Aggressive Aneurysmal Bone Cyst Research Articles

A remarkable and aggressive aneurysmal bone cyst ravaging the femoral shaft, advancing to lung metastases: An extremely rare case

Aneurysmal bone cysts (ABCs) are relatively uncommon tumor-like lesions that require careful management. Reporting such cases is crucial to highlight the importance of understanding the physiopathology and treatment options associated with ABCs. Literature-based writing emphasizes the significance of reporting cases like the one presented here. The aneurysmal bone cyst, classified as a Tumor Rich in Giant Cells according to the latest World Health Organization (WHO) classification of soft tissue and bone tumors, has posed several hypotheses and challenge. This aggressive form and rare localization of this lesion necessitates thorough discussions regarding its management.We present a compelling case of a 37-year-old patient, without any specific pathological history, with a giant diaphyseal aneurysmal bone cyst located in the right femur. Remarkably, the lesion had been progressing for a decade, leading to extensive destruction of the entire femoral diaphysis despite undergoing previous surgical interventions. The patient's unique circumstances highlight the unpredictable behavior and destructive potential of aneurysmal bone cysts in rare anatomical locations.This case underscores the need for a comprehensive understanding of aneurysmal bone cysts and their management. The utilization of denosumab, an inhibitor of the RANK/RANKL system, as a medical treatment in conjunction with surgery resulted in a favorable therapeutic response, including a reduction in tumor mass. The current WHO classification, recognizing ABCs as Tumors Rich in Giant Cells, consolidates previous hypotheses and enables the development of new therapeutic protocols. The integration of surgery and medical treatment holds promise for improving outcomes in patients with aneurysmal bone cysts. In conclusion, advancements in understanding the physiopathology and treatment options are crucial for developing effective therapeutic protocols to these aggressive forms of ABCs.

Aggressive Aneurysmal Bone Cysts: Endoscopic High-Speed Curettage Combined with Percutaneous Bone Grafting—Case Report

An aneurysmal bone cyst (ABC) is a benign, locally destructive hemorrhagic lesion, usually eccentrically located in the metaphysis of the long bones. A variety of treatments are available for the aggressive forms of aneurysmal bone cysts, ranging from curettage to en bloc resection technique in which the bone defect is reconstructed with vascularized or nonvascularized fibular autograft or allograft. We report a case of a 12-year-old boy with an aggressive ABC of the proximal humerus. This aggressive form of ABC had penetrated the proximal growth plate of the humerus and had expanded to the humeral epiphysis, up to the subchondral bone of the humeral head. He had been treated surgically, with an aggressive, high-speed endoscopic curettage and bone grafting of the cyst. To assess the functional recovery of the patient, the Modified Musculoskeletal Tumor Society Score was used. Successful healing of the ABC of the proximal humerus was evident 4 months postoperatively. The Modified Musculoskeletal Tumor Society Score was increased from 21 points preoperatively to 30 points, 5 years postoperatively. Endoscopic high-speed curettage allows a precise, thorough, and aggressive resection of the pathological tissue, which is essential for the successful healing of an aggressive ABC.

Treatment of bone cysts by percutaneous injection of demineralized bone matrix mixed with bone marrow.

Bone cysts whether aneurysmal or simple, are known for their tendency to recur. To replace the classical aggressive surgeries, minimally invasive techniques were developed giving differing results based on variable radiographic criteria. No unique percutaneous treatment has proven effective on both types of cysts. The purpose of this study was to evaluate with volumetric MRI calculations the benefit of percutaneous injection of demineralized bone matrix mixed with autogenous bone marrow on both types of cysts. Twenty-seven cysts; 6 aggressive aneurysmal bone cysts (ABCs) and 21 active simple bone cysts (SBCs) were treated with our percutaneous treatment in this case series. Regular MRIs were performed to calculate their volumetric evolution starting before treatment and with a minimal two-year follow-up. A cyst was considered healed when its final residual volume shrank to less than 50%. To allow statistical comparison between both types of cysts, 13 previously reported ABCs treated with the same protocol in our institution were joined to the 6 present ABCs. Four ABCs healed with a single injection while the 2 others recurred. Five SBCs healed with a single injection, 9 others after a second injection and 2 others after a third injection. Five SBCs were considered non-healed. The present healing rate in 67% of ABCs is consistent with the previous series as there was no significant difference (p=0.37). The better global healing rate for ABC (79%) was not statistically different from the SBC healing rate (76%) (p=0.83). The percutaneous injection of demineralized bone matrix mixed with bone marrow is an effective treatment for both types of cysts.

