Pancreatic Neuroendocrine Tumors (PNET) - Typical and Atypical Imaging Characteristics
1Radiology, Assaf Harofeh Medical Center, Affiliated to Sackler School of Medicine, Israel
2Radiology, Montefiore Medical Center, Albert Einstein College of Medicine, USA
3Center for Carcinoid and Neuroendocrine Tumors, The Tisch Cancer Institute, Mount Sinai Health System, Affiliated to Icahn School of Medicine, USA
PURPOSE: To demonstrate the variety of imaging features of PNETs, including diagnostically challenging or atypical cases, and to assess relative prevalence of different PNET appearances.
MATERIAL & METHODS: We retrospectively analyzed our neuroendocrine tumor database and identified patients with PNET who were presented at Montefiore NET boards during 2015-2017. Radiologic studies including CT, MRI and Ga 68 PET/CT were reviewed along with patients’ charts by 2 radiologists and imaging features of the lesions were recorded. Assessed characteristics were tumor borders (well circumscribed vs ill-defined); tumor consistency (solid or cystic), enhancement pattern (hypervascular vs iso- or hypovascular), presence of calcifications, number of lesions (single vs multiple lesions), and presence of pancreatic duct (PD) dilatation.
RESULTS: Out of 44 patients with PNETs, 36 patients had solitary and 8 had multiple pancreatic masses. Five out of eight patients (63%) with multiple lesions had associated syndromes such as MEN and von-Hippel Lindau. Three patients with multiple lesions had concomitant solid and cystic masses, with two patients demonstrating both hypervascular and hypovascular tumors. Six patients were excluded from the final analysis due to lack of preoperative imaging. In two more patients enhancement pattern could not be assessed due to lack of contrast-enhanced studies, but all other features could be analyzed. Fifteen out of 36 patients, demonstrated hypovascular tumors (42%), and two of them had both hyper- and hypovascular lesions. Sixteen out of 38 patients demonstrated an ill-defined margins or infiltrative pattern (42%). Finally, 8 out of 38 patients exhibited pancreatic ductal dilatation (21%). Some peculiar imaging features were very high T2 signal on MRI and gradual delayed enhancement with contrast retention by the masses. Rare cystic PNETs usually had a hypervascular rim of enhancement.
CONCLUSION: Although PNETs most commonly present as well-defined hypervascular masses, they frequently exhibit other features including hypoenhancement, ill-defined margins and pancreatic duct obstruction. Awareness of the different appearances of PNETs is necessary to avoid a diagnostic error.