Idiopathic Intracranial Hypertension (IIH)

A review of imaging manifestations and interventional treatment

J. Agraval1, B McGuinness1, S Brew1, A Hope1, M Moriarty1, 1Auckland City Hospital, Auckland, New Zealand

Definition

Raised intracranial pressure in the absence of an identifiable aetiology

Theories of aeitology 1,2

1. CSF homeostasis: Inadequate CSF resorption or increased production

2. Venogenica. Venous sinus thrombus

b. Extrinsic venous compression

c. Vasculitis

3. Venous outflow obstruction i.e. Venous sinus stenosis

Controversial regarding whether this is a causal factor or an effect

Cause or effect?Increased

intracranial pressure Intracranial

hypertension

Compression of the collapsible

transverse sinus

Venous outflow obstruction

Venous hypertension

Decreases CSF reabsorption

EpidemiologyThought to be rare (1 case per 100,000 5 ) but increasingly diagnosed due rising prevalence of obesity

Female predominance 8:1 5

“Classic patient”= Overweight woman of reproductive ageIncidence in 20-44y/o overweight women

19 per 100,000 5

Increased estrogen and leptin is also present in overweight patients with IIH

Obesity = substantial risk factor. Theories 1,3,

Increased BMI Increased intrathoracic and intrabadominal pressure elevated central venous pressure

Prothrombotic state in obesity

Increased leptin and estrogen levels in patients with IIH

IIH in Men – epidemiology 6

Older age group often >40 years

Symptom profilesLess likely to report headache

More common to report visual disturbance

Worse visual outcomes: acuity and visual fields

Increased risk of severe visual loss

No differences in BMI Smaller case series describe men less likely to be overweight but BMI not reported

Diagnosis 4

Symptoms and signs related to raised intracranial pressure

CSF opening pressure >25cmH20

Normal CSF composition

No evidence for underlying structural cause MRI with MR venography ideal

Typical Presentation 1

Headaches most common >90%Pressure-like unrelenting

Associated retro-orbital pain

Visual loss – most commonly transient Tunnel vision

Related to transient ischemia of the optic nerve from the increased CSF pressure in optic nerve sheath

Papilledema – often seen in routine or symptomatic visual testing

Typical Imaging findings

- Empty sella: downward herniation of an arachnocele through the diaphragma sella

- Posterior scleral flattening with enlarged and tortuous optic nerve sheaths

- Distal transverse venous sinus stenoses

MR venography

Should be routine in suspected cases to evaluate for either thrombus or stenosis1,12

• Stenosis can be seen in up to 90% of IIH patients12

TOF or PC MRV is usually inadequate and contrast enhanced MRV should be performed

It is the authors personal experience that where contrast MRV is not available, 3D gradient post contrast T1 reformatted in sagittal and coronal planes often enables accurate diagnosis of venous stenoses

CT venography is also a suitable test

Typical Imaging Findings23 year old female with headache, intermittent pulsatile tinnitus and visual disturbance

CSF distension of optic nerve sheaths with posterior scleral indentation on axial T2. Marked concavity to the superior surface of the pituitary on coronal T2 and sagittal T1. Fluid distension of the oculomotor cisterns has also been suggested as a sign of IIH (red arrows).

Venous Stenoses

37 year old male with IIH and typical distal transverse sinus stenoses on contrast MRV 18 year old female with IIH and in

addition to typical distal transverse sinus stenoses has a stenosis of the distal superior sagittal sinus which is a less common but recognised site of stenosis in this condition

Other Presentations 1,4

Pulsatile tinnitis Unilateral “whooshing sound”

Exacerbated by positional change

Relieved by jugular compression

Diplopia due to cranial nerve VI palsy

Skull base CSF leaks – sphenoid via lateral sphenoid cephalocele or mastoid via tegmun typani erosion

Lateral sphenoid cephalocele and Spontaneous Skull Base CSF leaks

Lateral sphenoid cephaloceles and other skull base CSF leaks have clinical manifestations and similar imaging findings to IIH 9,10,11

Retrospective review11 shows high recurrence rate of leak post surgical repair in “spontaneous” cephaloceles and leaks, this is improved if the IIH is also managed

Arachnoid pits (arachnoid granulations outside the dural venous sinuses) are commonly seen in these cases

Lateral sphenoid cephalocele

Multiple arachnoid pits within the middle cranial fossae (yellow arrows), small surgically proven cephalocele into lateral recess of sphenoid sinus (red arrow) with mild edema or gliosis in the adjacent temporal lobe (green arrow)

Distal transverse sinus stenoses and empty sella appearance suggest background IIH

61 year old female presents with recurrent bacterial meningitis and left nasal CSF leak

Other Skull Base Leaks and Meningoceles

58 year old male with longstanding headaches & bilateral mastoid CSF leaks. Surgically repaired with subsequent diagnosis of IIH requiring ventricular shunt

T2 coronalBilateral tegmen dehiscence, mastoid effusions and adjacent left temporal lobe edema

63 year old female with headaches. Other sequences showed empty sella and bilateral transverse sinuse stenoses.

