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In celiac disease, a major characteristic finding on biopsy is villus blunting and mucosal flattening, which indicate damage to the intestinal lining. This specific histological change occurs due to an inappropriate immune response to gluten, which leads to inflammation and results in the destruction of the villi within the small intestine. The blunted villi cannot effectively absorb nutrients, contributing to the malabsorption symptoms commonly seen in patients with celiac disease.

When considering the other options, transmural inflammation is more associated with inflammatory bowel diseases such as Crohn’s disease rather than celiac disease, which primarily affects the mucosal layer. Superficial mucosal inflammation is too nonspecific and could pertain to various gastrointestinal conditions but does not specifically represent the hallmark features of celiac disease. Increased granulation tissue is more indicative of healing or chronic inflammation and is not a characteristic finding in the early identification of celiac disease on biopsy. Thus, the finding of villus blunting and mucosal flattening is a definitive sign that supports the diagnosis of celiac disease when viewed in the context of the patient's clinical presentation.