- Email: [email protected]
Clinical outcomes in patients with Chiari I malformation: a review of 27 cases
Spine
Clinical Outcomes in Patients with Chiari I Malformation: A Review of 27 Cases Jose´ Dones, M.D., Orlando De Jesu´s, M.D., F.A.C.S., Chaim B. Colen, M.D., Marı´a M. Toledo, M.D., and Mariel Delgado, M.S. Section of Neurosurgery, University of Puerto Rico, San Juan, Puerto Rico
Dones J, De Jesu´s O, Colen CB, Toledo MM, Delgado M. Clinical outcomes in patients with Chiari I malformation: a review of twenty-seven cases. Surg Neurol 2003;60:142– 8.
KEY WORDS
Chiari malformation, clinical outcomes, outcome, syringomyelia.
BACKGROUND
Chiari I malformation is a congenital maldevelopment defined as downward herniation of the cerebellar tonsils through the foramen magnum. It has been treated using a variety of surgical procedures. Surgical outcomes have been reported with varying results throughout the literature. METHODS
We retrospectively reviewed 27 patients with Chiari I malformation operated at the University Hospital during a 9-year period from 1988 to 1997. We assessed preoperative and postoperative signs and symptoms in all the patients including headache, neck pain, nystagmus, vertigo, weakness, spasticity, atrophy, numbness, pain and temperature dissociation, diplopia, dysphagia, and sphincter dysfunction. Each patient was analyzed to determine if there was an arrest in the progression of the disease after surgical intervention. RESULTS
Syringomyelia was present in 59% of the patients. Only 1 patient who presented with neck pain improved. One patient reported new onset headache, and one patient described his headache resolved. Vertigo resolved in three patients; two patients stated mild improvement, and one patient reported worsening. Nystagmus improved or resolved in six patients. Weakness improved in only two patients who did not have syringomyelia. Dysphagia improved in two patients, and in the others it remained unchanged. Diplopia, spasticity, atrophy, and numbness remained unchanged. CONCLUSIONS
Our study provides evidence that the main benefit of the surgical management in patients with Chiari I malformation with or without syringomyelia is to arrest the progression of the disease. © 2003 Elsevier Inc. All rights reserved.
Address reprint requests to: Dr. Orlando De Jesu´s, Section of Neurosurgery, University of Puerto Rico, GPO Box 5067, San Juan, PR 00936. Received August 5, 2002; accepted January 29, 2003. 0090-3019/03/$–see front matter doi:10.1016/S0090-3019(03)00131-9
hiari I malformation is a congenital anomaly in which the cerebellar tonsils are displaced downward through the foramen magnum into the upper cervical spinal canal. In 1891, Chiari described a patient with herniation of the cerebellar tonsils below the plane of the foramen magnum [6]. He later described several other patients with tonsillar herniation associated to hydrocephalus [5]. The most common symptom is suboccipital headache that is aggravated by coughing, straining, physical exertion, neck extension, and other Valsalva maneuvers [20]. Weakness is also prominent especially in the hands [7]. Other signs and symptoms include neck pain, arm pain, leg pain, numbness, loss of temperature sensation, ataxia, diplopia, dysarthria, dysphagia, vomiting, vertigo, nystagmus, and tinnitus [4,15,18,20,25,26]. Loss of temperature sensation is seen when the condition is associated to syringomyelia in which there is a cyst in the spinal cord [26]. Syringomyelia occurs in about 32 to 73% of the patients with Chiari I malformation [9,15,20,25,26]. Magnetic resonance imaging (MRI) is the imaging modality of choice for evaluating patients with Chiari I malformation, because it clearly shows the degree of tonsillar herniation and the syringomyelia if present. Operative treatments for Chiari I malformation have been carried out for more than 100 years, but even today the best surgical management and the results expected from it are not well established. Throughout the years, multiple surgical procedures have been described in the literature with varying results. The clinical outcomes have been graded differently in the literature and may be confusing
C
© 2003 Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010 –1710
Outcomes in Chiari I Malformation
and difficult to interpret. Some series have reported an early postoperative improvement but with a subsequent deterioration to the preoperative state. The difficulty in assessing the benefits from surgery is due in part to the multiplicity of signs and symptoms, the long duration of them, and the difficulty in separating them in those patients who only have Chiari I malformation from those who also had associated syringomyelia.
Methods Our study retrospectively evaluated 27 patients with Chiari I malformation operated at the University Hospital during a 9-year period from 1988 to 1997. A detailed patient history and neurologic examination was obtained from the medical records. Clinical examinations were carried out at the time of discharge and about every 3 months until a year postoperatively, then at yearly intervals. Those patients without a recent follow-up were contacted by phone. There were 24 women (89%) and three men (11%) ranging in age from 14 to 59 years old (mean age was 39 years old). The preoperative and postoperative clinical signs and symptoms analyzed were neck pain, headache, vertigo, diplopia, nystagmus, numbness, pain and temperature dissociation, weakness, atrophy, spasticity, anal sphincter incontinence, constipation, urinary incontinence or retention, and dysphagia. The signs and symptoms in each patient were noted and compared to those present postoperatively. The mean follow-up period was 52 months (range 3 to 138 months).
