DFSP can be locally aggressive with a high recurrence rate, especially if it is not excised with negative margins . Therefore, it is important to evaluate the extent of the tumor involvement. Examination of imaging studies are important for surgical planning. High frequency ultrasound can be used to evaluate the extent of the tumor involvement as well as provide surgery guidance. Ultrasound is increasingly being used in DFSP. To our knowledge, the present study is the largest series to describe multimodal ultrasound features of DFSP, and the first to investigate the usefulness of elastography and CEUS.
In our study, the DFSP patients mostly demonstrated red nodule and skin-colored dermal plaque, frequently located on the trunk and had equal distribution between males and females, and mostly occurs in young and middle-aged patients, which were in accordance with previous studies [4,5,6,7, 18, 19].
The gray-scale ultrasound findings of this 40-case series are mostly consistent with those described to date. Most of the tumors in our study appeared as hypoechoic lesions with occasional hyperechoic bands within the tumor matrix and lobulated lateral margins. More than half (26/40, 65%) of all DFSP lesions were irregular margin, which was correlated with an invasive growth pattern. Eight (20%) cases on ultrasound showed multilayer involvement, which was consistent with a locally aggressive growth pattern. Sixteen (40%) cases showed finger-like projections; such projections have been reported as a classic ultrasound feature in DFSP [14, 15, 18, 19]. Correlations have been previously reported between finger-like projections on ultrasound and radial or vertical wedge-shaped extensions of DFSP along the septa on histopathology [12, 14, 15, 18]. Cases showed a hyperechoic posterior area surrounding these projections, which correlated with the classic histopathological honeycomb pattern . Cases with a mixed hyperechoic-hypoechoic pattern correlated with a multilayered histopathological growth pattern comprising bundles of spindle cells predominantly oriented parallel to the skin surface ; Cases with hyperechoic rings correlated with the compressive growth pattern . Cases present as hyperechoic with a few hypoechoic bands correlated with tumor cells and fibrous tissues that are mixed together and infiltrating the surrounding subcutaneous fat tissue . Previous study reported that one patient had one ultrasound pattern , however, we found that three kinds of ultrasound patterns could be presented on one patient, such as the case of Fig. 1.
There were four cases of ultrasound findings as inverted triangle hyperechoic subcutaneous with hypoechoic area in the sunken dermis, which was first reported in our study. Histologically, these cases were atrophic DFSP, a rare variant comprising only 1.7% of DFSP [22, 23]. The hypoechoic area also correlated with a classical pathognomonic storiform pattern, and the hyperechoic area correlated with fibrous tissues and small numbers of tumor cells [8, 22].
Cell density in DFSP is higher in the center of the tumor than at the edges, where finger-like projections containing small numbers of tumor cells can infiltrate tissue located far from the main tumor mass [24, 25]. Therefore, in our study the hypo-echo was mainly in the center of the mass, and the hyper-echo was mainly at the bottom or formed ring. One probable limitation of gray-scale ultrasound is underestimation of DFSP tiny extensions. Thus, we investigated the color Doppler patterns and found that 95% of lesions showed increased vascularity. This percentage is higher than the previously reported 85.7% , which revealed that increased vascularity supports an invasive growth pattern. On color Doppler, 52.5% of lesions were rich, which is higher than the previously reported 22.7% ; The hypo-echo was mainly in the center of the mass, which was consist with its intralesional vascular pattern. Furthermore, we found that many hyper-echo areas showed increased vascularity, which reflected some tiny extensions. Rich vascular lesions were primarily hypoechoic and mixed, which revealed that these two types of lesions had more blood vessels.
Regarding hemodynamics, our analysis revealed mainly artery of a moderate arterial peak systolic blood flow in DFSP, which reflects its markedly vascularized and invasive nature. A low RI reflected arteriovenous fistula, which prompted existing immature new blood vessels. On 3-D color Doppler ultrasound, DFSPs exhibited branch-shaped, striped, and wrapped color patterns, which was consist with intralesional, peripheral, and both vascular patterns. This feature supports DFSP as having moderate vascular density and an active nature.
The elasticity of a lesion can be used to differentiate it as benign or malignant, according to its score. This method of classification proved to be more accurate than palpation. Red, green, and blue colors represented soft, moderate, and hard, respectively. In our study, elastography showed the hypoechogenicity lesion area as mainly blue or green and the hyperechogenicity lesion area as primarily red. Accordingly, hypo-echo reflected tumor cells and hyper-echo reflected tumor and fat or fiber cells, revealing the more hypoechoic DFSP as more aggressive. Elastography demonstrated that DFSP was hard, further suggesting an aggressive nature consistent with its growth pattern.
Our study focused on the usefulness of CEUS as a preoperative planning tool for tumor resection. Unlike the conventional B-Mode ultrasound, CEUS uses contrast-enhanced agents such as SonoVue. Because tumor tissue has higher perfusion and thus, fills more rapidly with SonoVue compared to the surrounding normal tissue, CEUS outlines the border and blood flow perfusion of tumor tissue more precisely than the conventional ultrasound does. Ma C et al.  reported one DFSP case with CEUS of homogeneous iso-enhancement. In our 19-case series, 73.7% of lesions showed a heterogeneous contrast-enhancement and 89.5% of lesions showed hyper-enhancement, which reflects its malignancy. DFSPs showed long peak time and low peak, which is potentially related its presence as superficial or sometimes multi-layer-involved and not deep or extracutaneous.
CEUS is considered to be an effective technique to evaluate micro- vascularization. This is significant, because angiogenesis is the basis for neoplastic growth . Previous one case report found that CEUS could improve precision of resection . In our study, CEUS was more sensitive than color Doppler ultrasound to demonstrate blood perfusion, especially for peripheral vascularity. Nineteen DFSPs depth and the maximum diameter concordance between CEUS and histology were better than US and histology, with difference of only 0.01 cm and 0.03 cm respectively. This study showed that CEUS could be an effective pre-surgery inspection method for DFSP surgical treatment.
This study has a few limitations. First, elastography and CEUS applied only to a part of the population, according to this retrospective study we found that these two methods played important role for DFSP diagnosis, therefore in future work, we would continue to collect more cases of DFSP by CEUS and elastography. Second, the elastic scoring method was qualitative and lacked some objective basis. Third, there was insufficient correspondence between US and MRI features. Although the presence of DFSP could be suggested on US, it was difficult to evaluate its precise nature when the lesion was too large. Fourth, because the present case series constitutes a single-center study with a small sample size, multi-center studies and larger sample sizes are needed for continued research.