Venous Sinus Stenosis (VSS) and it's role in IIH

What is a venous sinus? Like other parts of the body, the brain also has veins. Veins are vessels (small tubes) that are part of the circulatory system that drains blood from the tissue back to the heart. In the skull, the veins drain into the venous sinuses before going down to the veins in the neck. The difference between a vein and a venous sinus is that a venous sinus has no valves and it also drains cerebrospinal fluidFluid that is made by specialized cells in the ventricles of the brain. Click the term to read more (CSFFluid that is made by specialized cells in the ventricles of the brain. Click the term to read more). There are several venous sinuses throughout the brain cavity and are found between the outer covering of the brain (dura) and the skull.

The cerebrum, cerebellum and brainstem are all drained by veins which empty into the dural venous sinuses. Within the dura mater – the dural venous sinuses lie between the periosteal & meningeal layers. The scalp, face and CNS are all drained into this system of sinuses. These sinuses are unique however as they do not contain valves.

There are 11 venous sinuses in total. The straight, superior, and inferior sagittal sinuses are found in the falx cerebri of the dura mater. They meet at the confluence of sinuses. The straight sinus is a continuation of the great cerebral vein of Galen and the inferior sagittal sinus. From the confluence, the transverse sinus continues bi-laterally and curves into the sigmoid sinusTermed for its s-shaped anatomy, the sigmoid sinus is a long vessel that runs along the inside of the skull like a long winding road Click the term to read more to meet the opening of the internal jugular vein.⁣⁣ The cavernous sinus drains the ophthalmic veins and can be found on either side of the sella turcica. From here, the blood returns to the internal jugular vein via the superior or inferior petrosal sinuses. Watch how venous drainage of the brain works!

This image shows the veins and main sinuses draining the brain down to the veins of the neck. The red arrows point to stenosis of the transverse sinuses seen in IIH.

When the venous sinuses are narrowed or blocked, it can affect the pressure in the brain and the flow of blood and CSF throughout the brain. If the venous sinuses are narrowed (stenosed) it can cause an increased pressure in the brain and impaired drainage of cerebrospinal fluid and deoxygenated blood in the brain. This process will cause a person to experience debilitating headaches, visual changes, papilledemaSwelling of the optic nerve that carries visual signals from the eye to the brain. Click the term to read more, have an increased opening pressure on lumbar punctureA procedure where a needle is placed in the lower part of the spine (the lumbar spine) to access cerebrospinal fluid. Click the term to read more, and countless other symptoms. These described findings and many other symptoms are seen in IIH.

The reason why a venous sinus would become narrowed is not fully known. The current theory is there is an enlargement of the arachnoid villi in the brain. The arachnoid villi is what helps move CSF into the bloodstream. If these villi increase in size, it will decrease the size of the vessel¹.

Using a Venn diagram, Dr. Pierre Gobin created a visual representation of how many common signs and symptoms of venous sinus stenosis are interrelated. The areas where the circles overlap shows a commonality between those two items. For example, a person IIH can have papilledema with visual field changes yet another person can have visual changes without papilledema.

Some people may have one, two, or a combination of described signs and symptoms but to receive a diagnosis IIH, the modified Dandy criteriaCriteria used for diagnosing patients with IIH. Click the term to read more is used:

Signs and symptoms of increased pressure within the brain or papilledema without an identifiable cause
Intracranial pressure is increased when measured in lateral decubitus position. This is obtained by performing a lumbar puncture and the opening pressure is measured at or greater than 25 cm of H20.
The composition of cerebrospinal fluid is normal: clear appearance, WBC count 0-5 cells/µL, glucose >60% of serum glucose, and protein <45 mg/dL
No evidence of hydrocephalus, tumor, infection, structural or vascular lesion
Other conditions associated with increased intracranial pressure are ruled-out²

The most reported signs of IIH are: headache and pulsatile tinnitusA whooshing or throbbing noise heard in one or both ears that can range from annoying to debilitating. Highly associated with venous sinus stenosis. Click the term to read more. There are other symptoms experienced with IIH such as chronic fatigue, loss of libido, cognitive impairment, dizziness and nausea. These other symptoms will be combined and labeled as various signs and symptoms (Vspt) for the duration of this article.

VFL: visual field loss PO: papilledema; OP: high opening pressure; HA: headaches VSpt: various symptoms; PT: pulsatile tinnitus; CSFI: cerebrospinal fluid leak (CSFI)

This picture is complex so we will go step-by-step on how the various signs and symptoms of venous sinus stenosis are related to IIH.

In IIH, Visual Field Loss (VFL) is secondary to papilledemaSwelling of the optic nerve that carries visual signals from the eye to the brain. Click the term to read more (PO) especially when pronounced. Visual field loss is at least partially reversible when reducing intracranial pressure as it resolves papilledema. Thankfully most patients with papilledema do not have visual field loss and treating those who have papilledema early will avoid visual field loss. A few patients with visual field loss will not have papilledema, these patients have irreversible optic nerve atrophy due to long-standing severe papilledema.

