Aneurysmal bone cysts of the spine

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Aneurysmal Bone Cysts of the Spine Vijay K. Gupta, M.S., M.Ch., Sunil K. Gupta M.S., M.Ch., Virinder K. Khosla, M.S., M.Ch., MNAMS, Rakesh K. Vashisth, M.D., and Vijay K. Kak, M.S., F.R.C.S. Departments of Neurosurgery and Pathology, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Gupta VK, Gupta SK, Khosla VK, Vashisth RK, Kak VK. Aneurysmal bone cysts of the spine. Surg Neurol 1994;42:428-32.

Aneurysmal bone cysts are uncommon bony lesions of the spine. Two such patients are reported in the study. The first patient had involvement of first and second thoracic vertebrae, and a preoperative diagnosis was made possible due to the typical magnetic resonance imaging appearances. A total removal was achieved in t w o stages. In the second patient the C2 spinous process was involved, and this patient presented as atantoaxial dislocation. Removal of the abnormal tissue and posterior fusion was done. Both the patients showed neurologic improvement. The relevant literature is reviewed. KEY WORDS: Aneurysmal bone cyst; Spine tumor, Surgical treatment

Aneurysmal bone cysts (ABCs) are uncommon bony lesions constituting 1.4% of all primary bone tumors [10]. These usually occur in the metaphyseal region of the long bones. ABCs are benign, locally aggressive, vascular tumors occurring in children, adolescents, and young adults [31]. Approximately 20% of the aneurysmal bone cysts occur in the spine, predominantly in the lumbar region [14,18]. These lesions commonly arise from the neural arch and occasionally invade the pedicle and the vertebral body [5,18,22,34]. Plain x-ray and computed tomography (CT) scan findings in the ABC have been described characteristically [21,25,36]. Recently magnetic resonance imaging (MRI) also has been used in the evaluation of these lesions [8,9,26]. Available treatment options include a complete excision or curettage of the lesion with bone grafting [1,5,13,18,28,32,35,36,39]. Where excision cannot be achieved, low dose radiation may be used [5,28]. Arterial embolization has been used both as an adjunct to

Address reprint requests to: V.K. Khosla, M.D., Department of Neurosurgery, Postgraduate Institute of Medical Education & Research, Chandigarh 160012, India Received March 8, 1994; accepted May 12, 1994.

© 1994 by ElsevierScienceInc.

surgery to reduce the vascularity [12,13] and as definitive successful treatment of ABCs [4,11,36]. W e report two cases of aneurysmal bone cysts treated successfully with surgery alone. Case

Reports

Case 1 A 19-year-old man presented having had neck pain for 1 year, numbness and tingling of the left upper limb for 8 months, and gradually progressive weakness of both lower limbs for 6 months. On examination, he had mild weakness of the left grip. Power in the right lower limb was grade 3/5 and in the left lower limb grade 2/5. There was 5 0 % - 7 5 % loss of pain and temperature sensation below D 4 level. Tone was increased in both the lower limbs and both the planters were extensor. Plain x-rays of the thoracic spine showed destruction of D 1 and D 2 spinous processes. An MRI scan showed an expansile lesion involving the spinous processes and laminae of D 1 and D2 vertebrae (Figure 1). It was isointense o n T 1- and hyperintense on T2-weighted images. The lesion had involved the pedicles of D 1 and D2 vertebrae on the left side, and the bodies of these vertebrae also demonstrated a hyperintense signal on T2-weighted images. The mass had a left paraspinal extension into the muscles as well (Figure 2 A, B). There was a rim of low signal intensity all round the lesion. The lesion had produced an extradural compression over the thecal sac from the posterior and the left side (Figure 1). A D1-D 2 laminectomy was performed. The tumor was highly vascular, and only a partial removal could be achieved at this stage because of the profuse blood loss. Post-operatively there was no change in the patients neurologic status. The histopathologic examination showed multiple blood-filled spaces of varying sizes lined by fibroblastic cells and osteoclastic type of giant cells. Few hemosiderin-laden macrophages were seen in the wall (Figure 3). This was consistent with the diagnosis of ABC. Repeat surgery was performed after 3 weeks and a total excision was achieved. The patient

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Figure 1. Sagittal Tl-weighted MRI scan showing an isointense expansile lesion involving the spinous processes of the first and second dorsal vertebrae with cord compression.

started improving neurologically and at 3 months follow-up was ambulant without support. He had grade 4 + 5 power in both lower limbs with no sensory deficit.

Case 2 A 35-year-old woman presented with a 1-year history of neck pain. After neck manipulations by a practitioner, the pain became severe. She was referred to our institute where she was diagnosed to have atlanto-axial dislocation. Posterior C 1 and C2 fusion with wire and acrylic was done (Figures 4,5). Ten months after the surgery she presented to us, again, with tingling sensation in both upper and lower limbs of 1 month's duration. Tone was increased in all four limbs, and she had grade 4/5 power. Plain x-rays showed destruction of C2 laminae and spinous process. The patient was put on cervical traction and was reoperared. The spinous process and laminae of axis were replaced by soft friable t u m o r of bone. Excision of this abnormal tissue was done. The C1 arch was removed and an occiput to C 3 fusion was achieved with wire and bone graft. The patient showed gradual neurologic improvement. The histopathologic diagnosis confirmed an aneurysmal bone cyst.

