This meta-analysis of 23 studies and 2,209 patients compared FDG PET/CT with pelvic MRI for detecting lateral lymph node metastasis before rectal cancer surgery.
Sensitivity was similar — PET/CT 0.63 (95% CI 0.49 to 0.76) versus MRI 0.76 (0.67 to 0.85), difference not significant (P = 0.09) — but PET/CT was much more specific: 0.97 (0.95 to 0.99) versus 0.82 (0.75 to 0.88), P < 0.01.
The practical division is clean. Neither test reliably excludes lateral nodal disease, so a negative scan does not settle the question. But a positive PET/CT is trustworthy, which can spare a patient an unnecessary lateral node dissection and its morbidity. Use MRI to find candidates and PET/CT to confirm before committing to surgery.
- PET/CT specificity 0.97 versus MRI 0.82 — the meaningful difference
- Sensitivity similar and modest for both (0.63 vs 0.76, not significant)
- A positive PET/CT helps justify lateral node dissection; a negative one does not exclude disease
- Diagnostic-accuracy meta-analysis, 23 studies, mostly patient-level data
The statistics, in plain English
Specificity 0.97 means only about 3% of truly node-negative patients are wrongly called positive by PET/CT, versus 18% with MRI — fewer false alarms that would trigger avoidable surgery. The non-significant sensitivity difference (P = 0.09) means we cannot say either test finds more true disease; both miss roughly a quarter to a third.
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