Commonly asked questions: imaging stroke and other types of neurovascular disorders

Abstract

The medical management of patients requiring imaging of the head is often complex. This is confounded by growth and development of neuroimaging technology. Summarizing established guidelines and provided answers to commonly asked questions about neurovascular imaging may aid in providing efficient medical care. Noncontrast head computed tomography (CT) is usually the first line in imaging because of its speed and wide-spread availability. More advanced techniques are reserved for more specific questions or when the CT head is non-diagnostic. MRI is the modality of choice for indications that include chronic headache, pulsatile tinnitus, and cerebrovascular diseases including stroke in the subacute or chronic setting. The imaging of stroke is evolving and many advanced techniques including CT and magnetic resonance perfusion are playing an increasing role in diagnosis. Digital subtraction angiography is widely accepted as the gold standard for evaluation of vascular pathology including aneurysm, vascular malformations, Moyamoya syndrome, carotid stenosis and dissection; and offers treatment options. Alternatives such as MR angiography, MR venography, and CT angiography offer similar sensitivity and specificity to conventional digital subtraction angiography. Safety considerations are an important concern. When using iodinated and gadolinium contrast agents, there are potential complications including allergic reactions, lactic acidosis, and nephrogenic systemic fibrosis. Impaired renal function requires modification in the use of contrast during neuroimaging. Neuroimaging during pregnancy is also discussed.

Keywords::

• carotid artery dissection
• carotid stenosis
• contrast allergy
• headache
• moyamoya
• nephrogenic systemic fibrosis
• pregnancy
• pulsatile tinnitus
• sinus thrombosis
• stroke
• subarachnoid hemorrhage

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Stroke or stroke-like symptoms are evaluated with noncontrast head computed tomography (CT). This is still the most expeditious choice for thrombolytic therapy selection in most hospitals. When available in a timely fashion, magnetic resonance (MR) offers greater sensitivity and specificity.

• Both CT and MR perfusion techniques demonstrate regional hypoperfusion abnormalities. Combining MR perfusion and DWI results may show an area of potentially reversible ischemia, penumbra. CT perfusion can also demonstrate the region of penumbra. While the role of these modalities in patient selection for intervention is still unclear, preliminary evidence suggests if an area of penumbra is identified, then the patient may benefit from thrombolytic therapy.

• Although carotid Doppler ultrasound is the most popular study for the evaluation and diagnose of significant carotid artery stenosis, MR angiography (MRA), CT angiography (CTA) and the gold standard digital subtraction angiography (DSA) are appropriate in the proper setting. CTA can be combined with CT perfusion and an acetazolamide challenge to help determine the need for endovascular or surgical intervention in symptomatic patients.

• If spontaneous subarachnoid hemorrhage is present on initial noncontrast head CT, both DSA and CTA are comparable options for further evaluation of potential causes, such as aneurysm or other vascular abnormality.

• Moyamoya syndrome may be idiopathic or secondary to a number of vascular disorders or tumors. DSA is considered the gold standard for diagnosis and additional evaluation. Diagnosis can also be made with MRI/MRA, but this technique may over- or underestimate the degree of stenosis and extent of disease.

• Both MRA and CTA can diagnose and characterize carotid and vertebral artery dissection. In an emergent setting, CT angiography is faster and requires less patient cooperation. MRI/MRA better demonstrates ischemic sequela, but requires patient cooperation.

• There are multiple causes of pulsatile and nonpulsative tinnitus including tumors and vascular malformations. CT temporal bone, MRI IAC protocol and angiography can be utilized to fully evaluate symptoms and give an accurate diagnosis.

• Sinus thrombosis can be diagnosed with either CT venography or MR venography. MRI/MR venography demonstrates sequela such as venous infarction, edema and vascular congestion.

• Allergic reactions to iodinated or gadolinium contrast are reduced by pretreatment with steroid and anti-histamine.

• Guidelines for the use of iodinated contrast in patients who take metformin include monitoring renal function, holding metformin for a defined time period and hydrating the patient.

• MRI and CT neuroimaging can be safely used during pregnancy.

• Gadolinium should not be used in patients on dialysis or with estimated glomerular filtration rate <30 due to the risk of nephrogenic systemic fibrosis.

• Cautiously use iodinated contrast in patients with renal insufficiency.

Notes