A thirty-six-year-old man was initially seen five months after an acute onset of pain in the cephalad portion of the neck while he was carrying a heavy weight. During the next five months, the pain had occurred in paroxysmal attacks and had been relieved only partially by medication and physical therapy. The patient had had no similar episode in the past. He was admitted to the Rheumatology Department, where he reported severe stiffness of the neck with pain radiating from the cephalad portion of the cervical spine to the left occipital region. Examination revealed no abnormal neurological signs.
Plain radiographs of the cervical spine demonstrated lysis of the left lateral mass of the atlas, and computerized tomography and magnetic resonance imaging revealed a tumor that was enhanced with contrast medium at that site; the tumor was in contact with both the vertebral artery and the dura (Fig. 1-A). An angiogram demonstrated vascularization of the lesion by branches of the vertebral artery (Fig. 1-B).
The differential diagnosis included plasmocytoma, osteosarcoma, aneurysmal bone cyst, and metastatic carcinoma.
Both serum protein electrophoresis and testing for urinary Bence-Jones protein revealed negative findings. No evidence of a primary malignant tumor elsewhere was found during the complete clinical examination or on computerized tomographic scans of the abdominal and thoracic areas, echography of the abdominal area, or isotopic bone-scanning.
Operative Technique
The tumor was removed through an anterolateral approach4, with the patient in the supine position and with extension of the neck and rotation to the contralateral side.
The skin was incised along the anterior border of the cephalad part of the sternomastoid muscle, along the tip of the mastoid and up to the superior crista of the occipital bone. The sternomastoid muscle was divided at its insertion on the mastoid process. The plane between the internal jugular vein and the sternomastoid muscle was then opened, permitting exposure of the transverse processes of the first and second cervical vertebrae. The accessory nerve crossing the field was dissected free and retracted gently inferiorly. The lateral muscles (the levator scapulae, inferior oblique, and superior oblique muscles) were then resected at their insertion to the transverse process of the first cervical vertebra, allowing for exposure of the posterior arch of the atlas and the vertebral artery cephalad to the first cervical vertebra and in the atlanto-axial interval. The transverse process of the first cervical vertebra was then unroofed, with preservation of the periosteal sheath surrounding the vertebral artery and the perivertebral venous plexus. The vertebral artery was released out of the groove of the posterior arch of the first cervical vertebra down to the transverse process of the second cervical vertebra and was transposed posteriorly and medially.
The remaining part of the transverse process of the first cervical vertebra was then resected, allowing direct visualization of the atlanto-axial and atlanto-occipital articulations. This provided good exposure of the tumor, which appeared as a soft-tissue mass with low vascularity. The branches to the tumor from the vertebral artery were divided during mobilization of the artery. The tumor was removed totally without any major bleeding with use of curets and suction until the intact cartilaginous cover of the occipital condyle, and the superior articular facet of the second cervical vertebra were reached (Fig. 1-C). The articular surfaces of the occipital condyle and the superior facet joint of the second cervical vertebra were preserved; their cartilaginous surfaces were resected, and the subchondral bone was removed with a drill in such a way as to prepare small grooves that would permit insertion of an iliac-crest bone graft between the occipital condyle and the superior articular facet of the second cervical vertebra. This graft was a square piece of cortical bone, fifteen by fifteen millimeters, that was impacted in the prepared grooves; pieces of cancellous bone were then placed around it.
The postoperative course was uneventful, and the patient was discharged from the hospital ten days after the operation. The neck was immobilized in a hard cervical collar for two months.
Histological examination of the specimen revealed trabeculated, dilated vascular beds consistent with the diagnosis of an aneurysmal bone cyst (Fig. 1-D).
One year postoperatively, the patient had moderate residual stiffness of the neck without pain or neurological deficit. At eighteen months, he was free of symptoms except for a slight limitation of axial rotation of the neck.
The first description of an aneurysmal bone cyst is credited to Van Arsdale in 1893, whereas the term aneurysmal bone cyst was introduced by Jaffe and Lichtenstein in 1942.
Approximately 12 to 20 per cent of aneurysmal bone cysts have been found in the spine1,2. Of ninety-five aneurysmal bone cysts that were treated at the Mayo Clinic, only fifteen were found to involve the spine and, of these, six were at the cervical level13. These lesions are found more often in the posterior elements of the spine than in the vertebral bodies1,7,10. Their occurrence in the first cervical vertebra is rare if not exceptional, and our review of the literature failed to identify any reports of a lesion in the lateral mass of the first cervical vertebra, although lesions in neighboring osseous structures have been described1,9,12.
Pouyanne et al. and Legre et al. reported two separate cases that were very similar. In both patients, the tumor originated from the posterior arch of the atlas, had a large expansion toward the posterior cervical muscles, and was amenable to treatment through a posterior approach. A third lesion1, located on the odontoid process in a seventy-four-year-old woman, was resected through a transoral transpalatal approach.
The pathogenesis of aneurysmal bone cyst is still debated, and the origin of this peculiar lesion is not yet clearly known1,3,11. Some authors have considered it to be a possible result of hemorrhage into either a giant-cell tumor or a chondroblastoma6. The lesion is not believed to be a genuine cyst as it does not contain an intracavitary epithelium.
The differential diagnosis includes plasmocytoma, metastatic carcinoma, and osteosarcoma. The radiographic and physical findings may suggest an aneurysmal bone cyst, but the definitive diagnosis is made by histological examination. Such examination reveals honeycombs of dilated vascular beds, with deposits of hemosiderin and connective-tissue stroma frequently containing giant cells and, occasionally, osteoids.
Operative treatment is generally recommended3,8, but radiation therapy, either alone or in combination with an operation, has also been proposed. In their review of the results for seventy-nine patients, which included fourteen of their own, Hay et al. reported no recurrence after total removal of eight lesions, two recurrences (6 per cent) after partial excision followed by radiation therapy in thirty-four patients, seven recurrences (25 per cent) after partial operative excision without radiation therapy in twenty-eight patients, and one recurrence after radiation therapy alone in nine patients.
The blood supply of an aneurysmal bone cyst in the cephalad portion of the cervical spine is usually through branches of the vertebral artery9; thus, the operative technique must allow safe control of this vessel (Fig. 1-C). An anterior transoral approach, although excellent for the exposure of extradural bone lesions, is difficult to extend laterally and does not allow sufficient control of the vertebral artery. Alternatively, a posterolateral exposure5,6, while readily allowing control of the vertebral artery, does not permit sufficient access to the anterior part of the lesion. Hence, an anterolateral approach, as used in our patient, appears to be optimum for complete and bloodless removal of the lesion. This approach provides easy access to the lateral half of the anterior and posterior arches, the transverse process, and the lateral masses of the first cervical vertebra through exposure, control, and, if necessary, transposition of the third segment of the vertebral artery (between the second cervical vertebra and the foramen magnum).
If the vascular supply of the tumor is expected to be difficult to control, preoperative embolization should be considered. We did not consider embolization in our patient although the tumor was vascular, as the blood supply to the tumor came entirely from the vertebral artery, which could be controlled during the operation.
We concluded the operation with the insertion of a bone graft between the occipital condyle and the superior articular facet of the second cervical vertebra. The need for such a graft is difficult to assess, but we thought that it provided stability.