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Aneurysmal bone cyst of the pelvis and extremities

Contemporary management

Noordin, Shahryar MBBS, FCPSa; Ahmad, Tashfeen MBBS, FCPS, PhDa,b,; Umer, Masood MBBS, FCPSa; Allana, Salim MBBS, MPHc; Hilal, Kiran MBBS, FCPSd; Uddin, Nasir MBBS, FCPSe; Hashmi, Pervaiz MBBS, FCPSa

doi: 10.1097/IJ9.0000000000000071
Review Article
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Aneurysmal bone cysts are tumors of bone occurring predominantly in the metaphyses of long bones and posterior elements of spine in adolescents and young adults. Radiographically, on x-rays they appear as eccentric metaphyseal expansile lytic lesions containing “fluid-fluid” levels. Computed tomographic scan and magnetic resonance imaging clearly define the cysts and fluid-fluid levels; the former delineates cortical expansion and the latter the fibrovascular component clearly. Magnetic resonance imaging is particularly useful in differentiating aneurysmal bone cysts from malignant lesions. Histologically, these cysts are characterized by fibrovascular tissue, multinucleated giant cells, inflammatory cells, fiber-osteoid, “blue bone,” and blood filled lacunae. Chromosomal translocation has been found, implying a neoplastic basis for the development of aneurysmal bone cysts. Malignant transformation has been reported where radiation therapy was used, and in cysts associated with sarcomas. A high ratio of cellular component as compared with osteoid, and a high mitotic index have been reported to be associated with higher recurrence after treatment. Management is aimed at addressing patients’ symptoms and preventing/treating fracture, and can broadly be divided into nonoperative management (drug and radiation therapy), minimally invasive strategies (angiographic embolization, percutaneous injections), and operative management (curettage and bone grafting, en bloc excision). To reduce chances of recurrence, adjuvants such as electrocautery, high speed burr, phenol, cryotherapy, and argon beam laser have been used with variable degrees of success. With contemporary management, a cure rate of 70%–90% is expected.

Departments of aSurgery

bBiological & Biomedical Sciences, Aga Khan University, Karachi, Pakistan

cDepartment of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA

Departments of dRadiology

ePathology and Microbiology, Aga Khan University, Karachi, Pakistan

This manuscript has been peer reviewed.

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Published online 2 July 2019

Corresponding author. Address: Department of Surgery, Aga Khan University, Stadium Road, Karachi 74800, Pakistan. Tel: +00922134864350; fax: +00922134932095. E-mail address: tashfeen.ahmad@aku.edu (T. Ahmad).

Received June 4, 2018

Accepted November 10, 2018

This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. http://creativecommons.org/licenses/by/4.0/

Aneurysmal bone cysts (ABCs) are benign, rapidly growing cystic tumors in the bone that were first described by Jaffe and Lichtenstein in 19421. These cysts usually appear as expansile lytic bone lesions that have a tendency to be locally aggressive. These cysts appear as primary lesions in ~70% cases with remaining 30% being secondary with preexisting osseous lesions2,3. ABCs represent about 1%–2% of all primary bone tumors4. Primary ABCs are seen at 0.14 per 100,000 of the population per year with a slightly female preponderance. ABCs are seen at all ages, but most patients have been reported to be in their second decade of life with 75%–90% cases occurring before the age of 20 years5.

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Topography

ABCs can appear in the entire skeleton but commonly appear in the metaphysis of long bones including femur, tibia, fibula, humerus, skull, and posterior elements of the spine. Usually these appear as a solitary lesion but can also occur as secondary lesions adjacent to osteoblastomas, chondroblastomas, giant cell tumors (GCTs), chondromyxoid fibroma, fibrous dysplasia or nonossifying fibroma5–8. There are many reports of ABCs affecting the skull and craniofacial bones, which can be associated with fibrous dysplasia alone9–11 or as part of a syndrome such as McCune Albright syndrome12 and cementoosseous syndrome13. Axial (vertebral and craniofacial) involvement has been reported in association with focal dermal hypoplasia, also known as Goltz syndrome14.

