Gray Matters: Bringing Polemic Issues with Inchoate Guidelines Into Sharper Focus
Type I Chiari Malformation with Cervical Syringomyelia
CASE DESCRIPTION This 19-year-old, right-handed man with no significant past medical, surgical or family history was referred with complaints of persistent left-sided hemifacial numbness, positional dizziness and tussive headaches. An MRI of the brain and cervical spine demonstrated greater than one centimeter of cerebellar tonsillar descent caudal to the foramen magnum and a cervico-thoracic syrinx extending from the level of the odontoid process to the upper thoracic spine. Mild decreased sensation to light touch in the left V1-3 distributions and diffuse, symmetric hyper-reflexia was noted on examination. The rest of his neurological examination was normal; his tandem gait was steady, unaided.
Chiari malformations describe a continuum of clinical, radiographic and symptomatic pathophysiology all associated with congenital or acquired hindbrain or posterior fossa abnormalities. Chiari I Malformation (CM1) implies greater than five millimeters of descent of the cerebellar tonsils caudal to the foramen magnum, as defined radiographically by McRae’s line.
There is no migration of the brainstem; however, in some cases, tonsillar descent disrupts the dynamic outflow of cerebrospinal fluid (CSF) which, in severe cases, may affect the circulation of CSF in the spinal cord resulting in an expansion of the central canal — syringomyelia. Any of a number of symptoms may prompt a patient to be referred to neurosurgery: headaches precipitated or exacerbated by coughing or Valsalva, cervical myelopathy and cranial nerve palsies. Patients with CM1 also present with a myriad of other, less specific, non-focal neurological complaints, such as neck and arm pain, migratory paresthesias, diplopia and tinnitus.
Although the constellation of findings was initially described in the late 19th century and much data exists the neurosurgical literature heralding posterior fossa decompression as an effective treatment for CM1, there remains contentious debate regarding the most appropriate extent of surgical decompression. While most experts agree that a suboccipital craniectomy for CM1 is incomplete without release of the posterior atlanto-occipital membrane, expansion duraplasty and arachnoid dissection for tonsillar cauterization remains controversial, largely surgeon-specific and based on the tendencies and preferences of that individual’s training program.
Recently, the group at Columbia published a retrospective cohort of 68 pediatric patients (ages 3-20) with CM1 who underwent suboccipital craniectomy, including atlanto-occipital ligament incision without dural opening. They reported all patients having at least some degree of symptom improvement, and 70 percent demonstrated radiographic improvement by a mean of 31 months.
Some routinely perform autologous expansion duraplasty by harvesting pericranium; others determine whether a duraplasty is indicated based on intra-operative ultrasound — if pulsatility can be documented, then one infers that CSF outflow has not been obstructed. Still, others advocate for an arachnoid dissection that may include a lysis of superficial arachnoid adhesions, opening of the foramen of Magendie, exploration of the obex and fourth ventricle, as well as separation and, in some cases, cauterization of the cerebellar tonsils.
The Johns Hopkins University group recently published a retrospective series of 171 consecutive pediatric patients with both a radiographic CM1 and a cervical syrinx who underwent cervicomedullary decompression. All patients underwent suboccipital craniectomy and expansion duraplasty, and one quarter, 43 patients, also underwent tonsillar cauterization — the remaining 128 did not have tonsillar cauterization. Not only was there a statistically significant reduction in the incidence of repeat decompression among the patients who underwent tonsillar cauterization, but also, radiographic resolution of the cervical syrinx was documented in more than 80 percent of patients at eight-month follow-up, compared to only 44 percent resolution demonstrated in the cohort who underwent craniectomy and duraplasty alone.
The patient described above underwent suboccipital craniectomy, cervical one laminectomy and expansion autologous duraplasty. Within several weeks, the patient’s facial numbness, positional dizziness and tussive headaches had largely resolved. Radiographically, one-year following the operation, only a faint remnant of the central cervico-thoracic syrinx remained.
1. Kennedy BC, Nelp TB, Kelly KM, Phan MQ, Bruce SS, McDowell MM, Feldstein NA, Anderson RC. Delayed resolution of syrinx after posterior fossa decompression without dural opening in children with Chiari malformation Type I. J Neurosurg Pediatr. 2015 Aug 28 [Epub ahead of print]
2. Oldfield EH, Muraszko 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.
3. Stanko KM, Lee YM, Rios J, Wu A, Sobrinho GW, Weingart JD, Jackson EM, Ahn ES, Chaichana KL, Jallo GI. Improvement of syrinx resolution after tonsillar cautery in pediatric patients with Chiari Type I malformation. J Neurosurg Pediatr. 2015 Oct 30 [Epub ahead of print]
The Experts Weigh In
Edward Oldfield, MD; Charlottesville, Va
In my view, a 19 year-old with Chiari I, syringomyelia and progressive neurological deficits should be treated in a manner that is almost certain to reverse the active pathophysiology, and to do so rapidly. Thus, in this patient, I would remove the posterior rim of the foramen magnum and arch of C1, attempt to open the dura, but not the arachnoid and place a pericranial graft. This provides rapid reversal of the process damaging his spinal cord almost immediately in nearly all patients and does so without the risk of arachnoiditis that is occasionally associated with tonsil cautery, which is unnecessary. That is, I favor the approach that was used in this patient, an approach that proved to be successful.