Clinical and surgical outcomes of enneking stage III aneurysmal bone cysts of the spine

Objective: To study the clinicoradiological characteristics and surgical outcomes in patients with aggressive aneurysmal bone cyst (ABC) of spine. Materials and Methods: In this retrospective study, data was collected from patients with aggressive ABC of spine managed between January 2007 and December 2016. Clinical findings, radiological, and histological characteristics were studied. Follow-up was done either in the outpatient clinic or through a telephonic interview. Results: Seven patients (mean age, 15.6 years, range, 6–23 years) diagnosed with Enneking stage III aneurysmal bone cyst of the spine were included in the study. Local pain with restriction of movement was the most common presenting complaint (100%). Four patients presented with myelopathy. Thoracic spine was the most common site of involvement (43%). Of the patients, 71% had involvement of all three columns. All patients underwent surgical management; gross total resection in four patients (57%) and subtotal in three patients (43%). Of the seven patients, six required instrumented fusion. None of the patients developed any perioperative complication except for one patient who developed transient hip flexion worsening. Two patients received conformal radiation therapy (RT) postoperatively. The follow-up ranged from 40 months to 108 months (mean follow-up was 4.5 years). There were no recurrences. At last follow-up, all patients were alive and had significant improvement. Conclusions: ABC of the spine is found predominantly in the pediatric population. Intralesional en bloc resection with instrumented stabilization provides effective and fast relief from pain, early mobility, good surgical, and long-term outcomes. Conformal RT following a planned subtotal excision prevents the progression of the disease.

Multifocal Polyostotic Aneurysmal Bone Cyst of Pelvic Bones

Aneurysmal bone cyst (ABC) is a very rare benign osteolytic bone tumor representing less than 2% of all bone tumors and 5 to 6% of benign bone tumors. Atypical or unusual variants of ABC group together unusual clinical presentations, unusual complication, rare locations, and unusual age of occurrence, representing a real diagnostic challenge for clinicians. From all so-called unusual variants of ABC, multifocal one is particularly exceptional with only seven cases described metachronously in the world literature. We report the original case of a bifocal synchronous poly-ostotic and locally aggressive ABC involving the right ilium and the left superior pubic ramus in 19-year-old Tunisian man.

Gene fusions PAFAH1B1–USP6 and RUNX2–USP6 in aneurysmal bone cysts identified by next generation sequencing

Aneurysmal bone cyst (ABC) is a locally aggressive, expansile, typically multilocular cystic bone tumor. ABC was previously thought to be a non-neoplastic lesion; however, it is now considered to be neoplasm that features recurrent chromosomal translocations resulting in gene fusions between ubiquitin specific peptidase 6 (USP6) and multiple partners, including COL1A1, CDH11, TRAP150, ZNF90 and OMD. Using next generation sequencing (NGS), we uncovered two fusion partners of USP6 in two ABCs: platelet activating factor acetylhydrolase 1b regulatory subunit 1 (PAFAH1B1), which is known to contribute to tumorigenesis in lung cancer, and runt-related transcription factor 2 (RUNX2), which is known to regulate osteoblastic differentiation, osteosarcoma tumorigenesis and its metastasis. In our study, the PAFAH1B1-USP6 fusion consisted of the promoter of PAFAH1B1 fused to the 5'-untranslated region (5'-UTR) of USP6 and was discovered in a typical ABC. The RUNX2-USP6 fusion had the promoter and a short coding region of RUNX2 fused to the translation start codon of USP6 and was detected in an unusually aggressive ABC with an osteosarcoma-like soft tissue extension. Our findings not only expanded the repertoire of the partner genes of USP6 in ABC but also can serve as a reference for future studies to better understand the correlation between various gene fusions and the progression of ABC.

