Aneurysmal Bone Cyst Treatment & Management
- Author: Nicholas Tedesco, DO; Chief Editor: Harris Gellman, MD more...
Selective arterial embolization has shown much promise for aneurysmal bone cysts (ABCs) in small studies. However, relatively few cases have been treated with this therapy because ABCs are rare and because selective arterial embolization has been available only since the 1980s.
With the use of angiography, an embolic agent is placed at a feeding artery to the ABC, cutting off the nutrient supply and altering the hemodynamics of the lesion. Various materials, such as springs and foam, have been used to create the emboli.
Selective arterial embolization has the advantage of being able to reach difficult locations, being able to save joint function when subchondral bone destruction is present, and making the complications that are associated with invasive surgery (eg, bleeding) less likely to occur. Selective arterial embolization may be performed within 48 hours before surgery to reduce the amount of intraoperative hemorrhage.
Some of the literature suggests that selective arterial embolization can be a primary treatment if the following conditions are met:
Histologically confirmed tissue diagnosis of ABC
Technical feasibility and safety
Stability; no evidence of pathologic fracture or impeding fracture
No neurologic involvement
Only case evidence exists for intralesional injection, but the injection may be attempted for cases in which surgical access is difficult and for those in which other modalities are contraindicated. (Note: Do not use this approach if the patient has allergies to the injection components, a pathologic or impeding fracture, neurologic symptoms, or unbearable symptoms such as pain. Do not use intralesional injection if a more proven treatment is indicated.)
There has also been case evidence for the use of calcitonin and methylprednisolone injections in the regression of ABCs. This is thought to combine the inhibitory angiostatic and fibroblastic effects of methylprednisolone with the osteoclastic inhibitory effect and the trabecular bone-stimulating properties of calcitonin. The injections are performed under computed tomography (CT) guidance and anesthesia. Growth of the ABC must be closely monitored, and the treatment may need to be repeated several times. Years may pass before the ABC resolves.
ETHIBLOC (Ethicon, Norderstedt, Germany) injection is also performed under CT guidance and anesthesia. The injected solution is a mixture of zein, oleum papaveris, and propylene glycol and acts as a fibrosing agent, and an inflammatory reaction may occur after its administration. Bony healing may take months to years. Side effects (eg, localized thrombosis, pulmonary embolus, osseocutaneous fistula formation, and severe surrounding tissue necrosis) make it a poor first-line choice in the absence of an obvious surgical contraindication.
Some case evidence also suggests healing improvement when systemic calcitonin treatment is used as an adjuvant to other treatment modalities.
An Australian study by Clayer in 15 patients with pathologically confirmed ABC suggests that percutaneous aspiration and injection of ABCs using an aqueous solution of calcium sulfate may have value. All patients except one who have reported pain before the procedure were completely without symptoms at 4 weeks post injection. The calcium sulfate was reabsorbed within 8 weeks.
During the minimum 2-year follow-up period, two patients developed local recurrence of the lesion, one of whom later developed a pathologic fracture. Two other patients sustained pathologic fractures at 12 and 22 months post injection, respectively. Clayer concluded that this procedure has "early clinical and radiological responses and a low complication rate in a consecutive group of patients with ABC."
The unusual stage 1 ABC can be treated with intralesional curettage ; the more common stage 2 ABC is treated by intralesional excision. The difference between curettage and excision is that excision involves wide unroofing of the lesion through a cortical window by careful abrasion of all the surfaces with a high-speed burr and, possibly, local adjuvants such as phenol, methylmethacrylate (MMA), or liquid nitrogen. These adjuvants are controversial because firm evidence that they are effective is lacking, and their use entails considerable risk.
En-bloc or wide excision is typically reserved for stage 3 ABCs that are not amenable to intralesional excision (eg, extensive bony destruction); the recurrence rate after en-bloc excision is about 7%. Reconstructive options after wide excision include structural allografting and reconstruction with either endoprostheses or allograft-prosthetic composites.