A few years ago, in a series of prospective clinical studies examining the pathophysiology underlying syringomyelia associated with Chiari I malformation, my colleagues and I demonstrated that the critical element is the obstruction of pulsatile movement of CSF across the foramen magnum (3-5, 9). Tonsil descent alone is not the issue, since impediment of free movement of CSF across the foramen magnum can occur even if the tonsils are not abnormally low and can produce syringomyelia, as in the “Chiari O” malformation described by Dr. Oakes and his colleagues (6).
Then, any operation that relieves the hindrance to free movement of CSF across the foramen magnum, whether it occurs with bone decompression alone (posterior fossa decompression, PFD) or after bone decompression with duraplasty (posterior fossa decompression and duraplasty, PFDD), should reverse the pathophysiology underlying the syringomyelia. Since the Chiari I “malformation” is simply the product of systolic impaction of the tonsils in the foramen magnum (4,9), which occurs about 120,000 times per day with a pulse of 80, it also addresses the abnormal tonsil anatomy, which consistently disappears after successful surgery (4). Thus, the goal of surgery in these patients is simply to provide additional space at the foramen magnum, enough space for the CSF to flow freely during the cardiac cycle.
In pediatric patients, the selection of either PFD or PFDD has certain advantages and disadvantages. In general, and as shown in most series comparing the two approaches, PFD is associated with faster recovery from the surgical procedure and fewer complications; whereas PFDD is more likely to provide resolution of syringomyelia and symptoms, does so faster and is associated with the need for fewer second operations compared to PFD.
See Table 1.
It is noteworthy that treatment with bone decompression only in adults has received scant attention. Whether this is because it has been tried, but was not effective, or it was just not examined in large numbers of adult patients, is not clear. Bond et al., used it in a small series of adult patients who received surgery in an intraoperative MRI (1).
In that study, the flexed position of the neck opened the space posterior to the tonsils, producing flow behind the tonsils on the cine MRI and gave the false impression that sufficient surgery had been done with bone decompression alone. Thus, in several patients, the surgery was stopped at that stage based on the results of the intra-operative MRI. However, almost all of those patients had persistent symptoms and required a second operation with duraplasty, which suggests, at least based on the results from that small series, that bone decompression alone may not lead to the same success in adults as it has in children (whose tissues are more pliable and whose dural sac is probably more likely to expand with time).
It should also be noted that the conclusion of that study was that the use of intra-operative imaging for Chiari I malformation in general, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery (1). Thus, the use of intra-operative ultrasound to assess adequacy of surgery is likely to be misleading, for the same reason as was the use of intra-operative MRI.
The patient being considered is 19 years old. Is he more likely to respond to PPD like a child or an adult? There is no answer to that in the existing published experience, as the likelihood of response to PPD in children in various age ranges has not been examined.
My own preference, in adults and children, is bone decompression, opening the dura while attempting to keep the arachnoid intact, to avoid blood entering the subarachnoid space and to avoid a postoperative CSF leak with a pseudomeningocoele and placement of an autologous pericranial graft. Opening the dura but not the arachnoid was recommended by Valentine Logue over 35 years ago in his summary of a career’s experience in the pre-MRI era (8).
This approach almost universally provides rapid response of the symptoms, early response of the syrinx and is rarely associated with complications. As reported by Wetjen, et al., in 29 consecutive adult patients with syringomyelia, all syringes had a measurable decrease in diameter three- to six- months after surgery (median time to decrease, 3.6 months) (11). Compare this to the pediatric series of bone decompression alone by Kennedy, et al., in which syrinx improvement occurred in only 70 percent of the 57 patients with MRI follow-up (23 percent remained stable, 7 percent increased or developed a new syrinx); 12 percent of the 68 patients with syringomyelia required another operation (7).
In the patients whose syrinx improved the reduction in size was detected at a mean of 31 months after bone decompression alone (7). Further, in a prospective study by Heiss et al., the pointed tonsils consistently became round within three- to six-months after surgery, cervicomedullary protuberance disappeared, and tonsillar ectopia diminished by 51 percent (to 6.0 ± 3.3 mm; p < 0.0001) (4). These responses of the syrinx and Chiari abnormality after dural opening and grafting occur much more consistently and much more rapidly than the responses reported for bone decompression alone in children, were accomplished without entering the subarachnoid space, and the approach greatly reduces the risk of needing a second operation, compared to bone decompression alone.
I have resorted to opening the arachnoid and coagulating the tonsils in one patient, a 16-year-old. That patient had a relentless course of severe arachnoiditis, ultimately requiring placement of a syrinx-to-pleural shunt for progressive syringomyelia with severe neurological deficits. I have seen two similar cases after tonsil cautery, which in my experience, is unnecessary, as an extra-arachnoid procedure is nearly universally effective. It should be noted that in the recent report by Stanko et al., the analysis is of the results of patients with bone decompression alone mixed with patients with duraplasty (10). The results of patients with bone decompression and duraplasty are not presented. Regardless, it should be noted that their results with bone decompression alone, or in the group in which patients with PFD are mixed with patients with PFDD, are poor compared to most reports.
