Abdominal Imaging
ª Springer Science+Business Media, LLC 2008 Published online: 4 March 2008
Abdom Imaging (2009) 34:265–270 DOI: 10.1007/s00261-008-9377-7
Renal involvement of polyarteritis nodosa: CT and MR findings Kumi Ozaki,1 Shiro Miyayama,2 Yasuyuki Ushiogi,3 Osamu Matsui1 1
Department of Radiology, Kanazawa University Graduate School of Medical Science, 13-1 Takara-machi, Kanazawa 920-8641, Japan 2 Department of Diagnostic Radiology, Fukuiken Saiseikai Hospital, Fukui, Japan 3 Department of Internal Medicine, Fukuiken Saiseikai Hospital, Fukui, Japan
Abstract Background: To evaluate the imaging findings in patients with renal involvement of Polyarteritis nodosa (PN) to diagnose as early as possible. Materials and methods: Four patients diagnosed as having PN participated in the present study. Two patients underwent abdominal dynamic CT, one underwent only pre- and post-contrast CT, and the remaining patient underwent only noncontrast CT and MR imaging, including dynamic contrast study. Results: The common findings of CT and MR imaging were diffuse enlargement, multiple small wedge-shaped less-enhanced areas on dynamic contrast study, and indistinctness of the margin between the cortex and medulla on equilibrium-phase CT. Renal arteriogram showed multiple microaneurysms on arterial phase image in all four cases, and PN was diagnosed. The common CT and MR findings of renal involvement of PN mimicked those of pyelonephritis, when microaneurysms were not demonstrated. Conclusion: The differentiation between PN and pyelonephritis on CT and MR imaging is difficult. Therefore, the radiologist should be familiar with the imaging findings of renal involvement of PN. When PN is suspected, angiography should be performed as early as possible to make a definite diagnosis. Key words: Polyarteritis nodosa—Wedge-shaped area—Microaneurysm—Angiography
Correspondence to: Kumi Ozaki; email:
[email protected]
Polyarteritis nodosa (PN) is a systemic necrotizing vasculitis of medium and small arteries [1], and is typically found in middle-aged men. The most common clinical symptoms are persistent fever, weight loss, and polyarthragia [2]. As these symptoms are nonspecific, diagnosing PN is sometimes difficult and delayed. The kidney is the most commonly involved [1], and multiple small wedge-shaped less-enhanced areas are typically seen on enhanced CT [3–6]. These are considered to be multiple bilateral renal cortical infarctions due to vasculitis of the interlobar arteries and arcuate arteries. If a diagnosis of PN is already confirmed, the involved visceral organs will be easily detected; however, the renal findings are similar to pyelonephritis and easily misdiagnosed in a patient with nonspecific symptoms. We retrospectively evaluated the imaging findings of CT and MR imaging of renal involvement in patients with PN.
Materials and methods The subjects were four patients (two men, two women; age range, 48–71 years) who were clinically (n = 3) and histologically (n = 1) diagnosed as having PN. Three patients had fever of unknown origin for 1–2 months and were referred to our hospital. The remaining patient (Case 4) had been treated with predonisolone for atypical pneumonia. Pneumonia gradually improved; however, serum levels of hepatobiliary enzymes suddenly elevated 2 months after the start of the treatment. The counts of white blood cells and the serum level of C-reactive protein were slightly elevated in all patients. A few weeks after CT or MR imaging, the patients were presenting with several other clinical symptoms; polyneuropathy, erythema, or polyarthralgia. The period between initial CT and the angiographic examinations was 7–28 days. PatientsÕ clinical backgrounds are summarized in Table 1.
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Table 1. Clinical background of the four patients Case Age Sex Initial symptom number 1 2 3 4
71 51 69 48
M M F F
Persistent Persistent Persistent Persistent
WBC CRP Additional symptoms (/UL) after admission
fever 12,500 13.6 Polyneuropathy fever 6100 3.7 Erythema, polyarthragia fever 12,600 15.6 Polyneuropathy, erythema fever, atypical pneumonia 17,800 12.1 Polyneuropathy, erythema
Urinalysis Days Angiographic Histological findings findings Clear Clear Clear Clear
20 28 8 7
Positive Positive Positive Positive
Not performed Negative Positive Negative
WBC: White blood cells (normal range, 3500–9100/UL) CRP: The serum level of C-reactive protein (normal range < 0.4) Days: Duration between CT and angiography.
