1 Introduction

Aneurysmal bone cysts (ABC) are locally aggressive, benign, cystic intraosseous lesion described by Liechtenstein in 1942.¹ The literature suggests that ABC comprise ∼ 1% of primary bone tumors. ABC comprises of blood-filled spaces separated by fibrous septa containing fibroblasts and reactive woven bone.² ABC's typically occur in the metaphysis of long bones and in the posterior elements of vertebral column.³ They are commonly seen in children and young adults with slight female sex predilection. These lesions are usually well-defined, highly vascular, lytic, expansile and eccentric in location.⁴ They are caused by hemodynamic disturbance, resulting in vasodilation leading to an increased venous pressure. Few studies demonstrated that chromosomal translocations are the primary abnormality in the development of primary ABC.⁵ Various treatment modalities include resection, bone cement, phenol, argon beam, ethanol and cryotherapy.⁶ Recent advancement includes selective arterial embolization, curettage with or without bone graft and sclerotherapy with polidocanol. First introduced a few decades back, sclerotherapy is the recent most non-invasive treatment modality. The concept of using sclerosants is based on the fact that ABC is a vascular malformation and it would heal if the vascularity is controlled.⁷ Polidocanol acts by damaging the endothelium. The damaged endothelium initiates the coagulation cascade resulting in thrombosis.⁸ Percutaneous sclerotherapy is a safer treatment modality for ABC with minimal morbidity. Our study reports the efficacy of sequential instillations of intralesional percutaneous polidocanol in the treatment of skeletal ABC. The study also analyses the pain relief, recurrence, radiological outcome and complications after percutaneous sclerotherapy.

2 Materials & methods

We conducted a single tertiary care centre, prospective study at our institution after prior approval for the same from Institutional Ethics Committee between July 2014 and October 2018. 47 patients presented to our Out-Patient Department (OPD) for the management of primary ABC. All patients who presented with clinico-radiological features of ABC for the first time, were included in the study (Fig. 1). Patients who had previously taken treatment for ABC somewhere else were excluded. 4 patients were excluded as they refused to take part in the long term follow up. After radiological suspicion of ABC, patients underwent biopsy of the lesion with an 18 Gauge needle. The patient and his relatives were briefed about biopsy and appropriate consent was taken. A total of 43 patients were included in the study after histopathological confirmation of the lesion. The demographic data of all patients were taken (Table 1). The histopathology proven cases of ABC were counselled for the future course of treatment. The cyst volume was calculated based on radiological imaging. The maximum length and width of the lesion was measured on anteroposterior views and the depth was measured on lateral views. MRI was done in all cases to know the soft tissue involvement and intramedullary extension.

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Fig. 1 Pre-procedure plain radiographs showing Aneurysmal Bone Cysts in different anatomical locations. The arrows point the exact location of the cysts. Figure 1A - proximal humerus; Figure 1B - proximal tibia; Figure 1C - talus; Figure 1D - proximal femur; Figure 1E - proximal phalanx; Figure 1F - distal fibula.

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The patient and his relatives were informed about the various available treatment options with their pros and cons. All patients were willing for management by percutaneous intralesional sclerotherapy. All cases were managed by fluoroscopy assisted percutaneous intralesional sclerotherapy with 3% injection polidocanol under suitable anaesthesia within a week of histopathological confirmation. Under the guidance of fluoroscopy, an 18-Gauge needle was introduced in the lesion and the fluid was aspirated. The Polidocanol was injected through the needle after confirming the correct position under fluoroscopy. The dose of Polidocanol was 3 mg per kg of body weight. Injection polidocanol contains 30 mg/ml. A maximum of 5 ml (150 mg) was injected into the lesion. The routine schedule we followed, was a total of 3 injections at one month interval. The pain relief was assessed by Visual Analog Scale (VAS) and the progressive healing of the lesion by Rastogi Classification. The VAS score is a subjective measurement of pain representing a continuum between ‘no pain’ (VAS score 0) and ‘worst pain’ (VAS score 10). Rastogi classification evaluates the residual lesion under four categories. Degree I represent excellent result (Residual lesion<25%), Degree II represents good result (Residual lesion 25–50%), Degree III represents poor result (Residual lesion 50–75%) and Degree IV represents unresponsive lesion (Residual lesion>75%). All patients were evaluated clinico-radiologically, pre-operatively and at monthly interval for the first three months and then at 6 months, one year and two years follow up (Figs. 2 and 3). Clinical evaluation includes pain and swelling at the local site and radiological evaluation includes cortical sclerosis, progressive reduction in cyst volume and increased opacity of the lesion. 5 patients reported with recurrence at 6 month follow up. One dose of polidocanol was repeated and all showed resolution of the lesion at one year follow up. All patients were allowed to do activities of daily living. Sport activities were avoided till the appearance of sclerosis on radiological imaging.

