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Polyarteritis nodosa is a progressive inflammatory vasculitis, characterized by progressive fibrinoid necrotizing inflammatory foci in the walls of small- and medium-sized muscular arteries; a characteristic finding is the presence of aneurysms as large as 1 cm in diameter. The incidence is unknown, but this uncommon disease affects people in their fourth and fifth decades of life; the male-to-female ratio is 2-3:1. The primary abnormal changes of the involved vessel consist of fibrinoid or hyaline necrosis of the media with simultaneous or subsequent involvement of the intima and adventitia. Secondary changes include aneurysm formation, hemorrhage, and thrombosis. The kidney is most commonly involved (80-100%), followed by the heart (up to 70%), gastrointestinal tract (50-70%), liver (50-60%), spleen (45%), and pancreas (25-35%) [1]. If untreated, polyarteritis nodosa is usually fatal as a result of progressive renal failure or gastrointestinal complications. However, therapy with corticosteroids and cyclophosphamide results in remission or cure in 90% of patients [2].

Until recently, little had been reported in radiology literature regarding polyarteritis nodosa [3]. To our knowledge, most of the reports have focused on angiography. The purpose of this study was to evaluate the radiographic and imaging findings of seven patients with polyarteritis nodosa involving the abdomen.

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We reviewed the medical records and radiologic findings of seven patients with polyarteritis nodosa involving the abdomen; these cases were collected from three institutions. The patients, three men and four women, were 23-58 years old (mean, 47 years). The diagnosis was made by angiographic findings (n = 6) findings and pathologic reports obtained from the surgical (n = 2) or biopsy (n = 5) specimens of the bowel, muscle, or skin. The patients had symptoms and signs of diffuse abdominal pain (n = 6), hypertension (n = 4), abdominal bruit (n = 1), hematochezia (n = 2), fever and chills (n = 3), skin rash (n = 1), and right-sided flank pain with gross hematuria (n = 1), with a duration of several days to more than four years. Positive laboratory findings included elevation of erythrocyte sedimentation rate (n = 7), leukocytosis (n = 5), and positive rheumatoid factor (n = 2). There was no positive hepatitis B—virus antigenemia in six patients tested. Of the three patients who underwent serologic tests for antineutrophilic cytoplasmic autoantibody, two had positive results. The radiologic studies available in these seven patients were angiography in seven, abdominal CT in four, MR imaging in two, and small-bowel follow-through examination in three. Surgery (segmental bowel resection) was performed in two of the seven patients. The indications for surgery were persisting hematochezia with rapidly decreasing hemoglobin level in one patient and clinical symptoms and signs of bowel obstruction in the other.

CT scans were performed using a 9800 Quick System (General Electric Medical Systems, Milwaukee, WI) and Somatom Plus-S, Plus-4, and Plus-40 (Siemens, Erlangen, Germany) with 8- or 10-mm slice thickness at 8- or 10-mm intervals from the dome of the liver to the symphysis pubis. Approximately 600-900 ml of oral contrast material ([2% barium sulfate suspension] E-Z CAT; E-Z-EM, Westbury, NY) was administered 1 hr before scanning in all patients except one who was suspected of having small-bowel obstruction. One hundred to one hundred twenty milliliters of IV contrast material ([iopamidol] Iopamiro 300, Bracco, Milan, Italy; or [iopromide] Ultravist, Schering, Berlin, Germany) was administered as a bolus at 3 ml/sec. Scanning was started 40-60 sec after IV infusion with a scanning time of 0.8-2.0 sec and an interscan delay of 1.8-3.5 sec.

MR imaging was performed in two patients because of the presence of residual barium in the bowel from a previous small-bowel follow-through examination in one and a physician's request in the other. MR imaging was obtained with a 1.5-T superconductive unit (Magnetom Vision; Siemens) using a body phased array coil. The MR imaging sequences used were breath-hold coronal and axial T1-weighted fast low-angle shot two-dimensional imaging and T2-weighted half-Fourier acquisition single-shot turbo spin-echo imaging.

We evaluated involvement patterns in the abdominal organs and radiographic and imaging features in these seven patients. The findings were retrospectively analyzed by two radiologists. If their interpretations differed, a consensus was reached for the final decision.

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Radiographic, CT, and MR imaging findings are summarized in Table 1.

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TABLE 1 Radiographic and Imaging Findings of Seven Patients with Polyarteritis Nodosa

Six of the seven patients had involvement of the gastrointestinal tract (Figs. 1A,1B,1C,1D,2A,2B,3). Mesenteric artery involvement was confirmed at angiography in five of the six patients. In the sixth patient, involvement was confirmed on histopathologic examination after segmental bowel resection for small-bowel obstruction. On angiography, multiple microaneurysms (Fig. 1B) were seen at the jejunal, ileal, right-colic, and midcolic branches of the superior mesenteric artery. In one patient, the inferior mesenteric artery branches were also involved. Other angiographic findings included vascular narrowing and irregularity in three patients and focal areas of hypervascularity in one. Of the six patients with involvement of the gastrointestinal tract, two underwent CT, one underwent MR imaging, and one underwent both CT and MR imaging. CT and MR imaging showed bowel wall thickening in three patients (small intestine in two patients and small intestine, colon, and rectum in one patient), with target sign in the thickened bowel wall in two, mesenteric vascular engorgement and haziness in three, and ascites in two. In one patient, MR imaging showed high-grade small-bowel obstruction with beaklike luminal narrowing at the distal jejunum (Fig. 2A,2B). In the other patient, in whom neither CT nor MR imaging was performed, small-bowel follow-through examination showed diffuse mucosal fold thickening from the duodenum through the ileum (Fig. 3).

