Post-operative decompression volume correlates with outcome in the Chiari malformation Type I

The goal of surgical decompression in persons with intractable symptoms from the Chiari I malformation is to alleviate crowding caused by cerebellar tonsillar herniation in the region of the foramen magnum. Expanding the posterior cranio-cervical volume can improve CSF flow and alleviate symptoms.

However, the correlation between the amount of CSF space surgically created and clinical improvement has not been well studied. In part, this due to the tedious nature of the current tools used to measure the pre- and post-operative posterior fossa and CSF space volumes.

In an article published online on in the Journal of Neurosurgery: Pediatrics on February 17, 2017, researchers from the Division of Neurosurgery, Children's National Health System in Washington DC, describe the development of a “semiautomated program for calculating the 3D posterior fossa CSF volume.” Using this technique, the authors determined the correlation of the posterior fossa and CSF space volumes (cisterna magna, prepontine cistern, and fourth ventricle) with the clinical outcome in 42 pediatric patients undergoing decompression surgery for CMI.

Posterior fossa and CSF volumes were measured on the axial T2-weighted MRI images on scans taken before and after surgical decompression. The change in these volumes were then correlated with the postoperative outcome in “headache, syrinx, tonsillar descent, cervicomedullary kinking, and overall surgical success.”

The study revealed that greater enlargement of the posterior fossa volume, resulted in greater clinical improvement. In addition, enlargement of the cisterna magna also resulted in improved outcome. Furthermore, enlargement of the lower portion of the posterior fossa correlated with reduction in syrinx size. In authors words: 

“A statistically significant association was found between a larger increase in the total posterior fossa volume and the cisterna magna CSF volume after CM-I decompression and improvement in headache, tonsillar descent, and surgical outcome. When the caudal portion of the posterior fossa volume was isolated, larger volume increases were associated with statistically significant increases in syrinx and cervicomedullary kinking in addition to headache, tonsillar descent, and surgical outcome.”

The authors also identified an area of future study: How large is large enough?

“Decompression volumes will need to be correlated with clinical outcomes in a prospective study before conclusions can be made on the optimal decompression size or technique.”

John Oró MD

 

Reference: Comparison of posterior fossa volumes and clinical outcomes after decompression of Chiari malformation Type I

Pseudomeningocele following Chiari surgery decreases quality of life

Pseudomeningocele (PM) is one of the more common complications following posterior fossa decompression for the Chiari I malformation (CM-I). A leak of spinal fluid through the duraplasty creates a pocket of CSF in the posterior cervical muscles. If the fluid collection enlarges, it pushes the duraplasty membrane into the foramen magnum region causing crowing and recurrence of the Chiari symptoms. In a few cases, spinal fluid leaks through the incision and, if untreated, leads to infection.

While a number of Chiari centers have been able to keep the risk of pseudomenigocele very low, rates as high as 18% patients have been reported.  

If the PM is small, it can be observed with follow-up MRI scans and may resolve on its own. However, large persistent PMs pose difficulties. The duraplasty can become adherent to the underlying cerebellar tonsils and block CSF flow. Once adherent, surgical revision is difficult.

Dr. Scott Parker and colleagues at the Department of Neurological Surgery at Vanderbilt University studied the effects of symptomatic PMs on the 1-year postoperative “pain, disability, and quality of life” in patients undergoing Chiari decompression.

The researchers found that “a postoperative symptomatic pseudomeningocele has lingering effects at 1 year, which significantly diminishes the overall benefit of suboccipital decompression for CM-related symptoms.”

While the authors use this finding to argue for a “less invasive approach,” I have a different view. The less invasive approaches, such as thinning of the dura by stripping its outer layer, have a higher a risk of failure than the duraplasty approach.

The goal of surgery for the Chiari malformation is adequate posterior fossa decompression with minimal surgical risks. Thus, the key is to use a duraplasty technique that markedly decreases the risk of pseudomeningocele. This is possible through the use of autologous pericranium harvested from a separate small incision in the midline occiput just above the main incision.

Using triangular silastic templates, the appropriate size of graft can be obtained. The pericranial graft is sutured in place with a monofilament running suture in a watertight fashion. Two Valsalva maneuvers to 35 cm are performed following the repair and if any leak is visualized under microscopic magnification, the area is oversewn or a secondary patch is used.

Durplasty using a patient’s own pericranial tissue has been effective in posterior fossa decompression for patients with CM-I. The leak rate can be reduced to a minimal level: 2% or less. The use of a duraplasty results in greater expansion of the subarachnoid space at the foramen magnum than possible in non-duraplasty procedures and allows the patient the best opportunity to improve.

If a leak does develop, it is followed closely and if it enlarges, treated with lumbar drainage or surgical revision. Fortunately, the likelihood is low in centers experienced with the pericranial duraplasty technique.

