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Another version of the truth
  1. Michael Levitt
  1. Departments of Neurological Surgery, Radiology, Mechanical Engineering, Stroke & Applied Neuroscience Center, University of Washington, Seattle, WA 98195, USA
  1. Correspondence to Dr Michael Levitt, Neurological Surgery, University of Washington, Seattle, WA 98195, USA; mlevitt{at}uw.edu

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Within the neurointerventional community, there has been growing interest in the intersection between idiopathic intracranial hypertension (IIH; sometimes referred to as pseudotumor cerebri) and venous sinus stenosis. Beginning in 2002,1 venous sinus stenting has emerged as an attractive alternative to ventriculoperitoneal shunting or optic nerve sheath fenestration in the treatment of medically refractory IIH. Since then, many aspects of the venous sinus–IIH relationship have been investigated, including the effect of anesthesia and physiological parameters on venous sinus pressure measurements,2–4 the cost of different surgical IIH treatments,5 the degree of venographic stenosis leading to intracranial venous hypertension,6 recommendations for selection of patients for stenting and the benefits of this treatment,7–10 among others. However, the term IIH has broadened in both scientific and clinical domains to encompass nearly any clinical syndrome of elevated intracranial pressure not explained by existing diagnoses, leading to a lack of clarity regarding the underlying cause of this rare but important disorder.

Recently, Fargen introduced a timely and updated consideration of the overall pathophysiology of IIH and its relation to intracranial venous hypertension.11 This work is a detailed and thoughtful update on the state of understanding of IIH, in the context of the relationship between intracranial pressure, CSF physiology, and dural venous sinus pressures. In addition to a concise and relevant review of these topics, the author reasons that because there is a relation between central venous pressure, superior sagittal sinus pressure, and intracranial pressure (with or without the effects of venous sinus stenosis), the term IIH should be replaced by chronic intracranial venous hypertension syndrome (CIVHS).

To support this name change, Fargen cites his work and others,12 describing the anatomical distribution of venous pressures from the superior sagittal sinus to the right atrium (in both pathological and non-pathological states) and goes on to define multiple types of CIVHS based on different pathophysiological characteristics. The 'classic' IIH patient with venous sinus stenosis is termed type 1, 'craniocervical origin', in which venous sinus pressure is elevated due to venous stenosis, but downstream of the stenosis the pressure is normal. These patients respond well to venous sinus stenting to alleviate the stenosis and normalize intracranial venous pressures.

CIVHS due to obesity or heart failure is termed type 2, 'central origin'. These patients have globally elevated venous pressures without a focal venous stenosis. Systemic treatment (such as bariatric surgery leading to weight loss) or CSF diversion with a surgical shunt or optic nerve sheath fenestration is the mainstay of treatment, and venous stenting is unhelpful.

Type 3 patients are of 'mixed origin', in which a focal stenosis is present (as in type 1 patients), but central venous pressure is also globally elevated due to factors seen in type 2 patients. The focal stenosis is thus only part of the problem, and stenting alone is not enough, and a multifactorial treatment strategy is required.

Patients with intracranial hypertension due to the after effects of chronic venous sinus thrombosis are categorized as type 4, 'post-venous thrombosis'. It is appropriate to include these patients in the classification given the origin of the disease (the venous sinuses); traditionally these patients were considered separately from other venous sinus disorders despite causing IIH-like symptoms. Treatment for such patients is either through venous sinus stenting (if a focal stenosis is present) or with shunt surgery.

Much is still not known about this challenging disorder. Perhaps most controversial is the 'chicken or egg' relationship between elevated intracranial pressure and intracranial venous hypertension: does the elevated venous sinus pressure (either globally or from a focal venous stenosis) prevent normal CSF flow via the arachnoid granulations, increasing intracranial pressure? Or does an increase in intracranial pressure, when acting on weakened sections of the dural walls of the venous sinuses (such as at the transverse–sigmoid junction), create a focal venous stenosis leading to elevated upstream venous pressures? What constitutes 'normal' intracranial pressure, and what is the effect of obesity, heart failure, and intra-abdominal pressure? What to make of those patients who symptoms and presentation are similar to IIH but fail to meet the accepted modified Dandy criteria, such as a lack of papilledema?13 Fargen suggests the term 'CIVHS spectrum disorder', although caution must be used in extending invasive treatments, such as venous sinus stenting, to those patients in whom objective criteria for treatment outcome (such as visual fields or papilledema) is lacking.

The system described by Fargen provides a useful language to describe the various causes of the elevated intracranial venous pressure that is common among this diverse group of patients. Perhaps just as importantly, it provides a framework for what is still unknown about this disease, and the work ahead of us.

References

Footnotes

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial, or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Commissioned; internally peer reviewed.

  • Data availability statement No data are available.