Date Published: March 8, 2019
Publisher: Public Library of Science
Author(s): Sebastian Eiden, Christopher Beck, Nils Venhoff, Samer Elsheikh, Gabriele Ihorst, Horst Urbach, Stephan Meckel, James West.
Vessel wall imaging (VWI) using T1 dark blood MRI can depict inflammation of intracranial arteries in patients with cerebral vasculitis. Recently, 3D VWI sequences were introduced at 3 Tesla. We aimed to compare 2D and 3D VWI for detection of intracranial vessel wall enhancement (VWE) in patients suspected of cerebral vasculitis.
44 MRI scans of 39 patients were assessed that included bi-planar 2D T1 and whole-brain 3D T1 SPACE dark blood VWI pre and post contrast. Visibility and VWE were analyzed in 31 pre-specified intracranial artery segments. Additionally, leptomeningeal and parenchymal contrast enhancement was assessed.
Overall, more arterial segments were visualized with 3D VWI (p<0.0001). Detection of VWE showed fair agreement between 2D and 3D VWI (κ = 0.583). On segmental level, more VWE was detected in intradural ICA by 2D VWI (p<0.001) and in VA V4 segment by 3D VWI (p<0.05). 3D VWI showed more leptomeningeal (p<0.05) and parenchymal (p<0.01) contrast enhancement. In patients with positive diagnosis of cerebral vasculitis, sensitivity was of 67% (2D and 3D VWI) and specificity was 44% (2D VWI) and 48% (3D VWI); more VWE was seen in arteries distal to VA and ICA compared to non-vasculitic patients. 2D and 3D VWI differed in the ability to detect VWE. Whole brain coverage with better evaluability of VAs and distal intracranial artery segments, and depiction of more parenchymal and leptomeningeal enhancement make 3D VWI more favorable. As VWE in arteries distal to VA and ICA may be used for discrimination of vasculitic and non-vasculitic patients, future increase in spatial resolution of 3D VWI sequences may be beneficial.
CNS vasculitis is a rare but potentially devastating disease that requires high diagnostic certainty and fast initiation of treatment. Particularly for primary angiitis of the CNS (PACNS) or secondary brain artery inflammation due to undiagnosed underlying systemic disease, the diagnosis remains challenging. For PACNS, biopsy of the leptomeninges and cortex remains the gold standard [1, 2]. However, several studies showed that sensitivity of invasive histopathologic diagnosis remains only 50–75% leading to many false negative results [3–5]. Standard MRI with MRA may depict large artery stenosis, parenchymal lesions, or parenchymal/leptomeningeal contrast-enhancement but lacks specificity to distinguish vasculitic stenosis [5–7]. The invasive technique digital subtraction angiography (DSA) detects intracranial vasculitis with a good sensitivity (60–90%), especially stenoses of the large and medium-sized intracranial vessels. Though, it misses most of the changes in smaller vessels or non-stenotic vasculitic lesions and may not differentiate between vasculitis and reversible cerebral vasoconstriction syndrome (RCVS) resulting in a very low specificity for intracranial vasculitis (6–30%) [5, 7].
In this study, we compared the detection and characterization of VWE of two commercially available 2D and 3D MRI VWI sequences at 3 T within a prospective cohort of patients that were examined under the clinical suspicion of intracranial vasculitis. 3D intracranial VWI sequences were recently introduced for high-field MRI since they offer high isotropic spatial resolutions with a good T1 contrast within clinically adequate scan times [21–23]. Our study showed that using 3D VWI with whole brain coverage both peripheral arterial segments (A2, P2, M2-4) and proximal segments, such as the extradural ICA, VA V3-5, and BA were better evaluable compared to a 2D VWI protocol acquired in two orthogonal planes. This was mainly attributed to the non-visualization of these vessel segments on both 2D planes due to limited spatial coverage. In addition, scan time was slightly shorter for 3D (6:45 min) vs. 2D (8:12 min for two orthogonal sequences) VWI protocol. For the detection of VWE, an overall fair agreement was found between 2D and 3D VWI which further improved when any enhancement per scan was regarded. At detailed analysis of arterial involved segments, VWE was more frequently observed on 2D VWI at the intradural ICA segment which may be attributed to the higher spatial resolution and signal-to-noise ratio of the 2D sequence. The latter may improve the visualization of faint VWE and the differentiation of VWE from closely enhancing venous structures such as the cavernous sinus (Fig 1). However, the higher in-plane resolution of 2D VWI sequences was at cost of a limited spatial coverage of the brain arteries compared to the 3D VWI sequence that covers the whole brain and upper cervical area. The latter was responsible for the better detection rate of VWE in the VA segments. A future direction to improve spatial resolution of 3D black blood imaging with whole brain coverage [22, 24–26] at adequate scan times may be the application of the recently introduced compressed sensing technology (CS-SPACE) .
In summary, 3D VWI MRI in general did not differ in the ability to detect VWE compared to bi-planar 2D VWI. Mostly the larger coverage of the 3D sequence appears advantageous in detecting more VWE lesions, as well as meningeal or parenchymal contrast enhancement in areas not covered by the 2D sequence and omits the need for exact planning of scan area. In patients with cerebral vasculitis, overall more VWE was detected, and specifically in the proximal MCA segments on both VWI techniques. Whereas, VWE may also be seen in the distal VA and extradural ICA segments in asymptomatic or non-vasculitic patients. Some VWE lesions of the intradural ICAs were not seen on 3D compared to 2D VWI. As the latter VWI sequence has a higher in plane resolution, future increase in 3D spatial resolutions, e.g. with application of compressed sensing MRI technology may be of potential benefit.