A patient develops rapid onset lip and facial swelling immediately following a local anesthetic injection. The swelling is non-pitting and involves the deeper dermal and submucosal tissues. What is the most likely diagnosis?

Angioedema is a rapid, localized, non-pitting swelling of the deeper dermis, subcutaneous tissue, and submucosa, caused by vasodilation and increased vascular permeability. It commonly occurs as an allergic reaction to local anesthetics (particularly those containing ester-type anesthetics or the preservative methylparaben) or as an idiosyncratic reaction. Unlike urticaria (which involves the superficial dermis), angioedema affects deeper tissues and may involve the lips, tongue, face, or larynx. Laryngeal involvement is life-threatening. Anaphylaxis involves systemic manifestations (hypotension, bronchospasm) beyond just localized swelling. Hematoma presents as a firm, tender swelling with ecchymosis. Angioedema is managed with antihistamines, corticosteroids, and epinephrine if severe.