Inflammatory and infected aneurysm

Synopsis

Distinguish sterile periaortic fibrosis from infected aneurysm, secure microbiology, and coordinate safe immunosuppression, antimicrobial therapy and repair.

Infected aneurysm causes destructive microbial aortitis with rapid expansion and rupture risk; obtain cultures, start intravenous antibacterial therapy and arrange prompt repair irrespective of diameter.
Inflammatory AAA is usually sterile chronic periaortitis with a thickened wall, fibrotic mantle, pain, weight loss and possible ureteric obstruction.
Never start corticosteroids for presumed inflammatory aneurysm until infected aneurysm, tuberculosis and other relevant infections have been actively assessed and reasonably excluded.

Key red flags

Periaortic gas, rapidly enlarging saccular or multilobulated morphology, adjacent tissue destruction, bacteraemia or sepsis strongly supports infected aneurysm.

Haematemesis or gastrointestinal bleeding with prior aortic repair can represent an aorto-enteric fistula and needs immediate aortic surgical management.

Pain, weight loss, inflammatory markers and a periaortic mantle occur in inflammatory AAA but do not exclude infection; cultures and targeted microbiology must come before steroids.

Hydronephrosis or declining renal function can result from ureteric entrapment in periaortic fibrosis and needs prompt urological as well as aortic review.

Immunosuppression, malignancy, invasive infection, endocarditis or recent bacteraemia increases infected aneurysm risk and lowers the threshold for urgent investigation.

Infected morphology

A painful rapidly changing saccular, eccentric or multilobulated aneurysm with gas or destructive periaortic change is highly concerning.

Septic presentation

Fever, rigors, bacteraemia, leukocytosis and high inflammatory markers with focal aortic pain support microbial aortitis.

Ureteric involvement

Flank pain, hydronephrosis, rising creatinine or reduced urine output can reflect fibrosis entrapping the ureter.

Fistula warning

Herald haematemesis, melaena or unexplained sepsis after aortic disease or repair may precede catastrophic aorto-enteric bleeding.

Investigation priorities

First-line: contrast-enhanced CT angiographyFirst stepFirst line

Define aneurysm morphology, rupture, gas, inflammation and repair anatomy.

Management branches

Worked caseSeparate infection from inflammation

A painful periaortic mantle and raised CRP are found around an abdominal aneurysm.

Check fever, haemodynamics, immune status, recent bacteraemia or procedures, exposure history, renal function and symptoms of rupture, fistula or ureteric obstruction.
Review CTA for aneurysm diameter including mural thrombus but excluding inflammatory mantle or wall oedema, saccular or multilobulated shape, interval growth, gas, collection, tissue destruction, fibrosis and hydronephrosis.

Key medicines

Empirical intravenous antibacterial therapyImmediately after multiple blood-culture sets are secured when safe, start the locally approved full adult intravenous regimen covering Staphylococcus aureus, including local MRSA risk, and Gram-negative rods; adjust for allergy, renal function, prior cultures and local resistance, then narrow to microbiology. After repair, individualize duration from 4–6 weeks through lifelong therapy according to organism, immune status, repair and debridement, and retained infected or prosthetic material.Obtain microbiology or infectious-diseases advice at once; monitor renal, hepatic and marrow toxicity, interactions and Clostridioides difficile risk, and narrow promptly to cultures. Antibiotics alone do not neutralize the rupture risk of an infected aneurysm.

Oral prednisolone for proven inflammatory diseaseOnly after infection is reasonably excluded, a specialist may use prednisone-equivalent 30–80 mg orally once daily for induction; after disease control taper individually according to symptoms, imaging, organ response and toxicity, aiming for no more than 5–10 mg daily after one year. Evidence does not establish one universal duration.Do not start empirically when cultures or imaging leave infection plausible; screen and protect against steroid complications according to dose and duration, including glucose, blood pressure, bone, gastric, psychiatric and opportunistic-infection risks, and involve urology urgently for obstructed kidneys.

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