What are the diagnostic criteria for idiopathic intracranial hypertension?

The revised Friedman criteria (2013) require papilledema, a normal neurologic exam apart from cranial nerve abnormalities, brain imaging with no hydrocephalus, mass or structural lesion, normal CSF composition, and a raised lumbar puncture opening pressure. Without papilledema, the diagnosis can still be made if the other criteria are met and there is a unilateral or bilateral sixth nerve palsy. Supportive MRI signs include an empty sella, flattened posterior globes, distended optic nerve sheaths and transverse sinus stenosis.

What opening pressure is diagnostic of pseudotumor cerebri?

Under the 2013 revised criteria, the lumbar puncture opening pressure must be at least 250 mm CSF (25 cm H2O) in adults and at least 280 mm CSF in children, or 250 mm CSF if the child is not sedated and not obese. The CSF itself should be normal, with no excess cells and normal protein and glucose. The tap is done after brain imaging has excluded a mass, hydrocephalus and venous sinus thrombosis, and before any pressure-lowering treatment.

Why is MR venography needed in suspected IIH?

Cerebral venous sinus thrombosis can mimic IIH, with headache, papilledema and raised intracranial pressure. Venous imaging, either MR venography or CT venography if MRI is unavailable, is therefore required to look for a clot. Telling them apart matters because venous sinus thrombosis is treated with anticoagulation, while IIH is treated with weight loss and acetazolamide. In IIH, the venogram may instead show narrowing of the transverse sinus, a supportive imaging sign.

What is the first-line treatment for idiopathic intracranial hypertension?

Weight loss plus acetazolamide. Weight loss is disease-modifying, and up to 15 percent loss may be needed for remission. Acetazolamide, a carbonic anhydrase inhibitor, reduces CSF production; in the IIH Treatment Trial, adding it to a low-sodium weight-reduction diet modestly improved visual fields, papilledema and quality of life in patients with mild visual loss. Topiramate is an alternative. Causative drugs are stopped, and surgery is reserved for vision that worsens despite medical therapy.

Which drugs can cause pseudotumor cerebri?

Classic triggers are tetracyclines such as doxycycline and minocycline, excess vitamin A and retinoids such as isotretinoin, growth hormone, and withdrawal of long-term corticosteroids. Others include lithium, nitrofurantoin, nalidixic acid, anabolic steroids, ciclosporin and the levonorgestrel implant. The isotretinoin label warns against combining it with tetracyclines because cases of intracranial hypertension have occurred, some with both drugs. When a drug is the cause, stopping it is part of treatment.

Can idiopathic intracranial hypertension cause blindness?

Yes. Permanent vision loss is the most serious complication, and once vision is lost it usually does not return, even after the pressure is lowered. Loss typically begins in the peripheral visual field, so visual acuity can stay normal while the fields shrink. That is why patients need formal visual field testing and fundus exams at diagnosis and during follow-up, and why worsening vision despite medical therapy prompts optic nerve sheath fenestration, shunting or venous sinus stenting.

IIH (Pseudotumor Cerebri): 3 Tips, Criteria & Treatment

Idiopathic intracranial hypertension (IIH), also called pseudotumor cerebri, is raised intracranial pressure with no mass lesion or hydrocephalus and normal CSF composition, seen mostly in women of childbearing age with obesity. It causes daily headache, transient visual obscurations, pulsatile tinnitus and horizontal diplopia from a CN VI palsy, and the exam shows papilledema, usually bilateral. Diagnose it with MRI plus MR venography first (to exclude a mass and venous sinus thrombosis), then a lumbar puncture showing an opening pressure of at least 250 mm CSF (25 cm H2O) in adults with normal CSF contents. Treatment is weight loss plus acetazolamide, with surgery if vision worsens despite medical therapy, because permanent vision loss is the complication that matters.

Tip 1: Recognize the patient and the symptoms

Who gets it. Mostly women of childbearing age. Incidence is about 1 per 100,000 in normal-weight women but 20 per 100,000 in women with obesity (Merck). More than 80% of patients are female, and about 85% are diagnosed before age 45 (ACNR review). PCOS and obstructive sleep apnea are associated conditions.

Symptom	How often (ACNR review)	What to know
Headache	75-94%	Daily or near daily and generalized; the pattern varies and can mimic migraine or other primary headaches
Transient visual obscurations	68-72%	Brief dimming or blacking out of vision
Pulsatile tinnitus	52-60%	A whooshing sound in time with the pulse
Back pain / neck pain	53% / 42%	Common but nonspecific
Visual loss or blurring	32%	Field loss starts in the periphery
Horizontal diplopia	18%	From a CN VI (abducens) palsy

The exam. Bilateral papilledema is common, although a few patients have unilateral or no papilledema. A partial CN VI palsy may be present; otherwise the neurologic exam is normal. Raised pressure impairs the abducens nerve along its long intracranial course, so the palsy reflects the raised pressure rather than a focal lesion along the nerve's path (a "false localizing" sign). Visual acuity is a poor early warning: Merck stresses checking visual fields and fundi, because acuity is not sensitive enough to flag impending vision loss.

