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Original Report |
1
Department of Radiology, Neuroradiology Division, The Johns Hopkins University
School of Medicine, The Johns Hopkins Hospital, Phipps B-108, 600 N. Wolfe
St., Baltimore, MD 21287-2182.
2
Department of Medicine, Division of Rheumatology, The Johns Hopkins University
School of Medicine, The Johns Hopkins Hospital, Baltimore, MD
21287-2182.
Received October 9, 2000;
accepted after revision February 15, 2001.
Presented at the annual meeting of the Radiological Society of North
America, Chicago, November 1999.
Abstract
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CONCLUSION. MR imaging findings may be negative in the setting of CNS vasculitis confirmed on angiography, indicating that advanced imaging techniques tailored to detect infarction (i.e., fluid-attenuated inversion recovery, diffusion-weighted, and perfusion imaging) may be necessary to enhance the sensitivity of an MR study and that despite the high sensitivity of MR imaging for CNS vasculitis, angiography may still be required to render an accurate diagnosis.
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The roles of angiography and MR imaging in the diagnosis of CNS vasculitis have been investigated [2,3,4,5]. Harris et al. [3] suggested that an MR study with essentially normal findings excludes CNS vasculitis more effectively than does an angiogram that does not reveal findings for CNS vasculitis. Greenan et al. [5] reported correlations between MR imaging and angiography, supporting the notion that patients with angiograms consistent with CNS vasculitis will have positive findings on MR studies, but conceded that normal findings on MR examinations in the setting of CNS vasculitis are theoretically possible.
We reviewed our experience with MR imaging and angiography in the diagnosis of CNS vasculitis to determine the reliability of an MR study with normal findings for excluding this diagnosis and obviating subsequent angiography.
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The inclusion criteria for this study were as follows: an angiogram interpreted as showing positive findings (defined in the following text) for CNS vasculitis by the attending neuroradiologist at the time that the angiogram was obtained; a clinical history consistent with CNS vasculitis as defined by Calabrese and Mallek [7] (i.e., an acquired neurologic deficit that remained unexplained after a thorough initial evaluation); and MR images of the brain interpreted as showing normal findings close to the time the initial angiography was performed.
Angiograms were considered positive if they displayed focal or diffuse areas of arterial stenosis, occlusion, dilatation, or beading. Findings considered normal on MR studies were those that showed no foci of high signal intensity on images obtained with a long TR. To evaluate the consistency of the original radiologic diagnoses, two attending neuroradiologists, who were not made aware of clinical data on the patients or results of other radiologic studies they had undergone, reviewed all of the available angiograms and MR studies. Discrepancies between the reviewers were submitted to a third attending neuroradiologist for arbitration.
Information was collected by review of each patient's medical records as described by Pomper et al. [2]. No patient had multiple sclerosis or another demyelinating disease. Pastients with diabetes were excluded.
Of 293 angiograms obtained at our hospital to exclude the diagnosis of CNS vasculitis between 1986 and 1998, findings were consistent with CNS vasculitis in 39 (13.3%). Among these 39 patients, the five (12.8%) in whom the corresponding MR findings were negative formed the basis of this report. One additional patient from an outside institution who had negative MR findings and positive findings on angiography was also included.
MR imaging was performed on a 1.5-T system. Spin-echo imaging was performed in each patient. T1-weighted sagittal (TR/TE, 600/20) and double-echo axial (3000/30, 100) spin-echo images were obtained for all six patients. In a 37-year-old woman with systemic lupus erythematosus, MR angiography was performed using three-dimensional time-of-flight imaging (Fig. 1A,1B,1C). T1-weighted axial and coronal spin-echo images were acquired after administration of IV contrast material (gadopentetate dimeglumine) in a 57-year-old woman with primary angiitis of the CNS (Fig. 2A,2B,2C,2D,2E). Conventional biplane film-screen or digital subtraction angiography was performed in all patients.
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MR Imaging
Initial MR studies for all six patients were interpreted prospectively as
showing normal findings. Abnormal vessels consistent with CNS vasculitis were
identified on the MR angiogram. Images obtained after administration of
contrast material showed no abnormal enhancement.
Angiography
The findings on angiograms of the six patients whose cases we describe
varied from mildly to severely abnormal despite the normal appearance of their
MR studies. Selected injections from the angiograms of two patients are seen
in Figures
1A,1B,1C
and
2A,2B,2C,2D,2E.
Four of the six patients had vascular abnormalities classified as severe
bilateral disease by the interpreting neuroradiologist. The anterior
circulation was involved in five of the six patients.
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MR imaging is considered to be an excellent screening tool for CNS vasculitis because of its reportedly high sensitivity (100%) [3,4,5]. In CNS vasculitis, MR imaging typically reveals multifocal white- and gray-matter lesions caused by ischemia, infarction, or both, with most lesions occurring in the distribution of the middle cerebral artery [2]. Duna and Calabrese [4] reported abnormal findings on MR studies in all seven cases of primary angiitis of the CNS that they studied. Harris et al. [3] reported abnormal findings on MR studies in nine of 11 patients with proven vasculitis. The remaining two patients did not have MR studies but instead had CT scans that showed infarctions. Eight of these 11 patients had abnormal cerebral angiograms, but angiography was normal in three patients. Greenan et al. [5] reported abnormal MR images in all seven cases of primary angiitis of the CNS that were studied, but because 12 of 33 vascular distributions with angiographic evidence of CNS vasculitis had no lesions on the corresponding MR images, the investigators suggested normal findings on MR studies are possible when findings on angiography are positive. In contrast, Harris et al. argued that it is more relevant to consider the brain as a whole when evaluating for CNS vasculitis and that it would be unlikely that the MR study would reveal no parenchymal findings if the symptoms and signs of the disease were significant enough to cause the patient to seek medical attention.
