A hypoechoic, tumor-like lesion in the pancreatic head and neck on endoscopic ultrasonography may be due to a high-grade pancreatic intraepithelial neoplasia/carcinoma in situ

High-grade pancreatic intraepithelial neoplasia (HG PanIN)/carcinoma in situ (CIS) in the pancreatic body and tail can induce parenchymal atrophy through chronic inflammatory changes presenting as a Hypoechoic area on EUS (Hypocho) or focal pancreatic parenchymal atrophy (FPPA) on computed tomography (CT) and magnetic resonance imaging (MRI). We herein discussed two patients with a hypoechoic area in the pancreatic head and neck on EUS resembling pancreatic ductal adenocarcinoma (PDAC). The lesions consisted of dense fibrosis and fat infiltration with pancreatic parenchymal atrophy around the HG PanIN/CIS in the main pancreatic duct (MPD), which penetrated the lesion and showed mild stenosis and upstream dilation. CT and MRI were unable to visualize the lesions. A specimen was obtained from one lesion by fine-needle aspiration under EUS (EUS-FNA) guidance for histopathological and cytological analysis, but the tests returned negative for adenocarcinoma. However, serial pancreatic-juice aspiration cytologic examination (SPACE) revealed adenocarcinoma in both lesions, prompting surgical resection. Histopathological examination revealed non-invasive HG PanIN/CIS in the MPD surrounded by dense fibrosis and fat deposition in the area of parenchymal atrophy. The CIS was restricted to the area of parenchymal atrophy.These two cases are noteworthy in illustrating a hypoechoic area appearing on EUS as a tumor-like lesion resembling PDAC. EUS-FNA has recently been used histopathologically to diagnose a pancreatic lesion. However, in the present and similar cases, EUS-FNA can only reveal secondary changes due to CIS unless the pancreatic duct covered by the CIS is accidentally punctured. We should bear in mind that CIS can appear as a hypoechoic area resembling PDAC on EUS, and that SPACE is the best method for diagnosing CIS in such cases.