Fig. 1. A 71-year-old man with fever of unknown origin (Case 1). (A) Noncontrast CT shows diffuse enlargement and slight thickening of GerotaÕs fascia of the kidney (arrows).
(B) Arterial phase CT shows multiple small wedge-shaped less-enhanced areas. (C) The margin between the cortex and medulla is indistinct on equilibrium-phase CT.
Two patients underwent abdominal dynamic CT, one underwent only pre- and post-contrast (equilibriumphase) CT, and the remaining patient underwent only noncontrast CT and MR imaging, including dynamic study. All CT images were obtained by using an Aquilion 16 (Toshiba Medical Systems, Tokyo, Japan) with a 5-mm collimation, a 15-mm pitch, and a 5-mm reconstruction. A dynamic contrast study was performed 30s (arterial phase), 45s (portal venous phase), and 120s (equilibrium-phase) after intravenous injection of 100 mL of nonionic 300 mg/mL contrast material. MR imaging was performed with a 1.5-T superconductive system (Gyroscan Intera; Philips, Best, the Netherlands). The slice thickness was 7 mm with a 2-mm intersection gap. A dynamic contrast study was performed 30s (arterial phase), 45s (portal venous phase), and 60s (equilibrium-phase) after intravenous injection of 10 mL of gadolinium DTPA. Angiography was performed to confirm the diagnosis in all four patients. We retrospectively evaluated the findings of CT and MR imaging.
Results The bilateral kidneys showed diffuse enlargement of on CT and MR imaging (Figs. 1–4), and showed diffusely decreased low attenuation on noncontrast CT in all patients (Figs. 1A, 3A). In addition, the bilateral kidneys showed diffusely hyperintensity on T2-weighted images (Fig. 2A). No kidneys showed deformation which suggested the prior episodes. Multiple small wedge-shaped less-enhanced areas were seen on dynamic CT and MR imaging (Figs. 1B, C, 2B, 4A). These areas showed hypointensity on T2-weighted images (Fig. 2A). The size and number of these wedge-shaped areas were individually various. Slight thickening of GerotaÕs fascia and perirenal fat stranding were seen in three patients on CT (Figs. 1A, 3A). The margin between the cortex and medulla was indistinct on equilibrium-phase CT in all patients (Figs. 1C, 3B). In one of the two patients who underwent dynamic CT (Case 4), multiple microaneurysms, 2–3 mm in diameter, were demonstrated in the bilateral kidneys
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dynamic CT. In the other three patients, the celiac arteriogram did not show any aneurysms. The superior and inferior mesenteric arteriogram also did not show any aneurysms in any patients. After arteriogram was obtained, PN was diagnosed and cyclophosphamide pulse therapy with prednisolone was started immediately in all patients. The clinical symptoms presented after admission supported the diagnosis of PN. CT obtained 4–5 months after treatment showed the disappearance of the above CT and MR findings, and multiple areas of focal parenchymal atrophy were observed (Figs. 3C, 4C–F).
Discussion
Fig. 2. A 51-year-old man with fever of unknown origin (Case 2). (A) Multiple small wedge-shaped areas show hypointensity (arrowheads) on axial T2-weighted fat-suppressed MR image. (B) On arterial phase image, T1-weighted fat-suppressed MR image shows multiple small wedgeshaped less-enhanced areas (arrows).