Surg Neurol 143 2003;60:142– 8
1
SIGNS/SYMPTOMS
N
%
Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
13 13 10 10 8 8 6 4 4 2 2 1
48% 48% 37% 37% 30% 30% 22% 15% 15% 7% 7% 4%
sis. The patients who had syringomyelia were reviewed separately from those who did not have it to analyze the signs and symptoms in each group (Table 2). Vertigo was only present in patients without syringomyelia. Dysphagia was mainly reported on patients without syringomyelia. Weakness, spasticity, atrophy, pain and temperature dissociation, numbness, and sphincter dysfunction were present mainly on those patients who also had syringomyelia. All the patients received treatment because of the intractable, progressive, and disabling symptoms. The main surgical procedure varied among patients. One patient had a syringosubarachnoid shunt placed as the only surgical procedure. In three patients a suboccipital craniectomy with removal of the posterior margin of the foramen magnum was performed. In 23 patients the suboccipital craniectomy was combined with an upper cervical
Results Preoperatively, 26 patients underwent MRI and one patient underwent computer tomography (CT) scan with intrathecal metrizamide. None of the patients had preoperative ventricular dilation. Of the 27 patients, 16 (59%) showed radiographic evidence of a syrinx. The most common signs and symptoms were neck pain in 13 patients (48%), weakness in 13 patients (48%), spasticity in 10 patients (37%), numbness in 10 patients (37%), headache in eight patients (30%), nystagmus in eight patients (30%), and vertigo in six patients (22%). Dysphagia was present in four patients. Atrophy was seen in four patients. Diplopia because of sixth nerve palsy was seen in two patients. Sphincter dysfunction was reported in two patients. Pain and temperature dissociation was noted in one patient. The results are summarized in Table 1. Duration of symptoms was reported from 2 months to 25 years before diagno-
Preoperative Signs and Symptoms in all 27 Patients
2
Preoperative Signs and Symptoms in Patients with Syringomyelia and in Patients Without Syringomyelia
PATIENTS
PATIENTS WITH WITHOUT SYRINGOMYELIA SYRINGOMYELIA (N ⴝ 16) (N ⴝ 11) SIGNS/SYMPTOMS
# (%)
# (%)
Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
7 (44%) 10 (63%) 8 (50%) 9 (56%) 3 (19%) 3 (19%) 0 (0%) 1 (6%) 4 (25%) 1 (6%) 2 (13%) 1 (6%)
6 (55%) 3 (27%) 2 (18%) 1 (9%) 5 (45%) 5 (45%) 6 (55%) 3 (27%) 0 (0%) 1 (9%) 0 (0%) 0 (0%)
144 Surg Neurol 2003;60:142– 8
laminectomy. Among them, four patients had only the posterior arch of C1 removed while 17 patients also had the C2 laminae and spinous process removed, and two patients also had the C3 laminae and spinous process removed. The level of the cervical laminectomy depended on the level of tonsillar herniation so that the level below the herniated tonsils was reached. Dural grafts were placed on 13 patients. Of the 16 patients with radiographic evidence of syringomyelia, six underwent placement of a syringosubarachnoid shunt. One patient had it performed at another institution before our initial evaluation and treatment that included a suboccipital craniectomy and upper cervical laminectomy. In two patients it was performed concurrent with the suboccipital craniectomy and upper cervical laminectomy. One patient had it performed as the only surgical procedure. Two patients had it performed between 1 and 2 years after their initial suboccipital craniectomy and upper cervical laminectomy. The other 10 patients did not have a direct surgical procedure for their syringomyelia and the syrinx decreased in half of them and collapsed in the other half. A ventriculo-peritoneal shunt was conducted in two patients that had postoperative radiographic evidence of hydrocephalus. Postoperatively, only one patient who presented with neck pain improved. In the others it remained unchanged. One patient reported new onset headache and one patient described the headache resolved. It was unchanged in seven patients. Vertigo resolved in three patients. Two patients stated mild improvement and one patient reported worsening. The patient who reported worsening had an associated basilar invagination. Dysphagia improved in two patients, and in the others it remained unchanged. Weakness improved in only two patients. The patients who presented with atrophy or spasticity remained unchanged. Nystagmus improved in six patients. One patient had new onset nystagmus. Diplopia, pain and temperature dissociation, numbness, and sphincter dysfunction did not improve in any patient. Results are summarized in Table 3. When these results are analyzed comparing those patients who had syringomyelia to those patients who did not have it, we found that neck pain and headache improved only on patients who had syringomyelia and that weakness improved only on those patients who did not have syringomyelia (Table 4).
Discussion Displacement of the cerebellar tonsils of at least 5 mm below the foramen magnum is commonly re-
Dones et al
Preoperative and Postoperative Signs and Symptoms in all 27 Patients with the Percentage of Improvement
3
% SIGNS/SYMPTOMS Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
PREOP POSTOP 13 13 10 10 8 8 6 4 4 2 2 1
12 11 10 10 7 2 3 2 4 2 2 1
IMPROVEMENT
8% 15% 0% 0% 12% 75% 50% 50% 0% 0% 0% 0%
garded as diagnostic for Chiari I malformation. In 1985, Aboulezz et al published a study describing the position of cerebellar tonsils in the normal population and concluded that tonsillar ectopia greater than 5 mm should be considered clearly pathologic [1]. This criterion remains in wide use [18,20]. Tonsillar herniation of less than 5 mm does not exclude the diagnosis. Barkovich et al conducted a study to evaluate the sensitivity and specificity in predicting symptomatic patients and found that if 2 mm below the foramen magnum was considered the lowest extent for the tonsils in a normal patient, the sensitivity for predicting symptomatic patients was 100% and the specificity was 98.5% [2]. Therefore, the range of 3 to 5 mm of tonsillar ectopia is usually pathologic but not absolute. About half of the symptomatic patients with tonsillar herniation of less that 5 mm have syringomyelia [20]. Asymptomatic tonsillar ectopia is a recognized phenomenon. Meadows et al reported that 14% of the patients with Chiari I malformation with tonsillar herniation of more than 5 mm below the foramen magnum were asymptomatic [18]. In a study by Elster and Chen, approximately 30% of the patients with tonsillar herniation between 5 and 10 mm below the foramen magnum were clinically asymptomatic [8]. Syringomyelia and osseous anomalies are very rare in these asymptomatic patients [18]. Nishizawa et al presented several patients with incidentally identified syringomyelia associated to Chiari I malformation with tonsillar herniation greater than 10 mm in which 89% of them remained asymptomatic after a follow-up period of more than 10 years [23]. The patients with Chiari I malformation who are asymptomatic usually remained asymptomatic at their follow-up [4].
