Current research situation of puncture location
With the wide application of low-dose CT, the detection rate of GGO increased significantly. Clinically, it was necessary to determine its benign/malignant nature before further treatment. However, due to the small GGO, clinical needle biopsy and imaging cannot clearly and accurately study nodules qualitatively. The Fleischner Society GGO treatment guidelines suggested that isolated pGGO and mGGO with a diameter greater than 6mm should be reexamined after 6-12months and 3-6months, separately. If the lesion was enlarged or the lesion density was increased, surgical treatment should be taken, and Uniportal VATS wedge resection of lung tissue, segmental and subsegmental pneumonectomy was recommended[13]. Studies had shown that about 50% of solitary pulmonary nodules were malignant, which should be treated early to prevent further deterioration[14]. Studies had shown that the GGO of stage IA lung adenocarcinoma was more than 50% on CT images, and the prognosis of GGO was better than that of solid nodules after resection, 5-year overall survival up to 97%[15]. Therefore, VATS provided a new choice for early treatment of pulmonary nodules, and it also made accurate positioning of pulmonary nodules an urgent problem to be solved[16]. At present, the localization methods for pulmonary nodules were diversified, including imaging localization method, injecting liquid materials-mediated localization method[17] and percutaneous placement of solid materials[18]. Each localization method had its own advantages and disadvantages. Imaging positioning methods include intraoperative ultrasonic positioning[19], near-infrared fluorescence imaging positioning[20] and surgical navigation puncture robot system[21], but the requirements for equipment and the technical level of operators were high, which was difficult to be widely popularized. However, injection of liquid material-mediated localization method, including injection of lipiodol[22], methylene blue[23], medical glue[24], indocyanine green fluorescent agent[25] and other liquids, had some shortcomings such as short retention time, easy diffusion and uncontrollable injection dose, and had not received more attention from thoracic surgeons.
However, percutaneous placement of solid materials was similar to injection of liquid materials-mediated localization, which needed to puncture to the vicinity of nodules under the guidance of CT and other auxiliary equipment, and place or inject corresponding markers in order to find and accurately locate nodules during operation. Among them, solid materials include hook-wire[26], microcoil[27] and other materials. Hook-wire was special for breast nodule positioning[28], due to there was no special instrument for lung nodule positioning before in the world, it was had to use hook-wire for lung nodule positioning. Moreover, the hook-wire was quite hard, which obviously increased the risk of pneumothorax, intrapulmonary hemorrhage and chest pain. However, the microcoil had the characteristics of good flexibility and elasticity, and the spiral structure did not affect the expansion of the surrounding lung tissue to compress the puncture point, thus reducing the occurrence of the above complications[29]. In addition, the artificial fiber hairs on the surface of the microcoils can increase the friction force, so that the microcoils were firmly fixed in the lung tissue, and the displacement and shedding were reduced[16]. Asamura et al. reported for the first time that microcoils were used to locate pulmonary nodules before VATS[11]. In recent years, many studies had confirmed the effectiveness of this method[30, 31].
In the past, most of the microcoil was placed around nodules, and pleural display still cannot directly show the location of nodules. In the present more researchers prefer to locate nodules by placing the end of microcoil in the pleural cavity, which can clearly show the location of coils in VATS, and had obvious advantages over previous methods. In this study, the application of this method for localization was analyzed retrospectively. The results showed that 147 patients with GGO were located preoperatively in the two groups, and the total success rate of nodule localization was 100%, and the incidence of total complications was low, including pneumothorax: 27.9%, intrapulmonary hemorrhage: 36.7%, chest pain: 28.6%, and coil displacement: 6.1%.
The basic situation of two groups of patients was comparable
The results showed that there was no statistical difference between the two groups in age, sex composition, nodule diameter, nodule nature, nodule location and the distance between nodule and pleura, so the two groups were comparable. The results showed that the average age of patients in both groups was over 55 years old, and the gender composition showed that female patients were higher than male patients (57.1% vs. 42.9%). The reasons for choosing such patients in the experiment were as follows: first, the elderly women over 55 years old in China had a higher proportion of lung cancer screening, and high-resolution CT found that pGGO and mGGO were higher in female patients[32]; secondly, studies by foreign scholars showed that women over 50 years old were the risk factors for judging the malignancy of pulmonary nodules[33, 34]. Therefore, women over 55 years old were mostly selected in this study.
However, the average diameter of nodules in both groups was larger than 5mm, and the proportion of mGGO was slightly higher than that of pGGO (56.5% vs. 43.5%). These kinds of patients were selected because pGGO and mGGO with diameters larger than 5mm were first reviewed after 3 months. If the lesion was enlarged or the lesion density was increased, the proportion of malignant lesions was higher, which required surgical treatment, so the proportion of patients with mGGO was higher. However, data such as nodule location and distance from nodule to pleura had not mentioned in many prediction models that may affect the judgment of benign and malignant diseases.