Apart from the usual metaphyseal location, literature reports rare cases of ABCs located in atypical sites such as cortical regions15 within the sternum16, vertebral body17, ribs18, and patella19,20.

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Clinical presentation

Patients usually present with pain and swelling in the vicinity of the affected bone. Constitutional symptoms are uncommon due to its benign nature. When the lesion continues to expand, it progresses to form an expansile mass which may be visible or palpable if superficial. Sometimes the symptoms may appear or worsen during pregnancy21.

Depending on the topography of the ABC, symptoms from pressure on adjacent structures can occur. If the vertebral column is involved, the patient may have neurological deficits due to the mass effect on the cord or nerve roots as well as torticollis and stiff and painful scoliosis6,21. In facial lesions located in orbital bones, swelling and diminishing vision have been reported10. Involvement of cortical regions can lead to pathological fracture15. In skeletally immature patients when the ABC is adjacent to the growth plate, children can develop limb length discrepancies in addition to coronal/sagittal deformities22.

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Classification

A number of classifications have been described. Enneking23 described 3 stages. Stage 1 is a latent cyst that remains static or heals spontaneously. The cyst has minimal inflammation or periosteal reaction. Stage 2 is the active cyst with progressive growth but no cortical destruction is seen. Patients will have mild symptoms and cortical thinning on roentgenograms with a layer of reactive bone separating the lesion from normal bone. Stage 3 cysts are locally aggressive cysts that rapidly expand with significant cortical destruction. These patients present with the most symptoms.

Capanna et al24 described 5 morphologic subgroups. Type 1 are central, well contained lesions with no or slightly expanded outline. In type 2 lesions the entire bony segment is involved with marked expansion and cortical thinning. Type 3 lesions involve only one metaphyseal cortex eccentrically. Type 4 lesions are subperiosteal lesions that expand away from bone and are least common. Type 5 lesions are periosteal and expand peripherally with cortical erosion.

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Pathogenesis

The exact pathogenesis of ABC is debatable. Although the presumed role of blood vessels in the pathogenesis of “aneurysmal” bone cysts has been challenged25 currently the most favored mechanism proposed is injury to the precursor lesion having numerous meshwork of capillaries. The capillary pressure thus increased by extravasated blood leads to destruction26–28. These cystic spaces are actively connected with the host capillary network. This has been demonstrated by various studies including blood pressure measurements in the cysts, lack of venular blood clotting, and venographic studies27,28.

Recently, cytogenetic and molecular studies suggested neoplastic nature of ABC by identifying the presence of t(16;17) in ABC, including solid variant. The most common translocation is t(16;17)(q22;p13) which leads to fusion of the cadherin 11 gene (CDH11) with USP 6 (ubiquitin specific peptidase 6/Tre-2)29. This fusion gene inhibits maturation of osteoblasts and dysregulate bone morphogenetic protein signaling pathway. USP6 gene rearrangements are seen in ~70% cases of primary ABCs employing fluorescent in situ hybridization, a figure increased to 100% when next generation sequencing is employed30, and are lacking in secondary ABC cases31. Interestingly, translocation occurs in stromal spindle cells and not seen in other components of ABC31. USP6 fusion genes are also found in nodular fasciitis32. This may be the basis for nodular fasciitis like areas seen in ABC. Moreover, USP6 fusion gene is present in other conditions such as myositis ossificans33, giant cell reparative granuloma (GCRG) in extremities34 and fibro-osseous pseudotumor of digits35. The frequency of USP6 gene rearrangements in these conditions ranges from 70% to 90% (Table 1).

Table 1

Table 1

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Gross features

ABC appears as a circumscribed spongy or multiloculated cystic lesion. The cystic spaces are of variable size ranging from few millimeters to several centimeters, and are filled with blood (Fig. 1). These spaces are separated by thin white septae. More solid areas are often present peripherally within the intramedullary component of the lesion. The extramedullary soft tissue component is demarcated by thin shell of reactive bone.

