I. CT manifestations of lung cancer
(I) Central type lung cancer
Central type lung cancer is mainly: masses in the bronchial lumen above the segment, thickening of bronchial wall: narrowing and obstruction of bronchial lumen, masses in the hilar region and other direct signs of lung cancer. Secondary changes include obstructive pneumonia and atelectasis, mucus embolism formed by bronchial dilatation distal to the obstruction, and enlarged lymph nodes near the lesion or (and) in the hilum; spiral CT, especially multilevel CT, using thin-layer scanning and coronal and sagittal reconstruction can clearly show early lung cancer infiltrating along the wall in the bronchial lumen.
CT scan is difficult to distinguish the tumor from its distal lung atelectasis, and enhanced scan can clearly show the actual size of the tumor and the atelectasis of the lung.
(II) Peripheral type lung cancer.
Peripheral type lung cancer shows certain features on CT, and even early lung cancer less than 2.0 cm has mostly clear signs of malignancy. The following is a brief description of the CT sign characteristics and the pathological basis of small peripheral carcinoma with a diameter of <3 cm.
1. Characteristics of tumor margin signs.
(1) Lobular sign: It is the most common basic sign of peripheral small lung cancer. The incidence of lobar sign in 100 cases of small lung cancer less than 3 cm in diameter was 84%. The majority of small lung cancers are deeply lobulated (the ratio of chord distance to distance length is more than 2/5. The pathological basis is firstly related to the different degrees of differentiation and growth rates of tumor cells in different parts of the tumor margin; secondly, the connective tissue interval of the lung, the blood vessels entering the tumor, bronchial branches, blood vessels and connective tissue growing outward from the tumor, etc. cause tumor growth restriction and produce depression, thus forming the lobulated form.
(2) Marginal roughness: fine and short burrs, spine-like protrusions or serrated changes can be seen. This is a common sign of lung cancer, and the incidence is about 80%-85%. These manifestations are due to the growth of tumor interstitium, blood vessels outside the tumor and the spread of tumor cells around the tumor.
2.CT performance characteristics inside the tumor
The density of most peripheral small lung cancers is relatively homogeneous, but some cases may have vacuolar sign, fine bronchial inflation sign, honeycomb sign and ground glass sign, and calcification can be seen in a few cases.
(1) Vacuolar sign: It is a small focal translucent area within the nodule. It is <5 mm in diameter, so as to distinguish it from lung cancer cavity. It can be single or multiple. If multiple dense vesicles are clustered together in a honeycomb pattern, it is called the honeycomb sign. The pathological basis is.
(i) Air-containing lung tissue that is not occupied by tumor tissue.
(2) Unconfined or dilated small bronchi.
(3) Air-containing lacunae between papillary carcinoma structures.
④The unclosed alveolar cavity or melting of cancerous tissue growing along the alveolar wall and destruction with enlarged alveolar cavity.
⑤ Formation of small focal necrosis within the tumor after discharge. This sign is mostly seen in fine bronchial alveolar carcinoma and adenocarcinoma, but also in squamous carcinoma. Sometimes, the presence of mucus, exfoliated tumor cells and other components in the alveoli may increase their CT values and resemble watery density. In the lung window, it appears as a small vesicular blurred hypointense shadow, and in the mediastinal window, it appears as a small vesicular translucent shadow.
(2) Fine bronchial inflation sign: air-density shadow in the form of thin strips, about 1 mm in diameter, or air-density shadow in the form of small vesicles (<1 mm in diameter), seen in several consecutive adjacent levels, pathologically dilated fine bronchioles. It is seen in fine bronchial alveolar carcinoma or adenocarcinoma.
(3) Honeycomb sign: It consists of multiple small alveoli integrated into a honeycomb shape, and its size is relatively uniform. This sign is only seen in alveolar carcinoma. Pathologically, the cancer cells grow along the alveolar wall and do not close the alveolar cavity, and mucus may be left in the cavity to make it expand.
(4) Ground glass sign: The whole tumor nodule or part of the nodule has a lighter density and is ground glass-like, without obscuring the pulmonary vascular texture. The boundary of the lesion is usually still clear. The pathological basis is that the tumor cells grow along the alveolar wall, the alveolar wall is thickened, but the alveolar cavity is not occluded, and there can be a small amount of mucus or detached tumor inside, this sign is only seen in alveolar carcinoma.
