Bone tumours, either primary or secondary, can present in various debilitating manners, including pain and pathological fracture. The situation is particularly problematic when the tumours are hypervascular, and located in regions where a high risk of neurological compromise is anticipated during operation, such as in the spine or sacrum. In such situations, bone tumour embolisation is a useful and effective adjunctive treatment for reducing intra-operative blood loss. This is particularly relevant in primary bone tumours such as giant cell tumours and metastatic renal cell and thyroid tumours. With a proper pre-embolisation angiogram and knowledge of anatomy, careful selective cannulation of the arterial supplies and experience in using embolic agents, the risks of non-target embolisation can be kept to minimum and the best result achieved.
Bone tumours typically present as pain, loss of function, pathological fracture or as an incidental finding. Embolisation of bone tumours has been accepted as a useful treatment for various reasons. For those tumours that require surgical resection, pre-operative embolisation reduces intra-operative blood loss.[1-6] For those inoperable tumours, palliative control of pain or bleeding can be achieved.[1, 6] For some benign tumours such as haemangioma, it can also serve as a curative treatment. Other indications, such as treatment of hypercalcaemia-related symptoms in inoperable tumours, or to increase the response to chemotherapy and radiotherapy, have also been described. In this pictorial essay, we would like to review the literature and illustrate with examples the importance of bone tumour embolisation.
Technique and embolic agents
Embolisation reduces tumour vascularity (Fig. 1) and assists in tumour excision with an adequate margin. The aim of embolisation is to occlude as much of the tumour arterial supply as possible, without sacrificing the non-targeted arteries. With the advance of microcatheters, selective cannulation of multiple arterial feeders can usually be achieved (Fig. 2). In cases where complex arterial feeders are anticipated, computed tomography (CT) angiography can be useful for pre-embolisation mapping (Fig. 3). This is particularly important when vital structures in proximity potentially share the same supply, such as identifying the Adamkiewicz artery, which originates between the T5 and L2 vertebra to avoid paraplegia in spinal osseous tumour.
Literature review shows that various embolic agents have been used.[1, 6] These include polyvinyl alcohol particles (PVA), calibrated microspheres, Gelfoam, alcohol, coils and liquid agents. There are, however, few studies that compare different embolic agents, although a study by Basile et al. showed no significant difference in intra-operative blood loss between using PVA or trisacryl gelatin microspheres. PVA is one of the more commonly used agents. PVA is a particulate material capable of penetrating and occluding the tumour arterial blood supply, has the advantage of quick preparation and is relatively inexpensive and easy to deliver. The size of PVA used depends on the individual situation, but generally small (100–200 μm) or medium (300–500 μm) sizes are used. There is, however, potential difficulty in precisely delivering these particles through small microcatheters or through tortuous anatomy.[3, 7] For these reasons, some operators favour liquid agents such as N-butyl 2-cyanoacrylate for a more controlled and permeative delivery.[7, 10, 11] Sun et al. showed that there is correlation between the degree of reduction in enhancement of the tumour to the reduction in intra-operative blood loss.
Post-embolisation radiographic changes include tumour size reduction and tumour calcification. In order to minimise intra-operative blood loss, surgery should be carried out within 1 to 2 days of embolisation, as recanalisation occurs if the operation is delayed.
Hypervascular spinal bone tumours impose one of the greatest challenges to the surgeon due to its high intra-operative blood loss and potential for neurological complications (Fig. 4). Guzman et al. has shown that there is significant reduction in the amount of intra-operative blood loss with pre-operative embolisation of metastatic lesions. Special attention has to be made for tumours of the cervical and lower thoracic spine, and detailed pre-embolisation angiography to identify the vertebral arteries and artery of Adamkiewicz to avoid non-target embolisation has to be undertaken.[6, 13] In cases where the patient presents with acute symptoms, such as cord compression, emergency pre-operative embolisation might have to be carried out (Fig. 5).
