Idiopathic normal pressure hydrocephalus (iNPH) represents a critical cause of reversible dementia, urinary dysfunction, and gait ataxia in older adults. Traditional pathophysiological models have focused almost entirely on impaired cerebrospinal fluid (CSF) resorption. However, new research reveals that choroid plexus enlargement plays an unexpected role in iNPH pathogenesis. By examining structural variations within cerebral ventricles, neuroscientists are reshaping our understanding of fluid production dynamics. Consequently, these findings challenge long-standing concepts and illuminate noninvasive therapeutic alternatives.

Understanding Choroid Plexus Enlargement in iNPH

Historically, clinicians attributed ventricular enlargement in iNPH primarily to defective outflow through arachnoid granulations and reduced lymphatic absorption. Nevertheless, cerebrospinal fluid formation remains an active biological process driven by the choroid plexus epithelium. In this retrospective study, investigators analyzed 3T brain MRIs of fifty iNPH patients and fifty age- and sex-matched healthy controls.

The investigators discovered that individuals with iNPH exhibited substantially larger lateral ventricular choroid plexus area and volume compared to controls. Moreover, this volumetric expansion persisted after normalizing values against total intracranial volume. Therefore, choroid plexus enlargement represents an intrinsic pathological feature rather than a secondary artifact of ventriculomegaly. Additionally, cellular hypertrophy and sustained neuroinflammation may accelerate this tissue expansion. As a result, neuroimaging experts now view the choroid plexus as an active driver of hydrocephalus dynamics.

Pathophysiological Implications for Cerebrospinal Fluid Dynamics

The discovery of choroidal hypertrophy introduces crucial questions regarding fluid hypersecretion and impaired intracranial compliance. Typically, the human choroid plexus secretes approximately 500 milliliters of fluid daily through specialized transmembrane transport systems. In iNPH, cellular expansion and vascular engorgement might accelerate fluid production beyond physiological resorption limits. Furthermore, choroidal enlargement can impair intracranial pulse dampening, transmitting damaging pressure waves through brain parenchyma.

Simultaneously, deficient parenchymal clearance worsens this fluid accumulation. Recent studies indicate that glymphatic influx and deep venous outflow decline with age and neurovascular disease. Consequently, when increased fluid secretion encounters diminished outflow capacity, ventriculomegaly inevitably progresses. Thus, choroid plexus expansion acts synergistically with impaired resorption to worsen clinical symptoms. Recognizing these dual pathophysiological forces helps clinicians better understand the development of Hakim's classic triad.

Limitations of Conventional Ventricular Shunting Procedures

For decades, surgeons have relied on ventriculoperitoneal or ventriculoatrial shunts as the primary therapy for iNPH. Although surgical CSF diversion often improves gait and cognition, it carries persistent procedural liabilities. For example, elderly patients encounter risks of intracranial hemorrhage, bacterial infections, and subdural hematomas from overdrainage. Furthermore, mechanical shunt malfunction occurs frequently, requiring emergency revisions under general anesthesia.

Additionally, many frail patients present with complex systemic comorbidities that make invasive operations hazardous. Anticoagulant regimens, severe heart failure, and advanced age often restrict surgical eligibility. Moreover, repeated valve adjustments require dedicated clinic visits and imaging surveillance, straining family caregivers and healthcare facilities. Therefore, modern neurology requires durable, noninvasive interventions that regulate fluid dynamics safely. Addressing choroidal hypersecretion could provide lasting functional recovery without implanting mechanical hardware.

Emergence of Noninvasive Volume-Reductive Therapies

To circumvent the risks of invasive shunting, clinicians are exploring noninvasive volume-reductive therapies targeting the choroid plexus. Historically, endoscopic choroid plexus cauterization proved effective in pediatric hydrocephalus. However, performing intracranial endoscopy in frail geriatric patients carries notable morbidity. Consequently, noninvasive platforms such as transcranial magnetic resonance-guided focused ultrasound (MRgFUS) offer a compelling alternative.

Through precise stereotactic acoustic sonication, MRgFUS can noninvasively ablate or modify choroid plexus tissue without surgical craniotomy. Furthermore, real-time MR thermometry provides continuous thermal monitoring, preserving critical adjacent thalamic and ependymal structures. By reducing secretory tissue volume, focused ultrasound can attenuate CSF overproduction and stabilize ventricular dimensions. In addition, targeted stereotactic radiosurgery presents an alternative modality for selective tissue devascularization. Accordingly, these noninvasive techniques could transform hydrocephalus treatment into an outpatient, incisionless procedure.

