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Chiari Malformation Treatment & Management

  • Author: Peyman Pakzaban, MD; Chief Editor: Brian H Kopell, MD  more...
Updated: May 13, 2016

Medical Therapy

Patients with Chiari I malformations who have minimal or equivocal symptoms without syringomyelia can be treated conservatively. Mild neck pain and headaches can be treated with analgesics, muscle relaxants, and occasional use of a soft collar. Frankly symptomatic patients should be offered surgical treatment.


Surgical Therapy

The goals of surgical treatment are decompression of cervicomedullary junction and restoration of normal CSF flow in the region of foramen magnum. Considerable controversy has existed throughout the years about the surgical steps that are required to achieve these goals. The author's preferred technique of suboccipital craniectomy, cervical laminectomy, duraplasty, and arachnoid dissection is described below. Alternatives approaches are discussed under Future and Controversies.

It has been noted in numerous studies that early surgical intervention is associated with better outcome in cases of symptomatic Chiari I malformation. Clinical series have advocated ample posterior fossa craniectomy, including suboccipital craniectomy and removal of the C1 posterior arch, for decompressing the cerebellum and the cerebellomedullary junction, along with an augmentative duraplasty. In cases of reoperation, arachnoid dissection may be advantageous for opening adhesions and thus restoring CSF circulation.[15]

In a study of 158 patients who underwent surgery, improvement was noted in 70% (111). In patients with less than 1 year of follow-up, 73% improved, compared to 79% with 1-3 years of follow-up, 67% with 4-7 years, and 61% with more than 7 years. The presence of myelopathic symptoms predicted the worst outcome (58% improved).[16]

A study of 95 pediatric patients (mean, 8 yr; age range,  9 mo to 18 yr) showed that appropriately selected symptomatic patients (eg, sleep apnea and dysphagia) and those presenting with syringomyelia should be considered surgical candidates because of the high rates of clinical (75%) and radiologic improvement (87.5%). In the study, 25 patients underwent posterior fossa decompression with either dural splitting or duraplasty, and 70 patients were managed without surgery. Over the course of follow-up, 20 (41.7%) of 48 nonsurgical patients who were symptomatic at presentation experienced improvement in symptoms, and 18 (75%) of 24 symptomatic surgical patients showed clinical improvement. Neither of the 2 patients in the conservative group with syrinx at presentation showed radiologic evidence of resolution of the syrinx, whereas 14 (87.5%) of 16 patients treated with surgery showed improvement or complete resolution of syringomyelia.[17]


Preoperative Details

Preparation for surgery for Chiari I decompression is the same as for any elective surgery and depends on the patient's general health. The author routinely obtains CBC, basal metabolic panel, PT, aPTT, chest radiograph, and ECG. Blood is typed and screened. The patient is restricted to nothing by mouth (NPO) after midnight and admitted on the morning of surgery.

Thigh-high anti-embolic stockings and sequential compression devices are applied. Antibiotic prophylaxis with cefazolin or vancomycin is given within 1 hour of making the incision. Dexamethasone is given. Mannitol is not given. If adequate peripheral venous access cannot be established, a central venous catheter is inserted. A Foley catheter is inserted. An arterial line may or may not be inserted, depending on the anesthesiologist's preference. Intubation is carried out, with careful attention given to the extent of neck extension.


Intraoperative Details

The patient is placed on the operating table in prone position. The author avoids the sitting position because of the potential risks of venous air embolism, intraoperative hypotension, subdural hygroma or hematoma due to excessive CSF loss, and the awkwardness of surgical access. The head of the bed is elevated 20-30° and the arms are tucked by the patient's sides. All pressure points are padded. The abdomen and the male genitalia are allowed to hang free between parallel gel rolls.

The neck is flexed at the craniocervical junction and extended at the cervicothoracic junction. Adequate flexion at the craniocervical junction is of paramount importance to safe and expeditious access to the foramen magnum. The head is fixed in neutral position in 3-point skeletal fixation in a Mayfield head holder. A strip of hair is shaved along the midline of the occiput, extending above the inion. The area is prepped and draped.

A midline incision is created, extending from 2-3 cm above the inion to the upper cervical spine. A large pericranial graft is harvested from the upper pole of the incision. An adequately-sized pericranial graft is of utmost importance in achieving a satisfactory water-tight duraplasty. One must not hesitate to extend the incision superiorly, if this is necessary to harvest a proper graft.

