Pseudotumor Cerebri

Etiology

The primary etiology is an accumulation of CSF either through decreased resorption and/or increased production; this leads to elevated intracranial pressure, the source of the associated symptoms and signs.[3] There is no proven cause for decreased resorption or increased production (hence the term idiopathic intracranial hypertension); however, descriptions of the proposed mechanisms are under the pathophysiology section.

Epidemiology

The condition most commonly affects women aged 20-44, with an annual incidence of 19.3/100,000 in those who weigh 20% or more than their ideal body weight. The annual incidence in all women aged 15 to 44 is 3.5 per 100,000. The annual incidence of PTC in the general populace is 0.9 per 100,000.[1] It disproportionately affects women, and when considering only post-pubertal patients, 90% of all cases occur in females. A positive relationship exists between the female sex, elevated BMI, and risk of PTC.[4] Children of both genders are affected equally before puberty (defined as an age of under 12 years old). Obesity less commonly correlates with the pre-pubertal patient.[2] Males aged 12 to 15 years have an annual incidence of 0.8 per 100,000; females aged 12 to 16 years have an annual incidence of 2.2 per 100,000.[5]

Pathophysiology

Proposed mechanisms involve the vascular, hormonal, and cellular systems. Vascular changes are among the most common radiologic findings; transverse sinus stenosis suggests a vascular component. However, the consensus is that this is likely secondary to the increased pressure rather than the cause of the increased pressure; this results in a feed-forward cycle that is relieved by the removal of CSF.[4] Hormonal changes seen include Aldosterone excess (associated with obesity and PCOS), which commonly correlates with PTC and is suggested to affect the mineralocorticoid receptor of the choroid plexus, leading to increased CSF production.[6] Unfortunately, this has not yet achieved validation.[3] Cellular changes seen include increased outflow resistance to CSF, which has been demonstrated in multiple experimental studies and is the leading theory for the causation of PTC. The outflow resistance could be due to an effect of estrogen or retinoic acid (both elevated by increased adiposity) on epithelial cells, leading to less outflow of CSF. Finally, decreased CSF production with aging could explain the predilection of PTC in younger populations. Approximately 600 milliliters are produced daily, but this decreases with increasing age.[3]

History and Physical

The classic historical findings include:

• Headache: any location (bilateral, frontal, retrobulbar), often daily, and sometimes associated with increased severity in the morning and with Valsalva.[7][8] Associated symptoms include nausea, vomiting, and photophobia, as well as neck and back pain. Headaches occur in up to 98% of cases.[9]
• Transient vision loss can be monocular or binocular, partial or complete, and typically lasts for a few seconds at a time. It is likely due to optic disc edema leading to temporary ischemia of the optic nerve. Transient vision loss occurs in up to 70% of cases.
• Diplopia: binocular and horizontal due to cranial nerve VI (abducens) palsy.[1]
• Pulsatile tinnitus: described as a heartbeat or whooshing sound. Tinnitus can be unilateral or bilateral.[10]  This tinnitus is hypothesized to be due to the transmission of vascular pulsations by CSF under increased pressure to the walls of the venous sinuses.[9] Tinnitus occurs in up to 60% of cases.[7]
• Photopsia: described as sudden flashes of light; occurs in up to 54% of cases.[11]
• Persistent vision loss occurs in up to 32% of cases, most of which are untreated.[12]

The classic physical exam findings include the following:

• Papilledema: due to increased intracranial pressure.[8]
• Cranial nerve VI (abducens)/lateral rectus palsy may result in esotropia. The patient may experience horizontal diplopia.[1]
• Visual field loss occurs more frequently than changes in visual acuity.[13] One study found that 96% of patients have vision loss of differing severities. The most common types of vision loss include increased physiologic blind spots and the loss of inferonasal portions of the visual field.[9]

Evaluation

Patient evaluation of those presenting with signs and symptoms of PTC includes neuroimaging, lumbar puncture with opening pressures and CSF analysis, ophthalmoscopy, visual acuity testing, perimetry testing, and complete blood count. 

Neuroimaging

• Magnetic resonance imaging with venography is the preferred modality to rule out other secondary causes of intracranial hypertension. Imaging reveals normal parenchyma and ventricles.[1] Other findings on magnetic resonance imaging that can suggest PTC but are nondiagnostic include transverse sinus stenosis,[3] flattening of the posterior sclera, distension of the perioptic subarachnoid space, empty sella, and vertical tortuosity of the orbital optic nerve.[14]
• Computed tomography can be performed if there are contraindications to magnetic resonance imaging, but it is less sensitive and specific.[9]

Lumbar puncture

• An opening pressure greater than 25cm H2O in adults and greater than 28cm H₂O in children aged 1 to 18, in normal CSF studies and negative neuroimaging, suggests PTC.[2][4]
• CSF analysis should include cell count and differential, glucose, protein, gram stain, and culture. 

