Clinicopathological Features of Small Pancreatic Neuroendocrine Neoplasms 10 mm or Smaller

<b>Background/Objectives:</b> There is limited evidence on imaging characteristics and pathological grading of small pancreatic neuroendocrine tumors (PNENs). This study aimed to compare imaging features and histopathological diagnoses of PNENs based on tumor size. <b>Methods:</b> Patients with PNEN who underwent pathological diagnosis at Hiroshima University Hospital were retrospectively reviewed. Detection rates, imaging findings, and diagnostic accuracy of endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) were analyzed according to tumor size. <b>Results:</b> Among 107 patients with PNEN, 42 had tumors ≤10 mm, and 65 had tumors >10 mm. The detection rate for lesions ≤10 mm was 92.3% according to EUS and 83.3% according to contrast-enhanced CT, showing the superior sensitivity of EUS. Typical imaging features-well-defined margins, homogeneous internal structure, and early enhancement-were significantly more frequent in tumors ≤10 mm (<i>p</i> < 0.001). There were no significant differences in imaging findings between G1 and G2 tumors ≤10 mm. The diagnostic sensitivity of EUS-FNA was 91.2% for tumors ≤10 mm and 86.3% for tumors >10 mm, with no significant difference. However, the concordance rate between EUS-FNA and surgical histology for tumor grading was significantly higher in the ≤10 mm group (87.5% vs. 56.3%, <i>p</i> = 0.012). <b>Discussion:</b> In small PNENs (≤10 mm), imaging features are often typical but do not reliably determine tumor grade. In our cohort, EUS-FNA showed high diagnostic accuracy and provided essential pathological information to guide management, including the choice between surveillance and surgery.