Sami Al Kasab, MD

Mossa-Basha M, Shibata DK, Hallam DK, de Havenon A, Hippe DS, Becker KJ, et al. Added Value of Vessel Wall Magnetic Resonance Imaging for Differentiation of Nonocclusive Intracranial Vasculopathies. Stroke. 2017

The term intracranial vasculopathy denotes any disease affecting the blood vessels of the brain and meninges. This includes vascular abnormalities due to inflammatory, metabolic, or hereditary conditions; coagulopathy-related disorders; and functional disorders of the blood vessels. Differentiating the type of vasculopathy is important, as treatment is different depending on the type of vasculopathy. Most common intracranial vasculopathies include intracranial atherosclerosis (ICAD), reversible cerebral vasoconstriction syndrome (RCVS), and infectious/inflammatory vasculopathies (IVas).

Recently, intracranial vessel imaging with magnetic resonance imaging (MRI) has emerged as a promising modality to characterize intracranial vasculopathies. Intracranial vessel imaging with MRI has been used to characterize vessel wall as well as vessel lumen. In this study, Mossa-Basha and colleagues compare the diagnostic accuracy of intracranial vessel wall MRI (IVWI) with luminal imaging to luminal imaging alone in non-occlusive vasculopathy differentiation such as ICAD, RCVS, and IVas.

This was a retrospective study in which the authors collected data on patients with arterial wall imaging from December 2012 through February 2016. Patients with documented luminal irregularity without occlusion on the clinically acquired computed tomographic angiography (CTA), magnetic resonance angiography (MRA), and digital substraction angiography (DSA) were included in the study. The clinical data and luminal imaging reports were reviewed by two vascular neurologists who were blinded to the IVWI information and clinical diagnosis. The vascular neurologists categorized the vasculopathy as ICAD, RCVS, and IVas after reviewing the available data. If there was a disagreement between the two neurologists, a third neurologist arbitrated. Cases with other diagnoses, multiple diagnoses, or a diagnosis that couldn’t be agreed on by the neurology reviewers were excluded from the study. The neurologist review served as the diagnostic gold standard.

For image analysis, a single rater reviewed luminal imaging of the included cases independent of the diagnosis, clinical data, and IVWI to determine the arterial segments with luminal irregularity. The identified lesions were then evaluated by two other raters who underwent training in IVWI interpretation. The two raters reviewed luminal imaging studies (CTA, MRA, and DSA) performed for each subject prior to IVWI. The raters evaluated luminal imaging for the pattern of involvement (concentric, eccentric), diagnosis (ICAD, RCVS, IVas, or unknown), and confidence in their diagnosis on a 4-point Likert scale. After 6 weeks washout period, the raters re-evaluated the randomized lesions using both luminal imaging and IVWI individually and independently. The raters evaluated the pattern of wall involvement, presence of enhancement, pattern of enhancement, diagnosis, and confidence in diagnosis.

For statistical analyses, clinical characteristics of each subject were compared between the 3 clinical diagnoses using the Kruskal-Wallis test and Fisher exact test. Diagnostic confidence, dichotomized as highly confident versus not highly confident, was compared between the luminal imaging and luminal imaging + IVWI sessions using generalized estimating equations-based logistics regression models.

Two hundred and twenty consecutive IVWI cases with luminal imaging were reviewed, of which 54 patients were included in this study. Thirty patients were diagnosed with ICAD, 12 with RCVS, and 12 IVas. IVas cases consisted of 4 varicella vasculopathies, 3 primary angiitis, 2 bacterial vasculopathies, and 1 each of Behçet-associated vasculopathy not otherwise specified, tuberculosis, and fungal vasculopathies.

Vascular risk factors were more common in patients diagnosed with ICAD compared to other vasculopathies (P<0.001).  There were variations in the frequency of DSA and CTA performance between the groups; however, these differences were not statistically significant.

Among the 54 lesions, 201 lesions (90 ICAD, 64 RCVS, and 47 IVas) were assessed by the two raters, for a total of 402 ratings. There were 10 lesions per patient (median 3). ICAD was significantly more likely to involve the internal carotid artery (42.2%) compared to IVas (9.4%; P=0.046) and RCVS (25.5%; p=0.001).

On vessel wall MRI, there were significant differences in the IVWI characteristics between ICAD, RCVS, and IVas. ICAD IVWI findings were remarkable for eccentric lesions (91.1%) that were enhancing (86.7%) (figure). RCVS lesions were concentric (80.5%) with no enhancement (53.9%) or diffuse enhancement (32.8%). IVas most commonly showed concentric (76.6%), diffusely enhancing lesions (81.9%).

When diagnosis was made based on luminal imaging alone, raters made the correct per-lesion diagnosis in 36.1% of their evaluations. When luminal imaging was combined with IVWI, the raters’ accuracy increased to 88.8% (P<0.001). The increase in diagnostic accuracy was significant for each rater individually as well. At the per patient evaluation level, using luminal imaging alone, raters made the correct diagnosis at the patient level in 43.5% evaluations. This increased to 96.3% when IVWI was added to the luminal imaging (p<0.001).

With regards to diagnostic confidence, there was a significant increase in confidence between luminal imaging alone compared with luminal imaging +IVWI (high confidence rating of 3: 17% vs. 44%; p<0.001).

The study has few limitations. The first limitation is derived from its retrospective nature. The second limitation is the fact that there was no histological confirmation available on the evaluated cases. Additionally, the number of RCVS and IVas cases is limited, and there were no healthy subjects to compare to.

In summary, this study shows that adding IVWI improves the ability to differentiate ICAD from RCVS and IVas when compared to intraluminal imaging alone.

Comparison of intracranial vasculopathies on luminal imaging and intracranial vessel wall magnetic resonance imaging (IVWI).

Figure 1: Comparison of intracranial vasculopathies on luminal imaging and intracranial vessel wall magnetic resonance imaging (IVWI).