In the past, intralesional excision was the mainstay of treatment. The ABC is accessed, a window is opened in the bony wall, and then the contents of the ABC are removed. Excision of the walls with curettes, rongeurs, or high-speed burrs has been described. The intralesional method leaves more bony structure intact than en bloc or regional resection.
Intralesional excision may also be used around joints and other vital areas to try to preserve function. The defect may then be filled with bone chips, bone strut, or other supporting material to add strength and to enhance healing of the excised area.
The surgeon may also use adjuvant therapy, which extends the area of treatment beyond that which can be physically excised. The use of liquid nitrogen, phenol, argon beam gas plasma photocoagulation, and polymethylmethacrylate (PMMA) may achieve an extended area of treatment.
The adjuvants involve the use of chemical, freezing, or thermal means to cause bone necrosis and microvascular damage to the walls of the physically excised cyst, disrupting the possible etiology. Compared with en bloc and regional resection, the use of adjuvants leaves more bone intact, and an increased area is treated compared with that treated with intralesional resection alone.
Liquid nitrogen is the most popular adjuvant, and it is often described in the literature. After the ABC is exposed and a window is opened, liquid nitrogen may be applied by pouring it into the cyst through a funnel or by using a machine that is designed to spray the liquid onto the walls of the lesion. The surgeon should be sure to leave the window open, allowing the gas to escape.
A total of two or three cycles of freezing and thawing should be used to obtain maximum bone necrosis. The surrounding tissue, especially the neurovascular bundles, must be protected to ensure these structures are not damaged. Avoiding the use of a tourniquet with cryotherapy is suggested to keep the surrounding tissue vascularized, making it more resistant to freezing.
Phenol is much less often used as an adjuvant. Some authors have questioned the effectiveness of phenol because of its poor penetration of bony tissue compared with that of liquid nitrogen. However, phenol has had some success in certain studies, and it has the benefit of being easy to use. Phenol is simply applied to the mechanically removed walls by using soaked swabs. Any remaining phenol is removed with suction, and the cavity is filled with absolute alcohol. Finally, the cavity is irrigated with isotonic sodium chloride solution.
PMMA may also be used, although the effectiveness of its thermal properties in causing bone necrosis has been questioned in the literature. However, PMMA does have the benefit of rendering a large lesion mechanically sound and making it easier to recognize a local recurrence. If PMMA is used in a subchondral location, the joint surface should be protected by cancellous grafts or Gelfoam (Pharmacia & Upjohn Co, Kalamazoo, MI) placed before cementation. It is not clear that removing the cement and replacing it with a bone graft is necessary.
Argon beam coagulation has also been used in several studies, with some promising results.[33, 34, 35] One study noted that surgical treatment with curettage and adjuvant argon beam coagulation is an effective treatment option for ABC; the primary complication was postoperative fracture.
An additional study found that argon beam photocoagulation while avoiding the toxic effects of phenol, yielded statistically equivalent recurrence rates, functional outcomes, and complication rates in the treatment of benign-aggressive bone tumors. However, the authors also noted an increased fracture rate in the argon beam photocoagulation cohort as compared with the phenol cohort.
NOTE: Special consideration is necessary in dealing with ABCs that are near open physes. The reader is referred to the literature for general considerations when operating around physes. The reported rate of physeal injury is significant, and patients and their families must be made aware of this possibility. Furthermore, it has been shown that attempts to spare the adjacent physes by performing a less-than-aggressive curettage of ABCs have resulted in increased risk of local recurrence in patients with open growth plates.[36, 37]
Spinal ABCs usually cause neurologic symptoms and pose treatment challenges. The details of surgical excision can be found elsewhere. There is evidence to support an attempt at one or two trials of selective arterial embolization before surgical excision.
A group in Japan developed an endoscopic approach to the treatment of ABC. They successfully treated four patients with ABCs that lacked the aneurysmal component. The technique was completed with a variety of curettes, ball forceps, Kirschner wires (K-wires), an arthroscope, and a drill. The method may leave a more stable structure and is minimally invasive.
