Mucocele: An unusual presentation of the minor salivary gland lesion.

A mucocele is a benign, mucus-containing cystic lesion of the minor salivary gland. This type of lesion is most commonly referred to as mucocele. The more common is a mucus extravasation cyst; the other is a mucus retention cyst. Other three clinical variants are: Superficial mucocele that is located directly under the mucosa, classic variant located in the upper submucosa, and deep mucocele located in the lower cornium. Mucocele occurs either due to rupture of salivary gland duct or by blockade of salivary gland duct. The common site of occurrence of mucocele is lower lip followed by tongue, floor of mouth (ranula), and the buccal mucosa.

Mucocele is a common lesion of the oral mucosa that results from an alteration of minor salivary glands due to mucus accumulation causing limited swelling.[1] Two types of mucocele can appear: Extravasation and retention. Extravasation mucocele results from a broken salivary gland duct and consequent spillage into the soft tissue around this gland. Retention mucocele appears due to decrease or absence of glandular secretion produced by blockage of salivary gland ducts.[23] The histological difference between extravasation and retention cyst is that the extravasation type has no epithelial lining and is formed by a mucus pool surrounded by granulation tissue and the retention cyst has an epithelial lining.[45]

Case Report

A 35-year-old female patient visited the Department of Oral Medicine and Radiology, K. S. R. Dental College, Trichengode, with a chief complaint of swelling in the left inner aspect of the cheek for the past 3 months. History revealed that she had a history of trauma to the left side of the face before 6 months and had mild laceration in that site which healed on its own. Three months later, she developed a small swelling which gradually increased in size. She also gave a history of traumatizing the swelling with a tooth pick, followed by recurrent development of swelling in the same region; there was no associated pain. Past medical and dental history was not contributory. On extraoral examination, there was mild asymmetry on the left side close to the angle of the mouth with bluish purple changes in the site of the lesion [Figures 1 and 2].

Figure 1

Mild facial asymmetry on the left side close to the angle of the mouth

Figure 2

Mild swelling with bluish color change in the site of the lesion

On intraoral examination, a solitary, well-defined, dome-shaped swelling was seen on the left buccal mucosa in the region of 34, 35, 36, measuring around 4×3 cm in size, which was oval in shape, with a smooth surface and a bluish translucent hue [Figures 3 and 4]. The swelling was soft in consistency, non-tender, fluctuant, compressible, non-reducible, and non-pulsatile, with no increase in temperature. A differential diagnosis of mucocele, oral hemangioma, oral lympangioma, lipoma, and soft tissue abscess was made. And since the swelling was large and the color was bluish purple, the patient was advised for ultrasound in the left cheek [Figure 5], which revealed a hypoechogenic cystic mass of 6×3 cm in size, with distinct margins; no echoes were seen within the mass. Fine needle aspiration cytology (FNAC) was done, and 1 ml of thick, viscous, sticky, and blood-mixed mucus secretion was collected [Figure 6] and sent for chemical analysis which showed increase in amylase and protein content. A final diagnosis was formulated as mucocele from the history of trauma, clinical features, and investigation (ultrasound, chemical analysis). Since the lesion was large, marsupialization was done and sent for histopathologic investigation which revealed a mucin-filled cyst-like cavity beneath the mucosal surface [Figure 7]. The lesion was packed with iodoform gauze for 10 days, which led to complete regression of the swelling, and the patient was kept under observation for 3 months with no recurrence.

Figure 3

A dome-shaped swelling of size 4×3 cm on left buccal mucosa

Figure 4

Swelling in region of 34, 35, 36 with bluish hue and smooth surface

Figure 5

Ultrasound shows hypoechogenic mass in left cheek with well-defined margins

Figure 6

Sticky, viscous mucus secretion aspirated from the lesion

Figure 7

An area of spilled mucin surrounded by a granulation tissue

Discussion

Mucoceles are mucus containing cystic lesions of the minor salivary glands; they are the 15th common oral mucosal lesion with a prevalence of 2.4 cases per 1000 people. Mucoceles occurs in young individuals, with 70% of them being younger than 20 years. Superficial mucoceles tend to occur in individuals older than 30 years and ranulas occur in children and young adults, with a peak frequency in the second decade. Mucus retention cysts occur in older individuals; the peak prevalence occurs in persons aged 50–60 years. Lower lip is the most common site of occurrence, followed by tongue, floor of mouth (ranula), and the buccal mucosa.[67]

The clinical appearance of a mucus cyst is a distinct, fluctuant, painless swelling of the mucosa. About 75% of the lesions are smaller than 1 cm in diameter; however, rarely, the size can vary from few millimeters to several centimeters. Superficial lesions take on a bluish to translucent hue, whereas deep lesions have normal mucosal coloration and bleeding into the swelling may impart a bright red and vascular appearance. The patient may relate a history of recent or past trauma to the mouth or face or the patient may have a habit of biting the lip. The various differential diagnoses are Blandin and Nuhn mucocele, oral hemangioma, oral lymphangioma, lipoma, and soft tissue abscess.[8]

The history and clinical findings lead to the diagnosis of a superficial mucocele. Radiographic evaluation is considered if sialoliths are considered a contributing factor in the formation of oral and cervical ranulas. Ultrasonography has been used to evaluate the lesions, and with high-frequency transducers, ultrasound demonstrates the internal structures more clearly than computed tomography (CT). Hence, congenital and acquired cysts of salivary glands are normally filled with transparent fluid; because of this, the typical sonographic criteria for cystic structures are identifiable: An echo-free tumor, sharply bordered with distal acoustic enhancement.

Lymphangioma and hemangioma show similar sonomorphologic characteristics. On examination, loosely connected alveolar, structural patterns composed partially of hypoechogenic and hyperechogenic areas can be detected.

Intra- and extraglandular lipomas appear as sharply demarcated, ovoid masses with hypoechogenic, homogeneous reflection patterns. Lipoma shows a more hypoechogenic reflection pattern than the remaining parenchyma of the salivary gland, but its echo texture is more hyperechogenic than that of other types of intraglandular tumors and exhibits a linear, hyperechogenic feathery texture.

Soft tissue abscesses appear hypoechogenic to echo-free with hyperechogenic border, and a distinct distal acoustic enhancement and roughly patterned hyperechogenic echoes at the center of liquefaction foci, can correspond to necrotic tissue contributors.[9] So, ultrasound can rule out the type of lesion before surgical interventions can be attempted. The demonstration of mucus retention phenomenon and inflammatory cells can be done by fine needle aspiration, and high amylase and protein content can be revealed in chemical analysis. The localization and determination of the origin of the lesion can be done by CT and magnetic resonance imaging.[10]

Surgical excision with removal of the accessory salivary glands has been suggested as the treatment. Marsupialization will only result in recurrence, but large lesions are best treated with unroofing procedures (marsupialization). It is done to prevent significant loss of tissue or to decrease the risk for significantly traumatizing the labial branch of mental nerve. If fibrous wall is thick, moderate sized lesions may be treated by dissection. If this approach is used, the adjacent minor salivary glands must be removed carefully to avoid injury to any marginal glands and ducts, which may lead to recurrence of the lesion. The excised tissue should be submitted to the pathological investigations to confirm the diagnosis. Laser ablation, cryosurgery, and electrocautery are approaches that have also been used for treatment of the conventional mucoceles, with variable success.[1112]