Surgical Management of Aneurysmal Bone Cysts of the Spine

James K. Liu, M.D.; Douglas L. Brockmeyer, M.D.; Andrew T. Dailey, M.D.; Meic H. Schmidt, M.D.

Disclosures

Neurosurg Focus. 2003;15(5) 

In This Article

Treatment Strategies

Treatment options for aneurysmal bone cysts have included simple curettage with or without bone grafting, complete excision, embolization, radiation therapy, or a combination of these modalities.[9,56,59] The optimal treatment of aneurysmal bone cysts of the spine, however, remains a subject of controversy in the literature. Because of their unique anatomical structure and function, there are special considerations when managing aneurysmal bone cysts of the spine. One must take into account the age of the patient, the surgical accessibility of the lesion, necessity to minimize intraoperative blood loss, the presence of neurological compression, the presence of a pathological fracture and deformity, and potential postoperative instability after complete resection.[2,41,43,56]

The use of preoperative embolization has been reported to reduce intraoperative blood loss.[16,18] Adjuvant radiotherapy appears to have no significant advantage over surgical treatment alone and may carry an increased risk of malignant transformation.[5,26] Excision, radiation therapy, and selective arterial embolization have been used successfully, alone or in combination. The clinical course of aneurysmal bone cysts is sometimes unpredictable and local recurrences have been described after various types of treatments.[2] Wide excision appears to yield the highest rate of cure; however, aggressive surgery may render the spine unstable. Complete resection followed by spinal stabilization appears to be the optimal method of acquiring a high degree of local control and preventing or correcting spinal deformity and instability (Figs. 2 right and 3E and F).[40,43,56] There appears to be little justification for needle biopsy sampling: the results are likely to be negative, and the procedure carries a potential risk of incurring an epidural hematoma.

Curettage. Although curettage and bone grafting have been reported to be successful in the management of aneurysmal bone cysts in the long bones of the extremities[9,50,59] the same does not apply to lesions of the spine. In a study by Ozaki, et al.,[40] nine patients who underwent complete excision did not suffer a local recurrence, whereas two who underwent curettage alone experienced local recurrences. Curettage has approximately a 19% recurrence rate, usually within the first 2 years posttreatment.[59]

Complete Excision. Complete resection is the treatment of choice with aneurysmal bone cysts of the spine, especially in patients who present with a neurological deficit. Total excision, en bloc if possible, provides the highest rate of cure, with an excellent prognosis.[1,2,40,43,56] Subtotal excision is associated with a high incidence of recurrence, which is seen within 6 to 12 months. Hay, et al.,[26] reported no recurrences after total excision and a 25% recurrence rate for partial excision. The growth of aneurysmal bone cysts is sometimes characterized by rapid enlargement and bone destruction, with occasional neurological compromise from spinal cord compression or instability.[43] Early surgical intervention with total excision of all affected bone is recommended for immediate decompression.[46] In cases of pathological and impending fractures, surgery followed by spinal reconstruction and stabilization provides correction of the deformity.

Total excision must include the entire cyst wall, all abnormal tissues that feel spongy, and bone surfaces that are lined with fragile and hypervascular membranes.[1,5,11,15,25,35,38,41,43,44,56,57] Excision must include the entire cyst wall because partial excision is related to a higher risk of recurrence.[2] Intraoperative bleeding generally subsides when this layer is removed. Aggressive curettage using a high-speed drill is often used to cut back to healthy, well-mineralized bone. For large and extensive lesions, complete resection will likely cause iatrogenic instability requiring instrumented fusion (Figs. 2 right and 3E and F).[41]

The surgical approach depends on the location and extent of the lesion. Because the posterior elements are almost always involved, a posterior approach should be considered initially. With a posterior exposure, any tumor involvement of the pedicles with extension into the anterolateral aspect of the VB is surgically accessible with a unilateral or bilateral transpedicular approach. If there is extensive anterior VB involvement and resection and decompression from a posterior approach is inadequate, then a separate anterior approach should be used, either in the same operation or at a later date.[35,38,41]

Reconstruction and Stabilization. Extensive bone destruction can involve multiple contiguous levels and result in loss of structural stability. Collapse of the VB can produce kyphotic deformity and resultant neurological compromise. Extensive tumor resection can also result in postoperative iatrogenic instability. If instability and/or deformity already exists, or if the amount of bone resection is expected to result in instability, then simultaneous reconstruction and instrumented stabilization should be planned (Fig. 2 right).[5,11,35,38,40,41,44,56,57] This strategy of preplanned spinal stabilization allows the surgeon to perform an aggressive resection that yields a high degree of local control.

Posterior instrumentation with lateral mass screws (cervical spine), pedicle screws (thoracic and lumbar spine), or hooks and rods can be effectively performed after posterior resection. If a combined anterior vertebrectomy is performed, the anterior column needs to be reconstructed with an interbody graft and plating (anterior cervical locking plate in the cervical spine; lateral interbody plate in the thoracolumbar spine).[52,58] We recommend bone grafting in the resection bed to promote fusion and to buttress the stability of the involved segments. Alternatively, interbody cages packed with bone can be used to reconstruct the anterior vertebral column.

