Imaging and physiology across the high-low cerebrospinal fluid pressure spectrum: Navigating diagnostic uncertainty...

This study was conducted to provide a clinically oriented, mechanism-based framework for interpreting neuroimaging across disorders of cerebrospinal fluid (CSF) pressure, with particular emphasis on patients who fall between classic diagnostic categories of spontaneous intracranial hypotension (SIH) and idiopathic intracranial hypertension (IIH).

Headache specialists are increasingly asked to evaluate patients whose symptoms, imaging, and opening pressures do not fit neatly within International Classification of Headache Disorders, 3rd edition criteria. At the same time, modern work in SIH, IIH, CSF-venous fistulas (CVFs) and rebound intracranial hypertension (RIH) has highlighted that these entities are better understood as dynamic expressions of a shared craniospinal physiology rather than isolated syndromes.

This narrative review synthesizes contemporary literature on SIH, IIH, CVF, and RIH together with the authors' experience in a tertiary CSF disorder program. We focus on imaging markers of buoyancy loss and venous adaptation, the Bern score and its extensions, adjunctive MRI features that refine pretest probability when the brain MRI is normal, evolving myelographic techniques including photon-counting computed tomography, modern MRI phenotyping in IIH, and recent data on opening pressures in SIH and CVF. These data are organized around a unifying physiologic model rather than by individual disease labels.

In SIH, the shift from a binary to a probability-based imaging paradigm-anchored by the Bern score-has been complemented by additional markers such as meningeal diverticula, optic nerve sheath narrowing, and imaging findings suggestive of migraine that further inform decisions about advanced myelography even when the brain MRI is formally normal. Recognition of lateral dural tears with small herniated arachnoid pouches mimicking meningeal diverticula and CVFs detectable with only advanced myelographic techniques underscores that absence of a localized leak does not exclude SIH. Most patients with imaging-proven SIH have normal or even elevated opening pressures, challenging current diagnostic criteria and suggesting that some leaks may arise in the setting of chronically increased craniospinal pressure. In IIH, only a subset of MRI features meaningfully discriminates true IIH from mimics, and venous sinus behavior emerges as a dynamic marker of compliance rather than a simple anatomic lesion. RIH after leak closure and "popping the balloon" in patients with established IIH who develop spinal leaks both illustrate how modest shifts in CSF volume and venous capacitance can drive rapid transitions between high- and low-pressure states.

Disorders of CSF pressure are best conceptualized as points along an interconnected physiologic continuum in which buoyancy, venous compliance, leak morphology, and CSF-venous communication interact to produce the observed clinical and imaging phenotypes. For patients with mixed or subtle findings, applying this mechanism-oriented framework can improve interpretation of MRI and myelography, prevent premature exclusion of SIH or IIH on the basis of normal opening pressure or "negative" imaging, and support more nuanced, individualized treatment decisions in clinical practice.