What are the high-yield CT scan findings in a young to middle-aged obese woman with suspected idiopathic intracranial hypertension (IIH) presenting with headaches and vision changes?

High-Yield CT Scan Findings in Idiopathic Intracranial Hypertension

While MRI is the preferred imaging modality for IIH, CT can identify several key findings when MRI is unavailable, though it is less sensitive than MRI for detecting the subtle secondary signs of elevated intracranial pressure. 1

Primary Role of CT in IIH

• CT should be performed urgently (within 24 hours) only when MRI is unavailable, followed by MRI when it becomes accessible 2
• The main purpose of CT is to exclude secondary causes of raised intracranial pressure, including hydrocephalus, mass lesions, structural abnormalities, or vascular lesions 2
• CT venography is mandatory within 24 hours to exclude cerebral sinus thrombosis, which is a critical secondary cause that mimics IIH 2

Specific CT Findings in IIH

Empty or Partially Empty Sella

• This represents one of the most recognizable CT findings, where the pituitary gland appears compressed or flattened within an enlarged sella turcica 2, 3
• The mean pituitary gland size is smaller in IIH patients (3.63 mm) compared to controls (5.05 mm) 2

Flattening of the Posterior Globe

• Posterior globe flattening has 56% sensitivity but 100% specificity for IIH diagnosis, making it highly reliable when present 2
• This finding represents deformation of the posterior sclera due to elevated CSF pressure transmitted through the optic nerve sheath 3

Optic Nerve Abnormalities

• Enlarged optic nerve sheath diameter, with mean size of 4.3 mm in IIH versus 3.2 mm in controls 2
• Intraocular protrusion of the optic nerve head has 40% sensitivity but 100% specificity 2
• Optic disk cupping may be visible on high-resolution CT 3

Transverse Sinus Stenosis

• Bilateral transverse sinus stenosis is frequently present and should be evaluated with CT venography 2, 3
• This finding has important implications for potential venous sinus stenting procedures 4

Critical Limitations of CT Compared to MRI

• MRI is significantly more sensitive for detecting secondary signs of increased intracranial pressure including dilated optic sheaths, tortuous or enhancing optic nerves, and subtle posterior globe flattening 1
• MRI provides superior soft tissue contrast resolution and is particularly valuable in pediatric patients 2
• Horizontal tortuosity of the optic nerve (68% sensitivity, 83% specificity) is better visualized on MRI than CT 2
• MRI is superior for evaluating meningeal infiltration and isodense tumors that may be missed on CT 1
• Coronal fat-saturated T2-weighted sequences on MRI are recommended for optimal evaluation of optic sheath dilatation, which cannot be adequately assessed on CT 1

Common Pitfalls

• Normal CT does not exclude IIH—many patients with confirmed IIH have completely normal CT scans, and MRI should still be performed 1
• CT may miss subtle findings that are readily apparent on MRI, potentially delaying diagnosis 2
• In non-obese prepubertal children, cerebral venous sinus thrombosis must be particularly considered, making venography essential in this population 2
• The absence of these findings on CT should never be used to rule out IIH; lumbar puncture with opening pressure measurement remains the definitive diagnostic test after normal neuroimaging 2