How to diagnose Idiopathic Intracranial Hypertension (IIH) in a patient with an empty sella?

Diagnosing Idiopathic Intracranial Hypertension (IIH) in Patients with Empty Sella

MRI of the head and orbits is the gold standard for diagnosing IIH in patients with empty sella, as it can detect multiple characteristic findings including posterior globe flattening, optic nerve sheath distention, and transverse sinus stenosis in addition to the empty sella. 1

Diagnostic Approach

Imaging Studies

1. MRI with high-resolution pituitary protocol

   • Primary imaging modality of choice 2
   • Allows visualization of:
     • Empty or partially empty sella (flattened pituitary gland against sellar floor)
     • Herniation of subarachnoid space into sella turcica
     • Pituitary stalk position
     • Optic chiasm assessment

2. MRI Head and Orbits with specific focus on:

   • Posterior globe flattening (56% sensitivity, 100% specificity) 1
   • Intraocular protrusion of the optic nerve (40% sensitivity, 100% specificity) 1
   • Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) 1
   • Enlarged optic nerve sheath (mean 4.3mm in IIH vs 3.2mm in controls) 1
   • Smaller pituitary gland size (mean 3.63mm in IIH vs 5.05mm in controls) 1

3. MR Venography (MRV) of the head

   • Essential to evaluate for:
     • Narrowing of distal transverse sinuses (supportive of IIH diagnosis) 1
     • Exclusion of cerebral venous sinus thrombosis (which can cause secondary pseudotumor cerebri) 1

4. CT Venography (CTV)

   • Alternative to MRV if MRI is contraindicated 1
   • Less preferred than MRI for initial evaluation

Clinical Evaluation

1. Ophthalmologic examination

   • Mandatory assessment for papilledema 1
   • Visual field testing to assess for potential compression of optic chiasm 2
   • Visual acuity testing

2. Lumbar puncture (after normal neuroimaging)

   • Measure opening pressure in lateral decubitus position 1
   • Diagnostic criteria: Opening pressure >250 mm CSF in adults or >280 mm CSF in children 1
   • CSF composition should be normal 1

3. Hormonal evaluation

   • Up to 40% of patients with empty sella may have at least one hormone deficiency 2
   • Evaluate:
     • Growth hormone
     • Thyroid function
     • Adrenal function
     • Gonadal hormones
     • Prolactin

Diagnostic Criteria for IIH

1. Modified Dandy Criteria with updates:

   • Papilledema
   • Normal neurological examination (except sixth nerve palsy)
   • Normal brain parenchyma on imaging (no mass, hydrocephalus, or abnormal meningeal enhancement)
   • Normal CSF composition
   • Elevated lumbar puncture opening pressure (>250 mm CSF in adults) 1

2. In absence of papilledema, IIH can be diagnosed based on neuroimaging findings:

   • Empty sella
   • Flattening of posterior aspect of globes
   • Distention of perioptic subarachnoid space
   • Transverse sinus stenosis 1

Clinical Pearls and Pitfalls

Pearls:

• Empty sella is found in approximately 30-33% of patients with IIH 3
• The empty sella appearance may be reversible after successful treatment of IIH 4
• Patients with IIH typically have smaller pituitary gland size compared to controls 1

Pitfalls:

• Empty sella alone is not diagnostic of IIH, as it can be found in patients with lateral sinus stenosis presenting with isolated pulsatile tinnitus without signs of intracranial hypertension 5
• Up to 30% of patients with empty sella may have hypopituitarism that requires treatment 2
• Visual impairment in IIH can be insidious and may not be recognized by patients, making objective assessment crucial 6
• Relying solely on CT imaging may miss subtle findings, as it is less sensitive than MRI for pituitary abnormalities 1

Special Considerations

• In atypical presentations (non-obese, male, or older patients), secondary causes of increased intracranial pressure should be thoroughly investigated 1
• Regular monitoring of visual function is essential as visual loss can be halted or occasionally reversed if treatment is begun early 6
• Consider comorbidities that may be associated with IIH, such as polycystic ovary syndrome, anemia, and hypertension 6, 3

By following this comprehensive diagnostic approach, clinicians can effectively diagnose IIH in patients with empty sella and initiate appropriate management to prevent vision loss and reduce symptoms.