Few cases of CNS vasculitis with negative MR studies have been documented [10,11,12]. Vanderzant et al. [10] described a single case of biopsy-proven CNS vasculitis in which the patient had normal findings on an MR study, but these findings are suspect in light of a CT study performed 2 days earlier that showed "generalized brain swelling and transtentorial herniation." In addition, the patient was reported to have negative findings on the cerebral angiogram. To our knowledge, the only reports of patients with positive findings at angiography but negative MR findings were by Imbesi [11] and Alhalabi and Moore [12]. Imbesi reported a single case of drug-induced CNS vasculitis in a patient with a normal MR study and abnormal cerebral angiogram. Alhalabi and Moore reported four such patients with primary angiitis of the CNS, but they did not provide the times of the MR studies relative to the angiograms or describe the MR sequences used. In addition, the angiograms in these four patients were described as having abnormal findings only in the abstract of that article and were not described fully in the remainder of the report [12]. Nevertheless, these cases have raised some question as to the value of angiography performed after a normal MR study for CNS vasculitis. Three groups of researchers [3,4,5] have reported 100% sensitivity of MR imaging in CNS vasculitis. Therefore, it may be that other patients with negative MR studies who have not undergone subsequent angiography remain undiagnosed.
Our research suggests that an MR study with normal findings executed with standard spin-echo sequences does not exclude CNS vasculitis definitively and that angiography should be performed if the clinical suspicion of CNS vasculitis remains high. MR imaging remains the best screening tool for CNS vasculitis because patient risk is low, it is widely available, and its sensitivity is high, but it may be inadequate in certain cases (e.g., when a vascular stenosis is not sufficiently narrow to cause infarction downstream).
In the appropriate clinical setting, CNS vasculitis has a characteristic angiographic appearance, which suggests that angiography is more specific than MR imaging for CNS vasculitis. Catheter angiography also has limited sensitivity because its resolving power, about 500 µm, is not sufficient for detecting the predominantly small-vessel changes in CNS vasculitis [13].
Although not investigated in our study, diffusion-weighted and perfusion sequences may enhance the sensitivity of MR imaging. Diffusion-weighted imaging may be helpful in the acute setting, when this technique may be more sensitive than spin-echo sequences for the detection of infarction. However, many patients who present with CNS vasculitis have lesions old enough to be revealed by T2-weighted spin-echo images. In none of our patients was the MR study performed less than 24 hours after the onset of symptoms, making parenchymal changes detectable by diffusion-weighted imaging but not by T2- or proton density—weighted sequences unlikely. Perfusion imaging may highlight areas of the brain that are at risk from vascular narrowing caused by CNS vasculitis but have not progressed to injury with parenchymal changes detectable by MR imaging. For this reason, perfusion imaging may be particularly helpful in light of a normal MR study.
Because of the retrospective nature of this study, fluid-attenuated inversion recovery (FLAIR) imaging was not available. The use of FLAIR was not described in the reports of patients who had positive angiograms but negative MR studies [11, 12]. Imbesi [11] specifically addressed the lack of this sequence in his article. Alhalabi and Moore [12] did not describe any of the MR sequences used, although it seems unlikely that FLAIR was among them, given that their manuscript was submitted in 1993. FLAIR is most advantageous in the detection of subtle changes at the periphery of the hemispheres and in the periventricular region close to cerebrospinal fluid. Because vasculitic lesions are typically located in deep white matter [5], FLAIR may not increase the sensitivity of MR imaging for detecting these lesions.
Although immune-mediated cases of CNS vasculitis are rare, they appear in the differential diagnosis of many perplexing neurologic presentations. Our data show that if there is sufficient clinical suspicion for primary angiitis of the CNS after a normal MR study, the likelihood of finding angiographic features supportive of this diagnosis is great enough to justify obtaining a cerebral angiogram. In our series, the overall yield of angiography performed to exclude CNS vasculitis was 13%. This is somewhat higher than that reported by others [3], but may reflect differences in the likelihood of disease before testing was done. In our experience, patients with CNS vasculitis who present with a negative MR study tend toward a more benign course than those with a positive MR study.
In conclusion, we have shown that conventional MR techniques (T1-, T2- and proton density—weighted spin-echo sequences) alone may be unreliable for excluding CNS vasculitis. The role of functional sequences, including diffusion-weighted and perfusion imaging, for the detection of vasculitic lesions appears promising but requires further investigation. Until the usefulness of these advanced MR techniques has been established, angiography may still be required after an MR study with normal findings to exclude the diagnosis of CNS vasculitis.
Acknowledgments
We thank Misty Uhlfelder for her assistance in the preparation of this
article.
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