Whipple Disease PAS-Positive Macrophages

A 52-year-old Caucasian male farmer presents with a 5-year history of migratory large-joint arthralgia followed by 18 months of chronic diarrhea with steatorrhea, weight loss of 15 kg, fever, and generalized lymphadenopathy. He reports progressive cognitive decline with memory impairment and abnormal jerky eye movements synchronous with jaw and palatal contractions. On upper GI endoscopy, the structure marked **A** is visualized. Biopsies from this region show the lamina propria densely packed with large foamy macrophages that stain strongly periodic acid-Schiff (PAS) positive and diastase-resistant. PCR of the biopsy confirms Tropheryma whipplei 16S rRNA. Which of the following best describes the endoscopic appearance of the structure marked **A**?