A 32-year-old overweight woman meets all clinical criteria for idiopathic intracranial hypertension. To confirm the diagnosis, cerebrospinal fluid opening pressure measured by lumbar puncture in the lateral decubitus position should exceed:

• A 10 cm H2O
• B 18 cm H2O
• C 25 cm H2O ✓
• D 40 cm H2O

Explanation

Modified Dandy criteria require a CSF opening pressure above 25 cm H2O in adults measured with the patient relaxed in lateral decubitus, along with signs of raised intracranial pressure, normal imaging, normal CSF constituents, and no secondary cause. Pressures up to about 18 cm H2O are normal, and 10 cm would be low. A value of 40 cm is far higher than required and would prompt search for a space-occupying lesion if imaging were unavailable.

Reference: Kanski's Clinical Ophthalmology, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.