Outcomes in Chiari I Malformation
4
Surg Neurol 145 2003;60:142– 8
Preoperative and Postoperative Signs and Symptoms in Patients with Syringomyelia and in Patients Without Syringomyelia and the Percentage of Improvement
PATIENTS SIGNS SYMPTOMS Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
PATIENTS
PATIENTS
PATIENTS
WITH SYRINX PREOP
WITH SYRINX POSTOP
IMPROVEMENT
WITHOUT SYRINX PREOP
WITHOUT SYRINX POSTOP
IMPROVEMENT
7 10 8 9 3 3 0 1 4 1 2 1
6 10 8 9 2 0 0 0 4 1 2 1
14% 0% 0% 0% 33% 100% – 100% 0% 0% 0% 0%
6 3 2 1 5 5 6 3 0 1 0 0
6 1 2 1 5 2 3 2 0 1 0 0
0% 67% 0% 0% 0% 60% 50% 33% – 0% – –
%
It is believed that in patients with Chiari I malformation, symptoms occur because the posterior cranial fossa is relatively too small for the hindbrain, resulting in an inferior tonsillar displacement that induces a blockage of cerebrospinal fluid (CSF) at the foramen magnum between the intracranial and spinal subarachnoid space [20,22]. This is considered an underdevelopment of the occipital somites that originate from the para-axial mesoderm [20,22]. The cisterna magna is usually small or absent in patients with Chiari I malformation [21]. In those patients with associated syringomyelia the exact mechanism for the formation of the syrinx is still unclear. It has been proposed that the CSF enters the spinal cord directly via the perivascular and interstitial spaces when the impacted tonsils raise the pressure in the spinal subarachnoid space [24]. The cerebellar tonsils block the CSF flow at the foramen magnum and act as a piston on the partially enclosed spinal subarachnoid space creating systolic pressure waves in the spinal CSF that compress the surface of the spinal cord and propels syrinx fluid caudally with each heartbeat [11,24]. This blockage is the most important factor exacerbating syringomyelia associated to Chiari I malformation. Cine MRI and intraoperative ultrasound showed that the syrinx fluid and the cervical CSF moved downward during systole and upward during diastole [11]. The disease is more common in females, with a female-to-male ratio ranging from 3:1 to 3:2 [15,20]. Series in which only patients with Chiari I malformation associated to syringomyelia were included had a female-to-male ratio ranging from 1:1 to 2:1 [9,10,12]. Others authors had reported a male pre-
%
dominance on this type of patient with a 2:1 maleto-female ratio [26]. Chiari I malformation is usually seen in middle-aged adults with a mean age of 36 to 45 years old but occasionally may be found in older individuals [4,7,10,15,20]. Milhorat et al found that 10% of the patients had a family history of Chiari I malformation in which the genetic transmission was due either to an incompletely penetrant dominant gene or a recessive gene [20]. Associated skull base and spine bone anomalies include occipital bone hyperostosis, atlanto-occipital assimilation, platybasia, basilar invagination, scoliosis, and fused cervical vertebrae [7,15,22]. Scoliosis is seen frequently in those cases of Chiari I malformation associated to syringomyelia [26]. The interval from clinical presentation to diagnosis can be only a few days but can be as long as 46 years [4,7,20,26]. There is a tendency for a shorter interval in those patients with associated syringomyelia when compared to those without it [15]. It must be clearly established that the herniation of the tonsils is the cause of the symptoms and that there is no intracranial mass lesion or hydrocephalus that may also lead to tonsillar ectopia. Hydrocephalus is present in 7% of the patients with Chiari I malformation [20]. If syringomyelia is present, a spinal cord tumor has to be ruled out. Although many surgical procedures have been utilized throughout the years, posterior fossa decompression remains the mainstay of treatment [15]. It involves removing bone in the suboccipital area along with the posterior margin of the foramen magnum and usually the posterior ring of the C1 vertebrae. Once the bone is removed the dura mater is opened. The dura mater is then usually closed with
146 Surg Neurol 2003;60:142– 8
a dural graft patch to increase the space for the intradural structures [4,15]. Duraplasty increases the size of the cisterna magna and improves the CSF flow between the intracranial and spinal subarachnoid space [21]. Dissection of arachnoid adhesions has been advocated by several authors to permit a patent outflow of CSF from the fourth ventricle [15,26]. Guyotat et al found better results in terms of clinical outcome and syrinx reduction when the tonsils were resected in those patients with Chiari I malformation associated to syringomyelia [10]. In our opinion, these dissections can lead to serious complications, and we have avoided them. Some authors recommended the syringosubarachnoid shunt as a major surgical option for Chiari I malformation associated to syringomyelia in those patients with a large syrinx who had very mild or no disturbance of cranial nerve and cerebellar function [12,14]. They reported that collapse of the syrinx occurred faster and that pain relief outcome was superior with this treatment than with foramen magnum decompression. The majority of our patient’s presenting signs and symptoms remained unchanged after the surgical treatment. Ninety-two percent of the patients reported no improvement in neck pain. Headache remained the same after treatment in 88% of the patients. Only two patients with weakness showed some improvement. All the patients with an initial presentation of diplopia, numbness, or spasticity reported no change in their symptoms. Dysphagia was unchanged in half of the patients. Vertigo resolved or improved in 50% of the patients. Neck pain and headache improved only in patients who had syringomyelia, while weakness improved only in those who did not have it. Bindal et al also found that patients with syringomyelia have better outcome on neck pain and headache [4]. Severe complications following treatment are rare. We found worsening of vertigo in 14% of the patients. New onset of headache was found in 12% of the patients, nystagmus in 12%, spasticity in 6%, and dysphagia in 4%. Other complications include hydrocephalus in two patients, pseudomeningocele in two patients, and CSF leak in 2 patients. One of the patients with a pseudomeningocele also developed postoperative hydrocephalus and was treated with a ventriculoperitoneal shunt. This patient also developed an increase in the size of the syrinx and was subsequently treated with a syringosubarachnoid shunt. In the other patient with a pseudomeningocele, the dura was originally left open, and upon re-exploration, no active leak was found so the wound was reinforced with a pericranium dural graft, fibrin glue applied, and a lumbar drain placed.
