MRI features that predict progression of residual disease after ablation of extra-abdominal desmoid fibromatosis.

Objective: To identify MRI features of desmoid tumors (DTs) that predict the growth of residual disease following ablation.

Methods: Patients who underwent MRI-guided ablation for DTs between February 2013 and April 2021 were included in this single-center IRB-approved retrospective study. MRI scans assessed three suspicious tissue features: intermediate T2 signal [+iT2], nodular appearance [+NOD], and contrast enhancement [+ENH]. Percent-monthly change in diameter (PMCD) of suspicious foci determined growth (PMCD > 1%), unchanged (PMCD between -1% and +1%), or regression (PMCD < -1%). Statistical tests compared mean PMCD between groups and evaluated sensitivity and specificity.

Results: Thirty-three patients (32 years ± 13.3; 22 females) with 34 DTs underwent 47 MRI-guided ablations, with a median follow-up of 269 days (IQR 147). Of 93 suspicious foci, 62 (67%) grew (PMCD: +5.6% IQR: 5.8), 13 (14%) remained unchanged (PMCD: -0.1% IQR: 0.6), and 18 (19%) regressed (PMCD: -3.9% IQR: 4.2). Features [+iT2], [+ENH], and [+NOD] were associated with PMCDs of +5.2% IQR: 6.0, +3.4% IQR: 6.0, and +3.4% IQR: 6.5, respectively, compared to -1.5% IQR: 4.7 (p < 0.0001), -0.5% IQR: 0.8 (p = 0.003), and +0.4% IQR: 7.5 (p = 0.0056) for their respective negative counterparts. Sensitivity, specificity, and accuracy for distinguishing growth were [+iT2]: 0.95, 0.71, 0.87, [+ENH]: 1.00, 0.32, 0.77, and [+NOD]: 0.84, 0.42, 0.70. Combining [+iT2 + NOD + ENH] yielded PMCD +5.9% IQR: 6.2 and the best performance for distinguishing growth (sensitivity 0.81, specificity 0.94, accuracy 0.85).

Discussion: MRI features reliably predict the growth of residual or recurrent DTs post-ablation, with [+iT2] being the most accurate. Adding nodular enhancement to [+iT2] improved specificity without sacrificing accuracy.

Key points: Question Post-ablation imaging of desmoids is challenging due to tumor heterogeneity and treatment-related inflammation. This study evaluates MRI features for assessing future tumor growth. Findings Foci of intermediate T2 signal post-ablation predicted desmoid growth with high sensitivity (0.95), while T2 signal, nodularity, and enhancement combined offer high specificity (0.94). Clinical relevance Intermediate T2 signal predicts desmoid tumor growth post-ablation with high sensitivity and accuracy but moderate specificity. Combining nodularity and enhancement improves specificity and predictive value, helping clinicians in managing desmoid tumor patients post-ablation.