What is the most common underlying cause of a ranula?

Most ranulas arise from trauma to the sublingual gland or its ducts of Rivinus, causing mucus to extravasate into surrounding tissue and form a pseudocyst (mucus extravasation phenomenon). Sialolith-related ductal obstruction is a less common (<10%) cause, typically producing a true epithelial-lined retention cyst rather than an extravasation pseudocyst.