Dones et al
In one patient with a CSF leak, the wound was reexplored and the defect closed. In the other patient, the leak was minimal and resolved with conservative measures including head elevation and pressure bandages. Some authors have reported cerebellar ptosis, an unusual complication following a large posterior fossa decompression [13]. These patients presented with intractable headache in the suboccipital region radiating into the frontal region or jaw and recurrence of the syringomyelic cavity. They recommended that these patients should be treated with a partial suboccipital cranioplasty and in some cases combined with reduction of the cerebellar tonsils. We have not seen any patient with this complication. Our study provides evidence that the main benefit of the surgical treatment in patients with Chiari I malformation is to arrest the progression of symptoms. Other authors also have concluded that surgical treatment results in the improvement or stabilization of the disease in the majority of the patients [4,7,15,17,26]. Bindal et al found that patients with Chiari I malformation without syringomyelia have marked improvement after decompression while those patients that also had syringomyelia stabilized or only slightly improved [4]. Logue and Edwards found that half of the patients with Chiari I malformation associated to syringomyelia stabilized [17]. Klekamp et al found that the most significant improvement on patients with syringomyelia was for pain and headache [15]. Our study also found similar results. The spinal curvature usually stabilized after the surgery [7,9,26]. Dyste et al reported that some preoperative signs were predictive of a less favorable outcome and included muscle atrophy, symptoms lasting longer than 24 months, ataxia, nystagmus, trigeminal hypesthesia, and dorsal column dysfunction [7]. Vanaclocha et al also found that the results of surgery were strongly influenced by duration of symptoms [26]. In those patients with syringomyelia in which no direct surgery was done to the syrinx, the cyst generally became smaller or collapsed after suboccipital decompression [3,10,11,15,21,24]. We found similar results in our study. In our series, all 10 patients who did not have a direct surgical approach to the syrinx had a reduction or collapse of the cyst. Klekamp et al reported unsatisfactory results in patients treated with shunting of the syrinx [15]. They did not recommend it as a primary form of treatment. The presence of a syrinx associated to the herniation of the tonsils should not distract the attention from decompressing the overcrowded posterior fossa and improving the CSF dynamics. Shunting of the syrinx should be reserved for those patients who fail to respond to the initial posterior fossa decompression. Some patients
Outcomes in Chiari I Malformation
may even benefit from re-exploration of the posterior fossa decompression if there is radiologic evidence of a CSF block at the level of the foramen magnum [21]. Approximately one-third of patients with Chiari I malformation have anterior encroachment of the foramen magnum by a retroflexed odontoid process or basilar invagination [20]. Goel et al recommended that these patients should be initially treated with foramen magnum decompression [9]. The procedure usually resulted in significant amelioration of symptoms and at least an arrest in the progression of the disability. Patients who have concomitant basilar invagination will need a posterior fusion if the compression is reducible, but irreducible lesions may benefit from transoral surgery [4,7,16,19,20]. Some patients need a combined transoral surgery and posterior foramen magnum decompression but rarely need a posterior fusion [9].
Surg Neurol 147 2003;60:142– 8
13. 14. 15. 16.
17. 18.
REFERENCES 1. Aboulezz AO, Sartor K, Geyer CA, Gado MH. Position of cerebellar tonsils in the normal population and in patients with Chiari malformation: a quantitative approach with MR imaging. J Comput Assist Tomogr 1985;9:1033–6. 2. Barkovich AJ, Wippold FJ, Sherman J L, Citrin CM. Significance of cerebellar tonsillar position on MR. Am J Neuroradiol 1986;7:795–9. 3. Batzdorf U. Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. J Neurosurg 1988;68:726 –30. 4. Bindal AK, Dunsker SB, Tew JM Jr. Chiari I malformation: classification and management. Neurosurgery 1995;37:1069 –74. ¨ eber Vera¨ nderungen des Kleinhirns des 5. Chiari H. U Pons und der Medulla Oblongata infolge von congenitaler Hydrocephalie des Grosshirns. Denschr Akad Wiss Wien 1896;63:71–116. ¨ eber Vera¨ nderungen des Kleinhirns infolge 6. Chiari H. U von Hydrocephalie des Grosshirns. Dtsch Med Wochenschr 1891;17:1172–5. 7. Dyste GN, Menezes AH, VanGilder JC. Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg 1989;71:159 –68. 8. Elster AD, Chen MYM. Chiari I malformations: clinical and radiological reappraisal. Radiology 1992;183:347– 53. 9. Goel A, Bhatjiwale M, Desal K. Basilar invagination: a study based on 190 surgically treated patients. J Neurosurg 1998;88:962–8. 10. Guyotat J, Bret P, Jouanneau E, Ricci AC, Lapras C. Syringomyelia associated with type I Chiari malformations. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection. Acta Neurochir 1999;140:745–54. 11. Heiss JP, Patronas N, De Vroom HL, et al. Elucidating the pathophysiology of syringomyelia. J Neurosurg 1999;91:553–62. 12. Hida K, Iwasaki Y, Koyanagi I, Sawamura Y, Abe H.
19. 20.
21.
22.
23.
24.
25. 26.
Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery 1995;37:673–9. Holly LT, Batzdorf U. Management of cerebellar ptosis following craniovertebral decompression for Chiari I malformation. J Neurosurg 2001;94:21–6. Iwasaki Y, Hida K, Koyanagi I, Abe H. Reevaluation of syringosubarachnoid shunt for syringomyelia with Chiari malformation. Neurosurgery 2000;46:407–13. Klekamp J, Batzdorf U, Samii M, Bothe HW. The surgical treatment of Chiari malformation. Acta Neurochir 1996;138:788 –801. Kohno K, Sakaki S, Shiraishi T, Matsuoka K, Okamura H. Successful treatment of adult Arnold-Chiari malformation associated with basilar impression and syringomyelia by the transoral anterior approach. Surg Neurol 1990;33:284 –7. Logue V, Edwards MR. Syringomyelia and its surgical treatment-an analysis of 75 patients. J Neurol Neurosurg Psychiatry 1981;44:273–84. Meadows J, Kraut M, Guarnieri M, Haroun RI, Carson BS. Asymptomatic Chiari type I malformations identified on magnetic resonance imaging. J Neurosurg 2000;92:920 –6. Menezes A, VanGilder J. Transoral-transpharyngeal approach to the anterior craniocervical junction. J Neurosurg 1988;69:895–903. Milhorat TH, Chou MW, Trinidad EM, et al. Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery 1999;44:1005–17. Munshi I, Frim D, Stine-Reyes R, Weir BKA, Hekmatpanah J, Brown F. Effects of posterior fossa decompression with and without duraplasty on Chiari malformation-associated hydromyelia. Neurosurgery 2000;46:1384 –90. Nishikawa M, Sakamoto H, Hakuba A, Nakanishi N, Inoue Y. Pathogenesis of Chiari malformation: a morphometric study of the posterior cranial fossa. J Neurosurg 1997;80:40 –7. Nishizawa S, Yokoyama T, Yokota N, Tokuyama T, Ohta S. Incidentally identified syringomyelia associated to Chiari I malformations: is early interventional surgery necessary? Neurosurgery 2001;49:637–41. Oldfield EH, Muraszk K, Shawker TH, Patronas NJ. Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. J Neurosurg 1994;80:3–15. Paul KS, Lye RH, Strang FA, Dutton J. Arnold-Chiari malformation: review of 71 cases. J Neurosurg 1983; 58:183–7. Vanaclocha V, Saiz-Sapena N, Garcia-Casasola MC. Surgical technique for cranio-cervical decompression in syringomyelia associated with Chiari type I malformation. Acta Neurochir 1997;139:529 –40.
