberculosis foci in the lungs.

② Miliary tuberculosis is easily confused with diffuse bronchioloalveolar carcinoma. Miliary tuberculosis is common in young people, with obvious systemic toxicity symptoms. Anti-tuberculosis drug treatment can improve symptoms and the lesions will gradually absorb.

③ Hilar lymph node tuberculosis may be misdiagnosed as central lung cancer on X-rays. Hilar lymph node tuberculosis is common in young children, often with symptoms of tuberculosis infection and rarely with hemoptysis. It should be noted that lung cancer can coexist with pulmonary tuberculosis. Clinical symptoms, X-rays, sputum cytology and bronchoscopy should be combined to make a clear diagnosis early to avoid delaying treatment.

2. Lung inflammation

① Bronchopneumonia: Obstructive pneumonia caused by early lung cancer is easily misdiagnosed as bronchopneumonia. Bronchopneumonia develops rapidly, with severe infection symptoms and obvious systemic infection symptoms. X-rays show flaky or spotted shadows with fuzzy boundaries, uneven density, and are not limited to one lung segment or lobe. After anti-infection treatment, the symptoms disappear quickly and the lung lesions are absorbed quickly.

② Lung abscess: When the central part of lung cancer necrotizes and liquefies to form a cavity, the X-ray findings are easily confused with lung abscess. Lung abscess has obvious infection symptoms in the acute stage, with a large amount of purulent sputum. On X-rays, the cavity wall is thin, the inner wall is smooth, and there is often a fluid level. The lung tissue around the abscess is often infiltrated, and the pleura has inflammatory changes.

3. Other lung tumors

① Benign lung tumors: such as hamartoma, fibroma, chondroma, etc., sometimes need to be differentiated from peripheral lung cancer. Generally, benign lung tumors have a long course, grow slowly, and are mostly asymptomatic. On X-ray films, they appear as round-shaped masses with uniform density and may have calcification points. They have neat contours and are mostly non-lobed.

② Bronchial adenoma: It is a low-grade malignant tumor. The age of onset is younger than lung cancer and it is more common in women. The clinical manifestations are similar to those of lung cancer, with irritating cough and repeated hemoptysis. X-rays may show obstructive pneumonia or localized atelectasis of segments or lobes. Soft tissue shadows in the lumen can be seen on tomographic films, and smooth-surfaced tumors can be found under fiberoptic bronchoscopy.

4. Mediastinal lymphosarcoma: It can be confused with central lung cancer. Mediastinal lymphosarcoma grows rapidly, and clinical symptoms often include fever and superficial lymph node enlargement in other parts of the body. X-rays show enlarged paratracheal and hilar lymph nodes on both sides. It is sensitive to radiotherapy, and the mass can be seen to shrink after low-dose irradiation.