"For surgical treatment of Chiari malformation type I (CM-I), there is no consensus among surgeons about which method is preferred."
This first sentence in the study by Yilmaz et al. on the surgical treatment of CM-I, published in February 2011 in World Neurosurgery, encapsulates the treatment dilemma surgeons face with this disorder. Adem Yilmaz, M.D. of the Sisli Research and Education Hospital in Istanbul and colleagues published a retrospective study comparing the surgical outcome in CM-I patients treated by duraplasty versus bony decompression alone (nonduraplasty).
Between 1998-2009, 82 consecutive patients over age 18 were included in the study. CM-I was defined as herniation of the cerebellar tonsils greater than 5 mm below the foramen magnum. Surgical indications included “headache or tussive headache; drop attacks, neck, arm or back pain; swallowing difficulties; or upper extremity numbness or tingling” and symptomatic syringomyelia.
The authors developed a new classification system based on cerebellar tonsillar descent (CTD). The scale consists of 3 grades:
- Grade I - “the tonsil descended more than 5 mm below the foramen magnum but did not reach the arch of C1”
- Grade 2 – “the tonsil reached the arch of C1”
- Grade 3 – “the tonsil descended over the C1 arch” (meaning below the C1 arch)
Posterior fossa decompression was performed by a “modest superior extension (approximately 1.5-2.0 cm) and a lateral extension to the lateralmost aspect of the foramen magnum and cervical spinal canal, and C1 laminectomy (and C2 if necessary)...” Depending on surgeon preference, graft material used in the duraplasty group was “cadaveric dura, bovine pericardium, fascia lata, or autologous pericranium.”
Post-operative outcome was assessed by the Japanese Orthopaedic Association scores and recovery rate. Average follow-up was 9 months. Outcome was analyzed by group (duraplasty or nonduraplasty) and by grade of tonsillar descent.
Fifty-eight patients underwent duraplasty. Symptoms improved in 89.6% and improvement was related to the preoperative herniation grade: the lower the grade, the more likely the improvement (grade I- 100%, grade 2 – 85.7%, grade 3 – 75%). Improvement in syringomyelia (n=45), while high in all grades, did not correlate with pre-operative herniation: grade 1 - 89.4%, grade 2 - 94.1%, grade 3 - 88.8%.
Complications in the duraplasty group included CSF leaks in 3 patients, focal neurological deficits in 2, superficial infection in 1, and meningitis in 1. Revision for CSF fistula was performed in 2 patients.
Of the 24 patients undergoing bony decompression without duraplasty, symptoms improved in 79.1%. The greater the grade of herniation, the less the degree improvement: grade I- 90.9%, grade 2 – 75%, grade 3 – 60%.
Syringomyelia was present in 19 patients in the nonduraplasty group. Follow-up MRI, available in 16, revealed syrinx reduction in 84.2%.
Complications in the nonduraplasty group included “superficial wound infection and temporary neurological deficit in one patient” and “reoperation because of inadequate decompression” in two patients. Syringomyelia improvement by grade was not reported.
The authors found that PFD with duraplasty was “associated with a greater risk for CSF-related complications.” However, in patients with Grade 3 tonsillar herniations “PFD and duraplasty seem to be the essential surgical treatment of this condition.”
"In our experience, PFD with or without duraplasty in symptomatic adult patients with CM-I is successful in most cases with minimal complications. We believe that the risk of CSF leak has to be accepted as a downside of the essential procedure, which is opening the dura and widening the cisternal space."
The authors “recommend using the CTD grading scale before planning duraplasty." Duraplasty "should be reserved for patients who are CTD grade 3.”
John J. Oró, M.D.
September 12, 2012
A subsequent post will review Dr. Ulrich Batzdorf’s “Considerations Regarding Decompressive Surgery for Chiari Malformations”, also published in the February 2011 issue of World Neurosurgery. In a subsequent post, I will provide my impressions of the study.