Pedunculated Pleomorphic Adenoma With Adipocytic Metaplasia of the Hard Palate: A Case Report

Introduction

Salivary gland tumors account for 1% to 4% of all neoplasms of the human body. ¹ Minor salivary gland tumors account for 10-25% of all salivary gland neoplasms. ² The most common sites in descending order of frequency are the palate, lips, buccal mucosa, floor of the mouth, tongue and tonsil. ³

Pleomorphic adenoma (PA) is the most common neoplasm of the major salivary glands, occurring predominantly in the parotid gland and less frequently in the accessory salivary glands. ⁴ Its prevalence rate is 60 to 73% of all salivary gland tumors.^5,6

PA can occur at any age, even in the newborn. However, patients in their fifth and sixth decades of life are commonly affected, and 60% of them are women.^2,6 It derives its name from the architectural pleomorphism seen by light microscopy, ⁴ a variety of cells including epithelial, myoepithelial, mesenchymal and capsular compartments may be observed. Because of this pleomorphism it is also known as “mixed tumor”. ³

The variations in epithelial and mesenchyme-like components with or without dysplasia add to this dilemma. ⁷ Malignant degeneration of this tumor is a potential complication. ⁶

Within this case study, we report a rare pedunculated PA with adipocytic metaplasia located on the hard palate. This report provides insight into the clinical presentation and management of this uncommon entity.

Case Presentation

A 46 year old female with no medical or surgical history, was referred to our department of dental medicine after the discovery of a slowly growing palatal swelling that had been evolving for 5 years. The patient did not report other complaints.

During the clinical examination of the lesion, a solitary, well delineated, exophytic nodular growth on the hard palate was present. The mass was in the form of an ovoid, with a budding appearance, located on the hard right palate extending from tooth 15 to the tuberosity. It was pedunculated with a 1.5-cm-wide base, located on the right side of the hard palate and it extended beyond the midline of 8 millimeters, measuring approximately 2.5× 4× 2 cm. The nodule was covered by an erosive and ulcerated mucosa with a bluish appearance in the posterior area (Figure 1).OPEN IN VIEWER

The swelling was painless, non tender, firm in consistency, non fluctuant, non compressible, and without any pus or discharge on palpation. No evidence of paresthesia, tooth necrosis, mobility, or regional lymphadenopathy was found.

Preoperative cone beam computed tomography (CBCT) revealed mild bony erosion of the palate in the same zone. The nasal floor and maxillary sinus were intact (Figure 2).OPEN IN VIEWER

After proper investigations excisional biopsy was indicated. The surgical steps consisted of disinfection of the site with betadine 10%, local anesthesia (1 % lidocaine with 1:200,000 adrenaline) and prehension of the mass with a suture thread followed by the dissection at the base of the nodule (Figure 3A). The mucosa which was not involved around the lesion was spared and separated from the rest of the mass (Figure 3B). The whole tumor mass was separated out along with periosteum from the underlying bone, with careful dissection (Figure 4).OPEN IN VIEWER

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Figure 4.

Excised specimens

After a supported debridement, the healthy edges were reattached with sutures (Figure 5). Hemostasis by compression was ensured and the rest of the site was left exposed in view of the non elasticity of the palatal fibro mucosa, resulting in healing by secondary intention.OPEN IN VIEWER

The prescribed medication regimen consisted of Amoxicillin at a dosage of 2g daily for 7 days, Paracetamol for 5 days (3g daily), and a 0.12% chlorhexidine mouthwash for 10 days.

Surgical biopsy specimens have been addressed to the pathology department for histopathological examination. Grossly, the fragments were whitish in color with a firm consistency. On the cut surface, there are small foci of hemorrhage with a myxoid appearance. The microscopic examination showed an ulcerated tumor consisting of a mixture of epithelial and myoepithelial cells. Epithelial component showed various patterns like ducts, acini, tubules, and sheets of cuboidal or columnar cells. The ducts contain eosinophilic secretory material. Focal areas of squamous and adipocytic metaplasia were observed (Figure 6A). The myoepithelial cells are plasmacytoid, polygonal, or spindle-shaped. These cells form sheets and small islands. Neither nuclear atypia nor mitoses were seen. The background is myxoid and hyalinized (Figure 6B).OPEN IN VIEWER

Following the surgical procedure, the patient experienced a comfortable postoperative recovery period. At the one week postoperative follow up, epithelialization from the surrounding tissue was observed. Additionally, evidence of fibrin deposition was observed at the surgical site and it is completely healed after 4 weeks. No recurrence was observed after a follow up of 12 months (Figure 7).OPEN IN VIEWER

The patient expressed satisfaction with the surgical management and the postoperative outcome. She reported significant relief after removal of the palatal mass, which had increasingly affected mastication and oral comfort over the years. She was reassured by the benign diagnosis and appreciated the rapid and uneventful healing of the palatal mucosa. The patient also acknowledged the importance of long term follow up to detect any potential recurrence at an early stage.

