Two rare gastric hamartomatous inverted polyp cases suggest the pathogenesis of growth

Figure 1 Esophagogastroduodenoscopy showed a submucosal tumor. A: The esophagogastroduodenoscopy (EGD) showed a gastric submucosal tumor (SMT) measuring 30 mm in diameter in the greater curvature of upper body with bridging folds and a tiny reddish spot on top (yellow arrow); B: Using NBI-ME, the tiny area was observed to be dilated with banded marginal crypt epithelium (yellow arrows); C: Milky white mucous and calcification structures (blue arrow) were exuding from the biopsy site (yellow arrow); D: The solid portion inside the wall of the SMT with small cystic changes were exposed using forceps (yellow arrow).

Figure 2 Endoscopic ultrasound before and after the biopsy and histology. A: An EUS before biopsy revealed a heterogeneous tumor with a cystic area and calcification spot (yellow arrow); B: An endoscopic ultrasound (EUS) from inside the submucosal tumor (SMT) filled with distilled water and an inserted EUS probe showed 5 specific layers (red circle); C: An HE stain (× 20) also showed the 5 structural layers. The hyperechoic portion showed proliferation of pseudo-pylorus glands and cystic gland dilatation without cytological atypia (blue circle); D: The 5 layers consisted of a normal mucosal layer (yellow arrow), immature fibroblasts (black arrow), pyloric glands (yellow arrow), muscularis mucosa (black arrow) and another normal mucosal layer (yellow arrow) (HE stain × 100).

Figure 3 An submucosal tumor measuring 40 mm in diameter was found in the greater curvature of the middle body. A and B: The size of the submucosal tumor (SMT) had increased from the 20 mm in diameter that was reported 5 years before. In addition, a reddish erosive part 10 mm in diameter was found on the top of the SMT (yellow arrows). C and D: An endoscopic ultrasound revealed a heterogeneous tumor with small spotty cystic areas, a large anechoic cystic part, with papillary structures and 5 specific structural layers as its wall.

Figure 4 Endoscopic submucosal dissection to resect the submucosal tumor. A: An en bloc resection using endoscopic submucosal dissection (ESD) was performed to obtain an accurate diagnosis; B and C: Similar to Case 1, milky white components were observed during the ESD (black arrows); D: The lesion was completely resected with a sufficient safety margin.

Figure 5 An endoscopic ultrasound and histological comparison. A: An endoscopic ultrasound (EUS) revealed a heterogeneous tumor; B: The 5 layers shown in the EUS and HE stain (× 20) (yellow circle) consisted of a normal mucosa layer, immature fibroblast cells, pyloric glands, muscularis mucosa, and another normal mucosa layer. The surface mucosa was inverted into the submucosal layer (red arrow); C and D: The hyperechoic solid portion had tiny low echoic cystic spots (blue circle) and showed the proliferation of pseudo-pylorus glands, cystic glands, fibroblast cells, smooth muscle, and nerve elements.