What is the difference between idiopathic intracranial hypertension (IIH) and pseudotumor cerebri?

Idiopathic Intracranial Hypertension vs. Pseudotumor Cerebri

Idiopathic intracranial hypertension (IIH) and pseudotumor cerebri are interchangeable terms referring to the same clinical condition, as stated by the American College of Radiology. 1

Definition and Terminology

• IIH and pseudotumor cerebri both describe a disorder characterized by increased intracranial pressure without clinical, laboratory, or radiologic evidence of an intracranial space-occupying lesion, meningeal inflammation, or venous outflow obstruction 2
• The term "primary pseudotumor cerebri syndrome (PTCS)" is specifically known as idiopathic intracranial hypertension in current medical literature 1
• The condition was historically called "pseudotumor cerebri" because it presents with symptoms that mimic a brain tumor (increased intracranial pressure) but without an actual tumor being present 3

Diagnostic Criteria

Both conditions share the same diagnostic criteria, which include:

• Papilledema (swelling of the optic disc) 1
• Normal neurological examination except for cranial nerve abnormalities 1
• Normal brain parenchyma on neuroimaging (absence of mass, hydrocephalus, or abnormal meningeal enhancement) 1
• Normal cerebrospinal fluid composition 1
• Elevated lumbar puncture opening pressure (>250 mm CSF in adults, >280 mm CSF in children, or >250 mm CSF in non-sedated, non-obese children) 1, 4

Patient Demographics

• Most commonly affects overweight females of childbearing age (female-to-male ratio approximately 7:1) 1, 5
• The incidence is rising in parallel with the obesity epidemic 1
• Can also occur in obese males and prepubertal children 1
• Obesity is present in approximately 88% of patients 2

Clinical Presentation

• Headache is the most common presenting symptom (92% of patients) 5
• Other common symptoms include:
  • Transient visual obscurations (brief episodes of vision loss) 6
  • Pulsatile tinnitus (whooshing sound in ears) 6
  • Diplopia (double vision), typically from sixth nerve palsy 3
  • Dizziness and nausea 5
• Papilledema is the hallmark ophthalmologic finding but may not be detected in approximately 21% of patients initially 5
• Atypical presentations may include:
  • Paresthesias, neck/back pain, unilateral headache, vertigo, and nystagmus 5
  • Isolated cranial nerve palsies (including facial nerve palsy in rare cases) 7

Secondary Forms vs. Idiopathic

• When the condition has an identifiable cause, it is termed "secondary pseudotumor cerebri syndrome" rather than IIH 1, 4
• Secondary causes include:
  • Cerebral venous abnormalities such as thrombosis 1
  • Medications (vitamin A, retinoids, steroids, tetracyclines, growth hormone, thyroxine, and lithium) 8, 1
  • Endocrine disorders 1

Imaging Findings

• MRI may show secondary signs of increased intracranial pressure, including:
  • Empty sella (flattening of the pituitary gland) 1
  • Dilated optic nerve sheaths 1
  • Tortuous or enhancing optic nerves 1
  • Flattening of the posterior aspects of the eyeballs 1
  • Transverse sinus stenosis 1
• MRI of the head and orbits is the most useful imaging modality for initial evaluation 8
• CT or MR venography is mandatory to exclude cerebral sinus thrombosis 4

Management Approach

• Treatment has three main principles: treat the underlying disease, protect vision, and minimize headache morbidity 6
• First-line treatment includes weight loss for patients with BMI >30 kg/m² (target 5-15% weight loss) 4
• Acetazolamide is the first-line medication for patients with mild visual loss 8
• Topiramate may help with weight loss and reducing intracranial pressure 8
• Surgical interventions are indicated for patients with severe or progressive visual loss:
  • Ventriculoperitoneal (VP) shunt is the preferred CSF diversion procedure due to lower revision rates 8, 4
  • Optic nerve sheath fenestration is an effective and safe procedure for protecting vision 8
  • Neurovascular stenting may be considered in selected cases 8

Pitfalls and Caveats

• Approximately 27% of patients may not be diagnosed on their initial emergency department visit, especially those with atypical presentations 5
• Serial lumbar punctures are not recommended for long-term management 8
• Treatment failure rates include worsening vision after stabilization in 34% of patients at 1 year and 45% at 3 years 8
• Failure to improve headache occurs in one-third to one-half of treated patients 8
• Patients with IIH often develop migrainous headaches superimposed on headaches from raised intracranial pressure, requiring specific treatment approaches 8