Figure 1

Figure 1

The more solid peripheral part may represent either solid portion of ABC wall or component of a tumor in which secondary ABC has developed. These areas need to be extensively sampled to rule out possibility of an underlying primary tumor36.

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Microscopic features

Multiple variable sized cystic spaces filled with blood are seen on low power examination (Fig. 2A). The cystic spaces do not have endothelial lining and are surrounded by variably thick fibrous septae. The septae contain uniform bland spindle cells, scattered osteoclast-like multinucleated giant cells, capillaries and varying amounts of matrix (Fig. 2B). Increased mitotic figures are sometimes seen within the stroma, however no atypical mitoses noted. Necrosis is not seen unless complicated by a fracture. The giant cells tend to cluster near the membrane surface. Osteoid is usually found as a thin layer (so-called fiber osteoid) along the long axis of the septae. Reactive woven bone with osteoblastic rimming also follows the contours of fibrous septae (Fig. 2C, arrow). Approximately half of cases demonstrate basophilic woven bone known as “blue bone” (Fig. 2D). A peculiar calcification called chondroid aura is sometimes seen. Other bony lesions do not exhibit this peculiar feature2. The septae and more solid areas are composed of loose, fibrous tissue rich in capillaries, inflammatory cells, multinucleated giant cells and extravasated red blood cells. These foci resemble and mimic nodular fasciitis or young granulation tissue36.

Figure 2

Figure 2

Apart from these histologic findings, immunohistochemical studies have been conducted on ABCs to identify possible association of specific markers with diagnosis and prognosis. P63 has been studied in giant-cell rich lesions, and shown to be present in only 22% of ABCs compared to 96% of GCTs15. CD68 is a macrophage lineage marker which is present in 93% of giant cells in ABC, but it is also highly present in other osteoclastic/giant cell lesions37. Thus CD68, P63 and no other immunohistochemical marker to our knowledge has been shown to be specific for the diagnosis of ABC. However, Docquier38 showed that if the ratio of CD68 negative/CD68 positive cells is ≥4.1, there is 100% positive predictive value for healing of the ABC and negative predictive value for recurrence, suggesting the potential role of this ratio in prognostication of ABC. USP6 is another promising marker as discussed above, and its specificity for the giant cells in ABCs can differentiate it, especially the solid variant, from other intraosseous giant cell-rich lesions such as GCRGs in the axial skeleton, GCT of bone and brown tumor30,39,40.

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Histologic variants

Secondary ABC

Primary ABC accounts for approximately 30% of all cases. ABC-like areas develop in the background of various secondary tumors including GCT of bone, chondroblastoma, chondromyxoid fibroma, fibrous dysplasia, ossifying fibroma, osteoblastoma and osteosarcoma8,27,41–45. The behavior and prognosis of these “secondary” ABCs” mirror those of the underlying tumor. Molecular studies employing fluorescent in situ hybridization have shown that gene rearrangements of USP6 are present in 70% of primary ABCs, and are highly specific because these are absent in secondary ABC associated with other lesions29,31,34,39.

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Solid ABC

Solid ABC shares the same components as those of fibrous septa of conventional ABC. There is florid fibroblastic and fibrohistiocytic proliferation with scattered osteoclast-type giant cells. Blue bone and small spaces filled with blood are helpful features in identifying solid ABC. Abundant woven bone with prominent osteoblasts and foci of degenerative calcifying fibromyxoid tissue is present. Focal small dilated blood filled spaces seen and clue to diagnosis46.