Atypical patient? Look harder for a secondary cause when the patient does not fit the usual phenotype, for example a man or someone with a BMI under 30.

Tip 2: Image first, then tap, and know the criteria

Order of tests:

Fundoscopy and formal visual fields.
MRI of the brain with MR venography (CT with CT venography if MRI is not available). The 2018 UK consensus makes venous imaging (CT or MR venography) mandatory to exclude cerebral venous sinus thrombosis, the key mimic, which causes the same headache and papilledema but is treated with anticoagulation.
Lumbar puncture after imaging: measure the opening pressure and send cell count, protein, glucose and cultures.

Revised (Friedman 2013) diagnostic criteria for pseudotumor cerebri syndrome:

	Criterion
A	Papilledema
B	Normal neurologic exam except for cranial nerve abnormalities
C	Neuroimaging: normal brain parenchyma with no hydrocephalus, mass or structural lesion
D	Normal CSF composition
E	Opening pressure ≥250 mm CSF in adults; ≥280 mm CSF in children (≥250 mm CSF if the child is not sedated and not obese)

Definite IIH: all of A-E.
IIH without papilledema: B-E plus a unilateral or bilateral CN VI palsy.
Probable: A-D met, but the opening pressure is below the cutoff.
Suggested only: B-E with neither papilledema nor CN VI palsy, plus at least 3 of 4 MRI signs: empty sella, flattening of the back of the globe, distended perioptic subarachnoid space, transverse venous sinus stenosis.

The older modified Dandy criteria required signs and symptoms of raised ICP, no localizing findings on neurologic exam, normal neuroimaging apart from evidence of raised CSF pressure, an awake and alert patient, and no other cause of raised ICP. The headache classification (ICHD-3) uses similar cutoffs: CSF pressure above 250 mm CSF, or above 280 mm CSF in obese children. On exams, "opening pressure above 25 cm H2O with normal CSF" is the classic phrase.

Quick recall: PRESSURE

Papilledema
Raised opening pressure (25 cm H2O or more in adults)
Empty sella on MRI (a clue, not a separate diagnosis; compare empty sella syndrome)
Sixth nerve palsy
Secondary causes excluded (drugs, venous sinus thrombosis)
Usually a young woman with obesity
Radiology shows no mass or hydrocephalus
Everything else in the CSF is normal

Tip 3: Treat to protect vision

Vision loss is the complication that matters. Merck calls permanent vision loss the most serious consequence: once vision is lost, it usually does not return, even after ICP is lowered.

Stop the trigger. Discontinue any causative drug (see the table below).
Weight loss is disease-modifying. Up to 15% weight loss may be needed for remission. In a trial summarized in the ACNR review, bariatric surgery lowered ICP more than a community weight-management program, an effect sustained at 2 years. Merck notes that bariatric surgery with sustained weight loss may cure IIH in patients with obesity who could not lose weight otherwise (eg, with GLP-1 receptor agonists). GLP-1 receptor agonists are promising but not an established IIH treatment: a 2025 systematic review found mostly retrospective data and only one small randomized trial (exenatide lowered ICP).
Acetazolamide, a carbonic anhydrase inhibitor, reduces CSF production. In the IIH Treatment Trial (NORDIC, JAMA 2014), 165 patients with mild visual loss received a low-sodium weight-reduction diet plus acetazolamide (up to 4 g/day) or matching placebo for 6 months. Acetazolamide modestly improved visual field function (perimetric mean deviation +1.43 dB vs +0.71 dB with diet alone; difference 0.71 dB, P = .05) and also improved papilledema grade and vision-related quality of life. Only 44% of participants reached 4 g/day. Expect paresthesias, altered taste, fatigue, nausea, diarrhea and, rarely, kidney stones.
Topiramate, another carbonic anhydrase inhibitor, is an alternative that suppresses appetite and can help headache; it can reduce the efficacy of hormonal contraceptives and carries teratogenic risk.
Headache care: NSAIDs as needed and migraine preventive drugs; avoid opioids. Serial lumbar punctures are not a long-term treatment (Merck calls them controversial; the ACNR review advises against them).
Surgery when vision deteriorates despite medical therapy: optic nerve sheath fenestration (ONSF), CSF shunting (ventriculoperitoneal or lumboperitoneal) or venous sinus stenting of a narrowed transverse sinus. The 2018 UK consensus preferred a VP shunt when CSF diversion is needed, noted that ONSF is used more in the US and Europe, and called the role of stenting not yet established. The evidence for all three procedures is still observational: a 2026 meta-analysis of 17 non-randomized studies found similar visual improvement after stenting and VP shunting (about 84%) and called for prospective comparative studies.
Follow-up: repeat formal visual field testing and fundus exams to judge response.