The puncture position may affect the position of the end of the coil
Comparison between the two groups showed that the ratio of supine and prone positions in the intracavity group was 82.1%, which was significantly higher than that in the extracavity group (66.7%). There was no significant difference in other puncture times, positioning time, distance between the head of the coil and the nodule, and puncture success rate. Therefore, we consider that the end of the coil was finally placed inside or outside the pleural cavity, to a certain extent, which may be related to the patient's puncture position. We suspect that when the patient was in supine and prone position, the body was relatively fixed, so it was difficult to move the position. Therefore, in the process of gradually withdrawing the needle according to the measured distance between the needle tip and the pleura, the needle withdrawal distance was accurate, and it was difficult to place the tail end outside the pleural cavity. On the contrary, when the patient adopts the lateral position, it was easy to move slightly, which led to inaccurate needle withdrawal distance and the situation that the tail end of the spring coil may place outside the pleural cavity.
In addition, we found that the positioning time of the intracavity group was slightly shorter than that of the extracavity group, and the distance between the head of the coil and the nodule in the intracavity group was slightly lower than that in the extracavity group. Although there was no statistical difference, we speculated that the proportion of patients who might take the lateral position with the extracavity group was higher than that in the intracavity group, which led to the patient's intolerance of puncture, which led to a slight shortening of the positioning time and a slight increase in the distance between the coil and the nodule. Therefore, it may be a better choice to choose a more stable body position for puncture positioning.
The proportion of pulmonary hemorrhage, chest pain and coil displacement in extracavity group was higher than that in intracavity group
The total incidence of complications after CT-guided puncture was lower in both groups, including pneumothorax (27.9%), pulmonary hemorrhage (36.7%), chest pain (7.5%) and coil displacement (6.1%). Compared with previous studies, the incidence of pneumothorax, bleeding and moderate and severe pain in Hookwire positioning method was 48.5%, 24.2% and 24.2%, respectively. Our research results showed that the incidence of bleeding was a little more than that in Hookwire positioning method, while the incidence of other complications was significantly lower than that in Hookwire positioning method. Considering the application of microcoil positioning method, the incidence of complications was significantly lower than that in Hookwire positioning method. Compared with other centers using microcoils, the incidence of pneumothorax, bleeding and moderate and severe pain was 15.2%, 7.6% and 6.3%, which were also significantly lower than our experimental results. The possible reason was that the nodules selected by other centers were superficial according to the pleural position, which was less than 1cm, while our nodules were about 3cm away from the pleura, which was significantly higher than the previous research results. Therefore, it may lead to more puncture paths passing through pulmonary vessels, and the incidence of bleeding was slightly higher than the previous experimental results. In addition, the average age of our patients was higher than the average age of the patients in the above study, which may lead to a slightly higher incidence of complications than the previous experimental results. Another study selected patients with an average age of over 60 years, and the incidence of pneumothorax was as high as 60%[35], which was significantly higher than our experimental results, which may support our conjecture.
However, the comparison of the incidence of complications after puncture between the two groups showed that there was no statistical difference in the incidence of pneumothorax. We consider that the puncture needle was thin, which causes less damage to the pleura, and whether the end of the micro coil was placed inside or outside the pleural cavity, it can block the puncture point to a certain extent, which will not lead to pneumothorax, so there was no significant statistical difference in the incidence of pneumothorax between the two groups. However, the proportion of bleeding, pain and coil displacement after puncture in extracavity group was higher than that in intracavity group, and the difference was statistically significant. First of all, we consider that the proportion of patients in the extracavity group who use lateral position for puncture was higher than that in the intracavity group. As mentioned above, patients may have slight displacement, which may lead to needle displacement, resulting in vascular damage around nodules and a small amount of bleeding; Secondly, the end of the coil was placed in the soft tissue in the chest wall, so the coil had certain elasticity and may rebound. During the rebound process, the coil may damage the small blood vessels in the puncture path and cause slight bleeding. For the reason of high incidence of pain, we consider that the end of the coil was placed in the soft tissue of chest wall and the head was placed in the lung tissue. When there was relative movement between the two parts, the coil will rub against the pleura, which may obviously stimulate the pleura and cause high incidence of pain, which can also explain the easy displacement of the coil. Although the above complications occurred to some extent, according to the American interventional radiology complication management standard, no further treatment was needed[35].
The VATS time and the rate of conversion to thoracotomy in intracavity group were significantly lower than those in extracavity group
Our results showed that the VATS time and the rate of conversion to thoracotomy in the intracavity group were significantly lower than those in the extracavity group. We consider that when patients in the extracavity group perform VATS, they need to remove the coil on the chest wall to the pleura and then perform wedge resection like those in the intracavity group, which may increase the VATS operation time of patients in the extracavity group. Another reason may be related to the easy displacement of the coil head. If the coil shifts or even falls off, it was difficult to accurately locate the nodule through the coil during operation. In addition, if the nodules with fallen coils and deep distance from pleura cannot be accurately located, they may be converted to open chest for surgery. Therefore, the rate of conversion to thoracotomy in patients with extracavity group was significantly higher than that in patients with intracavity group. However, the total conversion rate of thoracotomy was 2.7%, which was within the acceptable range[36, 37].
The results showed that the volume of lung tissue after wedge resection in extracavity group was slightly higher than that in intracavity group, which may also be related to the displacement of coils or transfer to thoracotomy, but there was no statistical difference, which needed further study. Nodules in both groups were resected at one time, which avoided the risk of reoperation and reduced the physiological and economic burden of patients. Therefore, CT-guided positioning of microcoils was of great significance to VATS surgery.