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Differential diagnosis

Differential diagnosis of ABC includes benign lesions, such as unicameral bone cysts, or tumorous lesions such as chondromyxoid fibroma, chondroblastoma, GCT or osteoblastoma2. Two findings differentiate ABC from unicameral bone cyst, septa and fluid-fluid levels, and magnetic resonance imaging (MRI) is an excellent modality to demonstrate these47. GCT is almost never seen before closure of the growth cartilage, and tends to involve the epiphyseal-metaphyseal region of long bones5. Histologically, solid foci of tumor show osteoclast type giant cells distributed homogenously among mononuclear cells in GCT in contrast to scattered distribution in ABC. The giant cells have usually fewer nuclei as compared with numerous nuclei in osteoclast cells of GCT. GCRG is another lesion which appears similar radiologically to ABC. Clinically, however, GCRGs typically arise in small bones of hand and jaw. Both GCRG and solid ABC show identical histologic features and may be difficult to differentiate, though blue bone and blood-filled spaces would be more suggestive of solid ABC. Distinction of ABC from telangiectatic osteosarcoma is of crucial importance especially in small biopsies. ABC grossly resembles telangiectatic osteosarcoma. Histologically, atypical cells and atypical mitoses are found in fibrous septae in telangiectatic osteosarcoma, these are not seen in ABC. The pathologist needs to examine the biopsy material carefully to rule out the presence of atypical cells and atypical mitoses. Osteoid may or may not be seen in telangiectatic osteosarcomas.

It is important to correlate with radiologic features and biopsy tissue should be thoroughly sampled especially from solid areas to exclude any underlying lesion. ABC-like areas can be seen secondary to a variety of lesions (as described above). The behavior of such a “secondary ABC” is determined by the primary lesion.

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Diagnosis

Clinical and radiologic features may be sufficient for a presumptive diagnosis of ABC, but establishing the diagnosis is essential before committing to definitive treatment. Percutaneous needle biopsy, with or without image guidance [fluoroscopy/ultrasound/computed tomography (CT)] depending upon location, is the preferred method for definitive diagnosis. The expected findings on the biopsy have been described in the previous sections. A presumptive diagnosis of ABC, however, is usually based on the appearance of the lesion on imaging.

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Plain radiography

Plain radiography has high diagnostic accuracy for cysts involving the appendicular skeleton especially long bone. The characteristic features in long bones on plain film eccentric metaphyseal lytic lesion comprised almost entirely of fluid-like radio-opacity. The growth plate grows away from lesion; hence long-standing lesions are located in the metadiaphyseal region of long bones. However, it has also been reported as a purely diaphyseal lesion in few cases27,48. A combination of plain film with MRI and CT is required on body part which are difficult to evaluate on plain film, for example, pelvis, chest wall, spine or temporo-mandibular joint.

The size of this lesion can be 2–20 cm. It appears as lytic expanded lesion which may have trabeculation which give soap-bubble appearance. The cyst is eccentric and expands into soft tissues. Erosion and thinning of cortices can be seen in big lesions (Fig. 3). These are geographic lesion with a narrow zone of transition. The margin of the lesion is sclerotic and thin can be complete or in complete. A periosteal reaction is usually absent; however, it is not uncommon to see it in case of the rare entity of surface type of ABC. The expansion or ballooning of cortex can result in loss of distinct margins. In this case lesion should be carefully evaluated and should be reported as aggressive lesion rather than neoplastic lesion.

Figure 3

Figure 3

ABCs are sometime hard to differentiate from aggressive neoplastic process such as sarcoma, especially in ribs, scapula, or sternum, when associated with a large soft tissue component27,49,50.

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CT

On CT, the visualization of depressions, defects, and protrusions in bone cortex is better seen than any other imaging modality including MRI. This finding helps surgeon for better surgical planning and to evaluate the exact extension of lesion. CT is also helpful to distinguish between intra and extra osseous component of cyst and its extension.

Thin cortical rim is better visualized on CT than on radiograph. The cortex appears as thinned, “eggshell” with focal cortical destruction and absent calcified tumor matrix (Figs. 4A–C). The zone of transition is narrow, and nonsclerotic. The lesion shows rounded “cysts” that show fluid-fluid levels which is caused by hemorrhage followed by blood component sedimentation. The septa and fluid-fluid levels are also visualized but better seen on MRI. Fluid-fluid levels are not specific for ABC and can be seen in other conditions like GCT or telangiectatic osteosarcoma.