Pathological fracture of proximal femur secondary to an aneurysmal bone cyst in a child

Aneurysmal bone cysts are enigmatic, locally destructive blood filled lesions of bone with unknown cause & unusual presentations. We report a case of an 8-year old male child who presented to us with a pathological fracture of right hip after a trivial fall. It was an aggressive aneurysmal bone cyst of the proximal femur complicated by a subtrochantric fracture. Treatment was done successfully with an intralesional curettage and implantation of a frozen cancellous cadaveric allograft of femoral head followed by internal fixation of the pathological fracture with plate and screw.

Children’s orthopaedics

The October 2015 Children’s orthopaedics Roundup360 looks at: Radiographic follow-up of DDH; When the supracondylar goes wrong; Apophyseal avulsion fractures; The ‘pulled elbow’; Surgical treatment of active or aggressive aneurysmal bone cysts in children; Improving stability in supracondylar fractures; Biological reconstruction may be preferable in children’s osteosarcoma; The paediatric hip fracture

Surgical treatment of active or aggressive aneurysmal bone cysts in children.

The aim of this study was to evaluate functional and radiological results, tumor control, and complications of the surgical treatment of aneurysmal bone cysts (ABCs) in children by extended curettage using a mechanical burr and cauterization, grafting, and internal fixation in specific locations. Sixty-four children [38 males, 26 females, median age=10 years (range, 5-18 years)] with active or aggressive ABCs of long and flat bones were subjected to a median follow-up of 66 months (range, 28-130 months) following surgical treatment. The pathological fracture rate was 72%. Surgical procedures included intralesional extended curettage (92%) or en-bloc resection (8%). Internal fixation was required in 53%. The pathological fractures healed successfully in 8-12 weeks. The median Musculoskeletal Tumor Society (MSTS) score at the last follow-up was 95% (range, 55-100%). Treatment failure (partial healing/recurrence) and complication rates following extended curettage were 7 and 5.2%, respectively. Statistically, the only parameter affecting partial healing and local recurrence was proximity of the lesion to the growth plate (P=0.011). Extended curettage using a mechanical burr and cauterization, grafting, and internal fixation in specific locations can promote healing in most cases of ABC, with low recurrence and complication rates.

Abstract No. 456 - Image-guided percutaneous treatment of aneurysmal bone cyst of the jaw with bone allograft and autologous bone marrow: a case report with five-year follow-up

No. 456 Image-guided percutaneous treatment of aneurysmal bone cyst of the jaw with bone allograft and autologous bone marrow: a case report with five-year follow-up R. Freitas, K. Fonseca, R. Procopio, L. Lehman; Radiology, Universidade de Sao Paulo Medical School, Sao Paulo, Brazil; Oncology pediatrics, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil; Interventional Radiology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil; Buco-maxillo Surgery, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil Purpose: A six-year old boy with an aneurysmal bone cyst of the jaw was treated by percutaneous injection of bone allograft particles mixed with autogenous bone marrow under computed tomography (CT) guidance and general anesthesia. Materials and Methods: A six-year old boy presented with a mass at the left angle of mandible, self-limited recurrent oral bleeding, pallor and severe pain partially controlled with opioids. Open surgical biopsy revealed a fibrous bone lesion with giant cells. A thin-walled 7 x 6 x 6 cm diameter (132 cc) expansible bone lesion at the left angle of mandible containing fluid-fluid levels was detected by X-ray plain film, CT scan, ultrasound, and magnetic resonance imaging. A diagnosis of an aneurysmal bone cyst was stated. A minimally invasive percutaneous approach was proposed after multidisciplinary review and an informed consent was obtained. Frozen dried bone allograft particles obtained from tissue bank were crushed, mixed with fresh autogenous bone marrow and injected into the lesion by a percutenous 11-gauge needle under CT and fluoroscopy guidance. No complications were observed. Results: The patient was discharged from the hospital the next day without symptoms. After two weeks he returned at consultation without bleeding or pain complaints. Normal serum hemoglobin was observed three months later. CT scans performed during five years of follow up showed progressive healing, ossification of the left branch of the jaw, tumor shrinking and remodeling. No pain or bleeding was reported since the percutaneous treatment. Conclusion: This case report shows excellent healing of a locally aggressive aneurysmal bone cyst after image-guided percutaneous injection of autogenous bone marrow mixed with elements of allograft bone matrix. Five years of follow-up showed excellent functional and cosmetic results. Further research is required to clarify the exact mechanisms of this potential treatment. Educational Exhibit Abstract No. 457 Ultrasound guided percutaneous tenotomy/ fasciotomy: indications, technique, and initial experience A.S. Johar, M.C. Switzer, A. Braun; Radiology, Maricopa Medical Center, Phoenix, AZ Learning Objectives: The objective of this poster is to 1) Discuss the pathophysiology of tendinosis and the common clinical presentations. 2) Review the US findings of chronic tendinopathy. 3) Describe the percutaneous tenotomy technique and its advantages over traditional tendinopathy treatments. 4) Outline our initial experience with outpatient ultrasound tenotomy. Background: Tendinopathy is a common and underdiagnosed pathology which often impairs daily and recreational activities. Given its debilitating nature, a range of treatment options exist, many of which are conservative and few of which provide durable complete symptom relief. Ultrasound guided percutaneous tenotomy is a relatively new and promising technique with the ability to remove pain causing diseased tendon tissue without damaging the adjacent healthy tendon tissue. This technique is gaining traction due to its minimally invasive nature, quick recovery time, low cost, low morbidity and durable positive outcomes. Clinical Findings/Procedure Details: We will demonstrate the findings of tendinopathy by presenting supporting US images from multiple cases. We will detail the percutaneous ultrasonic tendon cutting and debriding technique while describing pertinent pearls and pitfalls. Finally, we will discuss the outcomes from our cases. Conclusion and/or Teaching Points: After reviewing the poster, viewers will be familiar with the pathology, presentation and imaging findings of chronic tendinopathy. Viewers should appreciate US guided percutaneous tenotomy as a minimally invasive, fast and effective treatment option for tendinopathy pain. Educational Exhibit Abstract No. 458 Lymphangiography: not gone, not forgotten E. Lindgren, J. Friese, C.E. Bender; Radiology, Mayo Clinic, Rochester, MN JVIR ’ Posters and Exhibits S199

