Hindbrain decompression for Chiari-syringomyelia complex: an outcome analysis comparing surgical techniques

The natural history of Chiari malformation and our ability to alter it is poorly understood, and reported results of hindbrain decompression show high recurrence rates. We report 11 years of experience of hindbrain decompression, to evaluate long-term outcome related to surgical technique. The results of patients who underwent hindbrain decompression between 1994 and 2005 were retrospectively analysed. We identified 96 patients from operative records and reviewed all clinical records for presenting symptomatology and examination findings. Decompression technique includes traditional decompression, duraplasty and bone--only decompression. Symptoms at the last available follow-up visit were defined by the assessing clinician as resolved, improved, unchanged or worse. There were 35 males and 61 females with a mean age of 33 years (range 6 - 62 years). The mean length of follow-up is 3.6 years with a range of 6 months to 9 years. Postoperative resolution or improvement in symptoms was seen in 75 patients (78%). Drop attacks and headaches were the most likely to respond to hindbrain decompression, showing improvement or resolution in 100 and 92% of cases. Dysaesthetic arm pain and weakness carried the worse prognosis with only 20% having symptom resolution. Sixteen patients had only bony decompression leaving the dura intact. In eight patients (66%) the headaches resolved following bony decompression alone. However the headaches were unchanged in 25% of cases. Dysaesthetic pain and weakness was unchanged in 60%. Restoration of CSF flow dynamics at the foramen magnum by surgical decompression does not consistently result in resolution of symptoms in all patients. Identification of predictors of successful outcome following decompression, coupled with early intervention and appropriate choice of procedure may result in improved outcomes. Although this is a retrospective study it suggests that bone only decompression should be reserved for patients with isolated headache.