High opening pressure (OP) on lumbar punctureA procedure where a needle is placed in the lower part of the spine (the lumbar spine) to access cerebrospinal fluid. Click the term to read more is mandatory to define IdiopathicThe term idiopathic is used when there is no detectable reason for something. Click the term to read more Intracranial Hypertension (IIH). A high opening pressure is defined as greater than 25 cm H2O in obese patients (a BMIA value derived from the mass (weight) and height of a person. A healthy range is between 18.5-24.9, overweight is defined as 25-29.9 and obese… Click the term to read more of greater than 30) and an opening pressure of greater than 20 cm H2O in normal weight patients. All patients with papilledema will have a high opening pressure. Patients with visual field loss from optic nerve atrophy due to history of IIH that has receded may not have a high opening pressure.

VFL: visual field loss; PO: papilledema; OP: opening pressure

In this picture headaches (HA) are added to the figure. Headaches from venous sinus stenosis (VSSA minimally invasive surgery during which a metallic mesh in the shape of a tube (stent) is placed in the sinus. Click the term to read more) are a consequence of increased intracranial pressure. In the context of venous sinus stenosis, if the opening pressure during lumbar puncture is not increased then the headaches are due to other causes and will not improve with venous sinus stentingA minimally invasive surgery during which a metallic mesh in the shape of a tube (stent) is placed in the sinus. Click the term to read more. Note: almost all patients with papilledema have headaches, but not all.

VFL: visual field loss; PO: papilledema; OP: high opening pressure; HA: headaches

Here the various symptoms (VSpt) that accompany idiopathic intracranial hypertension (IIH) are added to the diagram. Patients with IIH describe a wide range of additional symptoms such as chronic fatigue, loss of libido, cognitive impairment, dizziness and nausea. These symptoms are often associated with a headache but are a distinct entity. These various symptoms are frequent in the population outside of IIH, so they must be associated with a high opening pressure to be attributed to venous sinus stenosis (and potentially improved by venous sinus stenting).

VFL: visual field loss; PO: papilledema; OP: high opening pressure; HA: headaches; VSpt: various symptoms

Pulsatile tinnitus (PT) is a symptom of venous sinus stenosis, not of IIH or a high opening pressure. Pulsatile tinnitus is a frequent symptom of IIH because both are due to venous sinus stenosis, but pulsatile tinnitus does exist without IIH or a high opening pressure. However, when exploring patients with isolated pulsatile tinnitus, it is not unusual to find on MRI some signs of IIH -such as empty sella turcica.

VFL: visual field loss; PO: papilledema; OP: high opening pressure; HA: headaches; VSpt: various symptoms; PT: pulsatile tinnitus

Cerebrospinal fluidFluid that is made by specialized cells in the ventricles of the brain. Click the term to read more leak (CSFl) is rare. Venous sinus stenosis must be suspected especially when cerebrospinal fluid leak recurs after surgical repair. A cerebrospinal fluid leak is a way for the brain to decrease intracranial pressure, opening pressure on lumbar puncture may be normal, and symptoms of IIH such as headache may improve. The sequence of headaches improving when the cerebrospinal fluid leak appears then recurring after surgical repair is a characteristic that is distinctive for venous sinus stenosis. Venous sinus stenting is very effective in preventing recurrences of cerebrospinal fluid leak. As with pulsatile tinnitus, when exploring patients with cerebrospinal fluid leak it is not unusual to find on MRI some signs of IIH.

With continued research into the causes of Idiopathic Intracranial Hypertension, more identifiable causes are being discovered. Venous sinus stenosis has been found in many patients with IIH and they have found significant improvement of signs and symptoms with venous sinus stenting³. As more investigation continues in this disease, there is hope to find more interventions to reverse and resolve IIH.

References

Venous Sinus Stenosis. Dr. Athos Patsalides. Accessed October 1, 2022. https://www.athospatsalidesmd.com/venous-sinus-stenosis-interventional-neuroradiologist-new-york-ny.html
Friedman D, Liu G, Digre K. Revised diagnostic criteria for the pseudocerebri syndrome in adults and children. Neurology. August 21, 2013;81(13):1159-1165.
Daggubati LC, Liu KC. Intracranial Venous Sinus StentingA minimally invasive surgery during which a metallic mesh in the shape of a tube (stent) is placed in the sinus. Click the term to read more: A Review of IdiopathicThe term idiopathic is used when there is no detectable reason for something. Click the term to read more Intracranial Hypertension and Expanding Indications. Cureus. 2019 Feb 4;11(2):e4008. doi: 10.7759/cureus.4008.

Edith Ruiz, PA-C

Edith Ruiz, PA-C is a certified physician assistant with over 14 years of clinical experience, including the care of neurological surgery and bariatric surgery patients. Additionally, she has several years of experience as a medical writer for healthcare companies to help connect patients to medical information.

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