The inion, the midline of the occiput down to the foramen magnum, the posterior arch of C1 and the upper aspect of C2 lamina are exposed. Additional laminae may be exposed, depending on the extent of tonsillar descent. Importantly, the muscular attachments to the superior nuchal line are left intact, but the muscles are stripped off the occipital bone just superior and lateral to the foramen magnum. Large epidural veins are encountered laterally between the occiput and C1 posterior arch. If bleeding occurs from these veins, it can be controlled with judicious use of bipolar coagulation and Gelfoam. The lateral exposure along C1 posterior arch may extend to vicinity of the medial rim of the sulcus arteriosus of the vertebral artery, but there is no need to expose that artery. The condylar emissary veins entering the occiput are generally too lateral to be of concern in this exposure.

A conservative suboccipital craniectomy is carried out from the inferior nuchal line to the posterior and lateral rims of foramen magnum. Occasionally, a prominent internal occipital crest extends deeply between the two cerebellar hemispheres' dura and must be resected with a small rongeur. Overzealous resection of occipital bone may result in cerebellar ptosis and should be avoided. The goal is to decompress the foramen magnum, not the entire posterior fossa. Removal of the bony edge of the foramen magnum must extend laterally until the lateral surface of foraminal dura is visualized. Similarly, a wide C1 laminectomy is carried out until the curvature of dura is appreciated. C2 and (rarely) C3 laminectomy may have to be carried out if the tonsils descend to those levels.

The dura is opened in Y-shaped fashion, with the oblique limbs of the Y transecting the paired inferior limbs of the occipital sinus. As the latter are transected, the dural edges are coagulated or oversewn. As the oblique Y limbs come together, the inferior extension of the cerebellar falx may have to be divided. The vertical limb of the "Y"-shaped incision extends down the midline of spinal dura. In patients with Chiari malformations, a tight dural band is often observed at the level of foramen magnum, constricting the dura. This is incised along the midline. The author prefers to then "T" the spinal dural incision transversely at the inferior extent of the Y. The dural leaflets are tented with sutures to the suboccipital muscles and fascia.

The cisterna magna arachnoid is opened under the operating microscope. The goal of arachnoidal dissection is to ensure unimpeded CSF flow through the fourth ventricle outlet and around the cervicomedullary junction, particularly in patients with syringomyelia. The arachnoidal adhesions between the two cerebellar tonsils and between each tonsil and the medulla are carefully divided to mobilize the tonsils superior-laterally and to expose the obex and floor of the fourth ventricle. Extreme care is taken to avoid injury to the tonsillar segments of the posterior inferior cerebellar arteries.

In a syringomyelic patient, if the tonsils are densely adherent to the medulla and cannot be readily resected, a limited subpial resection of the tonsils may be carried out. In a patient with high cervical syringomyelia or syringobulbia whose cervicomedullary neural tissue has been thinned down to a thin membrane, a limited midline myelotomy may be carried out to directly decompress the syrinx.

A careful watertight duraplasty is carried out using the pericranial graft harvested at the beginning of the operation. The intradural compartment is filled with warm saline before the last suture is tied. Any leakage is meticulously repaired. The duraplasty is covered with fibrin glue or DuraSeal glue. After the retractors are removed, meticulous muscle hemostasis is secured to avoid a postoperative epidural hematoma. The wound is then closed in layers.

Intraoperative photograph of duraplasty with peric Intraoperative photograph of duraplasty with pericranial graft. The duraplasty provides additional room for cerebellar tonsils at the craniocervical junction, while achieving closure of dura and prevention of cerebrospinal fluid leak.

Chiari II malformations are decompressed in a similar fashion, except that a multilevel cervical laminectomy may be required. No attempt is made to dissect the tightly adherent cerebellar tonsils from the brainstem in Chiari II.


Postoperative Details

The patient is carefully observed during the first 24 hours after surgery for any signs of brainstem dysfunction, particularly apnea, which is a rare but serious complication of Chiari surgery. In the author's practice, all Chiari patients spend the first postoperative night in the ICU. The patients are then rapidly mobilized and usually discharged home by the end of postoperative day 2, as long as they are neurologically intact, ambulatory, and able to eat without vomiting. Incisional pain and muscle spasms are common and are controlled with opiate analgesics and muscle relaxants. Some patients obtain partial pain relief by use of a soft cervical collar. Nausea and vomiting are also common and may prolong the hospitalization.



