Etiology

Yamasoba et al ^[5] has highlighted two crucial etiological factors for occurrence of mucocele:

Trauma to salivary gland.

Obstruction of salivary gland duct.

Pathogenesis

Extravasation mucocele results from broken salivary gland duct causing spillage into the soft tissues around the gland. Extravasation mucoceles undergo three evolutionary phases. In the first phase, mucous spills from the excretory duct into surrounding tissues where some leukocytes and histiocytes are found. In second phase granulomas become visible during the resorption phase due to histiocytes, macrophages and multi-nucleated giant cells associated with a foreign body reaction. In the final phase, connective cells form a pseudo capsule without epithelium around the mucosa. ^[6], ^[4], ^[7]

Retention mucoceles are formed by dilation of the duct secondary to its obstruction caused by a sialolith or dense mucosa. The majority of retention cysts develop in the ducts of the major salivary glands. ^[6], ^[4]

Clinical presentation

Clinical appearance of both extravastion and retention type mucoceles is similar. Incidence of mucocele in general population is 0.4 – 0.9 %. Most common in 1^st – 2^nd decade of life. There is no sex predilection. ^[8]

Location: Extravasation mucoceles appear frequently on the lower lip lateral to midline(53%) followed by buccal mucosa-4%, floor of mouth-5%, ventral surface of tongue-1%, palate -1%, upper lip 2% ^[9] and are rarely found in the retromolar region, soft palate and posterior dorsal area of tongue; in contrast, retention mucoceles appear at any site in the oral cavity. Majority of mucoceles occurred in the lateral part of the lower lip which is the more trauma prone site. This finding supports the role of chronic trauma as an etiologic factor either in the form of sharp tooth cusp, or proclined anterior teeth or biting habit for the formation of mucoceles. ^[1] Mucoceles arising on the ventral surface of the tongue are known as mucocele of the glands of Blandin-Nuhn. These glands are located near the ventral tip of the tongue and are arranged in a mass with a horseshoe shape. They are embedded in the muscles of the ventral aspect near the midline. Mucoceles of the glands of Blandin-Nuhn are considered to be rare. ^[10] When located on the floor of the mouth, these lesions are called ranulas because the inflammation resembles the belly of a frog. ^[4]

Mucoceles appear as asymptomatic pedunculated or sessile swelling or as fluid filled vesicle or blister in the superficial mucosa or as a fluctuant nodule deep within the connective tissue. But they may causes discomfort, interferes in speech and mastication.

Mucoceles present as bluish, soft, and transparent cystic swelling that frequently resolve spontaneously. Blue color is due to vascular congestion, cyanosis of the tissue above, and accumulation of fluid below. Colour may vary depending on the size of the lesion, proximity to the surface and elasticity of overlying tissue. Sometimes due to constant friction or trauma the lesion surface may appear whitish in color due to keratinization. These mucoceles are more commonly round to oval in shape having ill-defined borders. These swelling appears soft to rubbery in consistency. ^[4], ^[11], ^[8], ^[1], ^[12], ^[7] These mucoceles are fluctuant and they may rupture following trauma and reappear after epithelium heals. Traumatic neuroma, Traumatic fibroma, Lipoma, Haemangioma, Varix, Tumors of minor salivary gland, Lymphangioma are considered as differential diagnosis for mucocele of lip.

Diagnosis of mucocele can be done by taking proper case history, positive history for lip biting or sucking habit, trauma, rupture and reappearance of swelling, varying in size. Radiographic evaluation is needed to rule out if sialoliths are considered a contributing factor in the formation of oral and cervical ranulas. The fine needle aspiration cytology demonstrates the mucus retention phenomenon. The chemical analysis could disclose protein content and high amylase. The localization, determination of the origin of the lesion, visualize the form, diameter, position of lesion relative to adjacent organs can be done by computed tomography scanning and magnetic resonance imaging especially incase of ranula. ^[13] Histopathology in the case of retention mucoceles a cyst cavity can be found, this is generally well defined with an epithelial wall covered with a row of cuboidal or flat cells produced from the excretory duct of the salivary glands . Compared to extravasation mucoceles, retention mucoceles show no inflammatory reaction and are true cysts with an epithelial covering. Extravasation mucoceles are pseudocysts without defined walls. The extravasated mucous is surrounded by a layer of inflammatory cells and then by a reactive granulation tissue made up of fibroblasts caused by an immune reaction. Even though there is no epithelial covering around the mucosa, this is well encapsulated by the granulation tissue. ^[4], ^[14], ^[3] Treatment modalities include conservative surgery, marsupilization, micro-marsupilization, carbon-di-oxide laser ablation, intra-lesional injection, gamma linolenic acid and cryosurgery. Out of many advanced treatment modalities simple surgical excision with care is the treatment of choice. Surgical excision with removal of the involved accessory salivary gland has been suggested as the treatment. Reoccurrence can be avoided by removing adjacent surrounding glandular acini and removing the lesion down to the muscle layer. Special care should be taken to avoid injury to adjacent glands and ducts while placing sutures as this also causes reappearance. ^[15]