Surgical Treatment of Aneurysmal Bone Cysts of the Spine

Abstract

Objective

Our goal was to document the presentation, location, diagnostic modalities, preoperative embolization status, treatment, histology, complications, and recurrence rates for aneurysmal bone cysts of the mobile spine.

Methods

We reviewed our institution's database to identify patients diagnosed with aneurysmal bone cysts of the mobile spine (excluding the sacrum) from 1995 through 2006. Of those 17 patients, three were treated elsewhere and 14 underwent surgical treatment at our institution. Of those 14 patients, the nine (mean age at presentation, 17.2 years; range, 5‥32 years) with at least 2 years of follow-up (average, 49.6 months; range, 24‥88 months) formed our study group. For those nine patients, we tabulated the presentation, location, diagnostic modalities, preoperative embolization status, treatment, histology, complications, and recurrence rates.

Results

Pain was the presenting symptom in all nine patients. The lesion most commonly occurred in the cervical spine (five); two occurred in the lumbar spine, and two occurred in the thoracic spine. Patients underwent resection and combined anterior and posterior spinal arthrodesis (six) or resection and posterior spinal arthrodesis (three). There were four complications: one iliac crest donor site infection, one incidental durotomy, and two neurologic defcits. We noted two recurrences (both within 3 months).

Conclusions

Aneurysmal bone cysts of the spine can be successfully treated with surgical resection and instrumentation.

Introduction

Aneurysmal bone cysts (ABCs) are rare (1% of primary bone tumors), benign, highly vascular pseudotumors of unknown cause.¹ Approximately 6% to 22% of ABCs develop in the mobile spine; 13% to 21% occur in the sacrum.^2-6 ABCs can be classified as primary (no underlying lesion) or secondary (associated with bone tumors such as giant cell tumors, telangiectatic osteosarcoma, osteoblastoma, or chondroblastoma).¹ ABCs in the spine usually affect the posterior elements. The cervical spine is involved in 30% to 41%, the thoracic spine in 25% to 30%, and the lumbar spine in 40% to 45% of cases.^2,7 Treatment options include selective arterial embolization (SEA), radiotherapy, curettage, and en bloc excision with reconstruction.

The purpose of our study was to document the presentation, location, diagnostic modalities, preoperative embolization status, treatment, histology, complications, and recurrence rates for ABCs of the mobile spine.

Subjects and Methods

With approval from our institutional review board, we searched our histologic database for patients diagnosed with ABCs of the mobile spine (excluding the sacrum) from 1995 through 2006. Of those 17 patients, three were treated elsewhere, and were excluded from our study. Of the remaining 14, nine had at least 2 years of follow-up (average, 49.6 months; range, 24–88 months) and formed our study group. At presentation, the mean age of the three male and six female patients was 17.2 years (range, 5–32 years).

We tabulated the presentation, location, diagnostic modalities, preoperative embolization status, treatment, histology, complications, and recurrence rates for their ABCs of the mobile spine.

Results

Presenting Symptoms

All patients presented with pain localized to the site of the lesion for of an average of 5.9 months' duration (range, 1–18 months) (Table 1). Neurologic deficits were present in three patients, one of whom presented with signs and symptoms of cauda equina syndrome secondary to mass effect from the ABC at the L4-L5 level and underwent urgent decompression and reconstruction.

Table 1.

Surgical Management of Aneurysmal Bone Cysts of the Spine.

Patient no.	Gender	Age	Location	Presentation	Extent of resection	Reconstruction	Follow-up (months)	Histology	Recurrence	Complication
1	F	13	C6, C7	Pain	Complete intralesional excision	Anterior corpectomy and fusion, PSF C5 to T4	88	Secondary ABC (primary giant cell tumor)	Yes	2 neurologic deficits
2	F	26	C5	Pain and weakness	Complete intralesional excision	Anterior corpectomy and fusion, PSF C4 to C6	54	Primary ABC	None	None
3	M	27	C7	Pain and weakness	Complete intralesional excision	PSF C5 to T1	24	Primary ABC	None	None
4	F	9	C3	Pain	Partial intralesional excision	Anterior corpectomy and fusion	29	Primary ABC	Yes	None
5	F	16	C2	Pain	Complete intralesional excision	PSF C1 to C4	60	Primary ABC	None	Iliac crest donor site infection
6	F	14	T8	Pain	Complete intralesional excision	Anterior corpectomy and fusion, PSF T7 to T9	62	Primary ABC	None	Incidental durotomy
7	M	32	T7	Pain	Complete intralesional excision	Anterior corpectomy and fusion, PSF T6 to T9	24	Primary ABC	None	None
8	F	13	L4, L5	Pain and cauda equina syndrome	Complete intralesional excision	PSF L4 to L5	51	Primary ABC	None	None
9	M	5	L3	Pain	Complete intralesional excision	Anterior corpectomy and fusion, PSF L2 to L4	66	Primary ABC	None	None

ABC, aneurysmal bone cyst; PSF, posterior spinal fusion.