Common bone tumours
In the following sections, the common primary and secondary bone tumours that require embolisation are described and examples illustrated.
Primary bone tumours
Giant cell tumour (GCT) is a distinctive neoplasm that apparently arises from non-bone-forming, supporting connective tissue of the marrow. It is a local aggressive and highly vascularised tumour. Plain radiographs show rarefaction of bone with thinning and expansion of the cortex. Diagnosis is established by biopsy. Total excision along with the surrounding bone and the periosteum is curative, although significant bleeding can occur. In cases where this is not feasible, curettage and bone grafting are indicated. Embolisation can decrease the risk of bleeding and thus facilitate surgical excision (Fig. 6).
Giant cell tumours of the axial skeleton should be managed with en bloc resection to achieve the greatest chance for cure. In the axial skeleton, the sacrum is the commonest site of involvement by GCT, and overall the fourth most-common site after distal femur, proximal tibia and distal radius.[3, 14] Sacral GCT is notoriously difficult to manage, with problems arising from extensive haemorrhage, infection, neurological damage, and a high rate of recurrence. Radiation may be effective but also carries a risk of malignant change.[3, 14] The expected post-operative neurologic deficit is often high and, therefore, more conservative therapy involving arterial embolisation and intra-lesional resection rather than en bloc resection might be a better option. Therefore, tumour embolisation plays an important role in tumour management in this location (Fig. 7). Serial embolisation with good clinical outcomes has been described.[1, 3, 14, 16]
Another common hypervascular primary bone tumour is aneurysmal bone cyst. While curettage and resection are the treatments of choice, pre-operative embolisation has been shown to be effective in reducing blood loss.[1, 14]
Other bone tumours that could benefit from embolisation and have been described in the literature include vertebral haemangioma, sarcoma, osteoblastoma and arteriovenous malformation of bone.[1, 6]
Secondary bone tumours
Metastatic bone lesions can generate a lot of pain from mechanical instability, impending fracture, and existing pathologic fracture (Fig. 8). Despite being palliative, surgery can be useful in reducing the complications and improving the quality of life. There is however a high intra-operative blood loss associated with the operation. Studies have shown that pre-operative embolisation reduces intra-operative blood loss without adverse effects on healing. Care should be taken when choosing the correct size of the particles because potential collateral vessels and shunts are often present in hypervascular malignant bone tumours.
The commonest hypervascular osseous metastatic tumours are renal cell and thyroid carcinoma, and pre-operative embolisation carries good success in them. However, other less vascular metastases, such as those from the lung, might not benefit from the procedure (Fig. 9).
The role of trans-arterial chemoembolisation (TACE) for metastatic bone tumours has not been widely studied in the literature. However, in those cases that are refractory to radiotherapy, or as an adjuvant therapy, it might be beneficial in reducing the pain.
Pre-operative embolisation carries risk including complications from vascular access, radiation dose, iodinated contrast, vascular injury or embolisation. Care should be taken to minimise possibility of non-target embolisation, particularly for spinal tumour embolisation, where it might result in spinal or cerebral infarction. Study by Wilson et al. showed that pre-operative embolisation of spinal tumours is relatively safe, with 1 out of 100 patients complicated by acute stroke after the procedure. In the extremity, non-target embolisation could also result in complications including skin abscess and nerve palsy. For example, as reported by Kickuth et al., a case of complete occlusion of the deep femoral artery and superior gluteal artery had resulted in palsy of the sciatic nerve and gluteal abscess. For these reasons, it has been suggested that the size of PVA particles should be adjusted according to the diameter of potential collateral vessels and shunts.
Bone tumour embolisation is an effective treatment for various primary and metastatic bone tumours. With detailed pre-embolisation angiography for vascular mapping, as well as selective cannulation of the tumour arterial supplies, it can be carried out safely without non-target embolisation. It is especially useful for tumours that are hypervascular and located in regions where resection is difficult, with high risks of intra-operative bleeding and neurological compromise, such as the spine and sacrum.