Patchy mid-wall or subepicardial LGE in the basal septum and lateral wall — often crossing the septum to the RV side — on CMR; focal FDG uptake after proper dietary suppression on PET shows activity. Scar tells you where, PET tells you whether it is active.
Orient first
- Granulomas scar the myocardium in a non-coronary pattern; the basal septum is favoured, which explains conduction block.
- CMR is the most sensitive test for scar; FDG PET shows active inflammation and guides steroid therapy — the two are complementary.
- Normal myocardium uses glucose; without a high-fat, low-carbohydrate preparation (and/or heparin) physiological uptake mimics sarcoid.
Acquire the study
- Cine short-axis stack and long axes; T2 mapping or T2-weighted STIR; LGE with PSIR in short axis and long axes, windowed for the RV side of the septum too.
The manoeuvre
- LGE: patchy mid-wall/subepicardial enhancement in basal septum and lateral wall; RV-side septal and RV free-wall involvement ("hook" across the insertion point).
- Cine: regional wall thinning, aneurysm, RV dysfunction; T2 mapping for oedema.
- Chest images on the localisers: hilar and mediastinal nodes support systemic sarcoid.
What confirms it
- Non-ischaemic patchy LGE in a typical distribution and/or focal FDG uptake with a perfusion defect, with histology from any site.
What licenses you to exclude it
- A normal CMR with LGE has a high negative predictive value; a normal PET after adequate suppression argues against active disease.
The classic misread
- Missing septal RV-side LGE by windowing for the LV only.