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What is Oral mucocele and explain in detail?
Oral mucocele (also mucous extravasation cyst, mucous cyst of the oral mucosa, and mucous retention and extravasation phenomena.) is a condition caused by two related phenomena - mucus extravasation phenomenon and mucous retention cyst. 
Mucous extravasation phenomenon is a swelling of connective tissue consisting of a collection of fluid called mucus. This occurs because of a ruptured salivary gland duct usually caused by local trauma (damage) in the case of mucous extravasation phenomenon and an obstructed or ruptured salivary duct in the case of a mucus retention cyst. The mucocele has a bluish, translucent color, and is more commonly found in children and young adults.
Although these lesions are often called cysts, mucoceles are not true cysts because they have no epithelial lining. Rather, they are polyps.

Signs and symptoms
The size of oral mucoceles vary from 1 mm to several centimeters and they usually are slightly transparent with a blue tinge. On palpation, mucoceles may appear fluctuant, but can also be firm. Their duration lasts from days to years, and may have recurrent swelling with occasional rupturing of its contents.

Locations
The most common location to find a mucocele is the inner surface of the lower lip. It can also be found on the inner side of the cheek (known as the buccal mucosa), on the anterior ventral tongue, and the floor of the mouth. When found on the floor of the mouth, the mucocele is referred to as a ranula. They are rarely found on the upper lip. As their name suggests, they are basically mucus-lined cysts and they can also occur in the paranasal sinuses, most commonly the frontal sinuses, the frontoethmoidal region, and the maxillary sinus. Sphenoid sinus involvement is extremely rare.  When the lumen of the vermiform appendix of the intestine gets blocked due to any factor, a mucocele can also form there.

Variations
A variant of a mucocele is found on the palate, retromolar pad, and posterior buccal mucosa. Known as a "superficial mucocele", this type presents as single or multiple vesicles and bursts into an ulcer. Despite healing after a few days, superficial mucoceles recur often in the same location. Other causes of bumps inside lips are aphthous ulcer, lipoma, benign tumors of salivary glands, submucous abscesses, and haemangiomas.

Diagnosis
Microscopically, mucoceles appears as granulation tissue surrounding mucin