Introduction Chiari 1 malformation (CM1) is a structural abnormality of the hindbrain characterised by the descent of the cerebellar tonsils through the foramen magnum. The management of patients with CM1 remains contentious since there are currently no UK or international guidelines for clinicians. We therefore propose a collaborative, prospective, multicentre study on the investigation, management and outcome of CM1 in the UK: the UK Chiari 1 Study (UKC1S). Our primary objective is to determine the health-related quality of life (HRQoL) in patients with a new diagnosis of CM1 managed either conservatively or surgically at 12 months of follow-up. We also aim to: (A) determine HRQoL 12 months following surgery; (B) measure complications 12 months following surgery; (C) determine the natural history of patients with CM1 treated conservatively without surgery; (D) determine the radiological correlates of presenting symptoms, signs and outcomes; and (E) determine the scope and variation within UK practice in referral patterns, patient pathways, investigations and surgical decisions.

Methods and analysis The UKC1S will be a prospective, multicentre and observational study that will follow the British Neurosurgical Trainee Research Collaborative model of collaborative research. Patients will be recruited after attending their first neurosurgical outpatient clinic appointment. Follow-up data will be collected from all patients at 12 months from baseline regardless of whether they are treated surgically or not. A further 12-month postoperative follow-up timepoint will be added for patients treated with decompressive surgery. The study is expected to last three years.

Ethics and dissemination The UKC1S received a favourable ethical opinion from the East Midlands Leicester South Research Ethics Committee (REC reference: 20/EM/0053; IRAS 269739) and the Health Research Authority. The results of the study will be published in peer-reviewed medical journals, presented at scientific conferences, shared with collaborating sites and shared with participant patients if they so wish.