Aneurysmal bone cysts (ABCs) were initially described in 1893 by Van Arsdale [39] who referred to these lesions as ossifying hamartomas. An adequate histologic description was first provided by Cone [7] who used the term ossifying subperiosteal hematoma. It was described as a distinct clinical entity by Jaffe and Lichenstein [20] who coined the term "aneurysmal bone cyst." About 75% of ABCs occur before the age of 20 years and 90% are seen before the age of 30 years. In the extensive material of Tillman et al [36], 80% of the patients were under 20 years of age. O f the two patients seen by us, one was under 20 and the other was 35 years old. There are sporadic case reports of ABCs occurring in individuals above 30 years of age [16,30]. In the series by Reuter [31], 1.9% of patients were in this age group [16]. O f the ABCs seen in the spine, 40% are reported to occur in the vertebral bodies and 60% in the posterior elements [18]. The lesion begins eccentrically in the body, in a pedicle or in a lamina. Although, a single vertebra is commonly involved, it is important to note that the lesion may affect two or more adjacent vertebrae or a vertebra and an adjacent rib. In case no. 1, two adjacent vertebrae (Dl and D 2) were involved. Multiple involvement of vertebrae was reported by Tillman et al [36] also, with four adjacent vertebrae affected in one patient. Histologically ABCs consist of honeycombed dilated vascular beds with frequent hemosiderin deposits. The connective tissue stroma often contain gaint cells (Figure 3). Occasional bone and osteoid formation is also seen within the stroma. As they do not have epithelial lining, they are not true cysts. Although the pathogenesis is unclear, three major hypothesis dominate the literature. The first suggests that an ABC is caused by improper repair of a traumatic subperiosteal hemorrhage [17]. The second states that they represent a vascular disturbance of the underlying bone, in the form of a sudden venous occlusion or the development of an arteriovenous shunt [24]. According to the third hypothesis, ABCs represent bleeding into, and consequent obliteration of, a primary bony lesion [20]. Roentgenologic features of ABCs include expansile osteolytic cavities, occasionally filled with fine trabeculae. The surrounding cortex has an "eggshell" appearance with lobulated fluid filled spaces [6]. A thin shell of bone often remains, but it is not always visualized on the roentegenogram (case no. 1). CT and M R I add important diagnostic information in the evaluation of ABCs [3,19]. CT, because of its sensitivity to calcium, may show a thin rim of bone not evident on radiographs and helps to exclude calcified tumor matrix. Both CT and M R I may show fluid levels within the lesion be-

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Figure 2. Coronal MRI (T 9 demonstrating the involvement of body and pedicles of the first and second thoracic vertebraewith paraspinal extension to the left.

cause of layering of solid blood components [3,19]. The extent of bony involvement and the soft tissue component are well demonstrated on MRIs. The lesion has an expansile appearance with a lobulated contour. There is a thin outside rim of low signal intensity on both T, and T2 sequences with increasing signal strength of the contents with T2-weighting. MRIs often show septae

Figure 3. Microphotograph showing dilated, blood-filled spaces outlined by fibrous septae containing osteoclasts type of giant cells (H&E × 220)

within the aneurysmal bone cysts, and one loculation may have markedly different signal characteristics than an adjacent loculation. In the first case reported in the study, the plain x-rays suggested a destructive lesion involving the posterior elements, and it was the M R I that helped to reach an accurate diagnosis. A few septa were seen in the MRIs of the spine in this patient, but there were no fluid levels. The second patient was managed before the availability of M R I scan, and the diagnosis of an ABC was made peroperatively. The surgical treatment of the spinal ABCs may become difficult because of extensive hemorrhage or inaccessibility. Complete local excision when possible is the treatment of choice. The bleeding can be lessened to some extent by proceeding from normal tissue on both sides of the lesion. Hay et al [18] reported no recurrences in cases in which total excision was achieved, 25% recurrence in cases of partial excision, 6% recurrence in cases of partial excision followed by radiotherapy, and 11% recurrence in cases treated with radiation alone. Total excision of a large tumor often results in bony instability and grafting may be required to maintain structural integrity. Computed tomography and, more recently, M R I allow complete evaluation of the extent of the lesion and the need for spinal stabilization can be preoperatively assessed. In general the thoracic

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Figure 5. Postoperative x-rays after C1-C2 fusion with wire and acrylic. Figure 4. Plain x-rays showing atlantoaxial dislocation with an radiolucent lesion involving C2 lamina.

spine with its rib support affords greater stability than the cervical or lumbar spine. In case 1, only a part of one vertebral body was removed, and it was felt that a spinal stabilization procedure was not required. In case 2, stabilization was achieved by posterior fusion with wire and bone graft. Radiation therapy and embolotherapy [27] are usually used for treatment of lesions that are considered surgically inaccessible. Although good results have been reported using radiation therapy as the primary modality of treatment, most authors consider that radiation may not be necessary and should be used only exceptionally. Radiation damage to the spinal cord and radiation-induced sarcomas have been reported [25]. The tendency of the process to heal spontaneously has been reported by several authors [2,23,29,33]. The favorable response of the cyst to even incomplete removal has also been pointed out [4,24,37]. Detection of residual cysts in the postoperative period is not a reliable indication that recurrence will follow. As long as these relatively small cysts do not cause clinical manifestation, our attitude should be expectant, keeping the patient under regular follow-up. References 1. Akbarnia BA, Ganjavina MS. Aneurysmal bone cysts of the spine. Results of surgical treatment in 9 patients. 1986;10:9.

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