as well as in the liver (Fig. 4A, B). In the other three patients, no microaneurysm could be identified. No other abnormal findings were demonstrated on abdominal CT and MR imaging. Imaging findings are summarized in Table 2. In all four cases, renal arteriogram showed multiple microaneurysms of the distal interlobar arteries and the arcuate arteries on the arterial phase image (Fig. 5). The size and the number of microaneurysms were individually various. The microaneurysms which were also demonstrated on dynamic CT (Case 4) were more and larger than others. The microaneurysms which were not demonstrated on MR images (Case 2) were similar in size to those of Case 4. The size of microaneurysms ranged approximately from 2.5 to 4.5 mm on an average in diameter. Irregularity, narrowing, ectasia, and occlusion in small arteries were also seen on arterial phase images. Multiple wedge-shaped hypoperfusion areas were also demonstrated (Fig. 5). No abnormal findings could be identified in the main renal arteries or segmental arteries. In one patient (Case 4), the hepatic arteriogram demonstrated numerous microaneurysms of the medium and small hepatic arteries, which were also demonstrated on
Polyarteritis nodosa (PN) is a systemic necrotizing vasculitis of medium and small arteries. The kidney is the most commonly involved [1] and we sometimes obtain only renal findings from imaging. Most clinical symptoms are nonspecific [2]. These backgrounds sometimes make it difficult to diagnose PN from images. Some studies [3–6] reported that multiple small wedge-shaped less-enhanced areas were observed on enhanced CT, which were multiple bilateral renal cortical infarctions from vasculitis of the interlobar arteries and the arcuate arteries. In addition, perirenal hematoma by aneurysmal rupture [4–7], and small microaneurysms are sometimes observed [4, 5]. In the present study, multiple small wedge-shaped less-enhanced areas were individually various and seemed to be associated with the size and the number of microaneurysms on angiography. MR findings of renal involvement of PN have not been previously published. Multiple small wedge-shaped less-enhanced areas showed hypointensity on T2-weighted images and enhanced pattern on dynamic contrast study was similar to those on CT. The hypointense wedgeshaped areas on T2-weighted images seemed to reflect the absence of blood flow because of infarctions. Perirenal hematoma was not observed. It seemed that microaneurysms in the present study were relatively smaller than those in previous reports [4, 5]. Diffuse enlargement and diffusely decreased attenuation of bilateral kidneys, slight thickening of GerotaÕs fascia, perirenal fat stranding, and indistinctness of the margin between the cortex and medulla reflected nonspecific inflammatory changes. Retrospectively, multiple small wedge-shaped lessenhanced areas were typical of PN; however, in two of four patients we misdiagnosed at first because the findings except for microaneurysms on CT and MR imaging were exactly similar to pyelonephritis. Both size of wedge-shaped less-enhanced areas and the enhanced pattern on dynamic contrast study were indistinguishable. Other findings except for microaneurysm were nonspecific, and any inflammatory or infectious renal
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Fig. 3. A 69-year-old woman with fever of unknown origin (Case 3). (A) Noncontrast CT shows diffuse enlargement and slight thickening of GerotaÕs fascia of the kidney (arrows). (B) On equilibrium-phase CT, slight thickening of GerotaÕs fascia (arrows), perirenal fat stranding (arrowhead),
and indistinctness of the margin between the cortex and medulla are seen. (C) Equilibrium-phase CT obtained 7 months after treatment shows the disappearance of enlargement, slight thickening of GerotaÕs fascia, and perirenal fat stranding.
Fig. 4. A 48-year-old woman treated with predonisolone for atypical pneumonia (Case 4). (A) Arterial phase CT shows multiple diffuse enlargement, microaneurysms 2–3 mm in diameter (arrows), and multiple small wedge-shaped lessenhanced areas (arrowheads) in the bilateral kidneys. (B) Arterial phase CT shows multiple swelling, microaneurysms 2–3 mm in diameter (arrowheads), and inhomogeneous enhancement in the liver. (C) Seven months after treatment, diffuse enlargement, multiple microaneurysms and small
wedge-shaped less-enhanced areas have resolved in the bilateral kidneys on arterial phase CT. (D) Seven months after treatment, swelling, multiple microaneurysms, and inhomogeneous enhancement have resolved in the liver on arterial phase CT. (E) Seven months after treatment, multiple areas of focal parenchymal atrophy are seen in the bilateral kidneys on equilibrium-phase CT (arrows). (F) Seven months after treatment, diffuse atrophy is seen in the liver on equilibriumphase CT.
