Our technique
VWMRI was performed at our institution using a 1.5 T Signa HDxt scanner (General Electric Healthcare, Milwaukee, Wisconsin) with a 16-channel neurovascular head coil. Protocols are shown in Table 1. Presaturations bands were also used to aid the suppression of blood. The acquisition of other sequences or studies varied depending on the clinical context. 34 VWMRI studies were conducted between April 2018 and September 2019. Diagnostic reports and images were gathered and reviewed along with two neuroradiologists.
Table 1: Protocols used in intracranial and extracranial VWMRI studies at our institution.
Pathologies in VWMRI
Atherosclerosis
Plaques are visualized as eccentric non-uniform wall thickening with enhancement (Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6)
Plaque components are seen as:
- The fibrous plaque is iso/hyperintense in T1/T2 and enhances after gadolinium administration
- The lipid core is hypointense in T2 and isointense in T1, without significant enhancement. Its T2 signal is variable, being more hyperintense if it is liquified. Lipid core size and liquefaction are related to increased risk of plaque rupture.
- Sometimes vasa vasorum is seen as an enhancing peripheric rim in the adventitia.
- A plaque hemorrhage is seen as an increase of T1 signal that varies in time, becoming hypointense in 6 weeks.
- Plaque calcification is seen as a loss of signal in T1 and T2.
Vessels can also be dilated, secondary to positive remodeling, which is associated with plaque vulnerability and instability. Negative remodeling is also possible.
Atherosclerosis can affect any artery, but there's a predilection for bifurcation sites.
Fig. 2: 71 years old woman with past medical history of hypertension, chronic smoking and obstructive sleep apnea, presenting with acute transitory left hemiparesis and dysarthria with spontaneus resolve after 30 minutes. Axial CT angiography MIP (A) shows severe right middle cerebral artery stenosis (orange arrowhead). Sagital CUBE T1 BB before (B) and after gadolinium administration (C) shows middle cerebral artery eccentrinc thickening (orange thick arrow) with enhancement (orange thin arrow), which was interpreted as an atherosclerotic plaque.
Vasculitis
It is characterized by a homogeneous, uniform, and concentric (infrequently eccentric) thickening and enhancement of the vessel wall. It can compromise any vessel but has a predilection for medium and small caliber arteries (Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11).
Enhancement is caused by contrast extravasation, secondary to permeability dysfunction of vasa vasorum. Generally, this varies with evolution time and treatment.
Fig. 8: 43 years old male, with medical history of active chronic smoking, hypertension, overweight, presenting with acute left hemiparesis shortly after consuming cocaine. Axial DWI (A) shows acute deep right border zone infarcts (orangle circle). Axial arterial TOF 3D MIP shows severe right terminal carotid segment and right middle cerebral arteries stenosis (orange arrowhead). Sagital CUBE T1 BB before (C) and after (D) gadolinium administration show concentric thickening (orange thick arrow) and enhancement (orange thin arrow). Patient was diagnosed with cocaine-related vasculitis.
Arterial dissection
Double lumen
- Narrowed true lumen, hypointense in black blood sequences
- Pseudolumen containing blood between vessel wall layers, with a crescentic and heterogeneous shape
Intimal flap: hyperintense curved line in T2 splitting both lumen
Intramural hematoma: seen as an eccentric wall thickening, hyperintense in T1, easily detected in SWI images.
- As in intraplaque hemorrhage, findings change over time.
Segmental stenosis (pearl and string)
Dissecting aneurysm formation: irregular dilation of the affected segment, with mixed-signal intensity, bleeding and thrombus formation.
It can affect any artery, but it most frequently comprises the V3-V4 portion of the vertebral artery (Fig. 12, Fig. 13, Fig. 14, Fig. 15).
Fig. 16: 48 years old male with history of hypertension, presenting with transitory right hemiparesis and cervical pain. There were no brain infarcts in the CT and MRI study. Arterial 3D TOF reconstruction (B) shows a small pseudoaneurysm in the left internal carotid artery (orange arrowhead). Axial T1 BB (A and B) shows signs of dissection of the left internal carotid artery with double lumen (orange thick arrow) and intramural hematoma (orange thin arrow).
Reversible cerebral vasoconstriction síndrome
Vasoconstriction is caused by smooth muscle shortening, resulting in an overlap of muscle cells in the wall. In these conditions, a diffuse homogeneous and continuous concentric arterial thickening can be seen, with lesser enhancement than vasculitis. Reversibility is the most specific criterion.
Generally, it compromises medium and small-caliber vessels (Fig. 17).
Fig. 17: 10 years old female with a past medical history of a tectal glioma associated to supratentorial hidrocephalus, treated with endoscopic third ventriculostomy. Axial SWI (A) shows intraventricular hemorrhage (orange circles). Axial arterial TOF 3D MIP (B) shows severe bilateral anterior, middle and posterior cereberal arteries stenosis (orange arrowheads) . Axial T1 BB after gadolinium administration (C) shows no thickening or enhancement. Follow up axial arterial TOF 3D MIP (D) shows complete regression of the previous stenosis. Imagenological diagnosis was vasospasm (non-inflammattory arteriopathy).
Moyamoya disease
This disease is characterized by artery media thinning and lack of inflammatory cells. It is seen as a lack of arterial thickening, with mild concentric enhancement (less than atherosclerosis). Negative remodeling (decrease in external diameter) is also present.
It has a predilection for terminal ICA, proximal MCA, and ACA.
Some studies were not classificable in the previous diseases and were diagnosed as non-inflammatory arteriopathies (Fig. 18, Fig. 19, Fig. 20).
Limitations
The main technical problem in our center is cervical studies, which often show noise artifacts that decrease the quality of the image. This is related to inhomogeneity of the magnetic field caused by the presence of the patient's shoulders, the use of presaturation bands and the strength of the magnetic field.