Small nodules in the lungs are common and difficult to diagnose in thoracic surgery. With the development and increasing popularity of imaging, especially spiral CT, the detection rate of small nodular lesions in the lungs has increased significantly.
However, the qualitative diagnosis of pulmonary micronodular lesions is still difficult, and whether and when surgical intervention is needed remains a challenge for clinical treatment. Such microscopic pulmonary nodular lesions have a 73% malignancy rate, mainly pulmonary adenocarcinoma, followed by fine bronchoalveolar carcinoma; while the benign rate is 27%, mainly hemangiomas, abscesses, granulomas and tuberculomas. It is difficult to infer the nature of nodules based on clinical symptoms because of the small diameter of microscopic lesions in the lung, which have little impact on the structure and function of lung tissues.
For the diagnosis of isolated pulmonary nodules, imaging is currently the main method. Frontal and lateral standing chest radiographs are an important tool for the early detection of pulmonary nodules, which are simple and non-invasive and easily accepted by patients. CT examination of the lungs is a good method for further differential diagnosis, but although CT examination helps to detect the lesion and localize the lesion, there is a large error in qualitative diagnosis.
Fiberoptic bronchoscopy and sputum exfoliation cytology are very important in the examination of lung tumors, especially when the tumor invades the bronchi, and can make qualitative diagnosis with a high positive rate. However, it is limited in the diagnosis of small isolated nodules in the lung, with a low positive rate and little value in the differential diagnosis of small nodules in the lung.
In recent years, the development of imaging has been increasingly accelerated. In particular, the introduction of positron emission tomography (PET) has brought about significant changes in the imaging diagnosis in the field of oncology. PET detects tumors from the perspective of tumor cell metabolism through physiological rather than anatomical features, and therefore has greater sensitivity and accuracy than CT scan. It has become the most effective non-invasive diagnostic tool to identify malignant tumor. However, because PET examination is expensive and only a few large hospitals have the equipment, it is difficult to promote it universally. Also, false positives can occur in some diseases with high glucose metabolism such as active tuberculosis and acute inflammation.
CT-guided percutaneous lung mass aspiration biopsy is an important tool for confirming the diagnosis of isolated pulmonary nodules, and has a high accuracy rate for the diagnosis of peripheral type lung cancer. However, despite the high diagnostic compliance rate of CT-guided percutaneous lung aspiration biopsy, there is still a certain rate of misdiagnosis and missed diagnosis. Some scholars believe that a significant proportion of patients have suspicious results and suggest that fine needle aspiration may cause tumor implantation or metastasis.
The authors also believe that when comparing wedge resection of microscopic lung lesions with CT-guided aspiration, the former has 100% diagnostic accuracy and the latter has false negatives; the former plays a thorough therapeutic role and the latter only plays a diagnostic role, while there is a risk of hemothorax, pneumothorax, hemoptysis, cancer implantation and false positive rate, therefore, in actual clinical work, clinical application should be cautious for percutaneous lung aspiration biopsy results.
Since most of the microscopic lung cancers are early stage lung cancers with good surgical treatment effect, small surgical scope and less damage to tissues, therefore, how to diagnose microscopic lung cancers in lungs early and timely becomes the key to improve patient survival rate. If the diagnosis is delayed, with the increase of tumor diameter, lymph node metastasis and distant organ tissue metastasis may occur and lead to poor prognosis. For small nodular lesions, the presence of peripheral type lung cancer should be considered first and differentiated from pulmonary tuberculosis, inflammatory nodules and benign tumors.
Common CT manifestations of lung cancer.
(1) Lobular sign: there are deep and superficial lobes. The deep lobes can be well shown by conventional CT scan, while the fine and superficial lobes are better shown by thin layer high-resolution CT and target scan. Deep lobulation is of great diagnostic value for peripheral lung cancer, while superficial lobulation is also seen in benign tumors such as tuberculosis or inflammatory pseudotumor. There were 12 cases of lung cancer patients in our group showing lobar signs.
(2) Burr sign: the highest probability is shown on the distal hilar side of the lung. Short burrs are shown as halo-like or brush-like on conventional scans, while thin layer high-resolution target scans can clearly show them. Some scholars refer to solid nodules with lobar or burr signs as the “burr sign”. This sign is of great value for the diagnosis of peripheral type small lung cancer by CT.