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Reference

Effect of symptomatic pseudomeningocele on improvement in pain, disability, and quality of life following suboccipital decompression for adult Chiari malformation Type I

Related Posts

Another Reason to Evaluate the Foramen of Magendie during Posterior Fossa Decompression for Chiari-related Syringomyelia

Image from the Editor's files shows the median aperture of the 4th ventricle, also known as the foramen of Magendie, covered by a veil in this person with Chiari & syringomyelia. Image: CyberMed, LLC


Image from the Editor's files shows the median aperture of the 4th ventricle, also known as the foramen of Magendie, covered by a veil in this person with Chiari & syringomyelia. Image: CyberMed, LLC

When treating a patient with Chiari related syringomyelia by posterior fossa decompression, it is important for the neurosurgeon to open the dura and the arachnoid and evaluate the outlet of the fourth ventricle which drains CSF into the cisterna magna. The outlet called the foramen of Magendie after its discoverer is also known as the median aperture. Approximately 1 of 10 persons with Chiari/syringomyelia has a veil over the median aperture blocking or restricting CSF flow. Clearing the obstruction by microsurgically opening the veil facilitates syrinx decompression and helps avoid revision surgery.

In the December 2014 issue of the Journal of Neurosurgery, S. Grossaur of the Department of Neurosurgery, General Hospital of Klagenfurt, in Austria, and colleagues Koeck K, Vince GH published a report documenting significant improvement in the somatosensory evoked potentials (SSEPs) following the opening of an obstructed foramen of Mangendie. The authors describe the

case of a 32-year-old woman who underwent surgery for CM associated with extensive cervicothoracic syringomyelia and whose intraoperative somatosensory evoked potentials (SSEPs) did not notably improve after craniotomy or following durotomy; rather, they only improved after opening of the fourth ventricle and restoration of CSF flow through the foramen of Magendie. Postoperatively, the patient recovered completely from her preoperative neurological deficits. To the authors' knowledge, this is the first report of significant SSEP recovery after opening the fourth ventricle in the decompression of a CM-I.

When evaluating patients referred for persistent syringomyelia following posterior fossa decompression, who on MRI studies appear to have an adequate decompression, a careful review of the operative note should be performed to determine if the dura and arachnoid where opened during the initial procedure. If the dura or arachnoid had not been opened, the revision surgeon should consider exploration of the posterior fossa and examination for a possible median aperture veil (retained rhombic roof) as the preferred treatment strategy instead of placement of a syrinx stent or shunt. 

John Oró, MD
January 2, 2015

Theodor Langhans described the Chiari I malformation in 1881

Dr. Theodor Langhans, Professor and Chair of Pathological Anatomy in University of Bern, Switzerland.

Dr. Theodor Langhans, Professor and Chair of Pathological Anatomy in University of Bern, Switzerland.

Hans Chiari is appropriately recognized for describing and categorizing the Chiari malformations in reports published in 1891 and 1895. While others such as Jean Cruveilhier (1798-1874) and John Cleland (1835-1925) also made observations prior to Chiari, in an article published in the Journal of Neurosurgery: Pediatrics in March 2011 Martin M. Mortazavi and colleagues propose Theodor Langhans, the German pathologist remembered for describing “Langhans cells” in tuberculosis, as the first to describe the Chiari I malformation.

Mortazavi et al. review Theodor Langhans’ distinguished background:

“Theodor Langhans was born September 28, 1839, in Usingen (Nassau), Germany, and studied under Henle in Göttingen and von Recklinghausen in Berlin. He attended medical school in Heidelberg and, in 1864, completed his medical degree thesis on the structure of tendons in Würzburg. He was also a student under such names as Virchow, Trauber, and Frerichs. He served as assistant to von Recklinghausen until 1867. In Marburg, he collaborated with Lieberkölin and Wagner on anatomical research. He was later made Professor Ordinarius in Giessen and then moved to Switzerland in 1872 where he was appointed Professor and Chair of Pathological Anatomy in Bern, succeeding Klebs.”

In 1881, Langhans described a case of syringomyelia and “pyramidal tumors” of the cerebellum in the publication Über Höhlenbildung im Rückenmark als Folge Blutstauung. Mortazavi et al. translated the report (“Regarding cavity creation in the spinal cord as a consequence of obstruction to blood flow”) and believe “these were the first descriptions of what would become known as the Chiari I malformation described by Langhans as ‘pyramidal tumors.’” These selected passages are key to the description and reveal Langhans awareness of the anatomy and pathophysiology of CMI:

“In the case, which first brought to my attention the necessity to look for cavity formation in the spinal cord following a change in the cerebellar cavity, I could not find a cause for the increase in pressure; but great pressure on the pons and medulla oblongata from above was indeed apparent. Upon dissection of the cerebellum, nothing was of note except for an obvious/significant development of both tonsils, which protruded down in the form of two symmetrical pyramidal tumors and pushed the medulla oblongata in a frontal direction at almost a right angle.” (emphasis added)
“The increase in pressure in the cerebellar cavity will hinder or greatly impede the outflow of blood and cerebral spinal fluid.” (emphasis added)

Mortazavi and colleagues recognize Langhans' contribution and conclude:

“Although the association of Chiari I malformation and syringomyelia would not be commonly used until the late 20th century, it was Langhans in the 19th century who proposed this cause and effect. Therefore, appropriate recognition for this association should be given to this early pioneer who, with Chiari, helped provide us with details of hindbrain herniation that are still in use today.” 

John Oró, MD

 

Reference

The first description of Chiari I malformation with intuitive correlation between tonsillar ectopia and syringomyelia: Historical vignette

Martin M. Mortazavi, M.D., R. Shane Tubbs, M.S., P.A.-C., Ph.D., Maja Andrea Brockerhoff, M.A., Marios Loukas, M.D., Ph.D., and W. Jerry Oakes, M.D.