The Clinical Significance Of PET/CT Imaging In Differential Diagnosis Of Solitary Pulmonary Nodules

Objectives and purposeSolitary pulmonary nodule (SPN) is a single peripheric lesion with distinct boundary usually. But because of the un-typical imaging appearance, diagnose and differential diagnosis about SPN is a tough problem in radiology constantly. Although the full speed development in imaging diagnostic technique recently, there is still a great quantity wrong diagnosis which result in wrong treatment, for instance a benign nodule receive pneumonectomy but the malignant nodule didn't.A great quantity of study and clinical practice showed that because of the low density resolution and space resolution, conventional radiography had some difficulty in discriminate a SPN was benign or malignant, it usually be used in screening pneumonic lesion. Magnetic resonance imaging (MRI) is another auxiliary examination of SPN, but because of the influencing factor and complicate image formation, low space resolution, breath and heartbeat influence, MRI is used on lungs restrictly.Positron emission tomography (PET) is an unique technology which using anatomic form to function,metabolism and receptor developing, with no traumatogenic. PET is a best method which diagnose and guide treatment to tumor at present in clinic. PET/CT is a advanced molecule imaging technology which coalesce PET and CT, it has high sensitiveness,accuratissime,specific and precise positioning for identifying pulmonary nodule and staging to pulmonary carcinomatous. High-resolution computed tomography (HRCT) can clear display construction and shape of subtle refined anatomic site, is also be used in diagnosing and differential diagnosis of tumor in the lung.Some researches found that there were about 10% to 70% malignant nodules in SPN, and in the peoples of over 45 years old, there were 60%. In the malignant SPN, incidence of adenocarcinoma of lung was over 70%. So we can see, because of the increased disease incidence of bronchogenic carcinoma and adenocarcinoma of lung, the proportion of bronchogenic carcinoma in SPN was also increased. So if we can final diagnose the malignant SPN, whole therapic level of lung cancer would be improved materially. Another, as a subgroup of adenocarcinoma of lung, inception rate of bronchioloalveolar carcinoma (BAC) is ascent year by year, and oncological doctor pay more and more attention to BAC. Pathologist considered simplex bronchioloalveolar carcinoma as carcinoma in situ and pristine condition of adenocarcinoma of lung. And according to clinical characteristic of BAC, Japanese scholar produced concept of ground glass opacity (GGO). In clinic, owing to multicentre happening and good prognosis, bronchioloalveolar carcinoma is difficult to be included into existing TNM staging system of bronchogenic carcinoma exactly. And even if with regard to multiple bronchioloalveolar carcinoma, earlier period operation has an important effectiveness. Although complicated imaging appearances of BAC, it corresponds with pathological morphology, and solitary nodule type of BAC has a proportion of 43%, therefore, if we can precise diagnose pristine tumor which has a good prognosis, there will more and more pristine lung carcinoma patient can receive diagnosis and treatment in time.In a word, there are three purposes in this investigate. First is using PET/CT to explore applied value in diagnose solitary pulmonary nodule. Second is using PET/CT to research on value in diagnose solitary nodule type of bronchioalveolar carcinoma. Third is search for diagnostic value of SPN combining PET/CT and HRCT.Materials and MethodsWe had retrospectively reviewed the 18F-FDG PET/CT imaging and clinical records of standard 270 examples, all patients which have SPN received the PET/CT examination from August 2005 to December 2009, male 176 examples, female 94 examples, the age is between 18 years old and 84 years old, the middle age is 62.0±12.5 years. Their clinical manifestation had no specificity, and be found by health examination or conventional X ray or CT examination because of the cough and stethocatharsis and so on. All the patients received the 18F-FDG PET/CT examination and HRCT to the nodule at synchronization. Among the patients,50 examples received enhancement scanning. All patients had the pathologic diagnosis or be confirmed by followed-up over 1 year after treatment. 18F-FDG PET/CT adopted visualization and semiquantitative method. Using visualization to observe the nodule, such as position,size,shape and radioactive degree, using semiquantitative method to measure standardized uptake value (SUV), we considered SUVmax over or equal with 2.5 as positive finding, while less than 2.5 as negative finding. According to the morphologic characteristic of lesion, HRCT described internal and peripheric structural features and judged the consequences generally. The images were analyzed by 2 attending physicians, and the results were compared with pathologic diagnosis. Then we used Microsoft Excel to establish data base, transformed statistical software data base by SPSS 13.0. We expressed the measurement datas as mean±standard deviation, group comparison adopted t test. And the group comparison of