The aneurysmal bone cyst (ABC) was first defined by Jaffe and Lichtenstein, in 1942, as an intra-osseous and osteolytic lesion (1). ABC is a tumorous lesion with unknown aetiology, influencing the metaphyseal regions of the vertebrae and other bones (2). ABC is usually benign but may be locally aggressive, damaging the affected bones over time (3). ABC also exhibits high vascularity and does not often spontaneous heal (4,5). ABC commonly occurs in adolescents and children, effecting >70% of patients under 20 years old worldwide (4). The name ABC refers to its aneurysmal growth in the bone, where it exhibits a cystic bulge full of blood (4). Common locations for ABC are the metaphysis, vertebral body, and iliac and long tubular bones (4,6).

ABC occurring in the spinal column presents difficulties during surgical operation (7) due to unclear field of vision, increased blood loss and the possibility of not fully removing the lesions. The treatment strategies for ABC are embolization, injection with a fibrosing agent, intralesional curettage and resection (4,8). Rigorous imaging evaluations prior to surgery and arterial embolization can reduce intraoperative bleeding and improve therapeutic efficacy and treatment compliance (9). In the current study, it was demonstrated that preoperative embolization is effective and has practical clinical value for spinal ABC.

ABC occurred in the extraspinal part of the vertebral body in all 5 cases, showing expansive changes with varying degrees of bone involvement. Destruction and compression of the pedicle and spinous process were present (Fig. 1). The spinal canal at the corresponding level of the lesion was narrowed and the thecal sac was compressed with invasion of the right psoas major (Fig. 2).

Angiography indicated that the vessels most frequently supplying the lesions were the intercostal and/or lumbar artery, which were significantly thickened and showed spiral and tortuous forms, leading to compression in an arc in some cases (Fig. 3A). The lesions showed abnormal mass-like staining. The blood vessels were increased in number and disordered, displaying multi-vessel tumour-like changes, and the surrounding soft tissue formed small vessels of different sizes (Fig. 3A). Contrast media was patchy and irregular and no manifestations of arteriovenous fistula were identified. Following embolization, the vessels and lesions were not stained by the contrast media, indicating an adequate reduction in perfusion (Fig. 3B). Laminectomy and posterior fixation were performed 1-2 days after embolization (Fig. 4) and blood loss during surgery was between 500-1,000 ml. Images of haematoxylin and eosin staining were consistent with ABC, and no obvious inflammatory or pathological changes were observed in the samples (Fig. 5). The figures presented represent the imaging manifestations and endovascular treatment of all 5 patients.

ABC may occur at any segment of the spine and has different imaging characteristics at different stages and locations. Radiographic manifestations such as lytic bone destruction, thin layer ossification, bone surface roughness, bone ridge and bone separation can be detected by X-ray (12,13). As the lesion progresses, vertebral segments, including the vertebral arch and transverse process are damaged and become thinner, compressed and displaced, which may easily lead to pathological fracture (14). Computed tomography (CT) aids in the assessment of pedicle and vertebral body integrity prior to surgery. The presence of a multilocular cyst with a liquid-liquid interface on T₂WI is highly suggestive of ABC (6,15). Inside the tumour, multiple cysts with fluid matter are present, revealing a different signal intensity in T₁WI and T₂WI. These liquid-liquid manifestations are due to the varying degrees of blood oxidation and breakdown products in the cyst fluid (16,17).

Treatment for some ABCs is difficult, especially in the spine and sacrum. For large frontal lesions, local excision or scraping is not easy and disease tissue may remain after surgery. Simultaneously, massive intraoperative bleeding is a significant problem (18). Current surgical treatments are not satisfactory in the balance of trauma and therapeutic effect and the occurrence of relapse is high (19). Radiotherapy and hormone therapy are also ineffective treatment and can lead to recurrence (6,20). In addition, radiotherapy carries other risks such as myelopathy and radiation-induced spinal deformity. Interventional embolization can affect the lesion's hemodynamic features, thus promoting the repair process (21,22). Identification of the blood vessels responsible for the tumour's blood supply is critical for preoperative embolization. The purpose of angiography is to understand the extent of the lesion, the relationship between multiple supply arteries and to identify the relationship between the spinal cord feeding arteries and the arteries supplying the lesion (23).

The blood supply in the spinal ABC is complex and involves multiple blood vessels (13). In general, the lesion is supplied by the intercostal artery and lumbar artery at the same level as the vertebra, but adjacent arteries may also be involved. Therefore, preoperative abdominal aortography is of great significance in assessing the number supplying arteries. This technique can also determine whether there are vascular co-trunks in the vessels supplying the spinal cord, providing visual confirmation for vascular selection and embolization.

It is crucial to select the appropriate size of the materials used for embolization because of the potential of breaking off during the procedure, leading to ectopic embolization (24). Therefore, the embolization process should be hyper-selective, target the vessel furthest from the lesion to avoid the remaining small co-trunk vessels, and be performed slowly under fluoroscopy. When the blood flow velocity is visibly slowed, the main trunk of the supply artery is adequately embolized with appropriately-sized micro-coils. After embolization of the supply artery, the demarcation between the tumour-like tissue and the surrounding normal tissue becomes more clear, which is beneficial for reducing bleeding, separating the tissue during surgery and improving the therapeutic effect of the treatment. In the present study, surgical operations, including curettage and resection, were performed 1-2 days after interventional embolization and it was demonstrated that preoperative embolization was effective and is a valuable treatment method for this condition. Some studies have previously reported that zoledronic acid and other materials can be used to treat ABCs (25-27). In the cohort enrolled in the current study, preoperative embolization was only used as an adjuvant treatment in combination with other treatment methods, rather than a standalone treatment strategy.

The present study was a retrospective analysis, and no comparative analysis and case-control cohort were conducted. Additionally, the small sample size was also a limitation of the current study. In conclusion, interventional embolization can be used before surgery to optimise conditions for ABCs in challenging locations.