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Table 2. Imaging methods and imaging findings Case number
1 2 3 4
Imaging methods
Dynamic CT Noncontrast CT and dynamic MR imaging Pre- and post-enhanced CT Dynamic CT
CT and MR findings
Microaneurysms on arteriogram
1
2
3
4
5
6
Size (mm)
Number
+ + + +
+ + + +
+ + ) +
+ – + +
+ + + +
) ) ) +
2.5 3.8 2.7 4.5
1–2 3–4 1–2 4–5
1. Diffuse enlargement of bilateral kidneys 2. Diffusely decreased attenuation of bilateral kidneys 3. Multiple small wedge-shaped less-enhanced areas 4. Slight thickening of GerotaÕs fascia and perirenal fat stranding 5. Indistinctness of the margin between the cortex and medulla 6. Microaneurysms Size: approximate average diameter of microaneurysms Number: the average number of microaneurysms in each interlobar arteries + : The finding was seen ) : The finding was not seen.
Fig. 5. (A) A 51-year-old man with fever of unknown origin (Case 2). Arteriogram of the right renal arteries shows multiple microaneurysms in the distal interlobar arteries and arcuate arteries. Irregularity, narrowing, ectasia, and occlusion in small arteries are also seen. Multiple wedge-shaped hypoperfusion areas are demonstrated. (B) A 69-year-old
woman with fever of unknown origin (Case 3). Arteriogram of the right renal arteries shows several microaneurysms in the distal interlobar arteries and arcuate arteries. Irregularity, narrowing, ectasia, and occlusion in small arteries are also seen. Microaneurysms are smaller and fewer than those of Case 2.
disease may show the same findings. Wong et al. [8] reported that the best differential CT feature in distinguishing renal infarction from pyelonephritis was the demonstration of the cortical rim sign. However, the cortical rim sign is not always demonstrated particularly
in case of small infarctions. Pyelonephritis does not always occur in the bilateral kidneys and does not always show multiple lesions. However, the differentiation between PN and pyelonephritis which shows multiple lesions in the bilateral kidneys is difficult. We should
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always consider PN from the findings of multiple small wedge-shaped less-enhanced areas in the bilateral kidneys. On the other hand, infarction of the kidney can result from various cause including renal artery thrombosis or embolus, vasculitis, shock, and trauma [8]. Renal infarctions resulting from artery thrombosis or embolus, shock, and trauma often show a solitary, larger low attenuation area, and the differential diagnosis is not difficult [8]. All findings shown in the present study indicate the acute stage of PN. In contrast, in the chronic stage, the findings disappeared and the parenchyma shows localized cortical atrophy with deformation of the kidney by old infarction [9]. If localized cortical atrophies with deformation exist in the bilateral kidney, the prior infarctions will be suspected. However, no kidneys showed localized cortical atrophies in the present study. In addition, prior pyelonephritis may show the similar deformation [10]. When microaneurysms are detected on CT, PN will be easily suspected. Therefore, the detection of microaneurysms on CT is very important. The microaneurysms which were demonstrated on dynamic CT (Case 4) were more numerous and larger than the other two of three patients. Smaller and fewer microaneurysms in other two of three patients are difficult to demonstrate on CT. The size and the number of microaneurysms shown on arteriogram were similar in both Case 2 and Case 4. Dynamic CT (Case 4) could demonstrate microaneurysms, while MR imaging including dynamic contrast study (Case 2) could demonstrate no microaneurysms. It seemed that MR imaging was inferior to CT in respect of space resolution. In fact, MR imaging was not useful to diagnose PN, while CT should be recommended to demonstrate microaneurysms. Although the kidney is the most commonly involved, any visceral organ may be involved in PN. One of four patients had microaneurysms not only in the bilateral kidneys, but also in the liver. If other visceral organs are involved, diagnosing PN is easier. Nonradiologic factors are also helpful to diagnose. In the present study, the urinalysis was clear and the antibiotics were not effective in two misdiagnosed patients; therefore, we need to refer to clinical symptoms, laboratory data, urinalysis, and the effectiveness of antibiotics to make a diagnosis. Diagnosis is ideally made by biopsy of the involved tissue [11]; however, tissue biopsy often fails to confirm the suspected diagnosis, while an angiogram absolutely provides confirmation [1]. The value of angiography for diagnosing PN has been reported in many studies [1, 7, 9, 12]. The most well-known angiographic feature is the presence of microaneurysms in medium or small arteries.
