A Rare Benign Mimic of Gastrointestinal Stromal Tumor: Gastric Plexiform Fibromyxoma Presenting With Iron-Deficiency Anemia and a Hypervascular Ulcerated Pyloric Mass.

Gastric lesions with suspicious radiological and endoscopic features can remain diagnostically challenging when initial tissue sampling is benign or non-diagnostic. This case highlights the importance of correlating endoscopic appearance, cross-sectional imaging, endoscopic ultrasound (EUS) findings, histology, and multidisciplinary assessment when investigating a deeper gastric lesion. A 28-year-old man was investigated for iron-deficiency anemia associated with intermittent abdominal pain and altered bowel habit. Laboratory investigations demonstrated microcytic iron-deficiency anemia, with a hemoglobin nadir of 95 g/L, below the reference range of 130-180 g/L, and markedly reduced iron stores. Colonoscopy, including terminal ileal and colonic biopsies, was normal. Gastroscopy identified an ulcerated polypoidal lesion in the antral/prepyloric region. Computed tomography (CT) demonstrated a 3.5 cm highly vascularized lesion within the pylorus, with no lymphadenopathy or distant lesions. Initial mucosal biopsies showed benign foveolar hyperplasia but contained no submucosal tissue, limiting assessment of a deeper lesion. EUS demonstrated an approximately 4 cm lesion arising from the muscularis propria with ulceration; however, fine-needle biopsy was hemorrhagic and non-diagnostic. Repeat tissue sampling showed benign hyperplastic-type gastric mucosa without evidence of gastrointestinal stromal tumor (GIST), neuroendocrine tumor, dysplasia, or malignancy in the available tissue. Owing to the lesion's transmural nature and discordant clinicoradiological findings, it was considered unsuitable for endoscopic submucosal dissection (ESD). The patient underwent robotic-assisted distal gastrectomy with Roux-en-Y reconstruction. Specialist Liverpool pathology review of the distal/subtotal gastrectomy specimen reported a final diagnosis compatible with gastric plexiform fibromyxoma. This case highlights that benign superficial biopsies and non-diagnostic EUS-guided sampling should not be considered definitive when CT and EUS suggest a deeper transmural gastric lesion. Adequate tissue assessment and specialist pathology review are essential when endoscopic, radiological, and histological findings are discordant.