The characteristic “alveolus nest sign” in solid pseudopapillary neoplasm of the pancreas

A 23-year-old woman presented with a 1-week history of abdominal pain radiating to the back. The pain was not relieved by proton pump inhibitors. Contrast-enhanced abdominal computed tomography scan demonstrated a round, well-defined, hypodense lesion within the pancreatic body ([Fig. 1]). On endoscopic ultrasound (EUS) elastography there was a 2 × 2.5-cm hypoechoic mass that was predominantly hard (blue) with dispersed heterogeneous soft (green) areas ([Fig. 2]). Contrast-enhanced harmonic endoscopic ultrasound (CH-EUS) revealed hyperechoic solid granular components interspersed with small anechoic regions within the pancreatic mass ([Fig. 3]). These characteristics were typical of the "alveolus nest sign" and were present during the arterial and venous phases of CH-EUS ([Video 1]). EUS-guided fine-needle biopsy with subsequent histopathologic examination ([Fig. 4]) and immunohistochemical analysis ([Fig. 5]) yielded a definitive diagnosis of solid pseudopapillary neoplasm (SPN). The patient underwent distal pancreatectomy for definitive treatment.