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Fig. 2 Sequential radiographs showing Aneurysmal bone cyst in proximal humerus pre-procedure and at regular follow ups. Figure 2A - pre-procedure radiograph showing aneurysmal bone cyst; Figure 2B - Radiograph at three month follow up; Figure 2C - radiograph at six month follow up; Figure 2D - Radiograph at one year follow up.

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Fig. 3 Sequential radiographs showing Aneurysmal bone cyst in proximal femur pre-procedure and at regular follow ups. Figure 3A - pre-procedure radiograph showing aneurysmal bone cyst; Figure 3B - Radiograph at three month follow up; Figure 3C - radiograph at six month follow up; Figure 3D - Radiograph at one year follow up.

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The collected data was compiled and analysed. The mean and standard deviation (SD) which are descriptive data, were calculated for continuous variables. The frequencies and percentages are calculated for categorical variables. Association between Variables were analysed by Chi-Square test for categorical Variables. Level of significance was set at 0.05. MS Excel and GraphPad software (SPSS Inc., Chicago, IL, USA) were used for data entry and analysis.

3 Results

Forty-three patients with confirmed diagnosis of primary ABC were included in the study, of which 22 were males and 21 females. The initial cohort comprised of 47 patients. Four patients refused to give consent for long duration follow up and were thus, excluded from the study. Out of these 43 patients, most of them were in second decade of age with a mean age of 14.2 years (Range: 7–19 years). The mean follow-up time was 28 (25–36) months. The most common location of ABC was proximal humerus followed by proximal femur. The mean pre procedure VAS score was 7.68 ± 1.24. The patients were followed up pre-operatively and at monthly interval for the first three months and then at 6 months, one year and two years follow up. The VAS score at six months follow-up decreased significantly to 2.6 ± 0.42. Clinically patients were having no pain at one year follow up with VAS score being 0. (Table 2) The patients were evaluated radiologically as per Rastogi classification at initial presentation and at regular follow ups. Out of 43 patients, 37 patients had Degree I (excellent) residual lesion and 6 patients had degree II (good) lesion at one year follow-up. The lesion resolved completely by two-year follow-up with all 43 patients having Degree (excellent) I resolution. (Table 3) None of the patients reported infection, anaphylaxis or neurovascular injury. Few patients developed local complications at the injection site. Induration of skin was noted in seven patients and four had hypopigmentation at the injection site.

4 Discussion

There is no global consensus among the surgeons regarding the optimal treatment modality of primary ABC. The debate still exists because of multiple options available and lack of study comparing the different management modalities. The most accepted treatment mode few decades back was open curettage with or without bone grafting.⁹ The curettage procedure was associated with high recurrence rate which can be reduced by using high speed burr. Wide resection of the lesion is not feasible as there are high chances of injury to the neurovascular structures and its associated morbidity.¹⁰ Radiation therapy is a non-invasive procedure with minimal morbidity but carries the risk of secondary malignancies. In young patient, radiotherapy can arrest the physis which results in deformity.¹¹ Selective arterial embolization has good results but the procedure itself is technically demanding. Arterial embolization in spine can lead to ischemia of spinal cord.¹²