(5) Cavity: It is a round or circular air-like low-density shadow larger than 5 mm. The incidence of cavity in 100 cases of peripheral type small lung cancer is 4%. The cavities in small lung cancer have uneven wall thickness, uneven inner wall, and wall nodules. The cavities occurred centrally or eccentrically. In individual cases, the cavity wall is thin. The edges of the tumor can still be seen as lobulation and burr. Most of the cavities are formed when the necrotic liquefied material of tumor tissue is connected with bronchus and discharged.
(6) Calcification: Calcification can be found in peripheral small lung cancer. The literature reports that the detection rate of calcification in lung cancer on HRCT can reach 15.8%. The authors detected 3 cases of 100 small lung cancers with thin-section CT scans. The calcifications appeared as fine gravelly, small nodules with diffuse or lateral or central distribution. Calcification in lung cancer is mainly seen in squamous carcinoma and adenocarcinoma.
Its pathological basis is.
① Dystrophic calcification, due to tumor blood supply disorder, tumor cell degeneration, necrosis, local acid-calcium change and calcium deposition.
② Calcification that was previously present in the tumor package, which occurred from pre-existing granulomatous calcification.
③ Primary tumor calcification, mainly seen in mucinous adenocarcinoma.
3. CT signs of structural changes adjacent to the tumor
(1) Vascular aggregation sign It refers to the aggregation of surrounding blood vessels to the nodule. The blood vessels interrupt at the edge of the tumor or penetrate the tumor. Both arteries and veins can be involved. Among them, the involvement of pulmonary veins is important for the differentiation of benign and malignant. The presence of vascular aggregation is associated with a fibroblastic reaction within the tumor, thickening of the supply vessels to the tumor, and invasion of the pulmonary vasculature by the tumor. Although the literature reports that vascular aggregation signs can also be seen in benign lesions, our experience is that the detection rate of vascular aggregation in benign lesions is low, whereas it reaches 64-67% in small lung cancers.
(2) Pleural depression sign; there are three main presentations.
1.When the center of the recess is parallel to the scan level, it shows the typical pleural depression sign–a triangular shadow or trumpet between the tumor foci and the adjacent chest wall, the tip of which is connected with the linear shadow;
2.When the scan level deviates from the center of the depression, the linear shadow is divided into two or more, and sometimes it is gradually separated from the tumor, and the triangular shadow becomes larger and smaller and divided into two small triangles;
The horizontal and oblique cleft thoracothoracic depressions showed curved shadows depressed to the side of the tumor, etc. Zhang Zhiyong reported that the detection rate of pleural depression sign in peripheral type small lung cancer was 93%. It is mainly seen in adenocarcinoma and fine bronchoalveolar carcinoma. The pathological basis is generally believed to be caused by the contraction of fibrous scar tissue within the lesion. The contraction of the scar is transmitted to the dirty pleura through the fibrous meshwork adjacent to the tumor, which pulls the dirty pleura toward the tumor. The space between the recess and the mural pleura is filled with physiological fluid.
(3) Truncation and narrowing of bronchi below the subsegment
(4) Fuzzy small film shadow on the pleural side of the tumor, with an occurrence rate of about 10%, is a sign of fine bronchial obstruction.
(5) Satellite foci: except for individual cases of adenocarcinoma, all of them showed isolated nodules without satellite foci, and the authors did not see any case of small lung cancer with satellite foci in 100 cases.
4.CT enhancement features of lung cancer
The blood supply and metabolism between lung cancer and benign lesions are very different, so it is important to use enhancement scan to distinguish benign and malignant lesions.
The enhancement pattern of lung cancer has the following characteristics.
(i) The enhancement magnitude is large, exceeding 20 HU, and the curve is maintained at a high value after reaching the peak;
(ii) rapid rise of the temporal density curve; (iii) high perfusion; (iv) 85% of patients eventually show homogeneous enhancement. These features are related to the high number of small neovascularization in lung cancer and its structural characteristics, and to the high metabolism of tumor tissue.
(iii) Diffuse type lung cancer.