COMMENTARY
In this report, the authors present a retrospective review of 27 patients with Chiari I malformation operated upon during a 9-year interval from 1988 to 1997. The report examines surgical outcome and compares the results with those reported in the
Clinical Outcomes in Patients with Chiari I Malformation: A Review of 27 Cases Jose´ Dones, M.D., Orlando De Jesu´s, M.D., F.A.C.S., Chaim B. Colen, M.D., Marı´a M. Toledo, M.D., and Mariel Delgado, M.S. Section of Neurosurgery, University of Puerto Rico, San Juan, Puerto Rico
Dones J, De Jesu´s O, Colen CB, Toledo MM, Delgado M. Clinical outcomes in patients with Chiari I malformation: a review of twenty-seven cases. Surg Neurol 2003;60:142– 8.
KEY WORDS
Chiari malformation, clinical outcomes, outcome, syringomyelia.
BACKGROUND
Chiari I malformation is a congenital maldevelopment defined as downward herniation of the cerebellar tonsils through the foramen magnum. It has been treated using a variety of surgical procedures. Surgical outcomes have been reported with varying results throughout the literature. METHODS
We retrospectively reviewed 27 patients with Chiari I malformation operated at the University Hospital during a 9-year period from 1988 to 1997. We assessed preoperative and postoperative signs and symptoms in all the patients including headache, neck pain, nystagmus, vertigo, weakness, spasticity, atrophy, numbness, pain and temperature dissociation, diplopia, dysphagia, and sphincter dysfunction. Each patient was analyzed to determine if there was an arrest in the progression of the disease after surgical intervention. RESULTS
Syringomyelia was present in 59% of the patients. Only 1 patient who presented with neck pain improved. One patient reported new onset headache, and one patient described his headache resolved. Vertigo resolved in three patients; two patients stated mild improvement, and one patient reported worsening. Nystagmus improved or resolved in six patients. Weakness improved in only two patients who did not have syringomyelia. Dysphagia improved in two patients, and in the others it remained unchanged. Diplopia, spasticity, atrophy, and numbness remained unchanged. CONCLUSIONS
Our study provides evidence that the main benefit of the surgical management in patients with Chiari I malformation with or without syringomyelia is to arrest the progression of the disease. © 2003 Elsevier Inc. All rights reserved.
Address reprint requests to: Dr. Orlando De Jesu´s, Section of Neurosurgery, University of Puerto Rico, GPO Box 5067, San Juan, PR 00936. Received August 5, 2002; accepted January 29, 2003. 0090-3019/03/$–see front matter doi:10.1016/S0090-3019(03)00131-9
hiari I malformation is a congenital anomaly in which the cerebellar tonsils are displaced downward through the foramen magnum into the upper cervical spinal canal. In 1891, Chiari described a patient with herniation of the cerebellar tonsils below the plane of the foramen magnum [6]. He later described several other patients with tonsillar herniation associated to hydrocephalus [5]. The most common symptom is suboccipital headache that is aggravated by coughing, straining, physical exertion, neck extension, and other Valsalva maneuvers [20]. Weakness is also prominent especially in the hands [7]. Other signs and symptoms include neck pain, arm pain, leg pain, numbness, loss of temperature sensation, ataxia, diplopia, dysarthria, dysphagia, vomiting, vertigo, nystagmus, and tinnitus [4,15,18,20,25,26]. Loss of temperature sensation is seen when the condition is associated to syringomyelia in which there is a cyst in the spinal cord [26]. Syringomyelia occurs in about 32 to 73% of the patients with Chiari I malformation [9,15,20,25,26]. Magnetic resonance imaging (MRI) is the imaging modality of choice for evaluating patients with Chiari I malformation, because it clearly shows the degree of tonsillar herniation and the syringomyelia if present. Operative treatments for Chiari I malformation have been carried out for more than 100 years, but even today the best surgical management and the results expected from it are not well established. Throughout the years, multiple surgical procedures have been described in the literature with varying results. The clinical outcomes have been graded differently in the literature and may be confusing
C
© 2003 Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010 –1710
Outcomes in Chiari I Malformation
and difficult to interpret. Some series have reported an early postoperative improvement but with a subsequent deterioration to the preoperative state. The difficulty in assessing the benefits from surgery is due in part to the multiplicity of signs and symptoms, the long duration of them, and the difficulty in separating them in those patients who only have Chiari I malformation from those who also had associated syringomyelia.
Methods Our study retrospectively evaluated 27 patients with Chiari I malformation operated at the University Hospital during a 9-year period from 1988 to 1997. A detailed patient history and neurologic examination was obtained from the medical records. Clinical examinations were carried out at the time of discharge and about every 3 months until a year postoperatively, then at yearly intervals. Those patients without a recent follow-up were contacted by phone. There were 24 women (89%) and three men (11%) ranging in age from 14 to 59 years old (mean age was 39 years old). The preoperative and postoperative clinical signs and symptoms analyzed were neck pain, headache, vertigo, diplopia, nystagmus, numbness, pain and temperature dissociation, weakness, atrophy, spasticity, anal sphincter incontinence, constipation, urinary incontinence or retention, and dysphagia. The signs and symptoms in each patient were noted and compared to those present postoperatively. The mean follow-up period was 52 months (range 3 to 138 months).