Lesion Location

The lesions were most often located in the cervical spine (cervical, five; lumbar, two; thoracic, two); one lesion extended from C6 to T1. The lesions were found in the following portions of the spine: anterior (vertebral body), one; posterior (lamina, spinous process, pedicle, transverse process), three; and anterior and posterior, five.

Diagnostic Modalities

Imaging consisted of radiographs (eight patients), magnetic resonance imaging (MRI; eight patients), computed tomography (CT; seven patients), and a combination thereof (eight patients). CT scans typically showed a lytic lesion with a thin rim (Fig. 1a), whereas T2-weighted MRI showed multiple fluid levels (Fig. 1b).

Figure 1. This 26-year-old female patient had an ABC lesion of C5 that was managed surgically. (a) Axial CT scan of the cervical spine showing the lytic ABC lesion at C5 in the right posterior and anterior elements. (b) T2 sagittal MRI study of the cervical spine showing the fluid levels in the vertebral body of C5 and the posterior elements. Anteroposterior (c) and lateral (d) views of the cervical spine 54 months after a C5 corpectomy with autograft strut support and combined anterior and posterior spinal fusion with instrumentation. (e) Histology of the lesion.

Biopsy

Biopsies were obtained in eight patients (open, five; CT-guided, three); the type was at the surgeon’s discretion. An intraoperative pathology specimen was obtained from the patient who presented with the signs and symptoms of cauda equina syndrome and underwent surgical intervention.

Preoperative Embolization

Preoperative embolization was ordered at the surgeon's discretion. Preoperative angiograms were obtained for three patients, two of whom underwent successful embolization with 350 to 500 µ of polyvinyl alcohol particles (Boston Scientific, Natick, MA, USA). Two other patients had recurrence and underwent preoperative embolization; one embolization was successful.

Surgical Treatment

Surgery was performed by orthopaedic surgeons (seven patients) and neurosurgeons (two patients). During the index procedure, resection of the lesions and combined anterior and posterior spinal fusion were performed in six patients. Of the five patients with cervical spine ABCs, three underwent lesion resections and combined anterior and posterior spinal fusion (Figs. 1c, d). One of the two lesions in the lumbar spine and two of the lesions in the thoracic spine were treated with corpectomy and combined anterior and posterior spinal fusion. Complete intralesional excision was performed in eight patients; one patient had partial intralesional excision.

One patient with an ABC of the cervical spine (C7) had posterior cervical fusion only and was disease free at 2 years after surgery. One patient with an ABC of the lumbar spine (L4-L5) underwent posterior resection/laminectomy with in situ fusion and was disease free at 51 months after surgery. One patient with an ABC of the cervical spine (C3) initially underwent anterior fusion only and had a recurrence of the lesion within 3 months; during revision, combined anterior and posterior fusion was performed. Estimated blood loss averaged 1368 ml (range, 100–2700 ml).

Autograft was used in eight patients (iliac crest, four; rib, three; fibula, one). Allograft was used in two patients. Resected tumor-free bone was used as autograft in two of the eight patients without any recurrence.

Somatosensory-evoked potentials and motor-evoked potentials were used in all patients. There was one case of intraoperative loss of motor signals in the lower extremities (after corpectomy of a T8 ABC). A wake-up test was performed, and the patient was able to move her lower extremities. No neurologic changes were present after surgery.

Postoperatively, seven patients were immobilized in a halo, thoracolumbosacral orthosis brace, cast, or cervical collar.

Hospital stay averaged 8.1 days (range, 2–17 days). This time included: (1) an international patient who underwent an open biopsy and lesion resection during the same admission, with a total of 17 days in the hospital; and (2) a patient with a postoperative cerebral spinal fluid leak requiring a return to the operating room for durotomy repair during the same admission, who spent a total of 14 days in the hospital. Excluding these two patients, hospital admission averaged 6 days.