Une nouvelle alternative pour le traitement du kyste osseux anevrysmal – résultats préliminaires du Surgiflo percutané

Aneurysmal bone cysts (ABC) are benign bone lesions that can be locally aggressive causing bone destruction and pathological fracture. Traditional treatments consist of surgery (curettage or excision), and or intralesional sclerotherapy. Ethibloc was one of the most effective fibrosing agents but was withdrawn because of reported local and general complications. The purpose of this preliminary study was to evaluate the results of a percutaneous haemostatic agent Sugiflo (Ethicon) in the treatment of active and aggressive ABC. Thirteen consecutive patients with ABC were treated in our institution between December 2009 and June 2013, at an average age of 10.1 years (3.2–17.4) by percutaneous intracystic administration of a mixture of a haemostatic agent Surgiflo and pure alcohol. The cysts were located in the proximal humerus (5), proximal tibia (3), distal femur (2), iliac bone (1), L3 (1), and C4 (1). Six patients were previously treated with surgical curettage (3), internal fixation (2) or surgical excision (1). The mixture was administered under fluoroscopic and or computed tomographic guidance under local, regional or general anesthesia. Patients were assessed clinically and radiologically at an average follow-up of 16 months (6–42). The number of required procedures per patient, the improvement of pain, rate of pathologic fracture if any, tumor volume, distance to the physis, as well as improvement in cortical thickness were assessed. Complications and recurrences were recorded. The procedure was performed once in 12 patients, and twice in 1 patient. At last follow-up, 12 patients were pain free. One patient with a very aggressive ABC of C4 developed neurologic symptoms 2 months following the procedure due to vertebral collapse and cord compression and required surgical resection and cervical fusion. There was a decrease in mean tumor volume by 13%, an increase in mean distance between physis and tumor of 7.9 mm, and in mean cortical bone thickness of 2.5 mm. The complications were minor and included postoperative pain for 3 weeks (1 case) and slight limb shortening (3 cases). Percutaneous administration of Surgiflo for active and aggressive ABCs seems to be effective and safe and shows promising results. It is an easier alternative to surgery mainly in some specific locations for which surgery may be associated with a high morbidity.

