Polyarteritis nodosa (PAN) is a necrotizing vasculitis affecting medium-sized muscular arteries. There is NO small vessel (arteriole, venule, capillary) involvement — this feature distinguishes PAN from microscopic polyangiitis (MPA). ANCA negative. Two main forms exist: hepatitis B-associated PAN (30-40%, declining) and idiopathic PAN. Renal arteries (70-80%), mesenteric arteries (50-60%), hepatic arteries (40-50%), coronary, and cerebral arteries are most commonly affected. On conventional angiography/CT angiography, multiple small saccular microaneurysms (<10-15 mm) and segmental stenoses ('beading' appearance) are pathognomonic. Microaneurysm rupture may lead to retroperitoneal or intra-abdominal hemorrhage. Treatment is immunosuppression (corticosteroids + cyclophosphamide) and antiviral therapy if hepatitis B positive.
Age Range
25-65
Peak Age
45
Gender
Male predominant
Prevalence
Rare
In PAN, immune complex-mediated necrotizing inflammation transmurally damages the wall at branching points and bifurcations of medium-sized muscular arteries. Pathogenesis: immune complexes (hepatitis B-associated or idiopathic) deposit in the vessel wall → complement activation → neutrophil infiltration → fibrinoid necrosis (involving all tunica layers — intima, media, adventitia) → destruction of internal and external elastic lamina → wall loses structural integrity. Under intraluminal pressure, saccular dilatations form at weakened wall segments → microaneurysms (<10-15 mm). The inflammatory process simultaneously causes intimal proliferation and wall edema → segmental stenoses and thrombotic occlusions → distal organ ischemia. On CT/conventional angiography, microaneurysms appear as contrast-filled small saccular outpouchings because the weakened wall balloons and fills with contrast — these saccular dilatations create a 'nodular' appearance compared to normal vascular diameter (hence the disease name 'nodosa'). Alternating narrowing-dilatation between segmental stenoses and microaneurysms creates the 'beading' appearance. In the chronic phase, fibrosis and scar tissue lead to organization of lesions and vessel wall thickening.
Multiple small saccular microaneurysms (<10-15 mm) at branching points of medium-sized arteries with alternating beading pattern from segmental stenoses is the pathognomonic angiographic finding of PAN. This pattern in the appropriate clinical context (ANCA negative, multi-organ involvement, hepatitis B) confirms the diagnosis.
Multiple small saccular (sometimes fusiform) microaneurysms (<10-15 mm) at branching points of renal, hepatic, and mesenteric arteries on arterial phase CTA. Microaneurysms are contrast-filled and appear as saccular outpouchings markedly larger than the parent artery diameter. Bilateral renal artery involvement is common. Multiple saccular aneurysms in the hepatic artery may be accompanied by focal perfusion defects in the liver parenchyma. Modern CTA (thin-section, high-resolution) approaches conventional angiography sensitivity.
Report Sentence
Multiple small saccular microaneurysms in renal, hepatic, and mesenteric arteries, consistent with polyarteritis nodosa.
Focal segmental stenoses in medium-sized arteries on CTA — focal narrowing from normal diameter artery followed by return to normal diameter or aneurysmal dilatation ('beading' pattern). Stenosis segments are 5-20 mm in length and result from inflammatory intimal thickening, edema, and thrombosis. Alternating stenosis-aneurysm pattern is highly specific for PAN and is distinguished from similar 'string-of-beads' pattern in fibromuscular dysplasia by clinical context.
Report Sentence
Segmental stenoses alternating with microaneurysms (beading pattern) in medium-sized arteries, consistent with polyarteritis nodosa.
Wedge-shaped hypoperfused areas (renal infarcts) in the kidneys on portal venous phase. Develops from segmental renal artery occlusion — classic infarct morphology with base at capsule and apex pointing toward hilum. Multiple bilateral renal infarcts are highly suggestive of PAN. In chronic phase, cortical thinning and focal scar formation are seen.
Report Sentence
Multiple wedge-shaped hypoperfused areas in bilateral kidneys, consistent with renal infarcts in the setting of vasculitis.