(3) Vascular concentration sign: It is shown near the hilar side of the lung, and the rate of thin layer enhancement and target scan is higher, which is twice as high as that of ordinary CT scan. Because some of the vascular concentration signs only exist at the level of 2 to 75 px, they are easily missed by normal CT. The vascular concentration sign can also be seen in other isolated lung diseases, but it is less frequent. The presence of this sign is proportional to the size of the tumor.
(4) Pleural depression sign: The typical presentation is triangular or trumpet-shaped, and the lung apices and diaphragm may be bar shaped. The main interlobular fissure sometimes only shows the interlobular fissure pleura tilted or stiffened towards the tumor, close to the tumor. This sign is also shown by thin layer high resolution.
(5) Vacuolation sign: The occurrence rate of this sign is not high. It is reported in the literature to be about 30%. It is mostly seen in malignant nodules and rarely in benign ones. Its occurrence rate decreases significantly with the increase of tumor. Therefore, the appearance of this sign has important diagnostic significance for early peripheral type small lung cancer. This sign is often undetermined on conventional CT scans and is shown exactly on thin layer high resolution and target scans.
(6) Ground glass sign: only seen in fine bronchoalveolar carcinoma. With the widespread use of MSCT, more and more subsolid nodules with ground glass shadows are found, which are closely related to adenocarcinoma or precancerous lesions. ground glass shadows may be associated with a squamous growth pattern of the tumor (growing around the alveolar wall without disrupting the lung reticular structure) or the production of mucin. a study by Aoki et al. showed that in small peripheral type of fine bronchoalveolar carcinoma (bronchiolo- alveolarcarcinoma (BAC), an increased solid component in subsolid nodules suggests increased malignancy. In our group, 10 of the 13 subsolid nodules with ground glass shadow were bronchiolo- alveolar carcinoma, and 3 subsolid nodules with increased solid component were moderately or highly differentiated adenocarcinoma, suggesting that the ratio of ground glass shadow to solid component was related to the malignancy of the tumor. Atypical adenomatous hyperplasia (AAH) is a precancerous lesion and a precursor to adenocarcinoma, and the typical presentation of AAH was found to be <10 mm< span=""> ground glass nodules in pathological and CT studies. In the differential study of AAH and BAC, Takeshima et al. found a progressive process from AAH to limited BAC (types A and B) and further to adenocarcinoma (type C), and it was not possible to distinguish AAH from early limited BAC on CT in terms of lesion size, proportion of ground glass shadow, lobar sign, burr sign, bronchial air phase, vacuoles, pleural tail sign, and proportion of solid portion. Nevertheless, the finding of simple ground-glass nodules <10 mm< span=""> is suggestive of AAH or a more early form of limited BAC. More in-depth studies would provide more information to identify these two lesions.
The results of this group of cases further confirm the six common CT manifestations mentioned above, with only the rate of occurrence varying from sign to sign, with higher rates of ground glass-like changes, lobar and burr signs, slightly lower rates of vascular concentration and pleural depression signs, and relatively low rates of vacuolation signs. The lobar sign of the mass is due to the inconsistent growth rate of the tumor and the contraction of the intra-tumor fibrous tissue; the infiltration of the tumor into the surrounding lung parenchyma may form short burrs; the vascular concentration sign is due to the collapse of the alveoli within the tumor and the contraction of the connective tissue proliferation, causing the surrounding pulmonary vessels to gather in the mass. The pleural depression sign is a dead cavity containing fluid between the dirty and wall layers of pleura caused by the contraction of pleura due to peri-tumor fibrous reaction hyperplasia, which is rarely accompanied by tumor infiltration.
The smaller the lung nodule is, the more difficult it is to characterize benign and malignant lesions. Usually, chest radiograph, CT, MRI can only suggest diagnosis but not characterization. The diagnosis must be based on CT signs, combined with other data and comprehensive analysis and follow-up. Differential points.
(1) Lung cancer: age >40 years, slightly more frequent in both upper lungs; short burr margins and tends to be distributed to the distal hilar side with lobulated margins, rarely with calcification; bronchial obstruction and pleural depression, few with hilar and mediastinal lymph nodes enlarged; CT enhancement mostly between 20 and 60 Hu, while benign nodules are mostly <15hu;< span="">moderate to slow growth rate with progressive enlargement at follow-up. However, it is noteworthy that the smaller the lesion the less obvious the lobulation and the lighter and more heterogeneous the density.