Hip Salvageable Surgery for an Extensive Aneurysmal Bone Cyst Complicated with Transcervical Neck of Femur Fracture

Aneurysmal bone cysts are enigmatic, locally destructive, blood filled lesions of bone with unknown cause and unusual presentations. We report a case of 16 year old female with aggressive aneurysmal bone cyst of proximal left femur complicated by transcervical fracture neck of femur. As the age of the patient was not suitable for replacement, a successful attempt was made to salvage the hip with intralesional curettage and fixation with 2 fibular struts and a cancellous hip screw. Femoral head is viable till date.

Successful Treatment of Aggressive Aneurysmal Bone Cyst of the Pelvis With Serial Embolization

Intralesional surgery is most commonly used for aneurysmal bone cysts. Rarely is en bloc resection used for active, aggressive, recurrent lesions and those located in expendable bones. However, persistence or recurrence of aneurysmal bone cysts is common. The clinical behavior of aneurysmal bone cysts is more aggressive in younger patients. Selective embolization is used as the primary treatment for aneurysmal bone cysts in surgically difficult anatomical locations and as an adjuvant to surgical treatment to reduce intraoperative blood loss and facilitate curettage.This article describes a 3-year-old boy with an aggressive aneurysmal bone cyst of the pelvis involving the right ischiopubic rami that achieved curative treatment with 3 embolizations with N-2-butyl-cyanoacrylate. Biopsy was diagnostic; however, the clinical course was misleading. Twenty days after the first embolization, despite complete occlusion of the feeding vessels, the patient experienced severe pain, increased size of the lesion, and lateral subluxation of the right hip. Based on the imaging and histological diagnosis, intralesional hemorrhage was assumed, and repeat embolization was performed. After the second embolization, the patient experienced perineal skin necrosis from normal vessel embolization; it was treated with wound dressing changes and healed uneventfully. A third embolization was performed because of a persistent lesion. Six years after treatment, the patient was symptom free, and imaging showed complete ossification of the cyst.Selective catheterization and occlusion of the feeding arteries with the appropriate embolic agent provide tumor devascularization, size reduction, pain relief, and induction of new bone formation. Multiple procedures are often necessary, and complications may occur.

An aggressive aneurysmal bone cyst of the proximal humerus and related complications in a pediatric patient

Clinical behavior of aneurysmal bone cyst (ABC) in younger patients can be more aggressive than that in older children and adults. Angular deformity and shortening can occur due to growth plate destruction or tumor resection. A 11-year-old boy who had been operated twice in another center for an ABC located in the left proximal humerus presented to the author’s institution with complaints of pain, deformity and shortening of the left arm. Plain radiographs revealed left proximal humerus nonunion with a large defect. Reconstruction with nonvascularized fibular autograft was applied and left upper extremity was immobilized in a velpou bandage. At the third-month follow-up, graft incorporation was observed in the distal part; however, proximal part did not show adequate healing on radiographs. Additional immobilization in a sling for 3 months was advised to the patient and his family. However, they were lost to follow-up and readmitted to the author’s institution at the 12th month postoperatively. Radiographs showed failure of the fibular graft fixation and nonunion of the humerus. Autogenic bone grafts, either vascularized or nonvascularized are the best treatment method for the large defects after tumor curettage or resection. Nonvascularized grafts are technically much easier to use than vascularized grafts and provide excellent structural bone support at the recipient side. However, they may take several months to be fully incorporated. In addition, good therapeutic outcomes require patience and collaboration with the patient and parents. Most importantly, the patient should be monitored closely.

Aggresive Aneurysmal Bone Cyst: Two Case Report

Two cases of an aggresive aneurysmal bone cyst that involved the distal femur and forearm in 20-year-old men were presented. The recurrence of the aggressive aneurysmal bone cyst with severe infection in the femur in spite of total excision caused deterioration of the extremity circulation. Hip disarticulation was applied for the treatment. The second case with an alytic expansile lesion involving the 2/3 of the right ulna was surgically treated by total excision and reconstruction of the ulna by using the ipsilateral fibula. At the 2-year follow-up, the patient had complete incorporation of the fibular graft.The differential diagnosis of the aneurysmal bone cyst from the local aggressive and malignant tumor and different treatment options were discussed with the literature. (JAREM 2011; 1: 65-8)

A Giant Scapular Aneurysmal Bone Cyst in a Child

Aneurysmal bone cysts (ABCs) are rare benign bone tumours. Scapula is a very rare location, and the relative literature is sparse. The purpose of this study is to present a case of a giant aggressive scapular aneurysmal bone cyst in a child. A 7-year-old boy presented to our hospital with pain and a palpated mass on the right scapula. Imaging studies (radiographs computed tomography scintigraphy) were indicative of aneurysmal bone cyst. We performed curettage and bone grafting after the diagnosis was set by pathological examination through a posterior shoulder approach. Five years later, the patient has only residual signs of the lesion on radiographic control without signs of recurrence.