Treatment for a secondary ABC is that which is appropriate for the underlying lesion.
Extensive preoperative planning should be completed with the use of cross-sectional imaging. Embolization as a treatment or preoperative technique should be considered. When possible, a tourniquet should be used.
Thought should also be given to what possible methods and materials may be needed to provide stability after ABC excision or resection.
Depending on the size and nature of the lesion, the patient's fluid volume and blood loss may have to be monitored closely.
Activity modification should be as tolerated to the fitness of the patient, the anatomic location of the surgery, and the extent of the surgery and reconstruction. Mechanical or chemical prophylaxis against deep vein thrombosis may also be indicated.
Recurrence usually happens within the first year after surgery, and almost all episodes occur within 2 years.[39, 40, 41] However, patients should still be monitored on a regular basis for 5 years. It is beneficial to detect recurrence early when the lesion is still small and easier to treat. Children should be monitored until they have reached maturity to ensure that any possible recurrence does not cause deformity or interfere with their growth. Any patients who have received radiation should be monitored for life because of the risk of secondary sarcoma.
Complications can vary with the location in which the ABC arises. Many of these are related to the proximity of the surrounding tissues.
Universal complications that have been described with surgery include the following:
Damage to the surrounding tissue
Possible physis damage
Additional complications that have been shown with spinal locations include the following:
Tear of the dura
Transient spastic paralysis from hematomas
Tear in the vena cava
Persistent back ache
Complications that are associated with liquid nitrogen include the following:
Rare gas embolism
Rare late fracture
Damage to the surrounding tissue (eg, neurovascular bundles, physis)
A complication that is associated with phenol is necrosis of the surrounding tissue exposed to the phenol (eg, neurovascular bundles, physis). A complication that is associated with selective arterial embolization is unintentional embolization of a vital area. Finally, fracture risk may be elevated in those adjuvantly treated with argon beam photocoagulation, particularly in weightbearing bones.
Outcome and Prognosis
The prognosis for an ABC is generally excellent, although some patients need repeated treatments because of recurrence, which is the most common problem encountered when treating an ABC.
The overall cure rate is 90-95%.[42, 43] A younger age, open growth plates, and a metaphyseal location all have been associated with an increased risk of recurrence. The stage of the ABC has not been shown to influence the rate of recurrence; however, most clinicians believe that stage 3 lesions have the highest recurrence rate, other factors being equal. Morphologic types I and II recur more often than types III, IV, and V.
Primary recurrence rates have varied greatly in several different studies. Small studies have shown a benefit to using selective arterial embolization, and some authors advocate it as a first-line treatment. Other authors argue that not enough data on selective embolization exist and that surgery is the first-line treatment. Intralesional excision has the most data to suggest that it is a safe and effective method.
Recurrence rates for different techniques have varied. Some studies have reported recurrence rates as high as 59% with intralesional excision and as low as 0% with resection. In a summary of studies of different treatment methods, the following rates of recurrence were reported :
Irradiation – 34 performed with 4 recurrences (11.8% recurrence rate)
Irradiation and curettage – 35 performed with 5 recurrences (14.3% recurrence rate)
Curettage and bone graft – 484 performed with 149 recurrences (30.8% recurrence rate)
Curettage and cryobiopsy – 78 performed with 10 recurrences (12.8% recurrence rate)
Marginal resection – 81 performed with 6 recurrences (7.4% recurrence rate)
Wide resection – 59 performed with 0 recurrences (0% recurrence rate)
Future and Controversies
Most authors agree that some vascular malformation precedes the appearance of an ABC, but the underlying cause of the vascular malformation is not clear. Approximately 30% of ABCs are associated with other benign and malignant bony tumors. The most common association is with the giant cell tumor of bone; because of this strong association, some authors believe that all ABCs are produced by an accompanying lesion that is then obliterated by the resulting ABC. Others believe that ABCs can develop de novo.
In the future, advancements in osteoinductive materials (eg, genetically engineered bone morphogenic protein) may offer a less invasive treatment of ABC.
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