Discussion

The prevalence of tumors in small salivary glands accounts for 20 to 40%. The smaller the salivary gland that is affected, the more likely it shows malignant behavior. ⁶ Mainly it occurs on the hard and soft palate because the majority of the minor salivary glands are located in this area. ⁵ This tumors are mainly seen at the junction of the hard and soft palates. ⁸

PA most commonly occurs between fourth to sixth decades, however, reported instances in a 7 years old patient and an 82 year old patient are also seen as it was mentioned in Deepak passi et al’s literature review. ⁹ It has a slow growth rate, which explains why patients may notice its presence for years before seeking a diagnosis, ¹ as in the incidental discovery of the present reported case.

It should be noted that PA tends to be small and fixed in the palate as well as in the other minor salivary glands compared to the parotid gland where the lesion rather tends to be larger and mobile. ⁸ In most cases, it presents as an asymptomatic, firm bulge in the palatal mucosa. ⁸ Sometimes it can cause dyspnea, dysphagia, acute airway obstruction, and obstructive sleep apnea. ⁹ The present case is noteworthy due to the particularly pedunculated form of the lesion which is extremely rare and may lead to diagnostic confusion, further compounded by the presence of surface ulceration resulting from masticatory trauma.

In fact, diagnosis is based on the history, physical examination, radiological investigation and histopathological examination report. During clinical examination, the differential diagnosis includes palatal abscess, odontogenic or non odontogenic cyst and soft tissue tumors such as neurofibroma, fibroma, neurilemmoma. However, palatal abscess can be excluded by vitality examination of the surrounding teeth. The odontogenic and nonodontogenic cysts can be excluded during exploration of mass as it does not reveal its cystic consistency.^4,10

In terms of radiographic evaluation, Magnetic Resonance Imaging (MRI) is important for demonstrating the tumor margins, precise location and involvement of surrounding tissues.^11,12 it provides excellent soft tissue characterization but it cannot evaluate the bone involvement in the case of a palatal localization.^8,11 Scanner and CBCT can aid in establishing a diagnosis ⁸ especially in case of bone invasion. PA can show a diffuse mottled radiolucency and cupped out bone resorption. ³

Histologically, PA comprises both epithelial and mesenchymal tissues, demonstrating a diverse microscopic pattern. The epithelial component manifests as ducts or cystic structures, alongside the presence of myoepithelial cells characterized by their angular, fusiform, or rounded morphology, eccentric nuclei, and eosinophilic cytoplasm. ¹³ The stromal component exhibits a wide morphological spectrum, encompassing fibrous, hyaline, and chondroid areas, with variable proportions relative to the parenchyma. ¹ In the “cellular” type of PA, epithelial elements predominate, while the “myxoid” type contains a myxomatous element. The classic form is a mixed type. Various epithelial cell types can be identified, including spindle, clear, squamous, basaloid, cuboidal, plasmacytoid, oncocytic, mucous, and sebaceous. ⁵

PAs, especially those originating from minor salivary glands of the palate, can exhibit extensive squamous and mucinous metaplasia, which may raise concerns for mucoepidermoid carcinoma. However, they are typically differentiated from mucoepidermoid carcinoma by the presence, at least focally, of characteristic ductal and myoepithelial proliferation, as well as myxochondroid stroma. ⁷

In our case, the epithelial component is predominant, consisting of tubes and dilated cystic structures, epithelial cells are devoid of nuclear atypia or mitosis. The myoepithelial component is made up of cells of variable shape, sometimes spindle-shaped, sometimes plasmacytoid, with low to moderate cellularity. The tumor contains a squamous clusters and islands of mature adipocytes. Highlighting the presence of adipocytic metaplasia, which is considered a rare histopathological feature in PA, despite the fact that approximately one quarter of PAs exhibit squamous metaplasia, a feature often associated with previously biopsied or ulcerated intraoral tumors.