During postoperative visits, patients are questioned about persistence or improvement of their preoperative symptoms. The incision is inspected for CSF leakage and pseudomeningocele formation. A small pseudomeningocele presenting as fullness in the back of the neck is managed conservatively and often resolves after a couple of months. A large symptomatic pseudomeningocele may necessitate percutaneous drainage or surgical repair. Heavy lifting and strenuous exercise are avoided for the first 2-3 weeks after surgery. Recovery is usually complete in 4-6 weeks for those with good preoperative neurological function. Patients who started with a major neurological deficit require postoperative rehabilitation. Patients with syringomyelia undergo repeat MR imaging to confirm that the syrinx has responded to Chiari decompression.



The most common complications of Chiari decompression are pseudomeningocele formation and CSF leakage. Early detection and repair of CSF leakage prevent the more serious complication of meningitis.

Wound infection and meningitis are rare. Patients with a high postoperative fever for which no other etiology can be found undergo a lumbar puncture. A CSF formula consistent with bacterial meningitis warrants initiation of broad-spectrum intravenous antibiotic treatment while awaiting CSF culture growth. Aseptic meningitis is treated with corticosteroids.

In the immediate postoperative period, lower brainstem dysfunction, apnea, and epidural hematoma are rare but serious complications. Close observation of the patient in the immediate postoperative period is warranted.

Other rare complications include vertebral artery injury and increased neurological deficit as a result of surgical manipulation of the brainstem and the spinal cord or due to vascular occlusion.

Cerebellar ptosis may occur when a large suboccipital craniectomy has been performed and may result in recurrent interruption of CSF flow across the foramen magnum and recurrent syringomyelia.[18] Pre-existing craniocervical hypermobility syndromes and basilar invagination may worsen and may require craniocervical fusion.

Persistent symptomatic syringomyelia after adequate decompression of the cervicomedullary junction may require direct shunting of the syrinx.


Outcome and Prognosis

Prognosis after surgery for Chiari I is generally good and depends on the extent of preoperative neurological deficits. Those with little or no neurological deficit, symptomatic primarily with pain, can expect an excellent outcome. However, individuals with severe and longstanding weakness and muscle atrophy are less likely to improve.

A systematic review of decompression surgery in adults for Chiari malformation with syringomyelia revealed that the syrinx persists after surgery at an average rate of 6.7% (range, 0-22%).[19] However, in all cases, the investigators observed a significant clinical improvement.


Future and Controversies

The main controversy is treatment of Chiari I malformation centers around the question of what surgical steps are necessary to achieve decompression of the cervicomedullary junction and restore CSF flow across foramen magnum. The most widely accepted approach consists of limited suboccipital craniectomy, C1 laminectomy, duraplasty and arachnoidal dissection as described above.[18] On the other side of the spectrum are recommendations for bony decompression without opening the dura.[20, 21]

Most surgeons who recommend this approach resect or incise the thick fibrous band that constricts the dura at foramen magnum without opening the dura. Some recommend serial incisions of the outer layer of the posterior fossa dura, with the expectation that this may expand the posterior fossa volume.[21] Others recommend opening the dura, but not the arachnoid, and then performing a duraplasty. Still others recommend keeping the arachnoid closed but leaving the dura open, without duraplasty.[22] Some recommend performing an occipitocervical fusion at the time of decompression, citing up to 19% rates of craniocervical instability in pediatric patients after Chiari decompression.[23]

Those who advocate the more conservative extradural and extra-arachnoidal approaches seek to avoid CSF-related complications (CSF leak, pseudomeningocele, aseptic meningitis), particularly in the pediatric population.[21] However, other studies indicate that the incidence of such complications is too low to justify a positionally suboptimal extradural decompression.[24]

The neurosurgery literature is replete with studies that support all of these approaches, but, unfortunately, most of the studies provide only class III or limited class II evidence. Prospective controlled trials are needed to compare the various techniques in adult and pediatric patients and in those with and without syringomyelia.

Contributor Information and Disclosures

Peyman Pakzaban, MD Consulting Neurosurgeon, Houston MicroNeurosurgery; Chairman, Department of Surgery, Bayshore Medical Center

Peyman Pakzaban, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Neurological Surgeons, American Medical Association, Texas Medical Association, American Stroke Association, Congress of Neurological Surgeons, Harris County Medical Society

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Ryszard M Pluta, MD, PhD Associate Professor, Neurosurgical Department Medical Research Center, Polish Academy of Sciences, Poland; Clinical Staff Scientist, Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health (NIH); Fishbein Fellow, JAMA

Ryszard M Pluta, MD, PhD is a member of the following medical societies: Polish Society of Neurosurgeons, Congress of Neurological Surgeons

Disclosure: Nothing to disclose.

