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ABSTRACT

Pleomorphic adenoma is the most common neoplasm in major and minor salivary glands. It constitutes approximately 90% of all benign salivary gland lesions and the parotid is the most affected location. When the minor salivary glands are affected, it mostly occurs at the junction of the hard and soft palates. The diagnosis is complex because of the great histological variety and biological behavior of this tumor, a histopathological examination being essential. The recommended treatment is surgical excision. For lesions located superficially in the parotid gland, superficial parotidectomy - identifying and preserving the facial nerve - is necessary. Lesions in the palate or gums sometimes demand a margin of safety, being excised below the periosteum, including the overlying mucosa. With correct surgical removal, the prognosis is excellent. The aim of this study is to report a case of an unusual minor salivary gland pleomorphic adenoma in the hard palate, describing the most important aspects of this pathology.

Indexing terms: Neoplasms. Pleomorphic adenoma. Salivary glands.

RESUMO

O adenoma pleomórfico é a neoplasia mais comum entre os tumores das glândulas salivares maiores e menores. Constitui aproximadamente 90% de todas as lesões benignas das glândulas salivares e a parótida é a mais acometida. A junção dos palatos duro e mole é o sítio de predileção mais comum, quando as glândulas salivares menores são atingidas. O diagnóstico é complexo devido a grande variedade histológica e comportamento biológico deste tumor, sendo imprescindível a realização do estudo histopatológico. O tratamento de escolha é a excisão cirúrgica. Para as lesões localizadas no lobo superficial da parótida é recomendada a parotidectomia superficial com a identificação e preservação do nervo facial. As lesões do palato ou gengiva por vezes podem exigir margem de segurança, sendo geralmente excisadas abaixo do periósteo, incluindo a mucosa sobrejacente. Com a remoção cirúrgica adequada, o prognóstico é excelente. O presente trabalho tem como objetivo relatar um caso de adenoma pleomórfico não usual de glândula salivar menor no palato duro, em região posterior direita, além de descrever os aspectos mais importantes dessa patologia.

Termos de indexação: Neoplasias. Adenoma pleomorfo. Glândulas salivares.

INTRODUCTION

Tumors of the salivary glands, though uncommon, are not that rare and constitute an important field in oralmaxillofacial pathology. The diversity of histological aspects displayed by neoplasms of the salivary glands causes great difficulty in terms of universal classification^1-2.

Pleomorphic adenoma (PA) is the most commonly found neoplasm amongst tumors of the major and minor salivary glands, originally called a mixed benign tumor in 1866^3-5. The change of name to "pleomorphic" adenoma was first suggested as recently as 1948, as this term describes the embryological basis for these tumors, which originate in the epithelial and connective tissue³. The classical microscopic description was applied in 1874, observing a variety of cell types as the main characteristic of pleomorphic adenoma, not just between the different samples examined but also in different parts of the same sample⁶. Even though it has an origin which is exclusive to epithelial tissue, the variety of components accords it a mesenchymal appearance as a result of the production of secretions from the tumor cells themselves, which may be ductal or myoepithelial⁷.

PA makes up approximately 90% of all benign lesions of the salivary glands^5,8-11. It represents between 53% and 77% of parotid tumors, 44% to 68% of tumors of the submandibular gland and 33% to 43% of tumors of the minor salivary glands². It almost never manifests itself in other areas of the head and neck. It occurs most frequently in the parotid gland and is more prevalent in women (1.5:1) and in black people⁶. The lesions may appear at any age, though rarely in children, being most common between the fourth and sixth decades of life^5,8,12.

Clinically, they are described as nodular lesions with a smooth surface that generally present without pain, having a firm consistency, slow growth and which do not attach themselves to the adjacent tissue (mobile lesion except when occurring in the hard palate). In the majority of cases it does not cause ulceration of the overlying mucosa³. The minor salivary glands, when affected, are normally located, in order of prevalence, at the junction of the hard and soft palates, lips, tongue, cheeks and floor of the mouth; the histological description in these cases is similar to that of adenomas of the major salivary glands^1,3,10,12.

The diagnosis of pleomorphic adenoma is performed based on a detailed clinical history and physical examination. Imaging exams, though not essential, have demonstrated a prominent role in establishing the origin, location and limits of the lesion, particularly tomographic techniques. Conventional radiography is limited, only being useful for the screening of lesions adjacent to mineralized tissue. Ultrasound (US), in spite of it not being invasive, is useful for differentiating between intraglandular and extraglandular lesions, but is also limited to the evaluation of the deep spaces in the region of the head and neck, particularly via interposition of the bone. Computer tomography (CT) is particularly recommended for identifying lesions with bone involvement, however it does not provide good definition of soft tissue detail, hindering the differential diagnosis of those lesions located deep in the region of the head or neck. Magnetic resonance imaging (MRI) is a tomographic technique that offers high definition of the soft tissue, permitting differentiation between lesions and better distinction between the salivary gland, lesion and adjacent tissue^6,10. Fine-needle aspiration puncture (FNAP) is another mode of diagnosis that could be used in terms of determining if the tumor is benign or not; however, it does not serve to define treatment⁵. The definitive diagnosis of pleomorphic adenoma, therefore, is carried out by means of a histopathological examination^6,10.

