Takayasu’s Arteritis: Utility and Limitations of Magnetic Resonance Imaging in Diagnosis and Treatment
Previous studies emphasized poor correlation of symptoms, signs and acute phase reactants with disease activity in about half of all patients with Takayasu’s arteritis (TAK). Invasive angiographic studies demonstrate vessel lumen anatomy. Sequential studies expose patients to high-dose ionizing radiation and catheter/procedure-related morbidity. Such studies do not provide qualitative information about the vessel wall. To determine the utility of vascular magnetic resonance (MR) technology in TAK patients, we previously reported (Tso E, et al. Arthritis Rheum. 2002;46:1634) our experience from 77 studies on 24 patients using ECG-gated MR images, “edema-weighted,” to evaluate the aorta and its primary branches in regard to the vascular lumen, vessel wall anatomy and vessel wall edema.
Ninety-four percent of studies, obtained when patients were thought to have unequivocally active disease, revealed evidence of vessel wall enhancement. In 81% of studies obtained during periods of uncertain disease activity, and in 56% of studies obtained during periods of apparent clinical remission, enhancement was also noted. The Westergren sedimentation rate and C-reactive protein did not correlate with either clinical assessment of disease activity or MR enhancement.
Following completion of our formal TAK-MR study, ten additional patients had MR images obtained just prior to vascular surgery procedures. In seven patients, the finding of edema on MR correlated with histopathologic proof of inflammation or vasculitis. In three patients, however, MR edema was present and inflammation absent within the biopsy, suggesting that vascular MR may not always be accurate.
This study was the first prospective analysis of the utility of recent technical advances in MR imaging in Takayasu’s arteritis. This technique can be an important supplement to the clinical and laboratory assessment of disease activity. The negative correlation we observed between ESR or CRP and MR signal intensity is similar to prior reports in which ESR was abnormal in 72% of patients during clinically active disease and was also abnormal in 44% of patients thought to be in remission.
Our observations should not be interpreted as suggesting that MR vascular imaging replace invasive angiography. Each technique has unique advantages and disadvantages. Sequential invasive angiography has been very informative in detecting new vascular lesions in TAK. It provides greater image resolution than MR in vessels other than the aorta, innominate and common iliac arteries, which makes it desirable for the preoperative planning of bypass surgery. Invasive angiography provides opportunities to record central blood pressure readings and gradient determinations in patients with vessel stenoses, allowing the clinician to assess the reliability of extremity blood pressure cuff measurements. Alternatively, the non-invasive, radiation-sparing qualities of MR and “edema-weighted” imaging techniques may lead to its preferred use for routine follow-up.
“Edema-weighted” MRI vs Invasive Angiography
A comparison of invasive angiography (A) and MR (B) demonstrates the superior resolution of the former study. The information gained from MR is considerable, and eliminates the risk of an invasive procedure and exposure to radiation.
A.
B.
Histopathologic specimen from a bypass procedure originating in the ascending aorta and inserting into the right subclavian and right carotid arteries.
Postscript
Since completion of this study, funding has been provided to the Vasculitis Clinical Research Consortium (Boston University, Johns Hopkins, Mayo Clinic and Cleveland Clinic) to further define the operating characteristics of MR, CT and PET scanning in large vessel vasculitis.
[KM McKinnon, TM Clark, GS Hoffman]
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