Inflammatory and infected aneurysm

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Infected aneurysm and inflammatory aneurysm can both cause pain, weight loss, raised inflammatory markers and periaortic soft tissue, but their immediate treatments diverge. Infected aneurysm is microbial destruction of the arterial wall, often called mycotic aneurysm although fungi are not the usual cause. Bacteria reach damaged aorta by haematogenous seeding, septic emboli, contiguous spread or inoculation. Staphylococcus aureus, Salmonella species and other Gram-negative rods are important; streptococci and less common organisms vary with host, geography and exposure. The wall may form a rapidly enlarging saccular pseudoaneurysm and rupture before reaching a usual degenerative diameter threshold.

Inflammatory abdominal aortic aneurysm belongs to chronic periaortitis and features marked wall thickening, a white fibrotic periaortic mantle and adherence or entrapment of neighbouring structures. Some disease is IgG4-related and may involve pancreas, salivary glands, kidneys or other organs; other cases are IgG4-unrelated. Patients often have chronic abdominal, back, flank or pelvic pain, weight loss and raised ESR or CRP. Retroperitoneal fibrosis can obstruct one or both ureters, causing hydronephrosis and renal impairment. Its rupture risk is not thought to exceed ordinary degenerative AAA at the same aneurysm diameter, including mural thrombus but excluding periaortic inflammatory mantle or wall oedema.

CTA defines morphology, gas, rapid interval change, inflammatory mantle, adjacent organ involvement, rupture and repair anatomy. FDG PET-CT can demonstrate metabolically active inflammation or infection and help assess extent or treatment response, but uptake is not organism-specific. Blood cultures should be taken before antimicrobial therapy when this does not delay resuscitation; negative cultures do not exclude infection. Serology or molecular testing for Coxiella, Bartonella, Brucella, syphilis, tuberculosis or fungi is guided by epidemiology, immune status and the infection team rather than ordered indiscriminately.

Suspected infected aneurysm is treated with broad intravenous antibacterial therapy after cultures and prompt aortic repair irrespective of size. Open surgery permits excision, extensive debridement and multiple tissue samples, followed by in-situ or extra-anatomic reconstruction selected to anatomy and contamination. Endovascular repair can provide rapid haemorrhage control or a lower-physiological-cost option, but leaves infected tissue in place and can require prolonged suppression, drainage or later definitive surgery. ESVS describes postoperative antimicrobial courses ranging from 4–6 weeks to lifelong; the organism, immune status, repair technique, completeness of debridement and retained infected or prosthetic material determine the endpoint with microbiology input. Management belongs in a high-volume aortic centre with vascular surgery, microbiology or infectious diseases, radiology and critical care.

Steroids are reserved for inflammatory disease after infection has been reasonably excluded. ESVS describes specialist prednisone-equivalent induction of 30–80 mg daily, followed after disease control by an individualized taper toward no more than 5–10 mg daily after one year, guided by symptoms, imaging, organ involvement and toxicity. Evidence does not define one optimal duration, so this is not a bedside empirical regimen. Repair decisions use aneurysm diameter between the defined aortic wall boundaries, including mural thrombus but excluding periaortic inflammatory mantle or wall oedema; ESVS suggests repair at 55 mm and prefers EVAR when anatomy is suitable because open dissection through dense fibrosis risks ureteric, bowel and venous injury.

Key points

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.
CTA is the key anatomical study: infected disease favours saccular or multilobulated change, rapid growth, gas and destructive inflammation; inflammatory AAA classically has a mantle and dense fibrosis.
Blood cultures can be negative, especially after antibiotics; collect multiple sets first when safe and send multiple operative tissue specimens for culture and histology.
Empirical therapy should cover Staphylococcus aureus and Gram-negative rods, then narrow with infection-specialist input; duration depends on organism, debridement, reconstruction and retained infected material.
Symptomatic inflammatory AAA may receive specialist corticosteroid induction, while hydronephrosis requires renal and urological protection; markers alone cannot prove remission.
Do not include periaortic inflammatory mantle or wall oedema when measuring inflammatory AAA diameter for repair decisions.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Haematogenous bacterial seeding

Bacteraemia or septic emboli can colonize diseased aortic wall, plaque or an existing aneurysm and initiate destructive infection.

Contiguous or procedural infection

Adjacent infection, fistulation, aortic intervention or infected graft material can directly inoculate the wall and surrounding tissues.

Sterile immune-mediated periaortitis

Inflammatory AAA reflects chronic local or systemic immune activation, sometimes within the spectrum of IgG4-related disease.