Aggressive aneurysmal bone cyst of the maxilla confused with telangiectatic osteosarcoma

Aneurysmal bone cyst (ABC) is a benign, expansile lesion typically affecting the long bones and vertebrae of patients younger than 20 years. Approximately 2% of ABCs occur in the head and neck region, most commonly affecting the mandible. Although the most common co-existing lesion associated with ABCs is the giant cell tumor, ABCs can be radiologically confused with telangiectatic osteosarcoma in cases of aggressive behavior and rapid growth. Here, we report a case of an aggressive ABC of the maxilla confused with telangiectatic osteosarcoma in a patient who underwent several operations for an osteoblastoma that was diagnosed histopathologically. This case highlights the need for a differential diagnosis both radiologically and histopathologically, because ABCs can easily be interpreted as a giant cell tumor or an osteoblastoma, and, on occasion, can be mistaken for osteogenic malignancies.

Évolution inhabituelle d’un kyste osseux anévrismal de l’humérus

A 9-year-old child presented an aggressive aneurysmal bone cyst of the humerus. Despite multiple treatments (intracystic steroid injections, curettage, Ethibloc ® injection), the lesion continued to progress. Surgical treatment was undertaken at the age of 19 years and enabled total tumor resection associated with reconstruction with a vascularized fibular flap. Five years later, the patient was free of recurrence. The graft was well integrated and shoulder function was normal. We present the diagnostic difficulties encountered in this case and discuss the therapeutic options. Biopsy is indispensable before instituting treatment.

Surgical treatment of primary tumors of the sacrum.

Twenty-two patients with primary tumors of the sacrum were surgically treated between 1983 and 1997. Seventeen male and 5 female patients were followed up for a mean of 53.6 months (range 12-203 months). The histopathologic diagnoses were giant cell tumor (GCT) in 7 patients, chordoma in 4 patients, aneurysmal bone tumor in 3 patients, chondrosarcoma in 2 patients, osteoblastoma in 2 patients, synovial sarcoma in 2 patients, Ewing's sarcoma in 1 patient, and simple bone cyst in 1 patient. Currettage and thermo- or chemocauterization was applied to 8 patients, a subtotal sacrectomy was done in 11 patients, and total sacrectomy and lumbopelvic stabilization was done in 3 patients. The surgical margins were wide in all patients with GCT. The surgical margins were wide in 3 patients and wide contaminated in 1 patient with chordoma. The 2 patients with chondrosarcoma had high sacral lesions and were managed with total sacrectomy and lumbopelvic fixation. The surgical margin was wide in 1 patient and wide contaminated in the other, who relapsed locally and systemically in the 30th postoperative month. Three patients with aggressive aneurysmal bone cyst and 1 patient with simple bone cyst were managed by curettage and thorough debridement. One patient with low sacral Ewing sarcoma was managed by subtotal sacrectomy with wide margins. The two osteoblastomas were localized to the posterior elements of the sacrum. None of the patients relapsed. Most of the tumors of the sacrum are benign aggressive lesions or low grade malignancies. Intralesional resections in the form of curettage, with the addition of chemo- or thermocauterization, provide a complete cure for benign lesions. In contrast, wide resections are necessary for complete disease control in radio- and chemoresistant malignancies. Nerve root dissection should be performed in order to achieve wide margins.

An Angiostatic Agent in Treatment of a Recurrent Aneurysmal Bone Cyst

Healing of an aggressive recurrent aneurysmal bone cyst of the distal humerus was induced by oral dexamethasone, an angiostatic agent. The severe pain and tenderness resolved rapidly. The soft tissue swelling subsided, and a thick layer of bone formed around the cyst. Complete healing followed saucerization and curettage of the remaining vascular tissue in the center of the cyst. We suggest that angiostatic agents be included in the nonoperative methods of treatment of aggressive aneurysmal bone cysts.