ⅠINTRODUCTION
Pleomorphic adenoma is the most common benign tumor of the salivary glands that represent about 3-10% of the neoplasms of the head and neck region1). It derives its name from the architectural pleomorphism seen by light microscopy2). Pleomorphic adenoma consists of epithelial and mesenchymal cells arranged with various morphological patterns, demarcated from surrounding tissues by fibrous capsule. So it is also called as mixed salivary gland tumor2). About 90% of these tumors occur in the parotid gland and 10% of them occur in the minor salivary glands. The most common sites for pleomorphic adenoma of the minor salivary glands are the palate (42.6%), with equal incidence in both the hard and soft palate, followed by the lips (10.1%) and the cheeks (5.5%)3,4). Pleomorphic adenoma may occur at any age, but the highest incidence is in the fourth to sixth decade of life. Forty percent of them are male, 60% female5). Pleomorphic adenoma usually presents as a mobile, slowly growing, painless, firm swelling, well-delineated and covered with normal mucous membrane. Sometimes mucosal ulcerations are observed. Major gland tumors are usually encapsulated, as opposed to minor gland tumors6,7). The potential risk of the pleomorphic adenoma becoming malignant is about 6%8). Simple enucleation of this tumor has a high local recurrence rate and thus treatment is wide local excision with the removal of periosteum or bone if they are involved7,9). Rupture of the capsule or tumor spillage is also believed to increase the risk of recurrence, so meticulous dissection is important10).
We present a case of pleomorphic adenoma of the palate in a 36-year old male patient whose initial diagnosis was vascular mass such as hemangioma or lymphangiohemangioma by preoperative CT and MRI. We report focusing on diagnosis of pleomorphic adenoma with literature review.
ⅡCASE REPORT
1.Diagnostic Work-up
A 36-year-old male patient is referred to our department from the local clinic with the chief complaint of a slightly painful swelling in the upper left palatal region. He detected the suddenly appeared mass about 7 months ago. The past medical history, the past dental history, the family history and the social history were not relevant. All the vital signs were within the normal range and no abnormality was detected on his systemic examination. The patient underwent panoramic radiograph (PR), computerized tomography (CT), magnetic resonance imaging (MRI) and histological examinations.
In the extraoral examination, there was no facial asymmetry, and no evidence of any trauma. Nothing abnormal was detected on examination of the lymph nodes. In the intraoral examination, a single ovoid shaped, circumscribed mass which approximately measured 2.0 × 2.2 cm in diameter was found at the junction of hard and soft palate on the left side, not crossing the midline. The overlying mucosa was not ulcerated. It was smooth and intact, but was stretched and thus shiny in comparison with the healthy area on the other aspects of the palate (Fig. 1). On palpation, the swelling was rubbery in consistency, compressible and non tender. On the basis of the clinical examination, a provisional diagnosis was made as benign tumor of the minor salivary gland.
In the radiographic examination, there was no evidence of adjacent bony change. CT face soft (enhance) finding revealed about 2.0 cm sized soft tissue mass with poor enhancement and heterogenous density at the left sided palate (Fig. 2). The venolymphatic malformation or other benign lesion was suspected and MRI was recommended for further evaluation. MRI mouth (enhance) taking was done and it revealed about 2.0 × 1.6 × 1.5 cm (Antero-Posterior × Transverse × Cranio-Caudal) sized, well-defined, T2 and T1 high SI (signal intensity) lesion with peripheral irregular enhancing portion at the left palate, suggesting hemorrhagic mass (Fig. 3). Differential diagnoses of vascular mass such as hemangioma or lymphangiohemangioma with hemorrhage were considered. Other lesions like schwannoma with hemorrhage and less likely malignant mass were also considered.
We considered the more possibility to the first diagnosis decided by clinical examination and referred to the other radiologist for the second opinion to make the exact diagnosis. In a timely manner, the radiologist gave us the answer that the disease is likely pleomorphic adenoma.
2.Treatment and outcome
After routine preoperative investigations, the case was planned for surgical excision and impression taking was done for fabricating a surgical splint. The patient was operated under general anaesthesia. Mucosa around the lesion was marked and surgical excision of the lesion including the periosteum was done with surgical blade and dissecting scissors (Fig. 4). Hemostasis was achieved by use of electrosurgery. The eroded bone of the palate was observed, but oro-antral communication was no detected. The residual site was filled with flagyl gauze (Fig. 5) and surgical splint was covered for decreasing post-op palatal swelling and gauze retention. To induce the gradual soft tissue healing for a month, flagyl gauze was inserted with gradual decrease of the size, and regular oral irrigation was done with povidone-iodine and saline to maintain good oral hygiene.
The excised mass was sent for histopathology study (Fig. 6). After 1 week, the histological result showed mucous salivary gland with well-circumscribed mass. It was biphasic and was characterized by an admixture of polygonal epithelial and spindle-shaped myoepithelial elements. The stroma was mucoid, myxoid, hyaline and chondroid. Epithelial elements were arranged in duct-like structures lined by cuboidal cells and the abluminal myoepithelial cells. There was no evidence of mitotic figures or necrosis (Fig. 7). The definitive histopathology report confirmed the diagnosis as benign pleomorphic adenoma of palate.
The patient’s postoperative course was uneventful and there was no complication. No recurrence was observed after a follow-up period of 1 year (Fig. 8).