A pleomorphic adenoma is a tumor with great histopathological variety, its characteristics including the occurrence of various architectural and structural arrangements and variations in cellularity, sometimes in just one sample. The lesion consists of epithelial, myoepithelial and mesenchymal elements, enclosed in a stroma that is myxoid, chondroid or even osteoid in nature^6,10. As far as Lima et al.¹ are concerned the diversity of histological aspects exhibited by neoplasms of the salivary gland has been attributed to the presence of the myoepithelial cell in these glands.

Lesions located in the minor salivary glands are histologically similar to those occurring in the major salivary glands, despite there being a tendency for many of the lesions in those glands to be predominantly cellular, with a minimum of stroma and cartilage component. Either they have no fibrotic capsule formation or just a very thin capsule, giving them the false impression of infiltration into the adjacent tissue. Another important characteristic is that they can present with incomplete encapsulation, particularly along the surface portion of those located in the palate, below the epithelial surface. Occasionally they may present neighboring, extracapsular lesions which, in cross-sectional images, show up as pedunculated areas of growth external to the principal neoplasm^6,10.

With the larger lesions, necrosis, hemorrhage and calcification or ossification may be present. The presence of areas of necrosis, atypical mitoses, invasiveness and extensive hyalinization suggests the possibility of malignancy. On the other hand, calcifications inside the mass suggest a benign neoplasm or, less commonly, schwannoma or mucoepidermoid carcinoma^1,5,10,13-14. Even though it has well-known clinical and morphological characteristics, the malignancy of the pleomorphic adenoma is the holder of a pathogenesis which is still uncertain, as is the expression of oncogenes and the factors that influence its transformation¹¹.

In the long run, malignant degeneration may occur, which is most likely in adenomas that have been evolving for over ten years. Therefore, early diagnosis is necessary and should be followed up by a suitable approach to treatment. Malignant neoplasms in the minor salivary glands represent less than 2% of all cases of tumors⁴. However, neoplasms in these glands that go untreated may undergo a malignant transformation in between 5% and 25% of cases, resulting in carcinoma ex-pleomorphic adenoma (Ca-ex-PA)¹⁰.

The treatment of choice is surgical removal. For lesions located in the superficial lobe of the parotid, a superficial parotidectomy is recommended with the identification and preservation of the facial nerve. Lesions of the palate or gums may sometimes demand a margin of safety, normally being surgically removed below the periosteum, including the overlying mucosa. The removal of bone is not generally required as the pleomorphic adenoma does not invade the bone tissue, although it may cause resorption from pressure. Given correct surgical removal, the prognosis is excellent^1-3,6,10,15.

The aim of the present study is to report an unusual case of a malodorous, pleomorphic adenoma of the minor salivary gland in the hard palate, with an extensive area of surface necrosis, resembling a malign tumor.

Female patient aged 21, pheoderma, appeared at the clinic of the Santo Antônio Hospital for Oral Maxillofacial Surgery and Traumatology – Sister Dulce Charitable Works Foundation, complaining of "something odd in the roof of her mouth" and reporting an evolution of a little over a year. Upon clinical examination, a volumetric increase was observed to the rear and right hand side of the hard palate, unique, fixed, circumscribed, hardened on palpation, with a large area of necrosis, without pain and malodorous, measuring 30 mm at its largest diameter, presenting with characteristics of nodular lesion and with a sessile base (Figure 1). On tomographic examination, a well-defined lesion was found, circumscribed in the right maxilla, with an area of superficial osteolysis in the hard palate, and no invasion of adjacent structures (Figure 2).

An incisional biopsy was performed, the histopathological examination of which diagnosed an ulcerated pleomorphic adenoma. Subsequently, the patient was subjected to a surgical procedure under general anesthetic for the complete surgical removal of the lesion, in which an intrasulcular incision of the palate was performed extending from the right molars to the left pre-molars, with the subsequent dissection of the mucoperiosteum. In the trans-operative period, an encapsulated lesion was observed, well circumscribed and with signs of superficial osteolysis on the palate (Figure 3).

The histopathological examination of the surgical element found evidence of a well-defined, pseudo-encapsulated nodular lesion, characterized by a proliferation of epithelial and plasmocytoid myoepithelial cells and ductal elements with pairs of cells, squamous metaplasia and areas of cyst formation with a conclusive diagnosis of pleomorphic adenoma of the minor salivary glands (Figure 4).

The patient progressed satisfactorily in the postoperative period and after twenty days the region of the surgery can be said, clinically, to have completely healed. The patient has been clinically monitored for four months and no recurrence of the lesion has been observed (Figure 5).

DISCUSSION