Mural enhancement of affected arteries on contrast-enhanced MRA — indicates active vascular inflammation. High-resolution vessel wall MRI (black-blood technique) demonstrates active inflammation foci as T2 hyperintensity and wall enhancement on contrast T1 sequences. MRA can detect microaneurysms and segmental stenoses with sensitivity comparable to CTA.
Report Sentence
Mural enhancement and T2 hyperintense wall edema in affected arteries, consistent with active vasculitis.
Increased flow velocities (stenosis) in renal arteries and focal hypoperfused areas in renal parenchyma on Doppler US. PSV increase (>150-200 cm/s) and post-stenotic tardus-parvus pattern in renal artery main trunk and segmental branches. Bilateral decrease in kidney sizes indicates chronic involvement. US is used for initial screening but diagnostic sensitivity is limited.
Report Sentence
Increased flow velocities in bilateral renal arteries and focal hypoperfused areas in renal parenchyma, further evaluation with CTA recommended for vasculitis.
Active contrast extravasation and/or perirenal/intra-abdominal hematoma on CTA in microaneurysm rupture. High-density (50-70 HU) hematoma around the ruptured microaneurysm and contrast accumulation (150-300 HU) at the active bleeding site are seen. Renal and hepatic artery microaneurysm ruptures are the most common hemorrhages. This finding represents a life-threatening emergent complication of PAN requiring selective embolization or surgery.
Report Sentence
Active contrast extravasation and hematoma around renal/hepatic artery microaneurysm, consistent with microaneurysm rupture; emergent selective embolization is indicated.
Criteria
HBsAg positivity + PAN vasculitis findings. Incidence declining (HBV vaccination programs). Antiviral therapy + immunosuppression.
Distinct Features
Hepatic artery involvement more prominent. Remission may be achieved with HBV seroconversion.
Criteria
Hepatitis B negative, no known etiology. Autoimmune mechanism. Has become the more common form.
Distinct Features
Renal and mesenteric artery involvement common. Requires long-term immunosuppression. Relapse risk 20-30%.
Criteria
Vasculitis limited to skin and subcutaneous tissue without systemic involvement. Good prognosis. No visceral organ involvement or microaneurysms.
Distinct Features
CTA/MRA normal — no angiographic findings. Diagnosis by skin biopsy. Local treatment may be sufficient.
Distinguishing Feature
FMD in young women, 'string-of-beads' in mid-distal renal artery — PAN multi-organ involvement at branching points, elevated inflammatory markers, ANCA negative.
Distinguishing Feature
In mycotic aneurysm usually single saccular aneurysm with periaortic inflammatory changes; in PAN multiple small microaneurysms with beading pattern and multi-organ involvement.
Distinguishing Feature
Isolated SMA aneurysm is usually single, larger (>15 mm), in setting of atherosclerosis/pancreatitis; PAN has multiple small microaneurysms (<10-15 mm) in multiple vascular beds.
Distinguishing Feature
Takayasu affects large vessels (aorta and primary branches), in young women, wall thickening predominant; PAN affects medium-sized arteries, microaneurysms and beading pathognomonic.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
3-monthPAN treatment is based on immunosuppression: induction with corticosteroids (prednisolone 1 mg/kg/day) + cyclophosphamide (for severe organ involvement); maintenance with azathioprine or methotrexate for 12-18 months. In HBV-associated PAN: antiviral therapy (entecavir/tenofovir) + plasmapheresis + short-course corticosteroids. Microaneurysm rupture is a life-threatening complication — selective embolization or surgical ligation required. 5-year survival with treatment 80-90%, without treatment 10-15%. Follow-up: CTA or MRA every 3-6 months for aneurysm size change, new lesion development, and organ perfusion assessment.
PAN treatment is immunosuppressive (high-dose corticosteroids + cyclophosphamide in severe cases) and antiviral therapy if hepatitis B-associated. Microaneurysm rupture can cause retroperitoneal or intra-abdominal hemorrhage (emergency). Renal artery involvement can cause renovascular hypertension. Untreated mortality is high; 5-year survival exceeds 80% with immunosuppressive therapy.