Craniocervical Junction Morphology and Cerebrospinal Fluid Spaces at the Foramen Magnum in Idiopathic Intracranial Hypertension: Implications for Pathophysiology

Background: Although numerous magnetic resonance imaging (MRI) findings have been described in idiopathic intracranial hypertension (IIH), the potential contribution of craniocervical junction morphology to disease pathophysiology and diagnosis remains largely unexplored. This study aimed to evaluate foramen magnum morphology and cerebrospinal fluid (CSF) spaces at the craniocervical junction in patients with IIH and to investigate their associations with disease severity and diagnostic performance. Methods: In this retrospective case–control study, 70 patients diagnosed with IIH according to the modified Dandy criteria and 70 age- and sex-matched controls were included. Brain MRI examinations were retrospectively reviewed. Optic nerve sheath diameter, optic nerve tortuosity angle, foramen magnum anteroposterior and transverse diameters, foramen magnum area, foramen magnum index, and anterior and posterior subarachnoid CSF spaces were measured. Correlation analyses with lumbar puncture opening pressure and papilledema grade were performed. Independent imaging predictors of IIH were identified using multivariable logistic regression analysis, and diagnostic performance was assessed using receiver operating characteristic (ROC) analysis. Results: Compared with controls, patients with IIH demonstrated significant alterations in craniocervical junction morphology, including smaller foramen magnum anteroposterior diameter, foramen magnum area, foramen magnum index, and anterior subarachnoid CSF space, together with increased optic nerve sheath diameter and reduced optic nerve tortuosity angle (all p < 0.001). Foramen magnum morphometric parameters and anterior subarachnoid CSF space were significantly associated with both lumbar puncture opening pressure and papilledema grade. Multivariable logistic regression identified optic nerve sheath diameter (OR = 2.143, p = 0.002), optic nerve tortuosity angle (OR = 0.925, p < 0.001), and foramen magnum index (OR = 0.526 per 0.1-unit increase, p = 0.001) as independent imaging predictors of IIH. The combined prediction model demonstrated excellent diagnostic performance (AUC = 0.901), with 81.4% sensitivity and 87.1% specificity. Conclusions: Craniocervical junction morphometric features and subarachnoid CSF spaces at the foramen magnum differed between patients with IIH and controls and may provide complementary imaging information. These cross-sectional associations do not establish whether the observed differences are pre-existing anatomical characteristics or secondary changes related to chronically elevated intracranial pressure. Prospective multicenter studies incorporating dynamic CSF-flow imaging are warranted to validate these findings and clarify the temporal relationship between these morphometric features and disease development.