This study showed a detailed analysis on the different diagnostic models for PA and WT patients. We not only calculated AUC, sensitivity and specificity of univariate and multivariate model, but also analyzed the differences between the AUC values. Our results indicated that textural IBMs might be helpful to diagnose patients with parotid PA and WT. Especially, the multivariate models including clinical parameter and textural IBMs showed better diagnostic performance in this study.
Nowadays, surgeons are in great efforts to reduce the incidence of post-parotidectomy complications, such as Frey’s syndrome (FS), facial palsy, depressed facial deformity and the like, under the advocacy of precision medicine. As a result, the selection of parotid tumor operations has become more and more limited. PSP as well as ECD are the most commonly used surgical modalities at present[5, 13]. ECD, which is often applied to excise tumors confined to parotid tail, has been evaluated as a minimally invasive operation, leading to fewer complications, higher efficiency, and better preservation of salivary function[6,14,15]. Parotid tail defined as inferior 2 cm of the superficial lobe, lies anterolateral to sternocleidomastoid muscle[16]. The surgical techniques used to treat neoplasms in the parotid tail may be quite different from other parotid areas, especially for WT[6]. In our study, most of WT were located in the parotid tail, while few of PA were discovered in the tail(P<0.001). Consequently, ECD is not quite suitable to be applied to PA. Furthermore, a historical review has demonstrated a significantly higher rate of recurrent PA with ECD compared to PSP[17].
Parotid PA and WT always present as painless, slow growing lumps with no specific manifestations in laboratory and traditional imaging examinations. Previous studies showed that smoking and elderly male were inclined to suggest WT. The WT shows male smoker predominance, with the ratio of male patients to female patients ranging from 1.7:1 to 11.5:1, and it tends to develop in older patients (mean age, 56.7–60 years) [18,19], which was consistent with the findings of the present study. While, the PA is more prone to occur in middle-aged women (P<0.001) compared to WT in this study, which was also in line with those found by the literature.
This study found that disease duration of PA is longer than WT. we speculate that WT is larger in size(P<0.001) and more superficial in location(P=0.003) compared with PA ,which is beneficial to early detection.
However, many confusing overlapping features of WT and PA lead to the dilemma of diagnosis before operation[20]. Fine needle aspiration (FNA) considered to be gold standard for the diagnosis of parotid tumors has some inevitable limitations too and may be associated with poor levels of diagnostic accuracy and low sensitivity[21]. The false positive rates of FNA in PA and WT were reported to be 9% and 8%, respectively, and the variegated cytomorphology of these tumors may lead to an error in interpretation[22]. Furthermore, intratumor heterogeneity from a single or limited tumor-biopsy sample can be underestimated[23]. Thus, pre-operation imaging examination may be a noninvasive and better approach to identify WT and PA.
At present, dual or three phases enhanced CT has been increasingly suggested for examination before parotidectomy,which has been currently the primary method for the assessment of the parotid tumors[20,24]. It is known that washout time of contrast agents in the tumors could provide many valuable physiopathology information and be helpful in differential diagnosis of pariod tumors[24,25]. As to PA and WT, quick expurgation of contrast material was unique for WT, while a delayed enhancement was for PA, which was consistent with the findings of the present study. But it turned out that was not always quite the case, for some WTs also present delayed enhancement and PAs present quick expurgation[20], which had been confirmed in this study. Furthermore, the delayed imaging would increase the radiation doses or reduce the temporal resolution.
Additionally, peripheral vessels sign was detected more frequently in WTs(P<0.001) compared with PAs in the arterial phase, which has not been previously reported. We speculate that WT is hypervascular lesion with abundant expanded blood capillaries according to histopathological features, which may contribute to its potential of stimulating peripheral angiogenesis.
The diagnostic efficiency of energy in all textural IBMs was the best in this cohort of parotid WT and PA patients, according to the univariate diagnostic models of this study. This was verified by the whole-volume textural analysis from arterial phase contrast-enhanced CT. That is to say, the textural IBM provided a stronger association with the diagnosis of WT and PA compared to clinical model and conventional image model. The textural IBMs were quantified by extracting features from the complete tumor volume in this study, which was quite different from other texture analysis of parotid disease, for the ROI was manually drawn around the tumor on its largest cross-sectional area, instead of the whole volume of the tumor[26]. In consequence, the overall tumor features were reflected by textural IBMs. In addition to some features on plain CT, contrast-enhanced CT can also reflect some heterogeneous features on tumor blood supply. For arterial blood supply is the main source of parotid tumors, arterial phase CT images were selected to analyze the texture features of PA and WT in this study.
Imaging features can be derived from CT, magnetic resonance imaging (MRI), and positron emission tomography (PET) without modification of the acquisition protocols and additional costs for patients[27,28]. Currently, texture analysis is mainly used to evaluate the treatment effect and prognosis of lung cancer, colorectal cancer, liver cancer and so on[29-31]. But it is rarely applied to parotid gland, except for several reports focusing on the alterations of parotid morphology and secretion function induced by radiotherapy for head and neck cancers[32,33]. However, to our best knowledge, there is paucity of studies to date about the potential diagnostic value of CT textural IBMs in parotid tumors, as well as the multivariate model.
Given the different surgical management of PA and WT patients, it is hoped that gathering clinical clues and CT IMBs together could augment the ability for treatment decision-making and aid in prognosticating surgical scenarios. In this study, the diagnostic performance was obviously improved by the combination of clinical parameter and textural IBMs, compared to univariate model, especially the conventional image model and clinical model. Our findings show that with minimal cost and no additional imaging burden, texture analysis of routine contrast-enhanced CT imaging before surgery may provide useful information for PA and WT patients undergoing different surgical resection. As our understanding of CT textural IBM continues to unfold, it is hoped that this may provide more insight into the likely benefit of new operative regimes in patients with parotid tumors.
The present study had several limitations. First, the sample size was relatively small, although it was larger than previous CT texture analysis studies on PA and WT[26]. Despite a relatively small sample size, we found strong association of the textural IBMs with the diagnosis of PA and WT, as well as the multivariate models. The findings of this study encourage investigating the association of a wider range of radiomic features with parotid tumors of other pathological types in a larger sample size. Second, all patients enrolled in this study were from one institution, so a large-scale randomized controlled trial needs to be performed to validate our results. Finally, there is a lack of understanding on the underlying relationship between textural IBMs and histopathology of parotid PA and WT which requires further work. Meanwhile,further work is also needed to address the repeatability of these quantitative IBMs as part of a biomarker validation process.