Surg Neurol 143 2003;60:142– 8
1
SIGNS/SYMPTOMS
N
%
Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
13 13 10 10 8 8 6 4 4 2 2 1
48% 48% 37% 37% 30% 30% 22% 15% 15% 7% 7% 4%
sis. The patients who had syringomyelia were reviewed separately from those who did not have it to analyze the signs and symptoms in each group (Table 2). Vertigo was only present in patients without syringomyelia. Dysphagia was mainly reported on patients without syringomyelia. Weakness, spasticity, atrophy, pain and temperature dissociation, numbness, and sphincter dysfunction were present mainly on those patients who also had syringomyelia. All the patients received treatment because of the intractable, progressive, and disabling symptoms. The main surgical procedure varied among patients. One patient had a syringosubarachnoid shunt placed as the only surgical procedure. In three patients a suboccipital craniectomy with removal of the posterior margin of the foramen magnum was performed. In 23 patients the suboccipital craniectomy was combined with an upper cervical
Results Preoperatively, 26 patients underwent MRI and one patient underwent computer tomography (CT) scan with intrathecal metrizamide. None of the patients had preoperative ventricular dilation. Of the 27 patients, 16 (59%) showed radiographic evidence of a syrinx. The most common signs and symptoms were neck pain in 13 patients (48%), weakness in 13 patients (48%), spasticity in 10 patients (37%), numbness in 10 patients (37%), headache in eight patients (30%), nystagmus in eight patients (30%), and vertigo in six patients (22%). Dysphagia was present in four patients. Atrophy was seen in four patients. Diplopia because of sixth nerve palsy was seen in two patients. Sphincter dysfunction was reported in two patients. Pain and temperature dissociation was noted in one patient. The results are summarized in Table 1. Duration of symptoms was reported from 2 months to 25 years before diagno-
Preoperative Signs and Symptoms in all 27 Patients
2
Preoperative Signs and Symptoms in Patients with Syringomyelia and in Patients Without Syringomyelia
PATIENTS
PATIENTS WITH WITHOUT SYRINGOMYELIA SYRINGOMYELIA (N ⴝ 16) (N ⴝ 11) SIGNS/SYMPTOMS
# (%)
# (%)
Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
7 (44%) 10 (63%) 8 (50%) 9 (56%) 3 (19%) 3 (19%) 0 (0%) 1 (6%) 4 (25%) 1 (6%) 2 (13%) 1 (6%)
6 (55%) 3 (27%) 2 (18%) 1 (9%) 5 (45%) 5 (45%) 6 (55%) 3 (27%) 0 (0%) 1 (9%) 0 (0%) 0 (0%)
144 Surg Neurol 2003;60:142– 8
laminectomy. Among them, four patients had only the posterior arch of C1 removed while 17 patients also had the C2 laminae and spinous process removed, and two patients also had the C3 laminae and spinous process removed. The level of the cervical laminectomy depended on the level of tonsillar herniation so that the level below the herniated tonsils was reached. Dural grafts were placed on 13 patients. Of the 16 patients with radiographic evidence of syringomyelia, six underwent placement of a syringosubarachnoid shunt. One patient had it performed at another institution before our initial evaluation and treatment that included a suboccipital craniectomy and upper cervical laminectomy. In two patients it was performed concurrent with the suboccipital craniectomy and upper cervical laminectomy. One patient had it performed as the only surgical procedure. Two patients had it performed between 1 and 2 years after their initial suboccipital craniectomy and upper cervical laminectomy. The other 10 patients did not have a direct surgical procedure for their syringomyelia and the syrinx decreased in half of them and collapsed in the other half. A ventriculo-peritoneal shunt was conducted in two patients that had postoperative radiographic evidence of hydrocephalus. Postoperatively, only one patient who presented with neck pain improved. In the others it remained unchanged. One patient reported new onset headache and one patient described the headache resolved. It was unchanged in seven patients. Vertigo resolved in three patients. Two patients stated mild improvement and one patient reported worsening. The patient who reported worsening had an associated basilar invagination. Dysphagia improved in two patients, and in the others it remained unchanged. Weakness improved in only two patients. The patients who presented with atrophy or spasticity remained unchanged. Nystagmus improved in six patients. One patient had new onset nystagmus. Diplopia, pain and temperature dissociation, numbness, and sphincter dysfunction did not improve in any patient. Results are summarized in Table 3. When these results are analyzed comparing those patients who had syringomyelia to those patients who did not have it, we found that neck pain and headache improved only on patients who had syringomyelia and that weakness improved only on those patients who did not have syringomyelia (Table 4).
Discussion Displacement of the cerebellar tonsils of at least 5 mm below the foramen magnum is commonly re-
Dones et al
Preoperative and Postoperative Signs and Symptoms in all 27 Patients with the Percentage of Improvement
3
% SIGNS/SYMPTOMS Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
PREOP POSTOP 13 13 10 10 8 8 6 4 4 2 2 1
12 11 10 10 7 2 3 2 4 2 2 1
IMPROVEMENT
8% 15% 0% 0% 12% 75% 50% 50% 0% 0% 0% 0%
garded as diagnostic for Chiari I malformation. In 1985, Aboulezz et al published a study describing the position of cerebellar tonsils in the normal population and concluded that tonsillar ectopia greater than 5 mm should be considered clearly pathologic [1]. This criterion remains in wide use [18,20]. Tonsillar herniation of less than 5 mm does not exclude the diagnosis. Barkovich et al conducted a study to evaluate the sensitivity and specificity in predicting symptomatic patients and found that if 2 mm below the foramen magnum was considered the lowest extent for the tonsils in a normal patient, the sensitivity for predicting symptomatic patients was 100% and the specificity was 98.5% [2]. Therefore, the range of 3 to 5 mm of tonsillar ectopia is usually pathologic but not absolute. About half of the symptomatic patients with tonsillar herniation of less that 5 mm have syringomyelia [20]. Asymptomatic tonsillar ectopia is a recognized phenomenon. Meadows et al reported that 14% of the patients with Chiari I malformation with tonsillar herniation of more than 5 mm below the foramen magnum were asymptomatic [18]. In a study by Elster and Chen, approximately 30% of the patients with tonsillar herniation between 5 and 10 mm below the foramen magnum were clinically asymptomatic [8]. Syringomyelia and osseous anomalies are very rare in these asymptomatic patients [18]. Nishizawa et al presented several patients with incidentally identified syringomyelia associated to Chiari I malformation with tonsillar herniation greater than 10 mm in which 89% of them remained asymptomatic after a follow-up period of more than 10 years [23]. The patients with Chiari I malformation who are asymptomatic usually remained asymptomatic at their follow-up [4].
