Idiopathic intracranial hypertension

Idiopathic intracranial hypertension (IIH), often referred to as pseudotumor cerebri or benign intracranial hypertension, is a condition of unknown etiology that manifests with chronically elevated intracranial pressure (ICP). It predominantly affects obese women, especially such who have gained significant weight over a short period of time, but certain drugs (growth hormones, tetracyclines, excessive vitamin A) are also associated with the condition. The most common symptoms are diffuse headaches, although various visual symptoms and pulsatile tinnitus are also common. Ophthalmologic examination is crucial for confirming the diagnosis and usually reveals bilateral papilledema and possibly loss of vision. MRI is often done to rule out other causes of increased ICP. Lumbar puncture typically shows an elevated opening pressure. Acetazolamide is the first-line therapy, whereas surgery is only used as a last resort. Even with treatment, the condition often worsens over the course of months to years, and permanent symptoms are common.

• Predominantly affects obese women aged 15–44 years ^[1][2]

Epidemiological data refers to the US, unless otherwise specified.

• Idiopathic
• Risk factors ^[1][2]
  • Female sex
  • Obesity
  • Certain medications (drug-induced intracranial hypertension), including:
    • Growth hormone
    • Tetracyclines
    • Excessive vitamin A or derivatives ^[3][4]
    • Danazol

A female TOAD: female sex, Tetracyclines, Obesity, excessive intake of vitamin A, and Danazol are the major risk factors for pseudotumor cerebri.

• Modified Dandy criteria: used to diagnose idiopathic intracranial hypertension ^[5]
  1. Symptoms of increased ICP (e.g., headache, visual changes, pulsatile tinnitus, papilledema)
  2. Absence of localizing neurologic 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 cerebrospinal fluid pressure (> 20 cm H₂O)
       • Neuroimaging showing an empty sella turcica, an optic nerve sheath with filled out CSF spaces, and/or smooth-walled nonflow-related venous sinus stenosis or collapse
  4. Awake and alert
  5. No other apparent cause of intracranial hypertension

• A mismatch between production and resorption of CSF (cause unknown) → ↑ ICP → damage to structures of the CNS and especially to the optical nerve fibers
• Orthograde axoplasmic flow stasis at the optic nerve head leads to bilateral papilledema.

References:^[6]

• Diffuse headaches
• Visual symptoms
  • Transient vision loss
  • Photopsia
  • Retrobulbar pain
• Pulsatile tinnitus (swishing sound)
• Cranial nerve disorders (especially CN VI → diplopia)
• Back pain ^[7]
• No cognitive impairment

References:^[8]

The following tests should always be performed: ^[9][10]

• Ophthalmologic examination
  • Ophthalmoscopy: bilateral papilledema
  • Visual field test may show an enlarged blind spot and peripheral loss of vision
• MRI: with contrast and MR venography (MRV)
  • To rule out other causes of increased ICP
  • Shows
    • Unremarkable brain parenchyma
    • Possible abnormalities of the sclera and/or optic nerve (e.g., scleral flattening)
    • Empty sella: an empty appearing sella turcica in cross-sectional imaging as a result of CSF displacing cerebral tissue (mainly due to shrinkage of the pituitary gland)
    • Possible cerebral venous sinus stenosis (especially transverse sinus)
• Lumbar puncture (LP)
  • Routinely performed for diagnostic and therapeutic purposes, despite increased intracranial pressure ^[11]
  • Exclusion of an intracerebral mass or obstructive hydrocephalus prior to LP
  • May show
    • Elevated opening pressure > 20 cm H₂O (with the patient lying on the side, legs extended) ^[12]
    • Normal CSF analysis with no signs of inflammation or bleeding
  • Temporary headache relief may be reported by the patient after LP.

In communicating hydrocephalus (e.g., in IIH), there is no pressure difference between the ventricles and subarachnoid space. Therefore, a decrease in intracranial pressure poses little risk of herniation. Unlike in meningitis, papilledema and other signs of increased intracranial pressure are not a contraindication for LP in IIH.

• General measures
  • Discontinue any offending agents.
  • Weight loss
• Medical therapy (first-line)
  • Acetazolamide
  • Add furosemide if acetazolamide alone is not sufficient
  • Alternative: indomethacin ^[13]
• Surgery: if conservative measures fail
  • Optic nerve sheath fenestration for visual loss: small patches of dura surrounding the optic nerve are removed, allowing CSF to drain into the periorbital fat
  • CSF shunt

References:^[6][8][10]

• IIH typically worsens over months to years, until the condition stabilizes.
• Even with treatment, many patients will have persistent symptoms (up to 79%). ^[14]
• Severe loss of vision (or even blindness) occurs in up to 24% of patients. ^[15]