ⅢDISCUSSION
There are numerous malignant and benign tumor arises from major and minor salivary gland. Pleomorphic adenoma is the most common benign tumor of salivary gland, while mucoepidermoid carcinoma is the most common malignant counterpart to be encountered in maxillofacial region11). Pleomorphic adenoma at the palate is rare.
The differential diagnosis for this case includes palatal abscess, odontogenic and non-odontogenic cysts, soft tissue tumors such as fibroma, lipoma, neurofibroma, neurilemmoma, and lymphoma as well as other salivary gland tumors. Palatal abscess could be ruled out by clinical examination since the source of a palatal abscess, which is typically a non-vital tooth in the vicinity or a localized periodontal defect, was not found. This patient also showed no sign of inflammation. Both odontogenic and non-odontogenic cysts could be ruled out at the time of exploration into the mass since it did not demonstrate a cystic nature. Palatal tissues contain components of soft tissue and harbor minor salivary gland tissues12). Therefore, soft tissue tumors and salivary gland tumors should also be considered in the differential diagnoses for this case. Also, if the overlying mucosa is ulcerated and ulceration is not due to any trauma or biopsy, malignancy should be suspected.
In the present case, the patient complained of slow growing non tender swelling in the junction of hard and soft palate on the left side. Panoramic X-ray plays no part in the diagnosis of minor salivary gland tumors of the palate7). CT face soft (enhance) may be helpful in evaluating the erosion and the perforation of the bony palate and the involvement of the nasal cavity or the maxillary sinus. MRI can provide a better information of the vertical and inferior tumor extension and it more accurately indicated the degree of encapsulation13-15). In our case, MRI was primarily used to determine size and more importantly infiltration of lesion into the surrounding tissue. 1.6 × 1.5 cm soft tissue dense mass was found, not involving adjacent tissue. The lesion could not invade bone but might lead to a cupped out resorption of bone due to pressure effect.
Pleomorphic adenoma was the first diagnosis based on our clinical examination. But, vascular mass such as hemangioma or lymphangiohemangioma, schwannoma and malignant mass were considered by preoperative CT and MRI that revealed T2 and T1 high SI (signal intensity) lesion with peripheral irregular enhancing portion at the left palate, suggesting hemorrhagic mass.
At this point, differential diagnosis was very important because the treatment plan could be changed by diagnosis.
At first, our clinical diagnosis was decided by high occurrence rate of palatal area of pleomorphic adenoma, intact mucosa and mucosa color similar to proximal surface tissue. But at radiological examination by MRI, differential diagnosis was hard to clarify because of the high signal intensity in case of palatal tumor16).
These diagnoses had the weak points like sudden occurrence of lesion within short time at clinical examination and high signal intensity at radiological examination.
As the vascular mass occurred primarily at a young age than that of our patient, we were weighted on our clinical diagnosis and referred to the other radiologist for the second opinion. We received the answer that was a high likelihood of pleomorphic adenoma through a re-reading.
Histologically the tumor was composed of island of stellate and spindle cell that were interspersed in a myxoid background and was confirmed the diagnosis as benign pleomorphic adenoma of palate. A histological diagnosis is essential to plan the definitive management. Differentiation between benign and malignant tumors is not possible without histopathology.
Simple enucleation of the tumor has been reported with high recurrence17). Therefore the treatment of choice is surgical excision. If pleomorphic adenoma is located in the superficial lobe of the parotid gland, an effective way of treatment is superficial parotidectomy with preservation of facial nerve. When the tumor is located in the deep lobe of the parotid gland, the method of choice is total parotidectomy and if possible with preservation of facial nerve4,18). Tumors of hard palate are usually excised down to the periosteum, including the overlying mucosa with 1 cm clinical margins at the periphery4). Excision of palatal bone is not required as periosteum is an effective anatomical barrier. Many authors had advocated surgical excision with curettage of the underlying bone with a surgical curette or bur11). The overlying mucosa can sometimes be required by using a local flap. Sometimes, reconstruction of the palate should be considered for functional and esthetic point of view. The soft tissue defect of the palate can be left to granulate, while the bony defect can be treated conservatively with an obturator19). In the present case, the patient did not require reconstruction as the palatal mucosa was regenerated and as there was no formation of oro-antral fistula. The excised region could be left to heal by secondary intention and flagyl gauze was inserted with gradual decrease of the size.
Pleomorphic adenoma generally does not recur after adequate surgical excision with a cure rate of more than 95%20). Reasons for recurrence include incomplete excision, seeding, cutting through the microscopic extracapsular projections thereby leaving some tumor behind, or rupture of the capsule and accidental seeding of tumor cells, as is more likely to occur when dissecting close to the capsule18). Our patient has not experienced any complaints and signs of recurrence after 1 year of follow-up.
In conclusion, the exact first diagnosis is very important in case of palatal mass to make the treatment plan. Differential diagnosis by CR or MRI is hard but these can contribute to evaluating the extent of the lesion and in guiding the surgical strategy. Most salivary gland tumors should be dissected due to the possibility of becoming malignant. A biopsy-proven diagnosis should be routinely taken after the excision of the neoplastic lesion. Adequate surgical excision and long-term follow-up are necessary because of the risk of recurrence after many years of initial excision.
