Patients
Institutional review board approval was obtained, and patient informed consent was waived due to the retrospective nature of this study.
We searched the radiology reports using the terms “lung adenocarcinoma”, “mucinous adenocarcinoma” “infectious lesions” and “pneumonia” on non-enhanced lung CT scans from January 2017 to January 2022 at six institutions (Affiliated Shandong Provincial Hospital of Shandong First Medical University; Shandong Province Yuhuangding Hospital; Shandong Tumor Hospital; Affiliated Hospital of Jining Medical University; Affiliated Hospital of Qingdao University; Qilu Hospital of Shandong University). Inclusion criteria for pneumonic-type IMA were: (1) pathologically proven IMA, (2) no radiotherapy or chemotherapy, and (3) presenting as consolidation on CT. Inclusion criteria for infectious pneumonia were: (1) pathologically proven pneumonia, or (2) clinically proven pneumonia and at least two CT examinations, the lesions completely disappearing on follow-up CT examination after anti-inflammatory treatment, (3) presenting as consolidation on CT, and (4) no treatment before the first CT examination. Common exclusion criteria for both diseases were as follows: (1) poor images, and (2) incomplete clinical data. If a patient had multiple lesions, then a single largest lesion was analyzed each patient. And if a patient had at least two CT examinations, the first CT examination was used for analysis. Two radiologists (S.Z. and X.X.Y., with 7 and 10 years of experience in lung radiology, respectively) made consensus decisions on correlation. To avoid recall bias, these two radiologists were not involved in CT image analysis evaluation. Flowchart for selecting the study population is shown in Fig. 1.
Demographic and clinical information including age, sex, smoking, cough, sputum, fever, no symptoms, laboratory results (elevation of white blood cell count [> 10 × 109/L] and C-reactive protein level [> 10 mg/L]), family history of cancer was collected from medical record.
CT protocols
All non-enhanced CT images were obtained on the multidetector CT scanners (Ingenuity CT, Philips; Brilliance iCT, Philips; Somatom Force, Siemens Healthcare; Somatom Definition Flash, Siemens Healthcare; Somatom Definition AS, Siemens; Optima CT660, GE Healthcare; Discovery 750, GE Healthcare). The chest CT scanning parameters were the following: tube voltage of 120 kVp, pitch of 0.8–1.0, 250–400 mA (using automatic tube current modulation technique) tube current, a matrix of 512 × 512, reconstructed slice thickness of 1 mm, reconstructed slice interval of 1 mm, rotation time of 500–600 ms. Non-enhanced CT scanning was performed with coverage from the thoracic inlet to the lung base in the supine position.
Image analysis
All images were independently evaluated by two radiologists (S.L. and X.M.W.) with more than 10-year’ experience in chest imaging, both of whom were blinded to patient clinical information with any disagreement in assessment resolved by consensus.
The pneumonia type IMA is defined as consolidation along the lung lobe or segment without definite shape on CT [5]. The assessments of CT features of lesions including location (unilateral or bilateral), margin (well-defined or ill-defined), air bronchogram (absence, regular, or irregular), interlobular fissure bulging (absent or present), air space (absent or present), satellite lesions (absent or present), pleural effusion (absent or present), lymphadenopathy (absent or present), and CT attenuation value were obtained by using post-processing workstation (Syngo.via, Siemens Force, Germany). Among them, air bronchogram was defined as air-filled bronchi within lesions, and irregular air bronchogram appeared as dilatation, stiffness, or narrowing of bronchi. Lymphadenopathy was defined as hilar or mediastinal lymph nodes > 1 cm in short axis diameter. On non-enhanced CT images, three circular regions of interests (ROIs) were selected at the maximum cross-sectional area of the lesions, avoiding vessels, bronchi, and air space. Then, we measured the non-enhanced CT values of the ROIs and calculated the mean value. All CT attenuation measurements are reported in HU. Inter-observer agreement in evaluation of CT image was calculated using the intraclass correlation coefficient and kappa statistics.
Statistical analysis
Statistical analysis was performed using SPSS (version 22.0, IBM) and R statistical software (version 3.3.3, https://www.r-project.org). Continuous variables were described as mean ± standard deviation, whereas categorical variables were expressed as percentage. Clinical information and CT image characteristics were compared between pneumonic-type IMA and infectious pneumonia by using Student’s t test and χ2 test. Moreover, multivariate logistic regression analysis with generalized estimating equation correction was performed to calculate odds ratio (OR) and the corresponding 95% confidence interval (CI) of the independent predictors. Receiver operating characteristic (ROC) curve analysis was performed to analyze statistically significant variables in differentiating pneumonic-type IMA and infectious pneumonia. The diagnostic performance was assessed by the area under the curve (AUC), sensitivity, specificity, and accuracy. Differences in the AUC values were estimated using the Delong test. A p < 0.05 was considered statistically significant. The logistic regression prediction formula was defined as: P(z) = 1/(1 + e−z), z = θX + b, where X is the characteristics variable, θ is the weight variable, and b is the intercept.