Histology

All biopsy (Fig. 1e) and intraoperative specimens were evaluated by one musculoskeletal pathologist. All patients with a preoperative biopsy were diagnosed with ABCs based upon the pathology. One preoperative biopsy was initially read as an ABC and was later determined to be a giant cell tumor with a secondary ABC based upon the intraoperative pathology specimen‥

Complications

We noted four postoperative complications in three patients within 4 weeks of the index procedure. One patient required surgery for closure of an incidental durotomy; one developed an infection at the iliac crest bone graft harvest site requiring irrigation, debridement, and intravenous antibiotics; and one with a secondary ABC and primary giant cell tumor developed two neurologic changes (Horner's syndrome and right upper extremity weakness) secondary to tumor recurrence that required surgical decompression.

Tumor Recurrence

Two patients had tumor recurrence. One had a giant cell tumor with a secondary ABC at C6 and T1. This patient required four revision anterior and posterior spinal fusions during a 28-month span after the index procedure. She also underwent a trial of radiation therapy (unsuccessful in preventing recurrence) and a preoperative embolization before the second revision. The patient has been disease free for 81 months after the last resection. The second patient had a C3 lesion that was treated with corpectomy, anterior-only spinal fusion, and anterior partial intralesional excision. The tumor recurred in the posterior elements within 3 months. The patient underwent repeat resection and combined anterior and posterior spinal fusion and has been disease free for 27 months.

Discussion

We report our experience with the surgical management of ABCs of the mobile spine over an 11-year period at our institution. The initial description of an ABC is attributed to Van Arsdale,⁸ who in 1893 reported a case of ossifying hematoma of the humerus that arose 6 weeks after a traumatic episode. The term “aneurysmal bone cyst” was first used in 1942 by Jaffe and Lichtenstein⁹ when they reported two cases of ABCs in male patients 18 years old and younger, one of which was in the posterior elements of the spine. The incidence of ABCs has been reported to be 1.4 of 100,000 and comprises 1% of bone tumors.¹⁰

Presentation

Pain is the most common presenting symptom of ABCs. Neurologic symptoms present if the lesion encroaches on nerve roots or the spinal cord. A palpable mass may be present in the posterior elements, and tenderness may be elicited. In our nine patients, the average duration of symptoms before presentation was 5.9 months (range, 1–18 months). This finding is consistent with the slow and gradual onset of pain described in the literature.^1,2,6

Diagnosis is confirmed via biopsy, and imaging modalities (radiograph, CT, MRI) should be part of the work-up. Enneking¹¹ classified ABCs as three types: I (latent), II (active), and III (aggressive). ABCs of the spine are not common in patients more than 20 years old; the incidence in large series (>20 patients) of such patients is 14% to 19%.^1,2,6,12 It is conceivable that certain ABCs that develop in the second decade can remain clinically silent until the third decade, as seen in 33% of our patients. ABCs can also cause vertebra plana, and it is important to consider ABCs in the differential for vertebra plana.¹³ An open or closed CT-guided biopsy can be performed preoperatively.

Lesion Location

In our series, the cervical spine was the most common location. Other series^1,2,6 have reported cervical spine involvement in 11% to 41%, thoracic spine involvement in 25% to 41%, and lumbar spine involvement in 17% to 50% of cases. In their epidemiologic study, Cottalorda et al¹⁰ reported on 161 ABCs in the mobile spine. They found 30% of the ABCs in the cervical spine, 30% in the thoracic spine, and 40% in the lumbar spine. Lesions were found in the anterior and posterior elements of the spine in 56% of our patients; 33% had lesions in the posterior elements only, and 11% had lesions in the anterior portion only.

Management

Surgical resection en bloc has the lowest recurrence rate when treating ABCs of the spine.^1,6 For ABCs of the mobile spine, we recommend surgical resection en bloc when possible or an aggressive complete intralesional excision and stabilization with instrumentation and bone graft. Several reports also advocate en bloc resection for the cervical spine.^14-20 Although the en bloc resection is technically challenging,¹ this technique minimizes the risk of recurrence.