Bilateral CSF enlargement of Meckel’s cave particularly on the left

Natural history

Historically thought of as a “benign” condition hence previous name “Benign intracranial hypertension” 1

Severe visual deficits can occur in 25% without treatment 7

Lower quality of life scores, greater incidence of depression and anxiety 8

Goals of management

Cessation of symptoms, in particular restoration of visual acuity and resolution of papilledema

Treatment (1,3,4): conservative

Weight loss

Carbonic anhydrase inhibitors decrease the rate of CSF production

Acetozolamide

Topiromate (partial antagonist)

Simple analgesics to relieve headache symptoms

Therapeutic lumbar puncture: effects often short lived

Treatment: surgical/endovascular

Reserved for patients with ongoing visual loss despite conservative management OR those with rapid symptom onset

3 Options:CSF shunting – ventriculoperitoneal or lumboperitoneal

Optic nerve sheath fenestration (ONSF)

Venous sinus stenting

Dural venous sinus stenting 3,4

Retrograde transvenous manometry is performed with patient awake as general anaesthesia can give false negative results

threshold for treatment if a gradient >8mm-10mmHg

Only one side needs stenting – usually dominant side

Premedication with dual antiplatelet medication required. The authors continue this for 3 months following stenting then switch to aspirin alone.

Stenting - Technical Issues

Stent trackability – carotid stents are typically used and navigation around the distal sigmoid and jugular bulb is often challenging. A long sheath is essential may need to be tracked intracranially to get stent into position

Post stenting manometry may show transference of stenosis to another site

Trigeminal nerve periorbital referred pain post-stenting is common and may last 2-3 days

Stent During Deployment

Sheath has been advanced to distal sigmoid sinus to enable the stent to track into position

Guidewire tip is in distal superior sagittal sinus with “J” tip to prevent engagement of cortical veins

Stenting Efficacy and Outcome

No prospective or randomized controlled trials

Retrospective cases series (largest 52 patients) suggest stenting is effective in improving symptoms and preserving vision3,4

Serious complications are uncommon but include intracranial (usually subdural) hemorrhage

Re-stenosis adjacent to the stent requiring further stenting occurs in approximately 10%3

Concerns exist about longterm stent patency although delayed in-stent stenosis has not been described.

Case: Adjacent Sinus Stenosis57 year old male with severe IIH presenting

as headache and diplopia due to bilateral VI nerve palsies

Cerebral angiogram shows severe stenosis of the distal superior sagittal sinus and dominant distal right transverse sinus. Right image shows tip and 3cm marker of microcatheter used to perform manometry (red arrows)

Case: Adjacent sinus stenosis

Initial pressure gradient was across the transverse sinus stenosis but after 1st stent was deployed (red arrows) repeat manometry showed transference of pressure gradient to the superior sagittal sinus stenosis and a 2nd stent was deployed (green arrows) with restoration of normal calibre at both sites

57 year old male with severe IIH presenting as headache and diplopia due to bilateral VI nerve palsies

Case: Adjacent sinus stenosis

57 year old male with severe IIH presenting as headache and diplopia due to bilateral VI nerve palsies

Represents 6 months later with recurrence of symptoms and papilloedema. Manometry showed new severe stenosis of mid superior sagittal sinus which was then stented. At 2 years of follow up he remains symptom free with normal vision and no papilloedema

Optic Coherence Tomography (OCT) 14,15

Can be used as an objective assessment of retinal thickness and papilledema to assess response to treatment

Analogous to ultrasound but uses light instead of sound to yield cross sectional images

Provides images on the micron scale Can image the retinal nerve fiber layer (RNFL)

Measure swelling at the optic

Functions as a type of “optic biopsy”

OCT Pre and Post Stenting

Pre-stenting

Post-stenting

Retinal fibre layer thickness (solid line = right eye, dotted line = left eye) is well above the normal range prior to stenting. Near normalization is seen following stenting (right image – small part of left eye is above normal range)

Summary

Posterior scleral indentation, empty sella and distal transverse venous sinus stenoses are typical imaging features of IIH

IIH patients can also present with skull base CSF leaks

Venous stenoses can also occur in the distal superior sagittal sinus

Stenting of the dural venous sinuses is an alternative to shunting for those patients that fail medical treatment

Recurrent stenosis adjacent to stented segments may occur requiring additional stent deployment.

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References

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