There can be two conditions.
① The lesion invades more than one lung segment, one lobe or several lobes;
(ii) Numerous small nodules or small patchy shadows are diffusely distributed in both lungs. Since most of the cases of this type of lung cancer are mucinous cell type, which often secrete large amounts of mucus, they can produce solid lung and air bronchial images, and the edges of solid shadows are blurred and the boundaries are unclear, so they are often mistaken for pneumonia or tuberculosis on plain films. This type of BAC accounts for approximately 37% of all BAC cases. The authors summarized the CT presentation of 30 cases of surgically or/and pathologically confirmed diffuse BAC.
According to the morphology of lesions, they can be divided into four subtypes: (i) hive type; (ii) solid type; (iii) multifocal type; and (iv) mixed type.
(II) Differential diagnosis
1. Differential diagnosis of central lung cancer: central lung cancer has typical CT manifestations and is generally not difficult to diagnose, but sometimes there is some difficulty in differentiating the bronchial obstruction changes caused by it from those caused by bronchial endotuberculosis. Endobronchial tuberculosis can cause lobar atelectasis or even total atelectasis on one side of the lung, and the bronchial lumen shows gradual narrowing and occlusion on CT, but no polyp-like or cup-like mass shadow is formed; endobronchial tuberculosis rarely forms obvious mass shadow around the narrowed bronchus, and there is usually no obvious hilar or mediastinal lymph node enlargement; if there is lymph node enlargement, it is usually small and located in the paratracheal area, and calcification is usually visible, and in the lung Bronchial spread lesions are often seen in the lungs for reference, and endobronchial tuberculosis is mostly seen in young people.
Central lung cancer needs to be differentiated from other diseases that cause hilar masses. These diseases include metastatic tumor, lymphoma, lymph node tuberculosis, nodular disease and purulent inflammation, etc. Among them, except for lymphatic tuberculosis, enlarged hilar lymph nodes, mostly seen on both sides, have no narrowing of bronchial lumen, no intraluminal mass, sometimes have pressure displacement, but the inner wall is smooth and enlarged lymph nodes are located outside the bronchial wall.
2.Differential diagnosis of peripheral type lung cancer: there are many etiologies of isolated spherical lesions in the lung, with lung cancer and tuberculosis spheres being the most common, others include metastases, benign tumors, spherical pneumonia, bronchial cysts, etc., which should be distinguished with attention.
(1) Tuberculosis: the margins are mostly smooth and clear, without lobulation or only shallow lobulation, and may have dotted or speckled or patchy calcification, or may have cavities, which are marginal or fissure-like, with satellite foci around the lesion in most cases, and these signs are easily distinguished from lung cancer. These signs are easily distinguished from lung cancer. In a few cases, the tuberculosis foci may show vacuolar changes after small focal dry cool-like necrosis, which need to be distinguished from fine bronchoalveolar carcinoma, but in combination with other imaging manifestations of lung cancer and tuberculosis, it is generally not difficult to distinguish.
(2) Malformation tumor: typical malformation tumor has fat and calcification inside, and its calcification is popcorn-like, with smooth and sharp tumor margin, mostly with shallow lobulation or no lobulation. In individual cases, there is neither calcification nor fat density, and the lobulation is deeper, so it is easily misdiagnosed as lung cancer. However, malignant tumors may occasionally have deep lobes, but generally lack other malignant features, such as hairiness, bronchial inflations, small cavities, vascular clusters, pleural depressions, etc. There are also no signs such as enlarged lymph nodes in the hilum and mediastinum. Enhancement scan is not obvious, and the CT increase value is mostly <20HU.
(3) Other benign tumors: lesions with uniform density, smooth margins, inconspicuous lobar cuts, and no malignant signs such as fine and short hairs and serrations and pleural depressions. It is not difficult to differentiate peripheral lung cancer from it.
(4) Metastases: Metastases have various forms, generally multiple lesions, different sizes and similar morphology, and the lesions are not related to the bronchi because they come from the postcapillary pulmonary veins. Isolated metastases with smoother margins, mostly without burr and serrated signs, and without pleural depression, combined with a clinical history of the primary tumor, are not difficult to make a differential diagnosis.
