Objective A common symptom of Chiari I malformation (CIM) is headache, which is diagnosed using non-validated criteria from the International Headache Society (IHS). CIM-associated headaches should resolve following neurosurgical treatment of the malformation by foramen magnum decompression (FMD). We aimed to validate the IHS criteria and determine (1) the efficacy of FMD in treating headache and (2) whether duraplasty confers an advantage over simple bony decompression in the treatment of this symptom.

Methods A retrospective review of CIM cases treated with FMD at Great Ormond Street Hospital from 1989 to 2014 was carried out. Clinical headache characteristics were compared against IHS criteria and correlated with outcome following FMD.

Results Headache was a presenting symptom in 57/102 (55.9%) of patients. Of these, 42/57 (73.7%) could be classified as Chiari I-type headache. Following FMD, 42/57 (73.7%) of all presenting headaches showed a sustained improvement (>3 months) compared with 32/39 (82.1%) of Chiari I-type headaches. Duraplasty led to a sustained improvement in headache in 32/38 (84.2%) cases compared with 9/16 (56.3%) cases treated with bone-only decompression.

Conclusions Our data suggest that 80% of headaches classified as Chiari I-type will show a sustained improvement following FMD, and, as such, the IHS criteria are clinically useful in evaluating symptoms attributable to CIM. For all headaches associated with CIM, duraplasty may confer a benefit in terms of long-term improvement, compared with bone-only decompression.