An extravasation mucocele occurs due to a rupture of the ductus of a salivary gland. As a consequence the secretion of the gland flows into the soft tissue around it, producing a mucous accumulation there, leading to an inflammatory reaction. Therefore an extravasation cyst is correctly a pseudo-cyst because there is no epithelial lining. These mucoceles appear mostly on the lower lip, seldom on the floor of the mouth or the buccal mucosa.
Normally they look like bluish colored bulging tumors with a diameter no more than 1 cm. The caused tenderness and the high recurrence rate of that mucocele make its total excision meaningfully.