Neurological deterioration after foramen magnum decompression for Chiari malformation Type I: old or new pathology?

Clinical article

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Object

Decompression of the foramen magnum is widely accepted as the procedure of choice for patients with Chiari malformation Type I (CM-I). This study was undertaken to determine the mechanisms responsible for neurological deterioration after foramen magnum decompression and the results of secondary interventions.

Methods

Between 1987 and 2010, 559 patients with CM-I presented, 107 of whom had already undergone a foramen magnum decompression, which included a syrinx shunt in 27 patients. Forty patients who were neurologically stable did not undergo another operation. Sixty-seven patients with progressive symptoms received a recommendation for surgery, which was refused by 16 patients, while 51 patients underwent a total of 61 secondary operations. Hospital and outpatient records, radiographic studies, and intraoperative images were analyzed. Additional follow-up information was obtained by telephone calls and questionnaires. Short-term results were determined after 3 and 12 months, and long-term outcomes were evaluated using Kaplan-Meier statistics.

Results

Sixty-one secondary operations were performed after a foramen magnum decompression. Of these 61 operations, 15 involved spinal pathologies not related to the foramen magnum (spinal group), while 46 operations were required for a foramen magnum issue (foramen magnum group). Except for occipital pain and swallowing disturbances, the clinical course was comparable in both groups. In the spinal group, 5 syrinx shunt catheters were removed because of nerve root irritations or spinal cord tethering. Eight patients underwent a total of 10 operations on their cervical spine for radiculopathies or a myelopathy. No permanent surgical morbidity occurred in this group. In the foramen magnum group, 1 patient required a ventriculoperitoneal shunt for hydrocephalus 7 months after decompression. The remaining 45 secondary interventions were foramen magnum revisions, of which 10 were combined with craniocervical fusion. Intraoperatively, arachnoid scarring with obstruction of the foramen of Magendie was the most common finding. Complication rates for foramen magnum revisions were similar to first decompressions, whereas permanent surgical morbidity was higher at 8.9%. Postoperative clinical improvements were marginal in both surgical groups. With the exception of 1 patient who underwent syrinx catheter removal and had a history of postoperative meningitis, all patients in the spinal group were able to be stabilized neurologically. Long-term results in the foramen magnum group revealed clinical stabilizations in 66% for at least 5 years.

Conclusions

Neurological deterioration in patients after a foramen magnum decompression for CM-I may be related to new spinal pathologies, craniocervical instability, or recurrent CSF flow obstruction at the foramen magnum. Whereas surgery for spinal pathologies is regularly followed by clinical stabilization, the rate of long-term success for foramen magnum revisions was limited to 66% for 5 years due to severe arachnoid scarring in a significant proportion of these patients. Therefore, foramen magnum revisions should be restricted to patients with progressive symptoms.

Abbreviations used in this paper:CM = Chiari malformation; CM-I = CM Type I; VP = ventriculoperitoneal.

Article Information

Address correspondence to: Jörg Klekamp, M.D., Department of Neurosurgery, Christliches Krankenhaus, Danziger Strausse 2, Quakenbrück D-49610, Germany. email: j.klekamp@ckq-gmbh.de.

Please include this information when citing this paper: published online October 5, 2012; DOI: 10.3171/2012.9.PEDS12110.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Images obtained in a 74-year-old man with a kyphotic deformity. A–C: Sagittal (A and B) and axial (C) T2-weighted upright MR images obtained 9 years after decompression of the foramen magnum in the neutral position, demonstrating profound spinal cord atrophy, a collapsed syrinx, a free CSF passage at the foramen magnum, and multilevel osteochondrosis in the cervical spine. He suffered a progressive tetraparesis, confining him to a wheelchair, with increasing weakness of his respiratory muscles and loss of upper-extremity functions. With inclination of his head (B and C), the compression of the cord by osteophytes is evident. D and E: Lateral functional radiographs in flexion and extension showing the fixed kyphotic deformity and inability to achieve a cervical lordosis. F: Sagittal CT reconstruction showing the multiple osteochondroses and swan-neck deformity. The patient underwent a combined decompression with corpectomies at C4–6, reconstruction and ventral fusion at C3–7 followed by posterior decompression at C3–6, and fixation with lateral mass screws at C3–7. G and H: Postoperative CT reconstruction (G) and lateral radiograph (H) demonstrating a good sagittal profile with decompression of the cervical cord. Postoperatively the patient made a slow recovery. Four months after surgery he was able to walk again for about 20 minutes and was gaining strength and coordination skills in his hands, whereas respiratory functions have improved only slightly.