Spinal stabilization should be considered after resection of lesions involving the cervicothoracic or thoracolumbar junctions because of the tendency for postlaminectomy kyphosis, especially in children.[43] In cases in which postoperative instability is not obvious, we recommend a trial of external bracing with close radiographic follow up. This is a reasonable alternative to instrumented fusion for children who have not reached skeletal maturity. If postoperative deformity develops, however, surgical stabilization is indicated (Fig. 3E and F).

Embolization. The main goal of selective arterial embolization in the management of aneurysmal bone cysts is to decrease vascularity and reduce intraoperative blood loss as a preoperative adjunct.[8,14,16,19,23,29] Although successful treatment with embolization alone has been reported for aneurysmal bone cysts of the pelvis and long bones,[10,17,36,37,45,60] its use as the sole mode of therapy has very limited applications in the spine, especially in the setting of pathological fracture and neurological involvement. In patients who present with spinal canal compromise and neurological deficit, immediate surgical decompression is warranted and the time required for embolization may delay surgery.[43]

Embolization may be considered as the primary therapy in patients with a recurrent lesion after previous surgeries or in patients who cannot tolerate surgery, but only if pathological fracture, spinal deformity, instability, and neurological compromise are absent. The long-term effect of embolization results in involution of the soft-tissue component, sclerosis, and ossification. This mineralization usually becomes apparent after 3 months to 2 years, and some authors have reported pain reduction and tumor shrinkage.[14,16,29,60] There are few reports of involution and diffuse ossification of the lesion, which would obviate any further surgery.[29] Presumably, the occlusion of feeding arteries dampens the hemodynamic forces that underlie the destructive bone remodeling and promotes spontaneous reossification. Reappearance of foci of bone rarefaction or cystic changes has been reported later than 2 years after embolization; thus, continued surveillance is recommended.

Medium-sized particles (250–350 µm) of polyvinyl alcohol are most often used as the embolic agent, because smaller particles might behave more like liquid agents and have a higher risk of causing ischemic complications to the spinal cord.[29] Once the feeding arteries are identified, a test occlusion is usually performed by injecting sodium amytal into the feeding vessels of the awake patient. If no neurological deficit is elicited, the embolic agent is injected into the feeding vessels with somatosensory evoked potential monitoring. After embolization, patients should be carefully monitored because of concerns for potential swelling that may result in spinal cord compression. Resection should be performed within 2 to 3 days after embolization, before collateralization of new blood vessels occurs.[23]

Occasionally, there are no identifiable arterial feeding vessels suitable for selective embolization. An alternative strategy is direct percutaneous embolization by entering the cyst with a needle under fluoroscopic or CT guidance (Fig. 2 center).[22,24] Injection of the cyst with a sclerosing solution has been used to induce involution of the lesion. Guibaud, et al.,[24] used an alcohol solution of corn protein (alcoholic zein) that induces intravascular thrombosis, marked local inflammation, and an ensuing fibrogenic reaction that triggers the reparative process of mineralization and bone reconstruction. They reported complete improvement in 87% of cases and partial healing in 13%, with a 5% incidence of serious complications.

Radiation Therapy. There is controversy regarding the role of radiation therapy. Although some authors have reported favorable results with radiation as the primary treatment,[28,39] this modality should not be the first line of treatment for spinal aneurysmal bone cysts. Capanna, et al.,[5] suggested that there was no benefit from the addition of radiation to curettage or to partial resection and curettage. Patients who received radiation in their series had poor outcomes: a delayed pathological fracture and kyphotic deformity developed in one; complications of cystitis, septicemia, and endocarditis in another; and a third experienced progression of disease that extended to adjacent levels resulting in quadriplegia. Radiation therapy does not treat pathological fracture, spinal deformity, instability, and neurological compromise.

Some opponents of its use argue that the risks of radiation therapy are not justified, given the benign behavior of aneurysmal bone cysts and the high rate of cure with complete excision.[2,40,54] The complications of radiation therapy include postradiation myelopathy, radiation-in-duced sarcoma, and possible growth disturbance in children.[21,32,33,43,48,54,55,57,59] Papagelopoulos, et al.,[43] reported on one case of postradiation osteosarcoma that occurred at the same site 7 years later, which resulted in death.

Indications for radiation therapy are limited, and it remains an adjuvant therapy for patients with inoperable lesions, aggressive recurrent disease, or medical conditions that place them at high risk during surgery. Some authors believe that embolization therapy should be attempted before the use of radiation therapy.[14,16]

When referring to aneurysmal bone cysts, recurrence is better defined as continued progression of residual disease left behind by incomplete treatment rather than regrowth of lesions, as in the context of neoplasia.[2,41] The rate of local recurrence after resection is related to the complete or incomplete removal of the lesion, including the cyst wall. In general, incomplete excision is associated with a relatively high recurrence rate and complete excision of the lesion is associated with a high cure rate.[5,26,59] Incomplete excision of aneurysmal bone cysts entails a 50 to 60% rate of disease progression;[41] 90% of the recurrences appear within 6 to 12 months after incomplete excision.[2,43] Patients should be monitored closely with follow-up imaging. Radiographic evidence of cure is manifested by shrinking of the lesion and reossification of the cystic areas. Recurrence of an aneurysmal bone cyst is unusual after 2 years and rare after 4 years.[55]

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