Prevalence of Chiari I malformation and cerebellar ectopia in patients with pseudotumor cerebri

Background: Chiari I malformation (CM) may be present pre-surgically in pseudotumor cerebri (PTC) patients. Whether inferior tonsillar displacement (ITD) is coincidental or linked to increased intracranial pressure is unclear. This study aimed to identify the prevalence of both CM and cerebellar ectopia (CE) (ITD below the foramen magnum ≥ 5 mm and 2-4 mm, respectively) in PTC patients. Methods: Retrospective review combined with prospective assessment of 68 PTC patients with available brain magnetic resonance imaging (MRI) scans and reports. Data collected included patient demographics, height, weight, co-morbid conditions, and medications. MRIs were analyzed for cerebellar tonsillar position, and results were compared with original reports. Results: Of 68 PTC patients, 60 (88%) had normal position of the cerebellar tonsils and 8 (12%) had ITD by report. Of the latter group, 4 were identified as CM and 4 as CE. On review of MRIs, however, 16 patients (24%) had ITD, 7 having CM and 9 having CE. All patients with ITD were female, most were overweight or obese, and most had presumed idiopathic intracranial hypertension (IIH). Conclusion: ITD exists pre-surgically in a significant percentage of PTC patients. ITD is most common in obese or overweight women with presumed IIH. In fact, this subset of patients may actually represent a secondary form of PTC and may benefit from correction of ITD to restore normal intracranial pressure.