(2) Tuberculous nodules: mostly occur in the posterior segment of the upper lung apices or the dorsal segment of the lower lobe, but also in other lung fields; tuberculous spheres are clearly outlined, with smooth margins and bilateral thin shadows when there is an envelope, while spherical caseous tuberculosis has blurred, hairy irregular margins, a few lobulated, but also shallow lobulation; density is uniform or heterogeneous, with some speckled calcification and circumferential calcification; there is bronchial drainage and dilatation, extrapleural adhesions near the lesion. There are satellite lesions in the adjacent lung fields, and tuberculosis nodules may have fine fibrous streak shadow in the direction of the pulmonary hilum; follow-up generally does not change for about six months, and may become smaller and calcified after anti-TB treatment, or remain unchanged for years.
(3) Inflammatory pseudotumor: mostly located in superficial parts of the lung, with different morphology, which can be round, oval or round-like, or hump-shaped or irregular-shaped. Most of them have moderate homogeneous density, and a few of them have small calcifications or small cavities; the edges are mostly clear and smooth, and a few of them are gross; most of them have significant homogeneous enhancement on enhancement scan, and a few have peripheral enhancement or no enhancement.
(4) Sclerosing hemangioma: Most of them appear as isolated pulmonary nodules or masses, and very few of them appear as multiple. The lower lobe is more than the upper lobe, and the right lung is more than the left lung (1.5:1.0). The CT scan of the chest has the characteristics of benign lesions in the lung in general, showing clear borders, smooth and sharp, uniform density, and scattered calcification points visible inside, and some lesions may have large irregular calcifications inside, which are difficult to distinguish from malignant tumors.
Because of the slow growth of malignant tumor in the lung, it is unreliable to observe its growth on a monthly basis to determine its characterization, but to observe its size change on a yearly basis. In accordance with the usual practice, if the nodules in the lung do not grow significantly within 3, 6 or 12 months, benign nodules are mostly considered. It is reported that the median time for malignant tumor cells to multiply is 120d, and it takes 10 years for tumor to grow to 10mm in diameter, 8 years for squamous carcinoma to grow to 20mm in diameter, and 6 years for adenocarcinoma, and it will grow and metastasize rapidly when the tumor is >20mm.
Benign nodules in the lung are the reason why it is difficult for both doctors and patients to decide whether to have open-heart surgery, but the preoperative diagnosis is not clear and the surgery is traumatic, etc. brings psychological stress to patients. The development of minimally invasive surgery in recent years has provided a better option for surgery of small pulmonary nodules. In particular, the rapid development of television thoracoscopic (VATS) technology has provided a better surgical route for patients with small pulmonary nodules, and VATS is a very ideal method for treating such diseases because of its advantages of less damage, full visual field exposure, clear images, and fewer postoperative complications. For small benign lung nodules, minimally invasive surgery is used to obtain pathological diagnosis and remove the lesions with minimal trauma, especially to remove the patient’s severe psychological burden and significantly improve the patient’s quality of life. In the case of small lung cancer, VATS can achieve the level of conventional open-heart surgery while avoiding unnecessary open-heart trauma. According to the literature, the 5-year survival rate of small lung cancer patients without lymph node metastasis is >80%, especially the smaller the primary small lung cancer, the lower the rate of tiny lymph node metastasis.
Most scholars do not advocate postoperative chemotherapy for early-stage lung cancer, especially for alveolar cell carcinoma, some scholars believe that its prognosis is good and chemotherapy is unnecessary, whether it is appropriate or not needs to be further discussed. Stage I small lung cancer is extremely early, with a low rate of distant metastasis, and surgery is radical. Those without lymph node metastasis may not be treated with chemotherapy or radiotherapy. This indicates that ultra-early treatment of tumors not only has a radical effect, but also eliminates the need for chemotherapy to treat patients. For those with lymph node metastasis, chemotherapy is required. One case of lung adenocarcinoma with lymph node metastasis and one case of squamous carcinoma with lymph node metastasis under the hilum and augmentation were treated with 4 courses of chemotherapy. Whether postoperative chemotherapy for early small lung cancer is beneficial to the prognosis of patients needs further study.
In conclusion, for patients with small nodular lung lesions, early and timely diagnosis of microscopic lung cancer becomes the key to improve patient survival due to the possibility of malignant lesions, and the rapid development of VATS technology provides a better surgical route for patients with small lung nodules. Early diagnosis (early diagnosis) and surgical treatment of small lung cancer can improve the survival and prognosis of patients. However, small lung cancer is not exactly early lung cancer, and some patients already have microscopic lymph node metastasis by the time of surgical treatment after detection, and appropriate chemotherapy should be administered to such patients after surgery.