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Fig. 1A. —42-year-old man with fever, myalgia, arthralgia, and peripheral neuropathy. Contrast-enhanced CT scan shows diffuse bowel wall thickening of small (asterisks) and large (arrowheads) intestine with target sign. Note bilateral ureteral dilatation (arrows) and large amount of ascites.

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Fig. 1B. —42-year-old man with fever, myalgia, arthralgia, and peripheral neuropathy. Superior mesenteric arteriogram shows multiple microaneurysms (arrows) in peripheral branches of superior mesenteric artery.

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Fig. 1C. —42-year-old man with fever, myalgia, arthralgia, and peripheral neuropathy. Hepatic angiogram shows multiple microaneurysms (arrows) in hepatic artery branches.

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Fig. 1D. —42-year-old man with fever, myalgia, arthralgia, and peripheral neuropathy. Follow-up contrast-enhanced CT scan obtained 1 month after A, after treatment with steroid therapy, shows improvement of bowel wall thickening. However, both bilateral ureteral dilatation (arrows) and ascites are still visible.

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Fig. 2A. —55-year-old woman with diffuse abdominal pain and vomiting for 5 days. Overhead radiograph in small-bowel follow-through examination shows abrupt, concentrical luminal narrowing (arrows) of jejunum with high-grade small-bowel obstruction, simulating jejunal malignancy.

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Fig. 2B. —55-year-old woman with diffuse abdominal pain and vomiting for 5 days. Coronal half-Fourier acquisition single-shot turbo spin-echo MR image (TR/TE, 4/59; matrix, 128 × 256; field of view, 338 × 450; flip angle, 140°; slice thickness, 7 mm; and no interslice gap) shows short length of luminal narrowing (arrowheads) of jejunum and diffuse dilatation of proximal intestinal loop. Note residual barium suspension (asterisks) in small-intestine loop, which appears to be hypointense.

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Fig. 3. —58-year-old man with abdominal pain and hematochezia. Upper gastrointestinal radiography shows diffuse fold thickening of duodenum. Similar findings were seen in small-intestine loop (not shown).

The genitourinary system was involved in five of the seven patients (Figs. 1A,1B,1C,1D, 4A,4B,4C, and 5); the unilateral renal artery in one; bilateral renal arteries in two; bilateral renal arteries and middle one third of the ureter in one; and bilateral renal arteries, bilateral ureterovesical junction of the ureter, and bladder in one. Renal artery involvement was confirmed on angiography on which multiple aneurysms (Fig. 4A,4B,4C) were noted in the arcuate and interlobar branches of the renal artery in these five patients and slight luminal irregularities of the arterial wall in two of the five. In these five patients, CT or MR imaging was available in four patients and showed multifocal areas of renal infarction in two, bilateral ureteral obstruction in two, perinephric hematoma (Fig. 5) caused by aneurysmal rupture in one, and diffuse bladder wall thickening in one.

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Fig. 4A. —57-year-old woman with ureteral obstruction caused by polyarteritis nodosa. Contrast-enhanced CT scan shows bilateral ureteral dilatation (arrowheads).

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Fig. 4B. —57-year-old woman with ureteral obstruction caused by polyarteritis nodosa. Renal angiograms show numerous microaneurysms (arrowheads).

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Fig. 4C. —57-year-old woman with ureteral obstruction caused by polyarteritis nodosa. Renal angiograms show numerous microaneurysms (arrowheads).

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Fig. 5. —42-year old man with abrupt right-sided flank pain and gross hematuria. Contrast-enhanced CT scan shows right perinephric hematoma (H). Note multifocal areas of tiny parenchymal defects (arrows) in spleen caused by infarction.

The liver was involved in four of the seven patients, with multiple aneurysms (n = 4) (Fig. 1C) in the hepatic arterial branches on angiography and focal parenchymal infarction (n = 1) on CT. The spleen was involved in three patients; multiple aneurysms were revealed on angiography in all three of these patients, and infarctions (Fig. 5) were noted in two of the three. In one patient, left gastric artery branches were seen to be involved with multiple aneurysms on angiography.

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The exact cause of polyarteritis nodosa is not clear. In the past, some investigators believed that drugs and serum therapy, including sulfonamides, serums, vaccines phenytoin sodium, iodine, thiouracil, and many other drugs, were possible causative agents [4]. However, other conditions, such as bacterial infection, toxic injury, diseases of the central nervous system, and viral infection, were also proposed as possible contributing agents [4]. Therefore, it is likely that polyarteritis nodosa creates a nonspecific hypersensitivity to numerous antigens. The disease process chiefly involves the small- and medium-sized arteries and arterioles in a segmental fashion; the venules are rarely involved. Although none of our patients had positive hepatitis B—virus surface antigenemia, 36% of patients with polyarteritis nodosa have been reported to have hepatitis B antigen in their serum [1].

