Inflammatory Aortic Aneurysm

An inflammatory aortic aneurysm is an aneurysm with a markedly thickened wall, dense perianeurysmal fibrosis, and adherence of neighbouring structures (duodenum, ureters, inferior vena cava, left renal vein). The abdominal aorta is the usual site.

It makes up about 3 to 10% of abdominal aortic aneurysms. Patients are about 5 to 10 years younger than typical patients, men outnumber women by about 6 to 1, and most are smokers.

Part of the group belongs to IgG4-related disease and idiopathic retroperitoneal fibrosis (periaortitis). Others are linked to autoimmune disease, drugs (methysergide) and infection.

Typical features are abdominal or back pain, weight loss and a raised ESR. Rupture is less frequent than in non-inflammatory aneurysms of the same size, though it still occurs.

Pathophysiology. An immune response to atherosclerotic plaque components and perhaps to ceroid in the wall causes lymphoplasmacytic infiltration and fibrosis of the adventitia and surrounding tissue. The posterior wall is usually spared. Fibrosis traps and obstructs the ureters, duodenum and veins.

• Abdominal, flank or back pain (about 80%), often constant, with weight loss, fever and malaise.
• Tender or pulsatile abdominal mass.
• Ureteric obstruction with hydronephrosis, loin pain and renal impairment (about 20 to 30%).
• Duodenal obstruction (vomiting), deep venous thrombosis from caval compression, and haematuria.
• Raised ESR and CRP, anaemia, hypergammaglobulinaemia.

Red flags.

• Sudden severe pain, hypotension or syncope (rupture)
• Hydronephrosis with a rising creatinine or anuria
• Persistent vomiting from duodenal obstruction
• Fever with raised CRP and gas on imaging (infected aneurysm)
• Rapid growth, or diameter of 55 mm or more (50 mm in women)

• CT angiography. Thickened enhancing wall with a surrounding soft tissue mantle that spares the posterior wall, aneurysm size, relation to the renal arteries, hydronephrosis, and involvement of the ureters, duodenum and vena cava. A rim of low attenuation outside the calcified wall is typical.
• MRI for the mantle and activity. FDG PET-CT for activity and extent, and for other sites of IgG4-related disease.
• Ultrasound for follow up of size and hydronephrosis.
• Laboratory. ESR, CRP, full blood count, creatinine, serum IgG4 and subclasses, ANA, ANCA, rheumatoid factor, complement, blood cultures, tuberculosis tests, and syphilis serology.
• Biopsy of the mantle or another IgG4 site when malignancy (lymphoma, sarcoma) or infection is possible. Needle biopsy of the aorta itself is avoided.

Differential diagnosis.

• Atherosclerotic abdominal aortic aneurysm with a chronic contained leak
• Infected (mycotic) aneurysm
• Idiopathic retroperitoneal fibrosis and periaortitis
• Retroperitoneal lymphoma, sarcoma and metastasis
• Erdheim-Chester disease
• Aortic dissection with intramural haematoma
• Aortitis from other causes (Takayasu, giant cell, Behçet)

Medical.

• Stop smoking. Blood pressure under 130/80 mm Hg. Atorvastatin 40 to 80 mg orally once daily, with liver enzymes at baseline and 3 months, and aspirin 75 to 100 mg once daily (usual maximum 325 mg daily) for atherosclerotic disease.
• Bisoprolol 2.5 mg orally once daily, increased to 5 to 10 mg once daily, maximum 20 mg daily (do not exceed 10 mg daily at creatinine clearance under 20 mL/min or in severe liver impairment), for hypertension and heart rate.
• Prednisolone 0.5 to 1 mg/kg orally once daily (usually 30 to 40 mg), for 4 weeks, then tapered over 3 to 6 months, for IgG4-related or active periaortitis, for pain and before repair when the mantle is dense. It shrinks the mantle and relieves ureteric obstruction. Add calcium, vitamin D, gastric protection, and monitoring of glucose and blood pressure. It does not stop aneurysm growth.
• Steroid sparing for relapse: azathioprine 1 mg/kg orally once daily increased to a maximum of 2 mg/kg daily (check TPMT or NUDT15 first, full blood count weekly for 4 weeks then monthly, reduce to a quarter of the dose with allopurinol), or mycophenolate mofetil 1 g orally twice daily (maximum 3 g daily, contraindicated in pregnancy), or rituximab 375 mg/m2 intravenously weekly for 4 weeks for IgG4-related disease.

Indications for repair. Diameter of 55 mm or more in men and 50 mm or more in women, symptomatic aneurysm, rapid growth (over 10 mm in 1 year), rupture, or progressive ureteric obstruction.

Options.

• Endovascular repair is preferred when the anatomy suits it. It avoids dissection through the fibrotic mantle, has lower early mortality (about 1 to 3%), and the mantle regresses in about half to two thirds of patients. Ureteric obstruction may persist and needs stenting or steroids.
• Open repair with a suprarenal or supracoeliac clamp, leaving the adherent duodenum and ureters alone, with the inflammatory rind left in place. Early mortality is about 3 to 8%, and injury to the duodenum, ureter, left renal vein or vena cava is the main hazard.
• Prophylaxis: cefazolin 2 g intravenously as a single dose 30 to 60 minutes before incision (3 g if over 120 kg), with vancomycin 15 mg/kg intravenously for severe penicillin allergy or MRSA.
• Rupture: emergency repair with permissive hypotension (systolic 70 to 90 mm Hg) until control, and crossmatched blood.
• Ureteric obstruction with renal impairment: ureteric stent or nephrostomy before or alongside repair, with steroids to shrink the mantle.
• After endovascular repair: aspirin 75 to 100 mg once daily long term.

Infected aneurysm. Manage with prolonged antibiotics and surgical debridement when blood cultures, gas or a fluid collection suggest infection.

Monitoring. CRP and ESR every 4 to 8 weeks on steroids. Creatinine and ultrasound for hydronephrosis. CT at 1 month, 6 months and 12 months after repair, then yearly. PET-CT if inflammation or IgG4-related disease is suspected to persist.

Referral and escalation. Refer to a vascular surgery service with endovascular capability, and to rheumatology or nephrology for IgG4-related disease and renal obstruction. Emergency for rupture, anuria or sepsis.