Figure 4

Figure 4

Fluid levels may not be identified by CT because body movement can mix the fluids. Patient has to remain motionless for some time to allow the fluid in cyst to settle and allow fluid levels to be seen on CT50. On unenhanced CT balloon-like expansile mass centered on posterior elements in spinal aneurysmal cyst which usually extends into epidural space and may cause spinal canal narrowing. On enhanced CT, enchantment of tumor margin and septae is seen. In cases of solid ABC diffuse enhancement is noted49–51.

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MRI

On MRI, ABCs appear as geographical lesions with thin, low signal sclerotic margins. These cystic lesions are isointense to skeletal muscle on T1 and hyperintense on fluid-sensitive sequences22,50,52–55 (Fig. 5A). Cysts are separated by septae of varying thicknesses (Figs. 5A, B). On postcontrast sequence, enhancement of septa is seen but not of the cystic component. A well-defined rim of low signal intensity around the lesion reflects periosteum or pseudocapsule. The surrounding edema, both in bone and soft tissue appears hyper intense on T2 and STIR sequences.

Figure 5

Figure 5

Fluid-fluid levels are excellently demonstrated by MRI on fluid-sensitive sequences, and are seen in 20%–100% cases of aneurysmal bone cysts41,52,56. These levels are produced by layering of the breakdown products of hemorrhage within the cyst. Signal of superior layer in cyst typically follows fluid and dependent portion shows decreased signal on T2WI relative to T1WI (Figs. 5A, B). Cysts of different signal intensity are seen on all sequences depending on different stages of blood components. O’Donnell and Saifuddin57 examined relation between fluid-fluid levels and malignancy and found that malignant neoplasms most commonly showed fluid-fluid level in less than third of the lesion. With increase in the total volume of fluid-fluid level, the chance of malignancy is very less likely; there was no malignancy in lesions with 100% fluid-fluid.

On MRI it is very important to evaluate permeativeness of lesion to differentiate it from telangiectatic osteosarcoma. Aggressive lesion like telangiectatic osteosarcoma can show 2/3 of lesion with fluid-fluid levels because of high grade predominantly necrotic bone tumors. These tumors show small solid component but differentiation with ABC’s can be difficult solely on MRI. In these cases plain radiography and clinical features should be used to differentiate between telangiectatic osteosarcoma and ABC57.

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Ultrasound

High resolution ultrasound can be used for initial assessment of uncertain soft tissue lesions and for ultrasound guided biopsy. But ultrasound has limited role in intramedullary bone lesions as sound waves cannot penetrate the normal cortex. Ultrasound can be used in evaluation of postoperative sites for tumor recurrence particularly if there is significant artifact on MRI or CT due to orthopedic metallic prosthesis.

Ultrasound features of ABC include, cystic mass with a thin echogenic shell and multiple intra osseous fluid levels. The cortices of the affected bones are markedly thinned allowing sound waves to be transmitted for further characterization of the inner structure of the lesions. Fluid-fluid levels move with change in patient position58.

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Natural history of ABCs

The fate of ABCs depends on the location and biological activity at the time of diagnosis. On the basis of x-rays, biological activity of ABCs can be classified as latent (or quiescent), active, and aggressive23. Latent lesions having an intact rim of cortical bone may not lead to a fracture. Spontaneous healing of these cysts has been reported59, and some lesions resolve after biopsy60. Active lesions pose a risk of fracture due to cortical thinning, may present with a fracture, or signs and symptoms of nerve compression due to bone expansion. Involvement of joints may lead to instability, especially in facet joints of the spine. In children, proximity to growth plate may lead to growth abnormalities resulting in limb length discrepancy or angular deformities over time. Aggressive lesions may manifest as bone destruction, erosion of articular bone, progressive neurological impairment, and appear similar to malignant tumors. True malignant transformation is rare; it has been reported in cases previously operated and irradiated for ABC60–62.