Other management options for ABCs include SEA, intralesional injection of calcitonin/steroids,²¹ radiotherapy, and curettage alone without fusion or instrumentation.²² Radiotherapy has been used in sites that are inoperable. However, its risk of postirradiation sarcoma, neurologic damage, scoliosis, and damage to surrounding structures has decreased its use for ABCs.^5,6 Recent reports have advocated the use of SEA for definitive management of ABCs.^5,6,23 The benefits are its minimally invasive nature, which reduces damage to the pediatric spine. Coils, corpusculated material such as polyvinyl alcohol, and liquid material such as n-butyl cyanoacrylate (Cordis, Miami Lakes, FL, USA) have been used during SEA.⁵ The risks of SEA include recurrence of the lesion and spinal cord ischemia.¹⁹ Multiple embolizations may also be needed to eradicate the lesion.²³ Intralesional curettage with or without bone grafting has been described.^1,6,7 Boriani et al¹ have advocated SEA as the first-line treatment for spinal ABCs except in the presence of pathologic fractures or neurologic deficit. However, in their series of 41 patients, SAE was used as primary treatment for only four patients.¹

Lesion Recurrence and Complications

Two of our patients had disease recurrence, both within 3 months of excision. One recurrence was in a patient with a secondary ABC. Although this patient's preoperative biopsy was thought to be a primary ABC, the intraoperative biopsy showed a giant cell tumor and a secondary ABC. Our experience with this patient, who required four revisions, led us to recommend an aggressive resection of the primary lesion in secondary ABCs during the index procedure. The role of aggressive initial surgical resection has been emphasized in a recent study reporting a 36% recurrence rate of giant cell tumors with secondary ABCs.²⁴ Our second recurrence was in a patient with a C3 lesion who underwent only anterior partial intralesional excision and reconstruction. Because of the incomplete resection, the lesion recurred in the posterior elements, and a combined anterior and posterior lesion resection and reconstruction was performed; the patient remains disease free at 27 months.

The four complications (incidental durotomy, iliac crest donor site infection, and two neurologic deficits) occurring in three patients were treated successfully with no permanent sequelae.

The largest study to date examining ABCs of the spine (including the sacrum) was by Papagelopoulos et al.⁶ In that study spanning 83 years, 41 of 52 patients had a lesion involving the mobile spine, and all were treated with surgical excision; 30 patients with primary occurrences were treated surgically with various modalities. There was a 13% recurrence rate and five cases of secondary ABCs with primary giant cell tumors. It is unclear whether the recurrences occurred in patients with secondary ABCs. There was a 31% complication rate, including two deaths. One patient was treated with radiation for an ABC with subsequent development of a postradiation sarcoma and another had massive intraoperative blood loss resulting in cardiac arrest.

In another large series, Boriani et al¹ reported on 41 patients with ABCs of the mobile spine (excluding the sacrum) treated over a 44-year period, 32 of whom were treated surgically. However, only six patients had a fusion performed, three of whom had fusion with instrumentation. A 5% recurrence rate was reported; one was attributed to an incomplete curettage and one was in a patient treated only with SEA. A 17% complication rate, including five surgical wound complications and one urethral compression, was reported.

In another large series, de Kleuver et al² reported on 31 patients with ABCs of the spine (28 in the mobile spine) over a 45-year period. Surgical excision was used in 93%; a variety of surgical procedures was used. The recurrence rate was 21% (six in 28 patients, attributed to incomplete excision). Complications included angular kyphosis in the thoracic spine after laminectomy without fusions or instrumentation.

Study Limitations

The limitations of our study are the small sample size and the multiple surgeons involved in the treatment of the patients. However, the oncologic principle of aggressive excision and reconstruction with fusion and instrumentation to maintain stability of the spinal column (except one case) was uniform among all of the surgeons. The rarity of these tumors and the 11-year study span account for the small sample size. Series with larger patient numbers have spanned an average of 57 years (range, 44–83 years).^1,2,6 However, the shorter study period is beneficial because surgical management techniques did not change much in comparison to studies spanning several decades. We also ensured adequate follow-up by limiting our study to patients with at least 2 years' follow-up. Two of the larger series included patients with 6 to 12 months' follow-up.^2,6

Conclusion

In our series, successful treatment of ABCs of the spine was achieved with aggressive lesion excision or en bloc resection with combined anterior and posterior spinal fusion with instrumentation. We continue to use this technique at our institution. SEA was used for preoperative embolization but not as a definitive treatment. Radiation therapy was not used as primary treatment for ABCs of the spine.