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    Images obtained in a 46-year-old woman with CM-I, basilar invagination, and syringomyelia. A: Sagittal T2-weighted MR image obtained 8 years after decompression of the foramen magnum at another institution. The syrinx appears to be of a small caliber, a small pseudomeningocele is apparent, and C2–3 is fused (Klippel-Feil syndrome). The patient complained about severe neck pain, dysesthesias, and a slight gait ataxia. B and C: Cine MRI showing no flow signals in the foramen magnum region. D and E: Functional lateral radiographs of the cervical spine demonstrating the laminectomy of C-2 and C-3 and instability at C3–4. Revision surgery incorporated a revision at the foramen magnum with arachnoid dissection and a new duraplasty, followed by occipitocervical fusion from the occiput to C-5 with lateral mass screws. F: Postoperative sagittal MR image demonstrating a large cisterna magna. G: Control radiograph obtained 7 years later showing the correct positions of all implants with a good sagittal profile. Postoperatively, the patient has remained neurologically stable for 7 years with some improvement of her neck pain.

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    Images obtained in a 15-year-old boy with occipital headaches. A: Sagittal T2-weighted MR image showing a classic CM-I without syringomyelia. B: After decompression of the foramen magnum with resection of both tonsils at another institution, the postoperative sagittal T2-weighted MR image demonstrates a large pseudomeningocele. There appears to be a membrane obstructing the foramen of Magendie. C and D: Cine MRI showing no flow signals in the area of the foramen magnum. The patient no longer complained about occipital headaches but reported quite severe local discomfort. At reoperation 2 years later, a large defect in the suture line for the duraplasty was evident. After removal of the duraplasty, profound scarring at both tonsillar stumps was detected. Both posterior inferior cerebellar arteries were embedded in this scar tissue, which also obstructed the foramen of Magendie. The foramen was not opened to avoid any vascular injuries and a new duraplasty inserted. E: Postoperative sagittal T2-weighted MR image showing a free CSF passage across the foramen magnum with normal soft-tissue healing. The patient made a full recovery.

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    Images obtained in a 25-year-old woman with a CM-I. A: Sagittal T2-weighted MR image demonstrating a CM-I combined with mild basilar invagination and a slight kyphotic deformity of the cervical spine. B: As shown in this sagittal T2-weighted MR image obtained 5 years later, a significant syrinx developed as well as an osteochondrosis at C6–7. Functional radiographs did not demonstrate an instability at this time. The patient underwent a foramen magnum decompression. Intraoperatively, the atlas was found to be hypermobile, suggesting abnormal movement of the occiput–C1 and C1–2 joints. C: Six months after decompression, the sagittal T1-weighted MR control image demonstrates a good resolution of the syrinx but also pannus formation around the odontoid peg. The patient complained about signs of a progressive myelopathy starting a few months after decompression and underwent posterior occiput–C3 fusion in a second operation. D: Postoperative lateral control radiograph obtained 6 months after stabilization showing the instrumentation in place and an improved sagittal profile of her cervical spine. The preoperative symptoms of her myelopathy had improved.

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    Kaplan-Meier analysis of progression-free survival for patients undergoing a foramen magnum revision with or without additional fusion.

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