Thus, ABCs may result in fracture and joint involvement, lead to deformity and restricted range of motion, compromise neurological function, affect epiphyseal growth in children and rarely transform into a malignant lesion.

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Management of ABCs

General principles

Management of ABCs entails addressing the patients’ symptoms and prevention/treatment of fracture. Symptoms may be due to pain from elevated intracystic pressure, bone expansion, and compression of adjacent structures. Nerve compression is common in spinal lesions, leading to neuropathic or myelopathic symptoms. The main stay of management remains the same as that described by Jaffe and Lichtenstein63, that is curettage of the cyst cavity and reconstruction of the defect with bone graft. This results in decompression of the cyst which relieves pain, and permits healing of the cavity. However, some lesions may resolve spontaneously without surgery, or with percutaneous treatment. Thus, broadly speaking management options can be divided into nonoperative management, minimally invasive strategies, and operative management, and decision-making requires assessment of patient, imaging and consideration of natural history.

Management choice depends on whether the lesion is latent, active or aggressive, and aims at preventing complications from the activity of the lesion.

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Nonoperative management

Considering the benign nature of the lesion, nonoperative management may be considered in selected cases. Options for nonoperative management include wait-and-watch, splinting of extremity lesions, drug treatment and radiation therapy.

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Wait-and-watch

For latent lesions causing pain alone, without neurovascular symptoms, and without impending fracture on x-ray it may be reasonable to just observe the lesion with serial x-rays, on 3–6 monthly follow-ups. Spontaneous healing of these cysts has been reported59. Analgesics and modification in activity level appropriate to the level of pain may be sufficient to control symptoms. Postbiopsy the lesions often show healing, thus it is prudent to wait for 4–6 weeks after the biopsy before deciding about further interventions as involution of the cyst may occur postbiopsy60. A percutaneous biopsy technique has been described as a “Curopsy” which includes use of core needle biopsy and pituitary rongeur/curette to obtain lining membrane from different parts of lesion, resulting in healing in majority of cases42. Pathogenetically, increased intracystic pressure due to hemodynamic abnormalities has been suggested64, hence it is likely that biopsy results in relief of pressure in the cyst and compartments within the cyst, leading to cyst healing. In case of active lesions in the upper extremity and lesions in the leg/foot, pain control may be achieved by splinting or casting, with or without restricting loading depending on cortical involvement on x-ray suggesting impending fracture.

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Drug treatment

Bisphosphonates have been used65 for their role in inhibiting osteoclasts on the pretext that cyst lining shows multinucleated giant cells and cyst formation in bone requires osteoclastic activity. Denosumab, an intravenously administered monoclonal antibody against RANK ligand approved for use in osteoporosis, has been used in a few cases to treat spinal and appendicular ABCs66–68 resulting in response within 2 months and subsequent healing and remodeling of the lesions. As for teriparatide, a parathyroid hormone analogue used in osteoporosis and fracture nonunions, we are not aware of any reports on its use in ABCs.

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Radiation therapy

Although this is effective for cyst resolution, it carries a risk of malignant transformation in the otherwise benign disease, as well as risk of ischemia to the viscera or spinal cord. Situations such as recurrence in spinal lesions not amenable to other methods may be an indication for radiotherapy62.

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Minimally invasive strategies

Angiographic embolization

The effect of angiographic treatment such as selective arterial embolization has been positive in spinal lesions69,70, but inconclusive as an independent treatment in the appendicular skeleton71. However, this may be used to reduce intraoperative hemorrhage in spinopelvic lesion surgery (discussed in the Operative management section).

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Percutaneous intralesional injections

Several agents have been reported to have been used to treat ABCs through percutaneous injections. These include methylprednisolone, calcitonin, bisphosphonate, alcoholic zein, bone marrow aspirate, bone substitute and doxycycline, but the experience is either limited to case reports or short series, results have been variable and contradictory, or multiple injections are required60,61,72–78. Methylprednisolone acetate injection alone has been reported to exacerbate the lesion, hence it is not recommended60,61. Two agents used for sclerotherapy, however, may be promising. Three percent polidocanol (hydroxypolyaethoxydodecan) or absolute alcohol appears to be effective in resolving the cyst in majority of cases75,79. Two to 3 injections may be required, but these are otherwise safe75,79–82.