(5) Spherical pneumonia: mostly located in the lower lung field, with blurred margins, increased and thickened surrounding vascular texture, more extensive adjacent pleural reaction, low CT value of the lesion, mostly in the range of 20 to 25 HU, often with clinical history of recent cold and fever and increased white blood cells, and the lesion mostly shrinks after short-term (7 to 10 days) anti-infection.
(6) Fine bronchial cysts: fluid-containing bronchial cysts occur in the lungs and may appear as isolated nodular shadows, with CT manifesting as well-defined marginal masses with uniform density and CT values in the range of 0 to 20 HU, but when the cysts are rich in protein components, the CT values can reach more than 20 HU, and enhancement scans show no enhancement. Sometimes air enters into the lesion to form vacuolar gas density shadow, which needs to be differentiated from fine bronchoalveolar carcinoma.
(7) Spherical pulmonary atelectasis: Spherical pulmonary atelectasis is a round or round-like mass with indistinct margins, which can be easily mistaken for lung cancer, but its performance is characteristic and it is not difficult to differentiate from lung cancer. The main manifestations include a. Round or ovoid masses of various sizes, commonly found in the subpleural area, mostly in the posterior basal segment or dorsal segment of the lower lobe. b. Twisted bronchi and blood vessels entering the mass, forming a “comet tail”. c. Blurring of the near hilar margin of the mass. d. Bronchial inflation signs are seen. e. Thickening of the adjacent peripheral pleura, with or without calcification; f. Reduced lung volume in the lesioned portion, with costal emphysema in the surrounding lung.
(8) Mechanized pneumonia: a chronic limited inflammation in the lung that has not yet formed a pseudo-envelope. The morphology is mostly irregular, the border is mostly blurred, there may be long burrs and sharp angles; some may have bronchial inflation signs; there is usually significant enhancement after enhancement; the adjacent pleura may be significantly thickened adhesions, the patient may have varying degrees of fever and respiratory symptoms. On the basis of active anti-inflammatory treatment, there will be some changes in lesion size.
3.Differential diagnosis of diffuse type lung cancer by CT.
DBAC with segmental or lobar distribution may have blurred margins and bronchial inflatable signs, which may be mistaken for lobar pneumonia and anhydrous pneumonia, and DABC with diffuse nodules resembles cornified pulmonary tuberculoma and hematogenous pulmonary metastases.
(1) lobar pneumonia: The typical CT presentation is a typical air bronchogram with soft, non-stiff, naturally branching bronchial walls and bronchial diameters that change from thick to thin, resembling green branches, whereas the bronchial inflation sign of DBAC is like a dead branch. Lobar pneumonia is not accompanied by honeycomb and ground glass signs, and there is often a clear history of acute infection.
(2) Tuberculous pneumonia: typical air bronchography signs are seen, and other lung fields are often associated with a variety of tuberculous lesions, with clinically significant signs of tuberculosis toxicity
(3) Lymphoma-like granuloma: bronchial inflation signs may be present. However, the lesions are often mass-like, with clear boundaries, and are not accompanied by the honeycomb and ground glass signs, and the lesions develop slowly.
The nodules of DBAC are often uneven in size and have well-defined margins, and the two can be differentiated clinically.
(5) Hematogenous disseminated lung metastases: generally have the performance of primary lung cancer, if the primary foci are not clear, it is difficult to distinguish between the two
4. Differential diagnosis of cavernous lung cancer.
Cancerous cavity is often combined with infection, clinically there is fever, even high fever, elevated white blood cells, and sometimes fluid planes can be seen on CT, which is similar to lung abscess and tuberculosis cavity, so attention should be paid to differentiation. Lung abscess has a more uniform wall thickness, a brighter inner wall, no wall nodules, and a more blurred outer edge due to inflammatory reaction, with a more extensive surrounding pleural reaction. In contrast, cancerous cavities have irregular morphology, uneven wall thickness, wall nodules, and clear outer edges with lobar changes, often accompanied by burrs or spine-like protrusions. In nodular cavities, the inner wall is smooth, the edges are blurred, there are mostly satellite foci around, and the rest of the lung fields often show a variety of infiltrative tuberculosis, which helps in the differential diagnosis.