The clinical diagnosis of polyarteritis nodosa is usually made on the basis of various symptoms and signs of abdominal pain, hypertension, arthralgia or arthritis, peripheral and central nervous system dysfunction, retinopathy, and cardiac, respiratory, and hepatic involvement [4]. Such protean clinical manifestations frequently present a diagnostic challenge. Without angiography, the correct diagnosis is established only by obtaining a biopsy of subcutaneous nodules or skeletal muscle; however, the diagnostic success rate of the biopsy has been disappointing (20-35%) [5]. Therefore, a negative biopsy does not rule out the condition. In addition, antineutrophilic cytoplasmic autoantibodies are antibodies directed against certain proteins in the cytoplasm of neutrophils and are often present in the serum of patients with polyarteritis nodosa and correlate with their disease activity. However, this test is not specific for cases of polyarteritis nodosa; it is also positive in Churg-Strauss syndrome, Wegener's granulomatosis, and microscopic polyangitis [6]. Many authors have agreed that angiography helps to confirm the suspected clinical diagnosis. Findings of multiple, small-sized aneurysms on angiography are pathognomonic for the disease. The aneuryms are usually multiple (most often 10 or more in any one visceral circulation) and 2-5 mm, commonly affecting the branch points of arteries. Studies regarding the frequency of this finding have been limited. According to a study by Travers et al. [1], angiography revealed aneurysms in 60-80% of patients.

The kidney is the most frequently affected organ. Depending on the vessels involved, renal polyarteritis nodosa may present clinically as acute or chronic renal failure or nephrotic syndrome or may be manifested by perirenal hemorrhage. With renal complications, hypertension often develops rapidly. Two characteristic lesions have been described in polyarteritis nodosa when the kidney is involved: an arteritis and a glomerulitis that may occur separately or together [7]. The arteritis primarily involves the arcuate vessels and consists of fibrinoid necrosis and vascular thrombosis. Thus, multiple small renal infarcts are a prominent feature. The aneurysm, forming as a result of focal necrosis of the vessel wall, may undergo necrosis and healing with fibrosis, but occasionally will rupture and produce perirenal and retroperitoneal hemorrhage [7], as occurred in one of our cases. Two of our patients had involvement of the extrarenal genitourinary system (ureter and bladder). Hydronephrosis can occur in patients with polyarteritis nodosa and in patients with other types of vasculitis such as systemic lupus erythematosus and Henoch-Schönlein syndrome and seems to be caused by either detrusor muscle spasm with subsequent vesicoureteral reflux or fibrosis of the ureterovesical junction [8].

Approximately one half to two thirds of patients with polyarteritis nodosa have abdominal pain, nausea, vomiting, or other gastrointestinal symptoms. The gastrointestinal lesions may take the form of ulceration, perforation, hemorrhage, or infarct and produce corresponding symptoms: gastrointestinal hemorrhage occurs in roughly 6% of cases; bowel perforation in 5%; and bowel infarction in 1% [1, 2]. In the gastrointestinal tract, the jejunum appears to be most commonly involved. Generally, when the aneurysms involve the mesenteric arteries, their number and size are fewer and smaller compared with those of the kidney and liver [9]. The infarcted bowel progresses into either bowel perforation or bowel obstruction caused by stricture. As in one of our cases with focal bowel stricture caused by mesenteric ischemia, differentiation from malignant or chronic granulomatous inflammatory bowel diseases may be difficult on barium or imaging studies.

In addition to the genitourinary and gastrointestinal tracts, any organ in the abdomen can be involved. The liver is the most common site of involvement in patients with polyarteritis nodosa. The vascular changes in the liver result in aneurysm formation, rupture of aneurysm, infarction, interstitial hepatitis, and liver cirrhosis. Although the liver is commonly involved, there are few clinical signs or symptoms suggesting hepatic involvement [9]. The cystic arteries are also a frequent site of developing arteritis, and subsequent acalculous cholecystitis and intracholecystic hemorrhage have been reported [10]. According to a series describing 17 patients with polyarteritis nodosa [11], the pancreas was involved in eight cases and the spleen in three cases.

Because a definite diagnosis depends largely on the detection of small-sized aneurysms on angiography, the specificity of this finding should be taken into consideration. Drug abuse is an accepted cause of multiple microaneurysms in various organs. Citron et al. [12] reported that the diverse clinicopathologic syndrome and angiographic findings of necrotizing angiitis associated with drug abuse were strikingly similar to those of polyarteritis nodosa with severe renal, gastrointestinal, cardiac, and neurologic involvement. Other vasculitides, such as Wegener's granulomatosis and systemic lupus erythematosus, have also been reported in the literature to have multiple aneurysms similar to those of polyarteritis nodosa [13].

In conclusion, the possibility of vasculitis should be considered when multiple abdominal organs have abnormal radiologic findings; however, angiography is necessary for establishing a specific diagnosis of polyarteritis nodosa.