Outcomes in Chiari I Malformation
4
Surg Neurol 145 2003;60:142– 8
Preoperative and Postoperative Signs and Symptoms in Patients with Syringomyelia and in Patients Without Syringomyelia and the Percentage of Improvement
PATIENTS SIGNS SYMPTOMS Neck pain Weakness Spasticity Numbness Headache Nystagmus Vertigo Dysphagia Atrophy Diplopia Sphincter dysfunction Pain and temperature dissociation
PATIENTS
PATIENTS
PATIENTS
WITH SYRINX PREOP
WITH SYRINX POSTOP
IMPROVEMENT
WITHOUT SYRINX PREOP
WITHOUT SYRINX POSTOP
IMPROVEMENT
7 10 8 9 3 3 0 1 4 1 2 1
6 10 8 9 2 0 0 0 4 1 2 1
14% 0% 0% 0% 33% 100% – 100% 0% 0% 0% 0%
6 3 2 1 5 5 6 3 0 1 0 0
6 1 2 1 5 2 3 2 0 1 0 0
0% 67% 0% 0% 0% 60% 50% 33% – 0% – –
%
It is believed that in patients with Chiari I malformation, symptoms occur because the posterior cranial fossa is relatively too small for the hindbrain, resulting in an inferior tonsillar displacement that induces a blockage of cerebrospinal fluid (CSF) at the foramen magnum between the intracranial and spinal subarachnoid space [20,22]. This is considered an underdevelopment of the occipital somites that originate from the para-axial mesoderm [20,22]. The cisterna magna is usually small or absent in patients with Chiari I malformation [21]. In those patients with associated syringomyelia the exact mechanism for the formation of the syrinx is still unclear. It has been proposed that the CSF enters the spinal cord directly via the perivascular and interstitial spaces when the impacted tonsils raise the pressure in the spinal subarachnoid space [24]. The cerebellar tonsils block the CSF flow at the foramen magnum and act as a piston on the partially enclosed spinal subarachnoid space creating systolic pressure waves in the spinal CSF that compress the surface of the spinal cord and propels syrinx fluid caudally with each heartbeat [11,24]. This blockage is the most important factor exacerbating syringomyelia associated to Chiari I malformation. Cine MRI and intraoperative ultrasound showed that the syrinx fluid and the cervical CSF moved downward during systole and upward during diastole [11]. The disease is more common in females, with a female-to-male ratio ranging from 3:1 to 3:2 [15,20]. Series in which only patients with Chiari I malformation associated to syringomyelia were included had a female-to-male ratio ranging from 1:1 to 2:1 [9,10,12]. Others authors had reported a male pre-
%
dominance on this type of patient with a 2:1 maleto-female ratio [26]. Chiari I malformation is usually seen in middle-aged adults with a mean age of 36 to 45 years old but occasionally may be found in older individuals [4,7,10,15,20]. Milhorat et al found that 10% of the patients had a family history of Chiari I malformation in which the genetic transmission was due either to an incompletely penetrant dominant gene or a recessive gene [20]. Associated skull base and spine bone anomalies include occipital bone hyperostosis, atlanto-occipital assimilation, platybasia, basilar invagination, scoliosis, and fused cervical vertebrae [7,15,22]. Scoliosis is seen frequently in those cases of Chiari I malformation associated to syringomyelia [26]. The interval from clinical presentation to diagnosis can be only a few days but can be as long as 46 years [4,7,20,26]. There is a tendency for a shorter interval in those patients with associated syringomyelia when compared to those without it [15]. It must be clearly established that the herniation of the tonsils is the cause of the symptoms and that there is no intracranial mass lesion or hydrocephalus that may also lead to tonsillar ectopia. Hydrocephalus is present in 7% of the patients with Chiari I malformation [20]. If syringomyelia is present, a spinal cord tumor has to be ruled out. Although many surgical procedures have been utilized throughout the years, posterior fossa decompression remains the mainstay of treatment [15]. It involves removing bone in the suboccipital area along with the posterior margin of the foramen magnum and usually the posterior ring of the C1 vertebrae. Once the bone is removed the dura mater is opened. The dura mater is then usually closed with
146 Surg Neurol 2003;60:142– 8
a dural graft patch to increase the space for the intradural structures [4,15]. Duraplasty increases the size of the cisterna magna and improves the CSF flow between the intracranial and spinal subarachnoid space [21]. Dissection of arachnoid adhesions has been advocated by several authors to permit a patent outflow of CSF from the fourth ventricle [15,26]. Guyotat et al found better results in terms of clinical outcome and syrinx reduction when the tonsils were resected in those patients with Chiari I malformation associated to syringomyelia [10]. In our opinion, these dissections can lead to serious complications, and we have avoided them. Some authors recommended the syringosubarachnoid shunt as a major surgical option for Chiari I malformation associated to syringomyelia in those patients with a large syrinx who had very mild or no disturbance of cranial nerve and cerebellar function [12,14]. They reported that collapse of the syrinx occurred faster and that pain relief outcome was superior with this treatment than with foramen magnum decompression. The majority of our patient’s presenting signs and symptoms remained unchanged after the surgical treatment. Ninety-two percent of the patients reported no improvement in neck pain. Headache remained the same after treatment in 88% of the patients. Only two patients with weakness showed some improvement. All the patients with an initial presentation of diplopia, numbness, or spasticity reported no change in their symptoms. Dysphagia was unchanged in half of the patients. Vertigo resolved or improved in 50% of the patients. Neck pain and headache improved only in patients who had syringomyelia, while weakness improved only in those who did not have it. Bindal et al also found that patients with syringomyelia have better outcome on neck pain and headache [4]. Severe complications following treatment are rare. We found worsening of vertigo in 14% of the patients. New onset of headache was found in 12% of the patients, nystagmus in 12%, spasticity in 6%, and dysphagia in 4%. Other complications include hydrocephalus in two patients, pseudomeningocele in two patients, and CSF leak in 2 patients. One of the patients with a pseudomeningocele also developed postoperative hydrocephalus and was treated with a ventriculoperitoneal shunt. This patient also developed an increase in the size of the syrinx and was subsequently treated with a syringosubarachnoid shunt. In the other patient with a pseudomeningocele, the dura was originally left open, and upon re-exploration, no active leak was found so the wound was reinforced with a pericranium dural graft, fibrin glue applied, and a lumbar drain placed.