Susceptible host state

Older age, atherosclerosis, diabetes, malignancy, immunosuppression and invasive infection increase vulnerability to destructive microbial aortic seeding.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Microbial wall destruction
Infection weakens media and adventitia, producing eccentric expansion, pseudoaneurysm, fistula, haemorrhage and rupture over a short interval.
2
Inflammatory fibrotic mantle
Sterile chronic inflammation surrounds the aneurysm with dense retroperitoneal fibrosis and adhesion to bowel, veins and ureters.
3
Ureteric entrapment
Fibrosis encases or displaces ureters, obstructing drainage and causing hydronephrosis, infection or chronic loss of renal function.
4
Systemic IgG4 involvement
A subset has plasma-cell-rich fibroinflammation across multiple organs, so aortic findings may be one component of systemic disease.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Infected morphologyRed flag

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

Septic presentationRed flag

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

Inflammatory triad

Chronic abdominal or back pain, weight loss and raised inflammatory markers with a circumferential mantle suggests inflammatory AAA.

Ureteric involvementRed flag

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

Fistula warningRed flag

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

Red flags requiring action

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.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line: contrast-enhanced CT angiographyFirst stepFirst line
Why
Define aneurysm morphology, rupture, gas, inflammation and repair anatomy.
Interpretation and limitations
Saccular rapid expansion, gas, periaortic collection or tissue destruction favours infection; a smooth mantle with ureteric entrapment favours inflammatory disease but is not diagnostic alone.
02
Multiple peripheral blood culture sets
Why
Identify bloodstream organisms before antimicrobial exposure whenever safely possible.
Interpretation and limitations
Positive concordant cultures guide therapy and prompt source search; negative cultures, especially after antibiotics, do not exclude infected aneurysm.
03
Full blood count CRP ESR renal and liver profile
Why
Assess systemic inflammation, organ injury and treatment safety.
Interpretation and limitations
Inflammatory markers support activity but cannot distinguish sterile from microbial disease or alone determine response and steroid withdrawal.
04
FDG PET-CT or labelled-cell imaging
Why
Map metabolically active periaortic disease and occult infectious foci.
Interpretation and limitations
Increased uptake supports active inflammation or infection but is non-specific; interpret with morphology, cultures, timing after surgery and specialist expertise.
05
Targeted microbiology and echocardiography
Why
Find organism, exposure and a potential endovascular or cardiac source.
Interpretation and limitations
Use serology, molecular assays and echo according to epidemiology and bacteraemia; broad untargeted panels can create misleading results.
06
Operative tissue culture and histology
Why
Secure microbiological and pathological diagnosis during definitive repair.
Interpretation and limitations
Send multiple deep samples before local antibiotics when possible; histology can separate suppuration, granulomatous disease, malignancy and IgG4-rich inflammation.
07
Renal tract imaging and IgG4 assessment
Why
Quantify ureteric obstruction and evaluate systemic inflammatory involvement.
Interpretation and limitations
Hydronephrosis changes urgency and may require drainage; serum IgG4 supports context but does not by itself establish tissue diagnosis.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Degenerative AAA

Ordinary fusiform aneurysm lacks convincing infection or a bulky fibrotic mantle but can still be symptomatic or ruptured.

Aortic graft infection

Prior prosthetic repair introduces biofilm, perigraft collection, gas and fistula patterns requiring a graft-specific surgical and antimicrobial strategy.

Malignancy or lymphoma

Retroperitoneal tumour can surround vessels and ureters, cause weight loss and mimic the mantle of chronic periaortitis.

Primary retroperitoneal fibrosis

Fibrosis may occur without aneurysmal dilatation and can be idiopathic, drug-associated, malignant or part of IgG4-related disease.

Large-vessel vasculitis

Giant cell or Takayasu aortitis causes wall inflammation and aneurysm but has a distinct systemic and vascular distribution.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Worked caseSeparate infection from inflammationFirst stepA painful periaortic mantle and raised CRP are found around an abdominal aneurysm.

1Check fever, haemodynamics, immune status, recent bacteraemia or procedures, exposure history, renal function and symptoms of rupture, fistula or ureteric obstruction.
2Review 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.
3Obtain multiple blood-culture sets and targeted infection tests before antibiotics when safe; do not let sampling delay treatment in sepsis or rupture.
4If infection remains plausible, start broad intravenous therapy and arrange prompt high-volume aortic-centre repair; do not expose the patient to corticosteroids.
5Only after reasonable exclusion of infection should specialist teams consider corticosteroids for symptomatic inflammatory disease and verify response with symptoms, imaging, renal function and toxicity monitoring.

02Infected aneurysmTreat infection and wall failure togetherClinical, microbiological and imaging findings make infected aneurysm suspected or probable.

1Secure cultures promptly and begin empirical intravenous cover for Staphylococcus aureus and Gram-negative rods with immediate infection-specialist input.
2Refer to a high-volume multidisciplinary aortic centre and plan prompt repair irrespective of aneurysm diameter because rupture risk is high.
3Choose open excision and debridement, in-situ reconstruction, extra-anatomic bypass or endovascular control according to anatomy, contamination and physiology.
4Collect multiple operative specimens, narrow treatment to microbiology and individualize prolonged or suppressive therapy and imaging surveillance.