Additionally, mucous (goblet) cell metaplasia may also be observed. When extensively present, squamous metaplasia can mimic squamous cell carcinoma or, when combined with mucous cell metaplasia, mucoepidermoid carcinoma. ¹⁴ Features distinguishing squamous cell carcinoma from PA with extensive squamous metaplasia include the absence of infiltrative growth, cellular and nuclear pleomorphism, nuclear hyperchromasia, increased mitotic activity (including atypical mitoses), and the presence of surface squamous epithelial dysplasia in minor salivary gland tumors.^1,15,16

Due to this histological variability, PA shares common features with other salivary gland tumors, benign and malignant alike.^1,15 Analyzing oral salivary gland tumors poses an additional challenge, as approximately 50% of them are malignant. Therefore, a comprehensive understanding of the architectural and cytological patterns of mucoepidermoid carcinoma, myoepithelioma, basal cell adenoma and adenoid cystic carcinoma is essential for achieving an accurate diagnosis of this neoplasm.^1,17 (Table 1).

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Table 1.

Differential Diagnosis of Pleomorphic Adenoma Versus Major Salivary Gland Tumors

Feature	Pleomorphic adenoma	Mucoepidermoid carcinoma	Myoepithelioma	Basal cell adenoma	Adenoid cystic carcinoma
Nature and clinico-pathology	Tumor of epithelial and myoepithelial cells with variable matrix component	Malignant tumour with mucous, intermediate, and epidermoid cells; grade and aggressiveness vary	Composed almost exclusively of myoepithelial cells; benign; lacks significant ductal structures seen in PA	Uniform proliferation of basaloid cells forming solid, trabecular, tubular, or membranous patterns, often encapsulated	Malignant tumor with characteristic cribriform pattern and perineural invasion
Growth pattern and pain/symptoms	Slow growing, expansile, well circumscribed. Usually painless	Variable; may be rapid. Pain possible, depends on grade	Slow growing. well-circumscribed Asymptomatic.	Slow, well-circumscribed growing. Painless.	Slow but infiltrative. Pain, paresthesia, perineural invasion common
Radiographic features	Well defined lesion; may show pressure induced “cupping” bone resorption	Ill defined bone destruction may be observed in aggressive lesions.	Minimal bone change	No bone destruction	Bone invasion with irregular borders
Recurrence risk	Low if fully excised	Depends on grade	Low	Low	High ( recurrence and metastasis)
Malignant potential	Possible: carcinoma ex-PA	Already malignant	None	None	Already malignant

The location, size of the tumor as well as its extension into the surrounding structures dictate the optimal management regimen and treatment approach. However, due to the recurrence rate, simple enucleation should be avoided. The treatment recommended for PA is excision. Complete excision, with establishing secure resection margins of normal tissue and removal of periosteum or bone if they are involved. ³ Palatal reconstruction is considered in cases of large palatal defects arising after surgical excision in very aggressive tumors. ¹⁸

Salivary gland tumors tend to recur after incomplete removal and PA may transform as a malignant neoplasm. ¹⁴ Thus, the success of primary treatment is essential, a long-term follow-up of least 5 years is necessary. Although intraoral PA have a good prognosis, they are slow growing tumors, and recurrent lesions may remain clinically silent for many years. Importantly, very late recurrences can occur. Most important feature of PA of minor salivary glands is the frequent absence of the capsule. This can gives an impression of infiltrating mass. ⁹ This capsule may be incomplete which is more common in minor salivary gland tumours.^3,4 Even in cases managed with more conservative or apparently complete excision, microscopic pseudopodia or capsular discontinuities may persist and contribute to delayed recurrence. ⁵ Over time, the cumulative risk of malignant transformation also rises, especially in long standing or recurrent tumors.

The main limitation of this case report is the relatively short follow up period of 12 months. Although no recurrence has been observed to date, extended follow up appointments are planned. Another limitation concerns the patient’s financial constraints, which prevented the use of advanced radiological investigations, such as CT scan and MRI, that could have provided additional radiological assessment.

Despite the clinical interest of this case particularly its rare pedunculated presentation associated with an uncommon adipocytic metaplasia, it describes a single observation. Therefore, the findings cannot be generalized, and no solid conclusions can be drawn regarding the prevalence, biological behavior, or optimal management of such variants. Further investigations, especially larger case series or multicenter studies, are needed to improve understanding and guide clinical practice.

Conclusion

In conclusion, PA of minor salivary glands are extremely rare and may mimic other soft tissue lesions, leading to diagnostic uncertainty. Adipocytic metaplasia, although uncommon, presents a diagnostic dilemma and should not be mistaken for malignant transformation. Histopathological evaluation remains mandatory to confirm the diagnosis and to distinguish this tumor from malignant salivary gland neoplasms.

Complete surgical excision with clear margins remains essential to minimize recurrence risk. Long term follow up of at least five years is recommended due to the possibility of late recurrence, malignant transformation and to prevent undue aggressive treatments.