The doctor told me that I have a cavity in my lung. What's going on?

Author: Zhao Liqiang, Chief Physician, Beijing Chaoyang Hospital, Capital Medical University

Reviewer: Zhi Xiuyi, Chief Physician, Xuanwu Hospital, Capital Medical University

Chest X-ray examination is a commonly used clinical examination method. When many people get the examination report, they are always puzzled by the unfamiliar term "cavity containing gas and fluid". What does it mean? Let's take a look.

The lungs are like a big tree, with leaves and trunks connected. If a branch dies, the substances produced after necrosis can return to the trunk. In other words, the infection in the lung tissue, including tissue necrosis, can be discharged to the large airways little by little through the beating of cilia, a special structure in the airway, and then discharged from the body through coughing.

Figure 1 Original copyright image, no permission to reprint

There are many reasons for tissue necrosis, such as infectious lesions, such as lung abscess and tuberculosis, and tumor lesions, such as lung cancer.

Regardless of the type of lesion, the closer the lesion tissue is to the center, the worse its blood supply will be. The surrounding blood vessels are abundant, but in the center, there is no blood supply, so the tissue will die. Then the necrotic tissue is discharged from the body, and the middle is empty, which is called a "cavity".

The "fluid level with gas" actually means that the necrotic tissue has not been completely discharged. Some of the necrotic tissue has been discharged, and some has not. The necrotic tissue that has not been discharged has turned into liquid substances. When standing, there is liquid in the cavity, which is equivalent to a horizontal plane, with gas on the top and liquid on the bottom. This is called the "fluid level with gas".

Figure 2 Original copyright image, no permission to reprint

When an X-ray examination finds a "cavity containing air and fluid levels", clinicians can often make a preliminary diagnosis of the disease based on the patient's symptoms and signs, including blood test results.

If you want to see more clearly, you can use better imaging technology, that is, chest CT to perform examinations, so as to make differential diagnoses, because the cavities caused by lung abscesses, tuberculosis, and lung cancer appear differently in images.

For example, the symptoms of lung abscess usually occur more frequently during the acute infection period. Of course, there are also chronic lung abscesses. The most obvious clinical symptom is coughing up a lot of yellow purulent sputum. The manifestation on X-rays or CT scans is relatively a sheet-like area. Because it is inflammation, the density is relatively light. After the cavity appears, the wall of the cavity is relatively round and complete.

Tuberculosis is generally more infiltrative. Unlike bacterial infection, tuberculosis bacteria are prone to calcification, so the density of the lesion is relatively deeper than that of lung abscess. However, it is also an infectious lesion and will also grow infiltratingly in the surrounding tissues, so the boundary between the lesion and the surrounding tissues is not very clear. There may also be small, jumping infection foci around, called satellite foci. Relatively speaking, the cavities of pulmonary tuberculosis are not as smooth as those of lung abscesses, but are relatively rough, like insect bites, and because tuberculosis bacteria continue to destroy tissues, there will be some calcification in the lesions. In addition, in terms of symptoms, patients with pulmonary tuberculosis will also experience symptoms of tuberculosis poisoning such as fatigue, low fever, night sweats, and loss of appetite; sputum examination or sputum culture can find tuberculosis bacteria, so that a clearer diagnosis can be made.

Generally speaking, the cavities of lung cancer are caused by abnormal cell proliferation. When the proliferation reaches a certain extent and the center has no blood supply, necrosis will occur. After the necrotic part is discharged, a cavity is formed, and most of them are eccentric dissolution. This cancerous lesion is expansive growth, not invasive growth. Chest CT shows that there are burrs around the tumor. Compared with lung abscess and tuberculosis, patients with lung cancer with cavities may have more severe symptoms, accompanied by cough, hemoptysis, hoarseness, chest pain and other symptoms. If the tumor metastasizes to distant places, extrapulmonary symptoms will also appear.

In general, doctors can make a clear diagnosis based on the patient's symptoms, signs, laboratory tests, and imaging examinations. For patients, when we find "cavities containing air and fluid levels" in the lungs, don't be too nervous. Under the guidance of a doctor, get a confirmed diagnosis and actively receive treatment in order to get a better prognosis.