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Radionuclide ablation

This entails intralesional injection of radioisotope emitting ionizing radiation which ablates adjacent tissue. For ABCs, CT-guided injection of chromic phosphate P32 into the cyst has been shown to result in cyst resolution in a series of 5 patients with spinopelvic lesions81.

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Cryoablation

Using image guided percutaneous probe, cryoablation has been used successfully in cases of spinal ABC83. Radiofrequency ablation, which generates heat, is not recommended due to risk of damage to surrounding neural structures.

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Stem cell injection

Studies on percutaneous injection of concentrated stem cells from bone marrow84 and injection of whole bone marrow have shown to be effective in resulting in cyst resolution85,86, presumably through bone marrow derived stem cell differentiation into osteoblastic lineage.

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Operative management

In preoperative planning, strategy to avoid potential intraoperative hemorrhage from the cysts needs to be incorporated. Lesions of the spine, sacrum and pelvis may bleed excessively, hence preoperative angiographic embolization may be justified60,61,87, with due consideration to the risk of ischemia to vital structures supplied by the same feeding vessels.

The mainstay of operative management has been intralesional curettage and bone grafting. This approach, however, is fraught with a substantial risk of recurrence. Thus, literature shows a recurrence rate of up to 20% by the use of curettage alone88. Wide margin (en bloc) excision is therefore sometimes preferred in aggressive lesions as it has the lowest risk of recurrence41,89, but carries a higher morbidity in the form of pain, limb length discrepancy, muscular weakness and restriction of joint motion. In periarticular lesions, excision of the articular segment may be required, necessitating arthrodesis or joint replacement. Moreover, en bloc resection may not be technically feasible in certain locations90. Hence, conservative surgery with intralesional curettage with or without bone grafting is now generally considered as the standard of operative care used in conjunction with adjuvants such as electrocautery, high speed burr, phenol (carbolic acid), cryotherapy (with liquid nitrogen) and argon beam laser. These adjuvant methods have been shown to result in reduction of recurrence rates to 5%91, but argon beam has been reported to increase risk of fracture92 presumably from osteonecrosis due to the laser. The cyst cavity can be managed with bone graft or polymethyl methacrylate “bone cement.” Moreover, β tri-calcium phosphate and atelocollagen combined with autologous bone marrow mononuclear cells has been reported to resolve the cyst in 1 case93. In children, 5% recurrence has been reported following surgical treatment (intralesional extended curettage/en bloc resection with or without bone grafting and internal fixation). Main factor associated with recurrence was proximity to the growth plate22,94.

Some of the treatment options are illustrated form our cases in the figures. Figure 6 shows images from a patient with ischial tuberosity ABC treated with excision of the lesion, intralesional curettage with high speed burr and obliteration of the cavity with bone graft and tricalcium phosphate bone substitute. Figure 7 shows images from a patient with an ABC of the lateral femoral condyle managed with intralesional curettage and use of structural bone grafting with tricortical iliac graft to buttress the buttressing subchondral bone and fibular strut grafts for structural support. Both these patients had successful healing without recurrence on 4-year follow-up.

Figure 6

Figure 6

Figure 7

Figure 7

A summary of the treatment options is provided in Table 2.

Table 2

Table 2

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Prognosis and outcome

Being a nonmalignant condition, the prognosis is generally good. For spinal lesions, pretreatment neurological impairment may recover to a variable degree, depending on severity and duration of neural compression. Fracture healing is generally successful using bony stabilization and bone grafts, and the above described methods generally result in resolution of the cyst. Surgical resection with intralesional curettage and adjuvants has been shown to result in recurrence-free outcome in 80%–90% of cases95,96. Considering the risk of recurrence, ABCs require long-term follow-up. There is no general protocol for follow-up; depending on the apparent biological activity of the lesion, more or less frequent follow-up visits may be required. Thus for quiescent lesions a yearly follow-up may be adequate, while for active and aggressive lesions follow-up visits may be warranted every 2–4 months.