We should not forget that the goal of surgery in these patients is simply to provide additional space at the foramen magnum, enough space for the CSF to flow freely during the cardiac cycle. In patients in whom that can be accomplished by bone decompression alone, PFD is the best option. However, the difficulty that we have today is that we have no means of predicting reliably which patients that will be. Until we have a successful strategy of selecting patients who will respond to bone decompression alone, duraplasty, ideally leaving the arachnoid intact, with or without a dural graft, should be the procedure of choice.
Edward H. Oldfield, MD, FAANS, is professor and Crutchfield Chair in neurosurgery and is the head of the neuroendocrine program at the University of Virginia.
1. Bond AE, Jane JA, Sr., Liu KC, Oldfield EH: Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation. J Neurosurg:1-8, 2015
2. Durham SR, Fjeld-Olenec K: Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation Type I in pediatric patients: a meta-analysis. Journal of Neurosurgery: Pediatrics 2:42-49, 2008
5. Heiss JD, Suffredini G, Smith R, DeVroom HL, Patronas NJ, Butman JA, et al: Pathophysiology of persistent syringomyelia after decompressive craniocervical surgery. Clinical article. J Neurosurg Spine 13:729-742, 2010
7. Kennedy BC, Nelp TB, Kelly KM, Phan MQ, Bruce SS, McDowell MM, et al: Delayed resolution of syrinx after posterior fossa decompression without dural opening in children with Chiari malformation Type I. J Neurosurg Pediatr:1-8, 2015
9. Oldfield EH, Muraszko K, Shawker TH, Patronas NJ: Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. J Neurosurg 80:3-15., 1994
10. Stanko KM, Lee YM, Rios J, Wu A, Sobrinho GW, Weingart JD, et al: Improvement of syrinx resolution after tonsillar cautery in pediatric patients with Chiari Type I malformation., in Journal of Neurosurgery: Pediatrics, 2015, pp 1-8
Neil Feldstein, MD; New York
The management of Chiari I Malformation, with or without syringomyelia, continues to pose difficulties with regard to operative and non-operative management. In the illustrated case above, a young adult with Chiari I had both a substantial associated syrinx as well as sensory deficits related to one or both of these inter-related conditions. This is not a situation in which I would have recommended conservative management, and I agree with the decision to operate.
The surgical options are as outlined, and they are all correct. The key is decompression, and any of these techniques can achieve this. As I look at my patient population, and this patient in particular, I try to weigh the risks and benefits of each of the three choices. At one end of the spectrum is risk avoidance, and at the other end is perceived surgical success. In practice, the majority of patients will have success and minimal risks with any of these decompressive techniques.
However, the risks will clearly be greater with open dural procedures than with extra-dural approaches. This increased risk will likely decrease with the experience of the operating neurosurgeon. In my experience, the non-dural opening techniques can, and will, treat both the CIM and the syrinx. However, it does appear that the rate and degree of syrinx resolution are related to opening of the dura. That said, in my experience, the ultimate clinical success is similar.
When I believe that time is of the essence due to the patient’s clinical findings, I am more inclined to open the dura. In the presence of a syrinx, if I choose to open the dura, I am likely to cauterize the tonsils, as I do not think that this increases risk and may lead to quicker resolution of the syrinx. Almost all surgical complications are due to opening of the dura and not the cauterization of the tonsils.
As I plan decompressive surgery for CIM patients, my default procedure is one of risk aversion, and thus, non-dural opening.
There are several scenarios in which I will open the dura, and they are as follows:
- 1. Rapidly evolving neurologic dysfunction;
- 2. The need for occipito-cervical fusion at the time of decompression or in the foreseeable future;
- 3. Scoliosis greater than 30-35 degrees in association with a syrinx;
- 4. Tonsillar herniation to C2, or lower; and/or
- 5. Failure of any prior decompressive surgery, whether dural or non-dural opening in nature.
If I am planning, or even anticipating, that a patient may require an occipito-cervical fusion, my justification for opening the dura is centered around my concern that, if I am wrong and that patient subsequently requires repeat surgical decompression and expansion duraplasty for progressive neurologic deterioration, then I will be forced to drill out a large fusion mass in order even to access the dura.
The majority of my patients with Chiari I do not fall within these categories, and thus, most are treated with non-dural opening. The question as to which procedure is best is not likely to be resolved. This is related to the nuances that exist in many of our surgeries. As the invasiveness of the procedure increases, the chance of improvement may rise, but at the expense of associated risks. This particular patient had an excellent result with dural opening and tonsillar sparing technique, but may have done equally well with either of the other surgical options. One cannot argue with success, and thus, the debate will continue to roll on.
Neil A. Feldstein, MD, is associate professor of neurological surgery and director of pediatric neurological surgery at Columbia University in New York City. He is also the director of the Adult and Pediatric Chiari Malformation Center.
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