Previous studies[17–19] have shown that two-phase CT is helpful for identifying various benign and malignant neoplasms in the parotid gland according to the CT enhanced pattern. Obviously, two-phase MSCT to access neoplasms only by CT enhanced pattern is not comprehensive. Texture analysis, which can characterize tissue organization by studying the spatial variation in the intensity of image pixel values, has greatly enriched information on pathologic features. Based on two-phase MSCT texture analysis of statistical parameters and MSCT image features, our study results demonstrated that two-phase MSCT texture analysis was conducive to differentiating between malignant and benign neoplasms in the salivary gland, especially when combined with morphological CT image features.
We statistically analysed these parameters of the texture analysis. First, the results revealed that the early phase had the advantage of differentiating between malignant and benign neoplasms in the salivary gland, based on the SGTs blood supply and histopathological characteristics. Moreover, compared with the benign group, malignant lesions had a lower entropy value in the early phase. In other words, malignant lesions were more random and dispersed due to the heterogeneity of the neoplasm. Our findings were similar to a CT texture analysis’s work focused on radiation-induced changes in parotids[20, 21]. The authors found a obvious decrease in local entropy in postradiation therapy subjects due to the reduction of acinar cells in the parotids. Our results can be interpreted in a similar way: normal acinar cells of the salivary gland were replaced with tumour cells in an disorganized way, which resulted in increasing randomness of the lesion area.
In addition, we also found that the kurtosis value of malignant tumours was higher than that of benign tumours in the early phase. Previous research[22] suggested that the kurtosis value was increased by intensity variations in highlighted objects (i.e., blood vessels). Scrima et al. found that kurtosis was associated with neovascularity in small renal masses[23]. Another study indicated that a higher rate of angiogenesis was noted in malignant tumours than in benign tumours by immunohistochemistry[24, 25]. Accordingly, we hypothesized that intratumoral microvessel density was elevated more obviously in malignant neoplasms, which was positively associated with the kurtosis value. Nevertheless, from our results, kurtosis is not an independent factor for differentiating between malignant and benign neoplasms. The reason could be that both malignant tumours and Warthin tumours tend to have higher microvascularity, which might cause no significant difference between them.
Finally, our results showed that the inverse difference moment value, inversely associated with local spatial variation, was higher in the malignant lesions than in the benign lesions. This means that local spatial variation in the benign salivary glands was more obvious. Previous research has suggested that cystic degeneration and tumour necrosis are common imaging features in SGTs, including pleomorphic adenomas[26], Warthin tumours[27], basal cell adenomas[28, 29], adenoid cystic carcinomas[30], mucoepidermoid carcinomas[30], acinic cell carcinomas[31], and salivary duct carcinomas[32]. One reason may be that cystic or necrotic regions in benign tumours were more common than malignant lesions in our results, which would cause higher local spatial variation in image texture.
Clinically, the size, morphology, vessels of lesions and nodal metastases were analysed on conventional CT images to differentiate between malignant and benign neoplasms. We used statistical methods to construct the 3 models by morphological parameters, MSCT texture analysis parameters and a combination of both. Our results demonstrated that the diagnostic capability (diagnostic accuracy, sensitivity and specificity) of morphological CT parameters was lower than that of MSCT texture analysis parameters, including kurtosis, entropy and inverse difference moment. (Model 1 87.8%, 65.2%, 95.5%; Model 2 90%, 69.6%, 97%, respectively). Furthermore, Model 3 constructed by the morphological CT features and MSCT texture analysis parameters had the highest diagnostic accuracy, sensitivity, and specificity among Models 1 and 2 (93.3%, 78.3%, 98.5%, respectively). Notably, Model 3 had greatly improved sensitivity from 65.2–78.3% compared with Model 1.
As seen from the above, 2-phase MSCT texture analysis parameters, especially combined with morphological CT features, can enhance diagnostic accuracy and help us gain insight into the underlying biological characteristics of salivary lesions.
the limitations of the study are presented as bellow. Firstly, our study was a retrospective single-centre analysis, and the inclusion of only 90 patients in a few years was not enough. Further long-term and multicentre studies are needed to confirm the results in larger cohorts. Next, the population of our study only included several types of malignant and benign salivary neoplasms, and more pathological types of tumours should be included in further research. Finally, even if 2-phase MSCT texture analysis can help differentiate malignant salivary tumours, it is still not adequate enough to analyse the complicated pathological features of salivary gland tumours. More research is needed to identify a direct correlation between pathology and CT texture analysis parameters.