enumeration data adoptedχ2 test, docimastic level is equal withα,we considered that there is significant if the P value is less than 0.05. Last we calculated sensitivity,specificity,accuracy,positive predictive value and negative predictive value using PET/CT to diagnose SPN.ResultsIn 270 SPN cases,225 cases were confirmed by pathological result and 45 cases by clinical follow up (over 1 year). There were 200 malignant SPN (including 125 cases of adencarcinoma,34 cases of squamous cancer,30 cases of bronchioalveolar carcinoma,4 cases of adenosquamous carcinoma,2 cases of metastatic lung cancer,2 cases of large cell carcinoma,1 case of small cell carcinoma and 1 case of carcinoid), the sizes were between 9mm×10mm×12mm to 28mm×30mm×30mm, SUVmax was from 0.5 to 25.1. And SUVmax value of 11 cases of bronchioalveolar carcinoma was less than 2.5. The presence in these malignant nodules of lobulation sign, spiculation sign, pleural indentation sign and vacuole sign were 156 cases with rate of 78%,144 cases with 72%,113 cases with 56.5% and 27 cases with 13.5% respectively. There were also 18 cases with 52.9% of blood vessel cluster sign in 34 patients which received enhancement scanning. There were 70 benign nodules (including 34 cases of tuberculoma,7 cases of inflammatory pseudotumor,3 cases of cryptococcus,7 cases non-specificity pneumonia are absorbed after eliminate inflammation treatment,1 case of pulmonary abscess,14 cases of hamartoma,3 cases of pulmonary sclerosing hemangioma and 1 case of bronchogenic cyst), the sizes were between 9mm X 9mm ×10mm to 30mm×29mm×28mm, SUVmax was from 0.5 to 11.1. The presence in these benign nodules of lobulation sign, spiculation sign, pleural indentation sign and vacuole sign were 30 cases with rate of 42.8%,21 cases with 30%,16 cases with 22.9% and 9 cases with 12.9% respectively. There were also 4 cases with 22.2% of blood vessel cluster sign in 18 patients which received enhancement scanning.The number of correct diagnose SPN with PET/CT were 192 malignant nodules and 46 benign nodules, the sensitivity,specificity,accuracy,positive predictive value and negative predictive value using simple PET/CT to diagnose SPN were 96%,65.7%,88.1%,88.5% and 86.8% respectively. The number of correct diagnose SPN with HRCT were 183 malignant nodules and 43 benign nodules, the sensitivity,specificity,accuracy,positive predictive value and negative predictive value using only PET/CT to diagnose SPN were 91.5%,61.4%,83.7%,87.1% and 71.7%. Using PET/CT,12 cases SPN were be considered as positive results, but we amended the diagnosis after we using PET/CT combined with HRCT, and they were confirmed by pathological examination finally. The sensitivity,specificity,accuracy,positive predictive value and negative predictive value using PET/CT combined with HRCT to diagnose SPN were 97.5%,82.9%,93.7%,91.2% and 89.2%.The 18F-FDG SUV of BAC was lower than others well-differentiated adencarcinoma remarkably. In 30 cases of BAC, PET showed that SUVmax of 19 cases were over or equal with 2.5, presenting positive change, the rate was 63%. Ground glass opacity was a typical appearance of solitary tubercle type of BAC. In this study,5 cases had GGO change, the rate was 16.7%.Aonther 3 cases were mixed nodules, showing GGO change around the solid nodule with rate of 10%. The others BAC in 22 cases were solid nodules with rate of 73.3%. HRCT showed that BAC was often in superior lobes of both lungs, below membrana pleuralis of surrounding lung field. The lesions were patchy or nodular with irregular shapes. The presence in BAC nodules of lobulation sign, spiculation sign, pleural indentation sign and vacuole sign were 22 cases with rate of 73.3%,15 cases with 50%,21 cases with 70% and 4 cases with 13.3% respectively.We found that the accuracy didn't have statistical difference if using PET/CT or HRCT only to diagnose SPN (the Z value is 1.606 and P value is 0.108). But there was significant difference between PET/CT combined with HRCT and PET/CT or HRCT, and the accuracy was much higher (χ2 value were 5.637 and 5.870 respectively, P value were 0.019 and 0.024 respectively).Conclusions1.18F-FDG PET/CT imaging had high sensitivity in diagnosing solitary pulmonary nodule, but the specificity was low relatively, some inflammatory granulation tumor such as inflammation or tuberculosis could lead to false positive because of the high FDG uptakes.2. HRCT scan could display small pulmonary nodule exactly, such as position,shape,density and relation with the surrounding tissue.3. In characteristic diagnosis of malignant tumor, lobulation sign, spiculation sign, blood vessel cluster sign and pleural indentation sign were very valueable, but excluding the vacuole sign.4. The long doubling time and slow speed of cell multiplication may be the reason of low FDG avidity of solitary tubercle type of BAC.5.18F-FDG PET/CT combined with HRCT is an effective and dis-vulnerarious way to discriminate a SPN is malignant or benign and stages of lung cancer. It has high sensitivity,accuracy,specificity and exact positioning. Some diseases can be found in earlier period and diagnosed in time。It also can reduce some unnecessary diagnostic test and thoracotomy greatly, has an extensive applied prospect.