Chief Editor

Brian H Kopell, MD Associate Professor, Department of Neurosurgery, Icahn School of Medicine at Mount Sinai

Brian H Kopell, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Neurological Surgeons, International Parkinson and Movement Disorder Society, Congress of Neurological Surgeons, American Society for Stereotactic and Functional Neurosurgery, North American Neuromodulation Society

Disclosure: Received consulting fee from Medtronic for consulting; Received consulting fee from St Jude Neuromodulation for consulting; Received consulting fee from MRI Interventions for consulting.

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Sagittal and coronal MRI images of Chiari type I malformation. Note descent of cerebellar tonsils (T) below the level of foramen magnum (white line) down to the level of C1 posterior arch (asterisk).
Axial MRI image at the level of foramen magnum in Chiari type I malformation. Note crowding of foramen magnum by the ectopic cerebellar tonsils (T) and the medulla (M). Also note the absence of cerebrospinal fluid.
Occipitalization of atlas in a patient with Chiari I.
T2 hyperintense region on MRI (arrow) depicting edema in central cord region of a patient with Chiari I malformation. Left untreated, this patient is likely to develop cavitation of the edematous central cord, resulting in syringomyelia.
CSF hypotension syndrome: Postcontrast MRI before (A) and after (B) treatment with lumbar epidural blood patch. Notice the thick meningeal enhancement (arrows), the relative paucity of CSF in front of the brainstem and behind the cerebellar tonsils, and the engorgement of the pituitary gland before treatment (A). Notice reversal of these abnormalities and ascent of the cerebellar tonsils after treatment (B). In this case, an acquired Chiari malformation was not present, but in some cases it is.
CSF flow study with phase-contrast cine MRI. Brain pulsations results in caudad and cephalad flow of CSF across foramen magnum during systole and diastole. The reversal in the direction of flow is picked up by alternating light and dark appearance of CSF in front and behind the medulla and upper spinal cord on phase-contrast cine MRI. In this case of Chiari I malformation, note the complete absence of CSF flow behind (arrowheads) and focal constriction of CSF flow (arrows) in front of cervicomedullary junction.
Resolution of syringomyelia (asterisk) after decompression of Chiari I malformation (white arrow).
Intraoperative photograph of Chiari type 1 malformation showing descent of cerebellar tonsils well below the level of foramen magnum.
Intraoperative photograph of duraplasty with pericranial graft. The duraplasty provides additional room for cerebellar tonsils at the craniocervical junction, while achieving closure of dura and prevention of cerebrospinal fluid leak.
Table 1. Comparison of Chiari I and II Malformations
Characteristic Chiari I Chiari II
Usual age of diagnosis Adults and older children Infants and young children
Clinical findings
  • Headache and neck pain (worsened by cough or Valsalva maneuver)
  • Myelopathy
  • Cerebellar symptoms
  • Lower brainstem symptoms (eg, dysarthria, dysphagia, downbeat nystagmus)
  • Central cord symptoms (eg, hand weakness, dissociated sensory loss, cape anesthesia)
  • In infants, signs of brainstem dysfunction predominate: swallowing/feeding difficulties, stridor, apnea, weak cry, nystagmus
  • Weakness of extremities
Primary anatomical abnormalities
  • Herniation of cerebellar tonsils through foramen magnum, producing compression of cervicomedullary junction
  • Herniation of lower brainstem through foramen magnum
  • Cephalad course of cranial nerves
  • Kinking of cervicomedullary junction
  • "Beaking" of tectum
  • Upward herniation of vermis through incisura
  • Nearly vertical tentorium
Myelomeningocele No Always
Hydrocephalus Less than 10% of cases Very common
Syringomyelia 30-70% Common
Associated abnormalities
  • Craniocervical hypermobility syndromes
  • Klippel-Feil anomaly
  • Hereditary connective tissue disorders and neurofibromatosis type II
  • Callosum corpus pellucidum septum of agenesis
  • Hypoplasia or
  • Enlargement of massa intermedia
  • Heterotopias and gyral abnormalities
Shared associated abnormalities
  • Basilar invagination
  • Occipitalization of atlas
  • Bifida of C1 posterior arch
  • Foramen magnum variant anatomy
  • Basilar invagination
  • Occipitalization of atlas
  • Bifida of C1 posterior arch
  • Foramen magnum variant anatomy
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