A semi-quantitative enhancement curve sharpens O-RADS MRI triage

Design

retrospective two-centre MRI review with surgical histology as reference, two readers

Population

341 adnexal masses in 321 women aged 18 to 89 resected between 2008 and 2018; 35.2% malignant

Primary outcome

per-lesion diagnostic accuracy and effect on surgical triage

Effect

specificity 0.84 to 0.92 (P = 0.007) and PPV 0.77 to 0.90 (P = 0.002) with the intensity curve

Two radiologists of differing experience scored 341 adnexal masses in 321 women, all with surgical histology, at two referral centres. Malignancy - including borderline tumours - accounted for 35.2%, and 96.2% of masses had some solid component. The comparison was between the standard visual assessment of enhancement in O-RADS MRI and a semi-quantitative intensity curve, a manual simplification of the time-intensity curve.

Visual assessment gave sensitivity 0.95 (95% CI 0.89 to 0.98), specificity 0.84 (0.79 to 0.89) and positive predictive value 0.77 (0.69 to 0.83). The intensity curve improved specificity to 0.92 (0.88 to 0.95, P = 0.007) and positive predictive value to 0.90 (0.83 to 0.95, P = 0.002). Translated into management, using the curve would have reduced the proportion of benign lesions operated on by gynaecological oncologists from 16% to 9%. Agreement within and between readers was moderate to high, kappa 0.63 to 0.85.

The gain here is on the false-positive side, which is where O-RADS costs patients most: a benign mass triaged to an oncological operation means a bigger procedure and a different consent conversation than a gynaecologist's cystectomy. The technique is a manual curve rather than a software package, so the barrier is protocol and habit, not capital - but it needs dynamic contrast sequences acquired properly, and reader training before the specificity gain shows up locally.

• Acquire dynamic contrast sequences with enough temporal resolution to draw a curve
• Add the intensity curve for masses with a solid component - that was 96.2% of this series
• Report the curve type alongside the O-RADS score so the surgical team sees the basis
• Audit your own false-positive rate before and after; the claimed gain is specificity, not detection
• Do not expect better sensitivity - visual assessment was already 0.95 and the curve did not raise it

Why it matters

It targets the failure that sends a woman with a benign mass to a cancer surgeon, rather than the one everybody measures.

Don't overread it

A retrospective surgical series selects for masses that were already thought to need an operation; these numbers do not transfer to unselected imaging.

The statistics, in plain English

Specificity rising from 0.84 to 0.92 means false positives fell by half in relative terms, and positive predictive value of 0.90 against 0.77 means nine in ten suspicious calls were right rather than eight. These came from the same readers on the same images, so the comparison is fair but not independent. The series is retrospective and every mass went to surgery, which enriches it for malignancy at 35.2% - far above a screening population, so the positive predictive value would be lower in routine practice.

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