Posterior fossa decompression with duraplasty for treatment of the Chiari I malformation is commonplace since it allows significant expansion of the intradural compartment, release of arachnoidal adhesions, shrinkage or excision of the cerebellar tonsils, and section of a retained rhombic roof or 4th ventricular arachnoid veil. However, the risks of duraplasty include pseudomeningocele, incisional CSF leak, and infection.
Research studies comparing extradural decompression vs. duraplasty
In order to reduce these risks, Isu et al (1993) investigated extradural posterior fossa decompression in 7 patients (age 23 to 54 years) with CM-I and syringomyelia. Syringomyelia was reduced in all patients within a couple of months following treatment.
Seven years later, Munshi et al. (2000) compared the results of extradural decompression to duraplasty in 34 patients age 6 to 65 years. Of the 23 patients undergoing duraplasty, 87% improved, 2 developed CSF leak, and 1 developed aseptic meningitis. Of the 11 extradural patients, 73% improved, 1 developed a superficial wound infection, and 2 required re-operation with duraplasty (9%). The improved outcome following duraplasty was counterbalanced by a small increase in risk; a result that serves to emphasize risk reduction as a key factor in improving outcome.
In 2009, Kotil et al. described 10 adults with Chiari and syringomyelia treated with extradural decompression. Eight completely recovered and two were unchanged. Syringomyelia resolved in two patients, decreased three, and persisted in five.
The same year, Chauvet et al. reported no incisional CSF leak, pseudomeningocele, or meningitis in 11 patients treated using the extradural approach. Symptoms resolved in 6 patients and improved in 5.
A previous Chiari Medicine post reviewed the retrospective study by Yilmaz et al. (2011) evaluating outcome in 82 adults with CM-I, with or without syringomyelia, treated by duraplasty or “nonduraplasty” (extradural decompression).
The authors stratified patients using a newly developed 3-tier classification system based on the extent of cerebellar tonsillar descent. Those with grade 1 herniations (tonsils below 5 mm and above the arch of C1) had equivalent outcomes with both procedures. Those with grade 2 herniations (tonsils reaching C1) had a much better outcome following duraplasty: 94% vs. 75% in the nonduraplasty group. An even greater disparity was found in grade 3 herniations (tonsils beyond C1) with 88.8% improving following duraplasty and only 60% improving following extradural decompression (a 40% failure rate).
Extradural decompression vs. duraplasty
- The Yilmaz study, the largest reported, reveals duraplasty provides a superior outcome in patients with herniations at or below C1.
- The neuroanatomical response of the brainstem, cerebellum, and tonsils following decompression should be considered. In patients undergoing duraplasty, the cerebellum ascends 4.3 +/- 4.8 mm, the mesencephalon-pons junction 4.3 +/- 3.3 mm, and the tonsils 6.5 +/- 4.8 mm (Vanaclocha et al. 1997). (Whether this normalization confers a long-term benefit is unknown.) Improvement in tissue deformity following extradural decompression has not been documented.
- Although the number of patients that require a secondary procedure following extradural decompression appears to be low, it remains a concern. In our experience, patients referred with persistent symptoms following extradural decompression present with protracted pain, ongoing narcotic use, and, at times, significant depression. They are faced with a possible second surgical procedure that further impacting the suboccipital and cervical musculature.
- The average follow-up in the Yilmaz study was 9 months. It is reasonable to assume that the duraplasty is more compliant during the initial months following decompression and that compliance decreases as the posterior epidural tissues become more rigid with wound healing. Thus, as in many clinical issues regarding this disorder, prospective studies with longer follow-up are needed.
- The choice of performing an extradural decompression has been based on its lower morbidity, especially in children. However, this has been questioned. Hoffman et al. (2008) presented 40 patients with the Chiari I malformation (ages 3 to 46 yrs), 24 with an associated syrinx, that were treated by autologous duraplasty and preservation of the arachnoid. There was no procedure-associated mortality. Two patients with persistent syringomyelia required syringosubarachnoid shunting, one pseudomeningocele was treated with a tap, and there were no incisional CSF leaks, meningitis, or hydrocephalus. The author’s conclusion:
The cerebrospinal fluid-related morbidity associated with autologous duraplasty for the Chiari I malformation in a uniformly treated population is negligible. These results challenge the current rationale for a less aggressive surgical approach to the Chiari I malformation.
Our experience, focused on older adolescents and adults, supports this view. Extradural decompression is reserved for the few instances of mild herniations with a relatively open angle between the posterior suboccipital and upper cervical dura. With the use of autogenous pericranium (harvested with use of a template to ensure adequate size and tension-free closure) along with the technical aspects of closure, valsalva-testing, and reinforcement as needed, the risk of pseudomeningocele and related difficulties can be kept to a minimum. Future posts will discuss our approach.
I welcome your thoughts on this important technical decision in the surgical treatment of persons suffering from the Chiari I malformation. You can comment by hovering over the icons below and selecting the Comment icon.
John Oró, MD
January 27, 2013