Imaging recommendation · Abdomen · Pelvis

Fever of unknown origin (FUO) — imaging workup

Q: What's the alternative imaging for fever of unknown origin (fuo) — imaging workup when endocarditis on the differential?

Transthoracic echo → TEE if negative (see endocarditis) (no contrast).

Q: What's the alternative imaging for fever of unknown origin (fuo) — imaging workup when suspected vasculitis (lvv / gca)?

NM — FDG-PET-CT or CTA/MRA (see lvv) (iv contrast).

Q: What's the alternative imaging for fever of unknown origin (fuo) — imaging workup when suspected hardware infection (graft, pacemaker, joint)?

NM — FDG-PET-CT or labeled WBC scan (iv contrast).

Q: What's the alternative imaging for fever of unknown origin (fuo) — imaging workup when lymphoma suspected?

NM — FDG-PET-CT (see lymphoma-staging) (iv contrast).

Q: What's the alternative imaging for fever of unknown origin (fuo) — imaging workup when splenic / hepatic abscess suspected?

CT — Contrast-enhanced CT or MRI (see liver-abscess, splenic-abscess) (iv contrast).

Recommended: Contrast-enhanced CT chest/abdomen/pelvis; FDG-PET-CT if non-diagnostic is the preferred imaging study for fever of unknown origin (fuo) — imaging workup. Imaging is one of the later steps in classic FUO workup (after history, exam, labs, cultures).

Recommended study

Contrast-enhanced CT chest/abdomen/pelvis; FDG-PET-CT if non-diagnostic

CT IV contrast Preferred Abdomen · Pelvis Acute inpatientOutpatient Reviewed 2026-05

Imaging is one of the later steps in classic FUO workup (after history, exam, labs, cultures). CT CAP with IV contrast covers most occult infections, abscesses, lymphoma, and solid malignancies. FDG-PET-CT is the highest-yield single study when CT is non-diagnostic — sensitive for vasculitis (LVV), infection, lymphoma, and many solid tumors.

If the default doesn't apply

Endocarditis on the differential

Transthoracic echo → TEE if negative (see endocarditis) No contrast

Suspected vasculitis (LVV / GCA)

NM FDG-PET-CT or CTA/MRA (see lvv) IV contrast

Suspected hardware infection (graft, pacemaker, joint)

NM FDG-PET-CT or labeled WBC scan IV contrast

Lymphoma suspected

NM FDG-PET-CT (see lymphoma-staging) IV contrast

Splenic / hepatic abscess suspected

CT Contrast-enhanced CT or MRI (see liver-abscess, splenic-abscess) IV contrast

Watch-outs

Don't lead with imaging in FUO

Imaging is high-yield only after appropriate history, exam, cultures, and serologies — premature scans often produce incidentalomas without answering the fever question.

FDG-PET in immunocompromised

Sensitive but less specific — colonic and lymphatic uptake from non-pathologic inflammation may confound. Correlate with anatomic imaging.

Pearls

Classic FUO: temperature > 38.3 °C lasting > 3 weeks with no diagnosis after 1 week of investigation.
FDG-PET-CT yield in FUO: ~50–60% diagnostic contribution in published series.
If TTE is non-diagnostic for endocarditis with persistent bacteremia, FDG-PET or labeled WBC scan can localize septic emboli foci.
Don't miss chronic intra-abdominal abscess (e.g., post-cholecystectomy biloma) — CT abdomen/pelvis catches these.