Diagnostic and Prognostic Value in Neuroimaging Protocols

Quantifying choroid plexus dimensions provides immediate diagnostic value for clinical neurologists and neuroradiologists. Differentiating iNPH from neurodegenerative conditions like Alzheimer's disease remains challenging in clinical practice. Although neuroimaging signs like disproportionately enlarged subarachnoid-space hydrocephalus (DESH) guide evaluation, their sensitivity varies widely. Therefore, incorporating choroid plexus volumetry into standard 3T MRI interpretation improves diagnostic confidence.

Furthermore, automated artificial intelligence segmentation can measure choroid plexus volumes during routine MRI processing. By combining these volumetric data with the callosal angle and Evans index, clinicians establish a comprehensive quantitative profile. Importantly, baseline choroid volume may predict patient responsiveness to diagnostic tap tests or targeted ablation. Thus, quantitative neuroimaging transforms qualitative assessment into personalized predictive medicine. Widespread implementation of these imaging biomarkers will optimize diagnostic pathways across clinical neurology centers.

Future Directions and Relevance for Clinical Practice

Translating these discoveries into clinical reality demands rigorous multicenter clinical trials and collaborative efforts across medical specialties. First, longitudinal investigations must verify whether choroidal enlargement precedes ventriculomegaly or represents a secondary inflammatory phenomenon. Moreover, future studies should establish standardized volumetric thresholds across diverse demographic populations to guide therapeutic decisions.

In healthcare systems across India and globally, noninvasive therapeutic alternatives offer profound economic and clinical benefits. Mechanical shunt expenses, surgical infection risks, and geographic barriers to revision surgery pose heavy burdens for elderly patients. In contrast, noninvasive volume reduction could deliver definitive single-session treatment at advanced regional medical centers. Additionally, early diagnosis enables prompt intervention before irreversible axonal degeneration occurs. Ultimately, clarifying the pathological role of choroid plexus enlargement heralds a new era of restorative care for adult hydrocephalus.

Frequently Asked Questions

How does choroid plexus enlargement contribute to normal pressure hydrocephalus?

Choroid plexus enlargement contributes to normal pressure hydrocephalus by accelerating cerebrospinal fluid secretion and impairing intracranial compliance. The expanded choroidal tissue produces excess fluid that overwhelms standard resorption mechanisms. Concurrently, altered vascular pulsatility and cellular hypertrophy within the ventricles exacerbate mechanical stress on periventricular subcortical motor pathways.

Why are noninvasive therapies preferred over conventional ventriculoperitoneal shunting?

Conventional ventriculoperitoneal shunts carry substantial clinical risks, including catheter blockage, surgical infection, overdrainage subdural hematomas, and recurrent revisions. In contrast, noninvasive volume-reductive therapies eliminate foreign implanted hardware entirely. Consequently, these innovative procedures minimize procedural trauma, reduce anesthesia exposure, and offer safe alternatives for vulnerable geriatric patients with severe comorbidities.

Can 3T MRI differentiate choroid plexus expansion from normal aging?

Yes, 3T MRI effectively differentiates pathological choroid plexus expansion from normal physiological aging. While mild volumetric changes occur with advanced age, patients with iNPH demonstrate significant tissue enlargement even after normalizing for total intracranial volume. High-resolution 3D volumetric sequences provide objective morphometric data that consistently surpass standard healthy control thresholds.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice, diagnosis, or treatment. Healthcare professionals should exercise their independent clinical judgment when managing individual cases. Refer to the latest local and national guidelines for clinical practice.

References

1. Dhawan SS et al. Choroid plexus enlargement in idiopathic normal pressure hydrocephalus and concept proposal for noninvasive volume-reductive therapies. Brain Res. 2025 Jun 15. doi: 10.1016/j.brainres.2025.149593. PMID: 40157411.
2. Relkin N, Marmarou A, Klinge P, Bergsneider M, Black PM. Diagnosing idiopathic normal-pressure hydrocephalus. Neurosurgery. 2005;57(3 Suppl):S4-16.
3. Hacein-Bey L, Massoud TF. MRI-Guided Focused Ultrasound: Establishing an Effective Innovative Paradigm to Treat Complex Neurologic Conditions. AJR Am J Roentgenol. 2026. doi: 10.2214/AJR.26.35070.