Secondary causes and drugs to exclude

These produce the same syndrome, so remove or treat the cause:

Category	Examples
Antibiotics	Tetracyclines (tetracycline, doxycycline, minocycline), nitrofurantoin, nalidixic acid
Vitamin A family	Excess vitamin A and retinoids such as isotretinoin; the isotretinoin label says to avoid combining it with tetracyclines
Hormones	Growth hormone, corticosteroid withdrawal after prolonged use, anabolic steroids, levonorgestrel implant
Other drugs	Lithium, ciclosporin
Venous outflow	Cerebral venous sinus thrombosis, jugular vein thrombosis
Medical conditions	Obstructive sleep apnea, severe iron-deficiency anemia, Addison disease, hypoparathyroidism, renal failure, right heart failure with pulmonary hypertension, PCOS

Vitamin A toxicity and its other features are covered in fat-soluble vitamins (A, D, E, K).

How USMLE tests it

Trap	What to remember
Doing the LP first	Image first (MRI with MR venography), then LP
Missing venous sinus thrombosis	Same headache and papilledema; MR or CT venography shows the clot; the treatment is anticoagulation
Acne patient with a new headache	Tetracyclines or isotretinoin, especially taken together
Normal visual acuity	Fields are lost first, and lost vision usually does not return
Abnormal CSF	Raised cells or protein point away from IIH, for example toward chronic meningitis
Focal deficits other than cranial nerve palsies	Not IIH; look for a structural cause

For the primary headache patterns that IIH can resemble, compare migraine vs tension vs cluster headache.

Practice question

A 27-year-old woman has 3 months of daily generalized headaches, a whooshing sound in both ears that pulses with her heartbeat, and brief episodes in which her vision grays out. She has taken oral minocycline for acne for 6 months. BMI is 37 kg/m2. Fundoscopy shows bilateral optic disc swelling, and she cannot fully abduct the left eye; the rest of the neurologic exam is normal. Visual acuity is 20/20 in both eyes, and automated perimetry shows mild peripheral field loss in both eyes. MRI of the brain with MR venography shows no mass, hydrocephalus or venous sinus thrombosis, with flattening of the posterior globes and a partially empty sella. Lumbar puncture opening pressure is 34 cm H2O, with normal cell count, protein and glucose. Which is the most appropriate next step in management?

A. Stop minocycline and start acetazolamide with a weight-loss program

B. Start therapeutic heparin

C. Optic nerve sheath fenestration

D. Schedule weekly lumbar punctures

E. Reassure her and repeat the MRI in 6 months

Answer: A. She meets the criteria for pseudotumor cerebri syndrome (papilledema, CN VI palsy, normal imaging apart from supportive signs, normal CSF, opening pressure above 25 cm H2O). Minocycline, a tetracycline, is a known trigger and should be stopped, and her mild visual loss matches the IIH Treatment Trial population, in which acetazolamide plus a low-sodium weight-reduction diet modestly improved visual field function.

B: heparin treats cerebral venous sinus thrombosis, which the MR venogram excluded.
C: surgery (ONSF, shunting or stenting) is for vision that deteriorates despite medical therapy, not first-line for mild field loss.
D: serial LPs are not a long-term treatment.
E: papilledema with field loss needs treatment now; vision that is lost usually does not come back.

Key takeaways

IIH = raised ICP, no mass or hydrocephalus, normal CSF, classically in a woman of childbearing age with obesity.
Headache, transient visual obscurations, pulsatile tinnitus and horizontal diplopia (CN VI), with bilateral papilledema.
MRI with MR venography first (exclude venous sinus thrombosis), then LP: opening pressure ≥250 mm CSF in adults, ≥280 mm in children (≥250 mm if not sedated and not obese).
Without papilledema, a CN VI palsy is required to make the diagnosis.
Triggers: tetracyclines, vitamin A and isotretinoin, growth hormone, corticosteroid withdrawal, lithium.
Weight loss plus acetazolamide (IIH Treatment Trial); topiramate is an alternative; ONSF, shunting or venous sinus stenting if vision worsens.
Follow visual fields, not just acuity: lost vision rarely returns.