DOI: https://doi.org/10.21203/rs.3.rs-2800065/v1
The most common location of pleomorphic adenomas within the minor salivary glands is the palate. These are rigid, immobile, slow-growing benign masses. In the presence of a slowly growing mass in which the mucosa is intact, it is one of the first masses to be considered. Fine-needle aspiration biopsy is not recommended due to disruption of the capsule structure and invasive metastasis. Information about the cranial bone invasion of the mass with computed tomography and the characteristic of the mass with magnetic resonance imaging can be obtained. Definitive diagnosis is established by histological evaluation. In our literature review, it was determined that some patients had their teeth extracted due to misdiagnosis.
Pleomorphic adenoma is the most common benign tumor of the salivary glands [1]. It has a mixed type structure containing epithelial, myoepithelial and stromal cells. It frequently occurs in major salivary glands (most often in the parotid gland, 65–80%), and more rarely in minor salivary glands. The most common locations in the minor salivary glands are the palate, nasal cavity, larynx, pharynx, and trachea [2]. Although it can also be seen in children, it often occurs in the 4th and 6th decades [3]. Its treatment is total resection of the tumor with its capsule. Rarely, it carries a risk of malignancy. This risk is higher in patients with a history of radiotherapy and recurrence [4].
Pleomorphic adenoma has an important role in the differential diagnosis of palate masses.
A 60-year-old male patient presented with the complaint of a mass in the palate region. The mass was located close to the gingiva on the right at the junction of the soft-hard palate and was approximately 3*4 cm in size (Fig. 1a). The patient did not have symptoms such as dysphagia, dyspnea, pain and speech disorder. In the computerized tomography (CT) examination, a benign polypoid mass was detected in the right half of the palate, which did not cause bone destruction (Fig. 1b). On the other hand, contrast-enhanced magnetic resonance imaging (MRI) was reported as a mass compatible with malignant character, and surgical operation was performed (Fig. 1c). After the mucosal flaps were elevated, the mass was dissected over the periosteum together with its capsule, and the excision was completed.
In the histopathological evaluation, it was observed that the epithelial component was lined with a double row of columnar epithelium and mostly showed squamous metaplasia. The stromal component consisted mostly of chondromyxoid cells and occasionally adipocyte cells. The epithelial component consisted of duct structures showing cystic dilatation in places. Ductal structures were generally lined with double rows of columnar epithelium, and even the luminal spaces were filled with keratin. There was no increase in mitotic activity and atypia. With trichrome staining, it was determined that the tumor was completely surrounded by the capsule. No stromal staining was observed with PAS and Musicarmin. With S100 staining, it was observed that the ductal structures were completely surrounded by myoepithelial cells. No increased proliferation index was seen with ki67 (Fig. 2).
Pleomorphic adenoma mostly affects the palate of the minor salivary glands. It usually appears as a hard, painless and slowly growing mass and is located posterolateral to the palate. Pleomorphic adenomas on the lips and oral mucosa are mobile, whereas masses located on the palate are fixed due to fibrous connections in the periosteum [5]. Benign cysts, abscess, neurofibroma, pleomorphic adenoma, adenocystic carcinoma and mucoepidermoid carcinoma are included in the differential diagnosis of masses located in the palate. Preferred imaging modalities in the diagnosis of palate localized tumors are conventional radiographs such as panoramic radiography, CT and MRI. With CT, more accurate information is obtained about the invasion of the mass into the surrounding tissues [6]. CT is the gold standard for assessing bone invasion of a palatal tumor and demonstrating its progression into the maxillary sinus or nasal cavity. With MRI, more accurate information is obtained with the dimensions and character of the mass. The best radiological diagnostic method for recurrent tumor detection is MRI. MRI makes the distinction between fibrosis and tumor more clearly [7]. The most important advantage of MRI is that it does not cause radiation exposure [8]. However, the definitive diagnosis is made histopathologically.
Immunohistochemical evaluation is one of the best options in the differential diagnosis of palate masses. While normal cells are not stained with vimentin, epithelial and mesenchymal differentiations of pleomorphic adenoma can be seen [9]. Staining with S100 antibody has almost the same characteristics as vimentin. Therefore, S100 antibody positivity supported the vimentin staining results. In addition, the presence of chondoroid differentiation was one of the findings in favor of pleomorphic adenoma.
The recurrence risk of pleomorphic adenoma is low. The treatment is surgical excision. The risk of recurrence increases in cases where adequate excision is not performed and capsule ruptures [10]. Since recurrence develops over the years, patients should be followed closely. It was determined that pleomorphic adenoma was multinodular in patients who developed recurrence after surgery. Local recurrence develops due to insufficient surgical excision and failure to remove the tumor with its capsular structure [11]. Recurrences develop due to pseudopodia originating from the surface of the tumor and seeding [12]. Metastasis develops with more hematogenous and less lymphogenous spread [7]. The mechanism of synchronized tumor development is not known yet. Some studies in the literature argue that RT reduces the risk of recurrence. McGurk et al in their series of 532 patients encountered local recurrence in only 1 of the patients who underwent RT after surgery [13]. In this patient, recurrence developed due to partial parathyroidectomy. Some authors think that RT is limited in preventing recurrence [7].
In the literature review, we observed that most of the patients had a history of dental extraction [4, 14, 15, 16] and misdiagnosis [17]. It is seen that the pleomorphic adenoma is lateralized to the gingival regions as localization. It is obvious that pleomorphic adenoma can cause tooth decay due to both mechanical pressure and the effect of inflammatory cells in its structure. Breitenecker determined that the inner epithelium of the dentigerous cyst in contact with the teeth was continuous with the pleomorphic adenoma [16]. Tanigaki et al. reported that a pleomorphic adenoma located close to the teeth can be confused with a malignant tumor developing due to irritation and may undergo aggressive surgery accordingly [18]. However, we determined that in some of the patients in the literature review and in the patient who applied to our clinic, there was no destruction in the bone cortex in the CT examination. When we deepened the anamnesis of our patient, it was learned that antibiotic treatment was applied for a while by the dentist and tooth extraction was performed when there was no regression in the panoramic radiography. It should be kept in mind that pleomorphic adenomas located close to the tooth roots can be interpreted as abscesses and healthy teeth can be extracted incorrectly. On physical examination, pleomorphic adenoma has a hard rigid structure, whereas dental abscess has fluctuation. In addition, the air-fluid level is seen in the radiological imaging of the cyst and abscess.
Tooth extraction with wrong diagnosis brings two problems with itself. The first of these is the spread of the tumor as pseudopodia and thus increasing the risk of local recurrence or metastasis. The second issue is infection of the tumor after tooth extraction. Palatal Pleomorphic Adenomas, which normally present as a painless mass, become painful with the effect of infection [19].
When a rapidly growing submucosal mass is encountered on the palate, pleomorphic adenoma should be kept in mind in the differential diagnosis. This tumor has a benign character and wide excision like other tumors will reduce the risk of recurrence.
Ethical approval For this type of study, formal ethical approval is not required.
Informed consent The study was prepared by obtaining informed consent from the patient in accordance with the Declaration of Helsinki.
Conflict of interest The author declare no competing interests.