Ophthalmologic evaluation

• Ophthalmoscopy evaluates for optic disc edema, known as papilledema. Typically, a higher grade of papilledema corresponds to more severe vision loss.
• Visual acuity testing assesses for visual sequelae of the disease. 
• Perimetry testing is more sensitive regarding vision loss than visual acuity testing.[9]

Complete blood count

• To rule out anemia or lymphoproliferative causes of papilledema.[15]

Diagnosis involves the utilization of the Modified Dandy Criteria [16]:

1. Signs and symptoms of increased ICP

2. The absence of localizing findings on neurologic examination

3. The absence of deformity, displacement, or obstruction of the ventricular system with otherwise normal neurodiagnostic studies, except for evidence of increased CSF (greater than 200 mm water). Abnormal neuroimaging, apart from empty sella turcica, optic nerve sheath with filled-out CSF spaces, and smooth-walled non-flow-related venous sinus stenosis or collapse, should lead to another diagnosis.

4. Awake and alert

5. No other causes of increased intracranial pressure present with CSF opening pressure of 20cm to 25 cm water required at least 1 of the following:

• Pulse-synchronous tinnitus (pulsatile tinnitus)
• Cranial nerve VI palsy
• Frisen Grade II papilledema
• Echography for drusen negative and no other disc anomalies mimicking disc edema present
• Magnetic Resonance Venography with lateral sinus collapse/stenosis, preferably using the ATECO technique
• Partially empty sella on coronal or sagittal views and optic nerve sheaths with filled-out CSF spaces next to the globe on T2 weighted axial scans

Treatment / Management

The mainstays of medical treatment include:

• Diagnostic lumbar puncture: can transiently relieve symptoms or, in some cases, lead to a complete resolution.
• Weight loss: weight loss of 5 to 10% of total body weight has been found to cause remission.[4]
• Carbonic anhydrase inhibitors (acetazolamide): decreases CSF production (up to 50%) and functions as a diuretic.[17]
• Topiramate: classically used for migraine prophylaxis. This medication is useful because it has weak carbonic anhydrase activity and can lead to weight loss.
• Diuretics (furosemide, chlorthalidone): less effective at symptom reduction than carbonic anhydrase inhibitors. When used with carbonic anhydrase inhibitors, it can lead to severe hypokalemia.[4]
• Steroids: can rapidly lower ICP. Caution is recommended as these can cause weight gain and rebound elevated ICP when tapered off. Steroid therapy should only be in cases with severe vision loss or cases refractory to other medical treatments.[1]
(A1)

For cases refractory to medical treatment, surgery can be an option:

• Optic nerve sheath defenestration (optic nerve sheath decompression): involves making slits in the dura and arachnoid posterior to the globe leading to an increased outflow of CSF and decreasing pressure on the optic nerve. This operation is mainly reserved for severe vision loss refractory to medical management.[4]
• CSF diversion: via either a ventriculoperitoneal or lumboperitoneal shunt.[18] CSF diversion is mainly effective in reducing headache symptoms and less effective in correcting vision loss.[4]
(B3)

Differential Diagnosis

The differential diagnosis for PTC includes etiologies that can lead to elevated ICP:

• Cerebral venous sinus thrombosis
• Intracranial mass
• Obstructive hydrocephalus
• Jugular vein compression
• Superior vena cava syndrome
• Decreased CSF absorption (secondary to meningitis or following a subarachnoid hemorrhage)
• Malignant hypertension

Prognosis

The disease prognosis depends on several factors, including:

• The rapidity of onset of symptoms: a more rapid onset requires more aggressive treatment
• Amount of vision loss at presentation: significant loss at the time of presentation suggests a higher risk of permanent vision loss.[19]
• The grade of papilledema at presentation: higher grades suggest a greater risk of permanent vision.[20]

It is not uncommon for this condition to cause symptoms for months to years, even with prompt treatment. Some patients have continued papilledema, increased ICPs, and residual visual field deficits.[13]

Complications

The most concerning complication of PTC is permanent vision loss because of compression of the optic nerve secondary to elevated intracranial pressure.[1] Other complications are mainly related to side effects from treatment of the disease.

• Acetazolamide: hypokalemia, paresthesias of the extremities, and dysgeusia.
• Steroids: weight gain, refractory ICP increase when tapered, and fluid retention.
• Diuretics (furosemide, chlorthalidone): hypokalemia, hypomagnesemia (furosemide), and ototoxicity. 
• Lumbar puncture: infection, damage to surrounding structures, and post-lumbar puncture headache.[4]
• Surgery: infection, diplopia (transient or permanent), and transient or permanent visual loss secondary to central retinal artery occlusion or ischemic optic neuropathy.[18]