03Inflammatory aneurysmProtect organs before immunosuppressionImaging suggests chronic periaortitis and targeted assessment has reasonably excluded infection.

1Measure aneurysm diameter between the defined aortic wall boundaries, including mural thrombus but excluding inflammatory mantle or wall oedema, and compare against the standard repair threshold.
2Assess pain, weight loss, hydronephrosis, renal function and other IgG4-related organs with vascular, rheumatology and urology input.
3Consider specialist corticosteroid induction for symptomatic disease below repair threshold, tapering according to clinical, imaging and toxicity response.
4Repair at appropriate diameter or for aneurysm indications, favouring EVAR when anatomy is suitable to avoid hazardous open adhesiolysis.

04Rupture or fistulaControl haemorrhage and sepsisShock, extravasation, contained rupture or gastrointestinal bleeding complicates suspected infected aneurysm.

1Activate massive-haemorrhage, vascular, anaesthetic and microbiology pathways while obtaining cultures if this does not delay control.
2Use immediate open repair or endovascular control according to anatomy, physiology and institutional expertise, recognizing that endovascular treatment may be a bridge.
3Continue prolonged targeted antimicrobial therapy, source control and individualized imaging because recurrent infection and late fistula remain possible.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Controls bloodstream and aortic-wall infection while urgent source control and definitive repair are organized.

Empirical intravenous antibacterial therapy

Immediately 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.

Reduces symptomatic sterile periaortic inflammation and fibrosis, particularly when pain, weight loss or ureteric obstruction is active.

Oral prednisolone for proven inflammatory disease

Only 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.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Rapid rupture

Infected wall may rupture at a small diameter, causing retroperitoneal or intraperitoneal haemorrhage and severe septic shock.

Aorto-enteric fistula

Erosion into bowel can present with herald bleeding, massive gastrointestinal haemorrhage, polymicrobial infection and recurrent sepsis.

Persistent prosthetic infection

Endovascular coverage or in-situ reconstruction can retain microbial burden, leading to recurrent bacteraemia, collection, fistula or late rupture.

Obstructive nephropathy

Ureteric encasement in inflammatory AAA causes hydronephrosis, progressive renal dysfunction and sometimes secondary urinary tract infection.

Treatment toxicity

Prolonged antimicrobials and corticosteroids can cause renal, hepatic, marrow, metabolic, bone and opportunistic-infection complications requiring active surveillance.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

For infected aneurysm, trend temperature, haemodynamics, pain, blood cultures, CRP, blood count and renal or hepatic function without using marker normalization as proof of cure.
Repeat CTA or selected PET-CT according to the multidisciplinary plan to assess repair integrity, residual collection, recurrent infection and new aneurysmal change.
After endovascular control watch especially for recurrent bacteraemia, perigraft gas, fistulation, sac enlargement and need for later debridement.
During corticosteroid therapy track symptoms, aneurysm diameter including mural thrombus but excluding inflammatory mantle or wall oedema, mantle or ureteric disease, renal function, glucose, pressure, infection, bone and eye risk.
Follow hydronephrosis with renal imaging and function and confirm that stenting, nephrostomy or anti-inflammatory treatment actually restores drainage.
Individualize postoperative antimicrobial duration across the ESVS range from 4–6 weeks to lifelong therapy using organism, immune status, surgical technique, debridement completeness and retained infected or prosthetic material.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Mycotic is historical

Most so-called mycotic aneurysms are bacterial; the term infected aneurysm avoids incorrectly implying a fungal cause.

Diameter does not protect

Infected aneurysms can rupture while small, so standard elective degenerative thresholds must not delay source control and repair.

Exclude the inflammatory mantle

Including periaortic oedema or fibrosis in diameter can falsely move an inflammatory AAA across an operative threshold.

Cultures may be sterile

Previous antibiotics and difficult organisms mean a negative blood culture cannot overrule destructive imaging and clinical sepsis.

EVAR controls but retains

Endovascular exclusion can rescue an unstable patient but leaves infected wall in place and may require prolonged therapy or later surgery.

Markers can mislead

ESR and CRP may normalize before metabolic or structural inflammatory disease resolves, so follow-up must include imaging and organ assessment.

11Common pitfallsFrequent interpretation and management errors.

01
Do not equate every periaortic inflammatory mantle with sterile disease and start corticosteroids before infection assessment.
02
Do not wait for a usual AAA diameter threshold when infected aneurysm is suspected.
03
Do not delay empirical intravenous therapy in sepsis while awaiting final culture identification.
04
Do not accept one negative blood culture or prior antibiotic exposure as exclusion of infection.
05
Do not confuse patent contrast-flow lumen with aneurysm diameter: include mural thrombus, but exclude inflammatory mantle or wall oedema from the diameter used for repair decisions.
06
Do not assume endovascular exclusion has eradicated infection or remove the patient from long-term surveillance.
07
Do not use CRP alone to decide that inflammatory periaortitis is controlled or steroids can stop.

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