Imaging Features of Pancreatic Neuroendocrine Tumors Following Radiofrequency Ablation: Early Experience

To describe the imaging appearances and treatment response patterns of the pancreatic neuroendocrine tumors (panNETs) following radiofrequency ablation (RFA).

From an internal database, 17 patients (8 male; mean age: 67±14 y) with 18 pathology-proven, localized, nonfunctioning panNETs <3 cm who underwent EUS-RFA for curative intent were included. A total of 32 preablation and 33 postablation scans were included (CT, MRI, or 68 Ga-DOTATATE PET). Lesion size and enhancement on CT/MRI were independently assessed by 2 readers, while SUVmax was extracted from the original PET reports by a separate reviewer. The Wilcoxon signed-rank and McNemar tests were performed. Treatment response is defined as a complete response (loss of enhancement and SUVmax), a partial response (decrease in size, enhancement, or SUVmax), or no response (no change).

Mean lesion size decreased from 1.4​​​​​​±0.5​ cm preablation to 0.3±0.5 cm postablation ( P <0.0001). Mean SUVmax declined from 17.3±11.2 to 3.1±6.0 ( P <0.001). Hyperenhancement was present in 15/18 (83.3%) lesions preablation versus 5/18 (27.8%) postablation ( P <0.01). Of these 15 hyperenhancing lesions, 11 were solid, 3 were cystic, and 1 was mixed cystic and solid. Complete response occurred in 12/18 (66.7%) lesions, with either complete disappearance 5/12 (41.4%) or bland cavity formation 7/12 (58.5%). Partial response occurred in 5/18 (27.8%) lesions; 4/5 decreased in size (mean±SD: 1.4±0.5 cm preablation vs. 0.6±0.7 cm postablation), and 3/5 demonstrated decreased SUVmax. One patient with partial response underwent 2 repeat ablations with an ultimate decrease in SUVmax from 34.1 to 5.9. One solid, hyperenhancing pancreatic body lesion demonstrated no response (1.3 cm); preablation SUVmax was 10.8, but they did not undergo postablation DOTATATE PET. One patient developed postablation pancreatitis. Mean clinical follow-up was 650 days (423).

RFA is an emerging treatment for small, nonfunctioning panNET. Postablation imaging findings most commonly included complete resolution of the tumor, decreased enhancement, decreased SUVmax, and formation of a bland cavity. As interest in this technique continues to grow, radiologists' familiarity with expected post-treatment imaging appearances and their associated response patterns is essential for accurate assessment.