Differential CT and MR imaging diagnosis between low- and high-grade malignant vascular tumors of bone

Pathologically, some vascular tumors described above are remarkably similar, which makes differentiating them from each other very difficult. Most published series of MVTB include low-grade and high-grade lesions. Errani et al. (2012) described AS and EA as HMT, while they considered HE and EHE as LMT, although EHE also had intermediate malignancy potential. Another type of intermediate vascular tumor, termed ES-H, was newly described in 2013 (Jo and Fletcher 2014) and Steven et al. (Billings et al. 2003) considered it as LMT. Therefore, in our study, we described HE, ES-H and EHE as LMT, AS and EA as HMT.

HMT is more likely to occur in elderly patient compared with LMT and there was no sex predilection in LMT but a slight male predominance existed in HMT (Errani et al. 2012). As a matter of fact, in a review of 50 ES-H cases, Hornick and Fletcher found 41 (82 %) patients were male (Hornick and Fletcher 2011). According to the present 21 cases, we believe that being a younger patient, especially <20 years old, and small in lesion diameter (<3 cm), was a contribution to the diagnosis of LMT, and for the elderly patients, especially being older than 60 years old and larger in lesion diameter (>10 cm) might be suggestive of HMT. It is not mentioned in the previous literature. Both LMT and HMT predominantly affect the long bones of the lower extremity (Vermaat et al. 2011; Wold et al. 1982; Amary et al. 2013; Fayad et al. 2006; Larochelle et al. 2006; Verbeke et al. 2011; Peacock et al. 2013). HE is relatively common in the tibia, femur and humerus. By contrast, all 2 cases in our study occur in the mandible and vertebral. Four cases with AS (36.4 %) occurred in the vertebrae, which may also be its predilection site. When the case is multifocal, it has a tendency to involve a single anatomic region or the extremities in ES-H and EHE, and one or more anatomical regions in AS (Wenger and Wold 2000a, b; Boutin et al. 1996). Clinical presentations of patients in our study are mainly painful (95.2 %) and may be associated with pathological fractures.

The imaging findings of MVTB have been reported in several previous literatures, and generally, it was considered very challenging to differentiate them from each other. According to the present 18 cases, MVTB usually reveal single or multifocal, osteolytic, and variably expansile lesions with heterogeneous signs and marked enhancement, and are frequently associated with soft tissue masses, without periosteal reaction. In our study, there was also one case of AS showing mixed lytic and sclerotic pattern. The reactive changes were seen in our series as ill-defined high signal on T2WI and enhancement on T1WI located in the surrounding bone and/or soft tissues, which may reflect the presence of reactive edema, neovascularization or diffuse tumor extension (Wenger and Wold 2000a, b). Nonetheless, we also noted some differences among the subtypes of MVTB in our study. Partial cases in our study pathologically confirmed negative margin, so we believed that it tends to be reactive oedema.

Besides, we found that LMT tends to have multifocal and well-defined lesions with residual bone tissue, peripheral sclerosis, and slightly hetergeneous enhancement, whereas HMT is more likely to be associated expansive, ill-defined, necrosis/cystic, hemorrhagic, pathologic fracture and often presents with obviously hetergeneous enhancement. The incidence of expansion, peripheral sclerosis, disrupted cortex, pathological fracture, and homogeneous enhancement in LMT and HMT was almost similar. These similar or different imaging features of LMT and HMT were not summarized in the previous literatures.

Although HE typically presents radiographically as single or multiple lesions with a lytic pattern of bone destruction, they may additionally present as mixed lytic and sclerotic lesions (Vermaat et al. 2011; Errani et al. 2012; Baliaka et al. 2013). The imaging findings in our study were similar to typical appearances. Furthermore, one patient with HE from our cases demonstrated both benign and malignant features, probably because of its low-grade malignancy, and this characteristic might be helpful to make the diagnosis. To the best of our knowledge, there has been no relevant literature reported previously. When the lesion featuring this appearance occurs in the vertebrae, HE should be entertained as a diagnosis. Lesions of EHE are characteristically multifocal, oval, well circumscribed, with marked peripheral sclerosis, and located around the knee, which are highly suggestive of the diagnosis (Boutin et al. 1996). EHE can also occur in other location simultaneously, but is rarely reported. We reported the case as having aggressive lesions centered in the medullary cavity but with extension through the cortex and into the surrounding soft tissue, which could occasionally be identified in the previous studies (Boutin et al. 1996; Weissferdt and Moran 2014). Such a case can often be quite complex and difficult to diagnose. Currently, there is little literature regarding ES-H of bone. Primary bone lesions may be aggressive, with cortical destruction and soft tissue invasion (Karakasli et al. 2014; Xu et al. 2012). ES-H in our study showed cortical destruction, marked cystic/necrotic component, and abnormally enhanced tumor tissue, which was suggestive of malignant vascular tumor of bone. According to our series, lytic lesions with marked enhancement, especially involving the vertebrae, are highly suggestive of AS. EA of bone is extremely rare and the literature is limited to only several case reports (Errani et al. 2012). This finding that heterogeneous sign with extensive hemorrhage in our case was seen is in agreement with a report that extensive hemorrhage, necrosis, and cystic degeneration were present in EA, which we believed that extensive hemorrhage was the predominant feature of the tumor (Chen et al. 2011). Whether these features are helpful to confirm the diagnosis of the disease requires further studies.

This study has several limitations. Firstly, the patient population in our study is relatively small with limited statistical power. Secondly, the lack of uniform imaging modalities and scan protocols were also secondary to the retrospective nature of this study.

In conclusion, there are some differences in the imaging features between LMT and HMT, while unifocal/multifocal, expansive, ill-defined, necrosis/cystic, hemorrhagic features with age, lesion diameter, peripheral sclerosis, residual bone tissue, pathological fracture and slightly/obviously hetergeneous enhancement highly suggest their differential diagnosis.