A Case of Pancreatic Neuroendocrine Tumor Growing Intraductal Extension toward the Main Pancreatic Duct Complicated by Thrombocytopenia: Diagnostic Challenges and Management Strategy.

We present a rare and diagnostically challenging case of a pancreatic neuroendocrine tumor (pNET) with intraductal growth into the main pancreatic duct (MPD), complicated by severe thrombocytopenia due to myelodysplastic syndrome. A 37-year-old male presented with thrombocytopenia. Abdominal imaging revealed an 11-mm hypervascular lesion obstructing the MPD in the pancreatic body. The initial serial pancreatic juice aspiration cytological examination (SPACE) demonstrated Class II cytology. Eight months later, the second SPACE revealed Class V cytology. Pancreaticoduodenectomy confirmed pNET G2 with clear intraductal extension. In the postoperative specimen, a portion of the tumor was exposed within the MPD, suggesting Class V cytology. pNETs with intraductal extension (I-pNETs) are rare, as pNETs typically exhibit expansive encapsulated growth. SPACE may be a valuable diagnostic alternative for patients with thrombocytopenia, although its accuracy may depend on factors such as capsular integrity and ductal communication. Tailored diagnostic strategies that balance invasiveness and safety are essential for managing pancreatic tumors in patients with hematological fragility. This case highlights the importance of considering I-pNET in the differential diagnosis of MPD-occupying lesions.