A 28-year-old woman from Delhi presents with a 6-month history of bloody diarrhea (8–10 stools/day), tenesmus, and left lower abdominal cramping. She denies weight loss and has no extraintestinal manifestations. Colonoscopy reveals continuous mucosal inflammation limited to the colon, with loss of haustra and a granular, friable mucosa. Biopsies show acute and chronic inflammation confined to the mucosa and submucosa, with crypt abscess formation but no granulomas. Which of the following pathological findings would be MOST helpful in distinguishing this condition from Crohn disease?