Multidetector spiral CT renal angiography in the diagnosis of renal artery fibromuscular dysplasia
Introduction
Secondary hypertension accounts for less than 5% of cases of hypertension in adult patients [1], [2]. Renal vascular disease, although rare, is one of the more common and potentially treatable causes of secondary hypertension [3], [4]. As a potentially reversible and curable cause of hypertension and renal dysfunction, physicians are increasingly devoting more effort to its diagnosis and management [5]. The two most common causes of renal vascular disease are atherosclerosis (70%) and fibromuscular dysplasia (25%) [6], [7]. Fibromuscular dysplasia (FMD) is a non-atherosclerotic, non-inflammatory vascular disease that most commonly affects the renal arteries [8]. FMD tends to affect girls and women between 15 and 50 years of age, and it frequently involves the distal two-thirds of the renal artery and its branches [9]. The pathological classification for fibromuscular lesions of the renal arteries is based on the arterial layer – intima, media or adventitia – in which the lesion predominates [10]. Medial fibroplasia, characterized by its classic “string of beads” appearance with or without aneurysm formation on angiography (Fig. 1, Fig. 2, Fig. 3), represents the most common form of FMD, accounting for 65–70% of cases. The subadventitial form, characterized by aneurysm formation and by focal or tubular stenoses on angiography, accounts for 15–20% of cases [11].
Conventional renal angiography (CA) remains the gold standard for the diagnosis of renal artery stenosis. However, because of the invasive nature of CA various non-invasive tests have been applied to detect renal artery stenosis. These non-invasive tests can be divided into those that rely upon an assessment of the functional (physiologic) effects of a renal artery lesion and those that rely upon direct imaging of renal artery anatomy [12]. Functional tests include plasma renin activity [3], captopril plasma renin test and captopril augmented scintigraphy [13]. Non-invasive imaging tests include duplex ultrasound [14], [15], [16] and magnetic resonance angiography [17], [18], [19]. The introduction of multidetector spiral CT angiography permits volumetric acquisition in apnoea with high-contrast enhancement of the vessel lumen [20], [21]. After data analysis using commercially available software, reconstructions such as multiplanar reformatted images (MPR), shaded-surface display (SSD) and maximum intensity projections (MIP) produce high-quality images of the vascular system [22], [23], [24].
Recently, favourable results of spiral CTA have been reported in the diagnosis of renal artery stenosis, in particular atheroscelerotic stenosis [25], [26]. Results of studies so far have proven CTA to be less reliable for visualizing distal segments of the main renal artery and accessory renal arteries [27], [28]. Since FMD primarily affects the distal two-thirds of the renal artery and its branches, CA is considered the gold standard for the diagnosis of FMD. To the best of our knowledge only one other study exists that compared CTA to CA in patients with angiographically proven FMD [29].
The aims of our study were to evaluate the efficacy of CTA in the detection of FMD as compared with CA, to compare the detection rates of the available CTA reconstruction methods, and to consider its role as a diagnostic tool in hypertension suspected to be secondary to FMD.
Section snippets
Patient population
Over a 3-year period, CTA results of 21 hypertensive patients (19 females and 2 males; mean age ± S.D., 62.33 ± 14.32 years; range, 24–85 years) with CA-proven FMD were retrospectively reviewed. We evaluated the CTA findings of these patients in whom the diagnosis of FMD could be verified with CA.
Clinical indications for referral included resistant hypertension (requiring greater than three antihypertensive medications), labile hypertension, hypertension in combination with renal impairment and the
Conventional renal angiography—reference standard
In the 21 patients studied, 42 main renal arteries were identified. In 7 of the 21 patients, the kidneys were supplied by more than 1 artery. Two patients had unilateral triple renal arterial supply, four patients had unilateral dual renal arterial supply and one patient had bilateral dual renal arterial supply (Fig. 1). Altogether, 10 accessory renal arteries (in 7 patients) were identified. Thus, a total of 52 renal arteries were identified, of which 37 had an abnormal appearance on
Discussion
Less than 5% of cases of adult hypertension are renovascular in origin, and approximately 25% of these cases are secondary to renal artery FMD [1], [2], [7]. Although infrequent in overall incidence, renal artery FMD is one of the potentially treatable causes of adult hypertension [3], [4]. Therefore, the detection of haemodynamically significant lesions due to FMD is crucial in the overall management of these patients [5].
CA is known to be the most accurate diagnostic modality, and hence it
Conclusion
Our experience suggests that CTA is a non-invasive, reliable and accurate method for the diagnosis of renal artery fibromuscular dysplasia. The diagnosis according to CTA requires review of axial source images with 3D coronal and sagittal MPR reconstructions and MIP (2D coronal and 3D) reconstructions. Moreover, CTA has many advantages as a diagnostic tool over CA, including accessibility, speed, lower complication profile, versatility and cost-effectiveness. The role of CTA as a diagnostic
Acknowledgements
The authors gratefully acknowledge the efforts of the following people for their contribution to this manuscript: W. Phillip Law, Pamela Dougan, Roger Kingston, Castlereagh Imaging—Westmead (Division of Sonic Health Pty. Ltd).
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