Dones et al
In one patient with a CSF leak, the wound was reexplored and the defect closed. In the other patient, the leak was minimal and resolved with conservative measures including head elevation and pressure bandages. Some authors have reported cerebellar ptosis, an unusual complication following a large posterior fossa decompression [13]. These patients presented with intractable headache in the suboccipital region radiating into the frontal region or jaw and recurrence of the syringomyelic cavity. They recommended that these patients should be treated with a partial suboccipital cranioplasty and in some cases combined with reduction of the cerebellar tonsils. We have not seen any patient with this complication. Our study provides evidence that the main benefit of the surgical treatment in patients with Chiari I malformation is to arrest the progression of symptoms. Other authors also have concluded that surgical treatment results in the improvement or stabilization of the disease in the majority of the patients [4,7,15,17,26]. Bindal et al found that patients with Chiari I malformation without syringomyelia have marked improvement after decompression while those patients that also had syringomyelia stabilized or only slightly improved [4]. Logue and Edwards found that half of the patients with Chiari I malformation associated to syringomyelia stabilized [17]. Klekamp et al found that the most significant improvement on patients with syringomyelia was for pain and headache [15]. Our study also found similar results. The spinal curvature usually stabilized after the surgery [7,9,26]. Dyste et al reported that some preoperative signs were predictive of a less favorable outcome and included muscle atrophy, symptoms lasting longer than 24 months, ataxia, nystagmus, trigeminal hypesthesia, and dorsal column dysfunction [7]. Vanaclocha et al also found that the results of surgery were strongly influenced by duration of symptoms [26]. In those patients with syringomyelia in which no direct surgery was done to the syrinx, the cyst generally became smaller or collapsed after suboccipital decompression [3,10,11,15,21,24]. We found similar results in our study. In our series, all 10 patients who did not have a direct surgical approach to the syrinx had a reduction or collapse of the cyst. Klekamp et al reported unsatisfactory results in patients treated with shunting of the syrinx [15]. They did not recommend it as a primary form of treatment. The presence of a syrinx associated to the herniation of the tonsils should not distract the attention from decompressing the overcrowded posterior fossa and improving the CSF dynamics. Shunting of the syrinx should be reserved for those patients who fail to respond to the initial posterior fossa decompression. Some patients
Outcomes in Chiari I Malformation
may even benefit from re-exploration of the posterior fossa decompression if there is radiologic evidence of a CSF block at the level of the foramen magnum [21]. Approximately one-third of patients with Chiari I malformation have anterior encroachment of the foramen magnum by a retroflexed odontoid process or basilar invagination [20]. Goel et al recommended that these patients should be initially treated with foramen magnum decompression [9]. The procedure usually resulted in significant amelioration of symptoms and at least an arrest in the progression of the disability. Patients who have concomitant basilar invagination will need a posterior fusion if the compression is reducible, but irreducible lesions may benefit from transoral surgery [4,7,16,19,20]. Some patients need a combined transoral surgery and posterior foramen magnum decompression but rarely need a posterior fusion [9].
Surg Neurol 147 2003;60:142– 8
13. 14. 15. 16.
17. 18.
REFERENCES 1. Aboulezz AO, Sartor K, Geyer CA, Gado MH. Position of cerebellar tonsils in the normal population and in patients with Chiari malformation: a quantitative approach with MR imaging. J Comput Assist Tomogr 1985;9:1033–6. 2. Barkovich AJ, Wippold FJ, Sherman J L, Citrin CM. Significance of cerebellar tonsillar position on MR. Am J Neuroradiol 1986;7:795–9. 3. Batzdorf U. Chiari I malformation with syringomyelia. Evaluation of surgical therapy by magnetic resonance imaging. J Neurosurg 1988;68:726 –30. 4. Bindal AK, Dunsker SB, Tew JM Jr. Chiari I malformation: classification and management. Neurosurgery 1995;37:1069 –74. ¨ eber Vera¨ nderungen des Kleinhirns des 5. Chiari H. U Pons und der Medulla Oblongata infolge von congenitaler Hydrocephalie des Grosshirns. Denschr Akad Wiss Wien 1896;63:71–116. ¨ eber Vera¨ nderungen des Kleinhirns infolge 6. Chiari H. U von Hydrocephalie des Grosshirns. Dtsch Med Wochenschr 1891;17:1172–5. 7. Dyste GN, Menezes AH, VanGilder JC. Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg 1989;71:159 –68. 8. Elster AD, Chen MYM. Chiari I malformations: clinical and radiological reappraisal. Radiology 1992;183:347– 53. 9. Goel A, Bhatjiwale M, Desal K. Basilar invagination: a study based on 190 surgically treated patients. J Neurosurg 1998;88:962–8. 10. Guyotat J, Bret P, Jouanneau E, Ricci AC, Lapras C. Syringomyelia associated with type I Chiari malformations. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection. Acta Neurochir 1999;140:745–54. 11. Heiss JP, Patronas N, De Vroom HL, et al. Elucidating the pathophysiology of syringomyelia. J Neurosurg 1999;91:553–62. 12. Hida K, Iwasaki Y, Koyanagi I, Sawamura Y, Abe H.
19. 20.
21.
22.
23.
24.
25. 26.
Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery 1995;37:673–9. Holly LT, Batzdorf U. Management of cerebellar ptosis following craniovertebral decompression for Chiari I malformation. J Neurosurg 2001;94:21–6. Iwasaki Y, Hida K, Koyanagi I, Abe H. Reevaluation of syringosubarachnoid shunt for syringomyelia with Chiari malformation. Neurosurgery 2000;46:407–13. Klekamp J, Batzdorf U, Samii M, Bothe HW. The surgical treatment of Chiari malformation. Acta Neurochir 1996;138:788 –801. Kohno K, Sakaki S, Shiraishi T, Matsuoka K, Okamura H. Successful treatment of adult Arnold-Chiari malformation associated with basilar impression and syringomyelia by the transoral anterior approach. Surg Neurol 1990;33:284 –7. Logue V, Edwards MR. Syringomyelia and its surgical treatment-an analysis of 75 patients. J Neurol Neurosurg Psychiatry 1981;44:273–84. Meadows J, Kraut M, Guarnieri M, Haroun RI, Carson BS. Asymptomatic Chiari type I malformations identified on magnetic resonance imaging. J Neurosurg 2000;92:920 –6. Menezes A, VanGilder J. Transoral-transpharyngeal approach to the anterior craniocervical junction. J Neurosurg 1988;69:895–903. Milhorat TH, Chou MW, Trinidad EM, et al. Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery 1999;44:1005–17. Munshi I, Frim D, Stine-Reyes R, Weir BKA, Hekmatpanah J, Brown F. Effects of posterior fossa decompression with and without duraplasty on Chiari malformation-associated hydromyelia. Neurosurgery 2000;46:1384 –90. Nishikawa M, Sakamoto H, Hakuba A, Nakanishi N, Inoue Y. Pathogenesis of Chiari malformation: a morphometric study of the posterior cranial fossa. J Neurosurg 1997;80:40 –7. Nishizawa S, Yokoyama T, Yokota N, Tokuyama T, Ohta S. Incidentally identified syringomyelia associated to Chiari I malformations: is early interventional surgery necessary? Neurosurgery 2001;49:637–41. Oldfield EH, Muraszk K, Shawker TH, Patronas NJ. Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. J Neurosurg 1994;80:3–15. Paul KS, Lye RH, Strang FA, Dutton J. Arnold-Chiari malformation: review of 71 cases. J Neurosurg 1983; 58:183–7. Vanaclocha V, Saiz-Sapena N, Garcia-Casasola MC. Surgical technique for cranio-cervical decompression in syringomyelia associated with Chiari type I malformation. Acta Neurochir 1997;139:529 –40.
COMMENTARY
In this report, the authors present a retrospective review of 27 patients with Chiari I malformation operated upon during a 9-year interval from 1988 to 1997. The report examines surgical outcome and compares the results with those reported in the