Sclerosants acts by damaging the endothelium of blood vessels and results in the formation of thrombus. Polidocanol has already been in use for non-orthopaedics indications. It is used to sclerose the bleeding oesophageal varices, varicose veins, vascular malformations and telangiectasis. Polidocanol is a safe, non-invasive procedure for the treatment of ABC. Rastogi et al. reported on 72 patients with primary ABC.¹³ The outcome was excellent with a success rate of 75% at one year and 97% at two years follow up. Otte et al. analysed 38 patients with ABC who were treated with repeat injections of polidocanol.¹⁴ They followed the patients for clinical and radiological signs of healing. All lesions healed except one after a median of four polidocanol instillation. They concluded that percutaneous intralesional sclerotherapy is highly efficacious in the treatment of ABC's with considerably minimal side effects. Batisse et al. reported 19 patients with ABC who were treated by sclerotherapy.¹⁵ The radiological ossification was assessed on plain radiographs and MRI and pain was assessed on VAS score. Complete ossification was seen in 85% of patients and partial ossification in the rest 15% at 3 months follow up. At two years follow up, none of the patient reported recurrence. There are few studies which compare the intralesional sclerotherapy with other modalities of treatment for ABC's. Varshney et al. in his study on 94 patients, concluded that repeat instillation of percutaneous polidocanol is equally efficient to intralesional curettage in the management of ABC.¹⁶ Schulze et al. reviewed 74 patients with primary ABC and compared the different treatment options i.e., resection, curettage and sclerotherapy.¹⁷ The study showed that intralesional polidocanol is as efficient as the other two modalities for the treatment of ABC's with minimal morbidity.

We studied the efficacy of percutaneous sclerotherapy in the treatment of ABC's. A total of 43 patients with ABC were sequentially instilled three doses of polidocanol at one month interval. They were regularly followed up for a mean of 28 months at monthly interval for the first three months and then at 6 months, one year and two years follow up. All patients had excellent outcome clinico-radiologically. Of 43 patients, 37 patients showed complete resolution of the cyst at one year follow up. At two years follow up, all patients had their cyst resolved with normal functional outcome. Five patients had recurrence who were treated by an additional dose of intralesional polidocanol. The local complications associated with percutaneous polidocanol include induration, hypopigmentation, infection and anaphylaxis. In our study, none of the patients reported infection, anaphylaxis or neurovascular injury. Few patients developed local complications at the injection site. Induration of skin was noted in seven patients and four had hypopigmentation at the injection site.

Our study has few limitations. First, our study lacks control group for comparison. Second, the sample size is small to comment on the efficacy of sequential instillations of percutaneous polidocanol in the treatment of ABC's. ABC is rare in general population with only three studies reported in literature having a sample size more than ours. Third, although most of the studies have showed that recurrences mostly occur in the first two year, the mean follow up of 28 months is short to comment on the incidence of recurrence after polidocanol instillations.

5 Conclusions

This study showed that percutaneous intralesional polidocanol is standard minimally invasive treatment modality for ABC at our institution. The procedure is safe, simple and effective with excellent outcome. Sclerotherapy is highly beneficial for deep lesions which are difficult to assess and for comorbid patients who are medically unfit for surgery. Our study strongly advocates the use of percutaneous intralesional sclerotherapy as the first line treatment for ABC, considering its clinical and radiological efficacy. The result of our study needs validation by a larger multi-centric randomized control study comparing the different modalities of treatment with longer follow up.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Informed consent

Written informed consent was obtained from all individual participants included in the study.

Institutional Ethics Committee

Approval taken by Institutional Review Board and Departmental Review Board (Date-20/07/2014; IRB approval No: IRB/F5/2015/27).

Author statement

Dr. Abhishek Kumar Rai – Writing original draft, review and editing.

Dr. Tushar Narayan Rathod – Supervision and validation.

Dr. Dixit Bansal: Methodology.

Dr. Bhushan Sunil Hadole: Investigations.

Dr. Syed Hifzur Rahman: Conceptualization.

Dr. Geekesh Kumar K G: Data acquisition.

Dr. Rudra Mangesh Prabhu: Formal analysis.