This young woman has evidence of elevated intracranial pressure (ICP), including headache, nausea/vomiting, and papilledema.  Mass lesions are unlikely because MRI is normal.  She is afebrile, has no meningeal signs, and reports symptoms as intermittent, so a CNS infection is unlikely.  Obesity and use of oral contraceptive pills are risk factors for both cerebral venous sinus thrombosis and idiopathic intracranial hypertension (IIH).  Brain magnetic resonance venography is normal, effectively ruling out cerebral venous sinus thrombosis.  Therefore, the most likely diagnosis is IIH.  In IIH, papilledema is characteristic and focal neurologic signs are usually absent, as in this patient.  Visual field defects (eg, peripheral vision loss, enlarged physiologic blind spot) and abducens nerve (CN VI) weakness can sometimes occur.

The pathophysiology involves increased intracranial venous pressure due to impaired reabsorption of cerebrospinal fluid (CSF) by the arachnoid granulations or CSF lymphatic drainage sites; obesity-related increased abdominal and intracranial venous pressure is another proposed mechanism.  Although headaches are commonly cited as the most bothersome symptom of IIH, the most serious complication is vision loss.  Transient visual loss may be related to acute compression of the optic nerve (CN II) in periods of further increased ICP (eg, straining, bending over).  Gradual, permanent vision loss is likely related to optic nerve atrophy that occurs due to chronic compression.

Management includes weight loss and carbonic anhydrase inhibitor therapy (eg, acetazolamide, topiramate).  When medical measures fail or visual field defects are progressive, shunting or optic nerve sheath fenestration is performed to decrease the risk of blindness.

(Choice B)  Intracranial bleeding is a complication of aneurysms or AV malformation of the brain, but these would not cause intermittent symptoms.  Signs of increased ICP would be unusual unless bleeding were to occur; in that case, the headache would have an acute onset and would be quite severe.

(Choices C and E)  Hydrocephalus can lead to an upper motor neuron pattern of weakness (weakness with brisk deep tendon reflexes) due to stretching of the periventricular white matter tracts and urinary incontinence due to damage to the frontal micturition center.  Although this patient has edema of CN II, there is no evidence of hydrocephalus on imaging (ie, ventricles are normal size).

(Choice D)  Seizures are possible complications of brain tumors, but this patient's imaging is normal.

Educational objective:
Idiopathic intracranial hypertension occurs most often in young, obese women and presents with headaches suggestive of a brain tumor, but with normal neuroimaging and elevated cerebrospinal fluid pressure.  The most serious complication is blindness.  Treatment includes weight loss and carbonic anhydrase inhibitors (eg, acetazolamide).  Shunting or optic nerve (CN II) sheath fenestration may be performed in patients experiencing progressive visual defects despite therapy.