Most aneurysms are 2–10 mm in diameter. In the present study, multiple microaneurysms, 2–3 mm in diameter, were observed in all patients. However, it is important to note that renal microaneurysms are not specific to PN. They may be demonstrated in other systemic necrotizing vasculitis, drug abuse, and bacterial endocarditis [1, 9, 11]. The specificity of angiographic findings of microaneurysm becomes much higher when the clinical symptoms are supportive [11, 12]. If untreated, PN is usually fatal [13], and the early initiation of treatment influences the prognosis. It took 3–4 weeks until angiography was performed in two of four patients, because we initially misdiagnosed them as pyelonephritis. One of the two patients (Case 1) died 4 months after the start of treatment; therefore, making a diagnosis as early as possible is important. In conclusion, the differentiation between PN and pyelonephritis on CT and MR imaging is difficult. Therefore, the radiologist should be familiar with the imaging findings of renal involvement of PN. When PN is suspected, angiography should be performed as early as possible to make a definite diagnosis.
References 1. Stanson AW, Friese JL, Johnson CN et al. (2001) Polyarteritis nodosa: spectrum of angiographic findings. RadioGraphics 21:151–159 2. Lightfoot RW, Michel BA, Bloch DA et al. (1990) The American college of rheumatology 1990 criteria for the classification of polyarteritis nodosa. Arthritis Rheum 33:1088–1093 3. Pope TL, Buschi AJ, Moore TS et al. (1981) CT features of renal polyarteritis nodosa. AJR Am J Roentgenol 136:986–987 4. Wilms G, Oyen R, Waer M et al. (1986) CT demonstration of aneurysms in polyarteritis nodosa. J Comput Assist Tomogr 10:513–515 5. Hekali P, Kivisaari L, Standerskjo¨ld-Nordenstam CG et al. (1985) Renal complications of polyarteritis nodosa: CT findings. J Comput Assist Tomogr 9:333–338 6. Kawashima A, Sandler CM, Ernst RD et al. (2000) CT evaluation of renovascular disease. Radiographics 20:1321–1340 7. Jee KN, Ha HK, Lee IJ et al. (2000) Radiologic findings of abdominal polyarteritis nodosa. AJR Am J Roentgenol 175:1747– 1748 8. Wong WS, Moss AA, Federle MP et al. (1984) Renal infarction: CT diagnosis and correlation between CT findings and etiologies. Radiology 150:201–205 9. Fisher RG, Graham DY, Granmayeh M et al. (1977) Polyarteritis nodosa and hepatitis-B surface antigen: role of angiography in diagnosis. AJR Am J Roentgenol 129:77–81 10. Kawashima A, Sandler CM, Goldman SM, Raval BK, Fishman EK (1997) CT of renal inflammatory disease. Radiographics 17(4):851–866 11. Miller DL (2000) Angiography in polyarteritis nodosa. AJR Am J Roentgenol 175:1747–1748 12. Jee KN, Ha HK, Lee IJ et al. (2000) Radiologic findings of abdominal polyarteritis nodosa. AJR Am J Roentgenol 174:1675– 1679 13. Guillevin L, Jarrousse B, Lok C et al. (1991) Long-term follow-up after treatment of polyarteritis nodosa and Churg-Strauss angiitis with comparison of steroids, plasma exchange and cyclophosphamide to steroids and plasma exchange: a prospective randomized trial of 71 patients. J Rheumatol 18:567–574