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Recurrence

With contemporary management the risk of recurrence is in the range of 5%–30%60. A number of risk factors have been postulated in the recurrence of ABCs. Mankin et al88 in a 20-year follow-up study of 150 ABC tumors, published a local recurrence of almost 20%. In some reports age younger than 12 years has been associated with an increased risk of recurrence2,22,96,97. Contrary to that Dormans et al95 did not report a significant difference in children older or younger than 10 years of age. Gibbs et al96 reported an increased rate of recurrence in skeletally immature patients undergoing curettage with a high speed burr. Histologic characteristics have also been evaluated as potential indicators of recurrence. In 201038, it was shown that a higher ratio of cellular component as compared with osteoid was associated with recurrence. Ruiter et al98 reported a higher recurrence rate with a mitotic index of ≥7 per 50 fields. De Silva et al99 postulated immature lace pattern and fibromyxoid nodular fasciitis like area to be associated with higher recurrence. Recurrent lesions generally require a more aggressive approach to management. With joint involvement and segmental instability, en bloc excision with prosthetic replacement or instrumentation may be required.

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Malignant transformation

Literature reports with malignant transformations of ABCs have been published60–62,100. Brindley and colleagues reported recurrence in cases where adjuvant radiation was used in addition to primary treatment. They also reported recurrence in secondary ABCs associated with telangiectatic osteosarcoma and fibroblastic osteosarcoma.

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Summary

ABC is a benign locally aggressive bone tumor that usually appears in the first 2 decades of life with a slight female preponderance. Decision-making in ABCs entails consideration of the location, for example, diaphyseal, periarticular, spinal, the lesion activity, that is latent, active or aggressive, the cortical thinning with likelihood of fracture, and the effect on surrounding tissues/organs, for example neural elements. In general, nonoperative measures can be applied in latent and active lesions including wait and watch, “curopsy,” percutaneous intralesional alcohol or polidocanol, and radionuclide ablation in resistant cases. For aggressive lesions intralesional curettage is the treatment of choice along with use of intraoperative adjuvants on the cyst wall such as electrocautery, high speed burr, phenol, and cryotherapy. Large cavities require bony reconstruction with bone graft or cement. En bloc resection may be required in aggressive lesions with major destruction of bone and joint. Preoperative angioembolization should be considered in spinal and pelvic lesions. The chances of local recurrence are increased in young children and those with stage 3 aggressive tumors. Surgical resection with intralesional curettage and adjuvants is the mainstay of treatment with successful outcome in the range of 70%–90%95,96.

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Ethical approval

As this is a review article and not a primary study, ERC approval was not sought. No patient identifying elements are included in any of the images.

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Sources of funding

No funding was obtained for this work.

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Author contribution

S.N.: Lead author, literature search, manuscript write-up. T.A.: Lead co-author, literature search, manuscript write-up. M.U.: Co-author, case details, imaging, final manuscript review. K.H.: Co-author, radiology images, Literature search, manuscript write-up. N.U.: Co-author, pathology images, Literature search, manuscript write-up. S.A.: Literature search, manuscript write-up. P.H.: Manuscript write-up and review.

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Conflict of interest disclosure

The authors declare that they have no financial conflict of interest with regard to the content of this report.

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Research registration unique identifying number (UIN)

Not applicable.

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Guarantor

Shahryar Noordin.

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References

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Keywords:

Aneurysmal bone cyst; Aneurysmatic bone cyst; Benign bone tumor; Upper limb; Lower limb; Pelvis; Management; Medical; Percutaneous; Surgical

Copyright © 2019 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of IJS Publishing Group, Ltd.