By way of introduction of the topic I will relay a case history of a 50 year old male who presented in 1999 with a very small pedunculated asymptomatic soft tissue lesion in the right midpalatal region of his mouth. (There is no initial photograph as this non-suspicious lesion was very small and benign in appearance.) He reported it being present for about two years and neither his dentist nor his family doctor had been “concerned” about it. An excisional biopsy was performed which revealed adenoid cystic carcinoma — “incompletely excised”. A CT scan was arranged, which did not show any detectable mass lesion of the palatal tissues but based on the histologic report showing microscopic disease, the natural history of this lesion and its duration, a subtotal hemimaxillectomy was planned with obturator placement coordinated with the maxillofacial prosthodontist. This surgery was performed about two weeks later and frozen sections of margins performed at that time. There was no clinically distinct lesion. All margins were clear via frozen sections except the posterior aspect where perineural spread was detected along the greater palatine nerve extending into the pterygoid process and skull base. A further resection of the pterygoid process was performed but we realized there would likely be residual disease and post operative radiotherapy was planned. He received 6500 Gray to the area over six weeks and has been followed every six months since with physical examination, yearly chest xray and MRI every few years. In September, 2011 (some 12+ years after original diagnosis) at a regular follow up visit he complained of “ear fullness” similar to what he had after his initial surgery due to eustachian tube dysfunction which can be a side effect of posterior maxillary surgery. A CT scan and MRI were ordered and only after close inspection of the MRI by a head and neck radiologist and comparison with previous imaging was a suspicious area seen at the base of his skull near foramen ovale which is distinct from the original lesion. This was confirmed with a PET scan and further radiation therapy has just been completed to this area. Close follow-up will ensue.
Palatal masses are a common clinical entity, which most clinicians will be faced with at sometime in their careers. These often can result in a diagnostic dilemma for those who are not familiar with the common conditions, which present in this manner. Thankfully the majority of the conditions, which present clinically as a palatal mass are benign.
Our best physical examination tools for assessing these lesions are inspection and palpation as with most oral lesions. Radiographs can help with ruling out odontogenic sources of pathology such as abscesses and periapical inflammatory conditions .
In addition bony masses arising from the maxilla can be discovered from routine panoramic radiography such as that in Figure 1 that reveals a bone-like mass in the posterior maxilla which presented as a firm expansion of the hard palate, alveolus and buccal vestibule. The molar teeth tested vital and the patient was asymptomatic aside from the expansion. An incisional biopsy was performed and the histopathology demonstrated a solid ameloblastoma. A CT scan was obtained and it showed the tumor extended into the sinus and posteriorly to the pterygoid process. Although this is a benign odontogenic tumour it is very aggressive and can cause significant destruction. Because of a high recurrence rate it must be completely excised with planned wide surgical margins. Obviously the sooner and smaller this tumour is when it’s excised the better the prognosis and the less debilitating the surgery. This neoplasm was successfully treated by way of a sub total hemi maxillectomy with free surgical margins. (Figure 2)
Another common group of neoplasms of the palate is salivary gland tumours. The palatal soft tissue has abundant minor salivary glands and these give rise to a host of neoplasms, both benign and malignant. Figure 3 reveals a discrete rather large grape sized mass of the palatal mucosa, which had been present for several years. Once again the overlying mucosa was intact and there were no obvious radiographic changes to the adjacent bone or teeth suggesting either an odontogenic or maxillary bone source. The lesion felt fluctuant on palpation — almost cyst-like. An incisional biopsy was performed which revealed pleomorphic adenoma of the benign salivary gland neoplasm group. This lesion, if not completely excised can recur and there is a connective tissue capsule surrounding this tumour that must be completely removed during the dissection. The T1 weighted Magnetic Resonance Image nicely delineates this lesion in Figure 4. The surgery in this case involved complete submucosal excision of soft tissue down to palatal bone including periosteum and coverage of the surgical site with a prefabricated palatal stent. The palatal tissue has tremendous capacity to regenerate and can literally be completely removed and will regenerate back to near normal looking tissue.
Fortunately this was a benign neoplasm of salivary gland origin. About half of the neoplasms that arise from minor glands of the palate are malignant.1 Many of these malignancies such as the adenoid cystic carcinoma can be very small, asymptomatic and yet very deadly!2 These will be discussed in more detail shortly.
NECROTIZING SIALOMETAPLSIA
This entity is singled out due to its malignant appearance yet benign behaviour.1 It may present as a palatal swelling initially but then become ulcerated and appear as a nasty looking neoplasm not unlike squamous cell carcinoma. Even the histologic appearance can look cancerous to the untrained eye. But the classic squamous metaplasia of the salivary gland ducts and pseudoepitheliomatous hyperplasia coupled with the clinical appearance is diagnostic of this lesion.1 The exact etiology of this disease is unknown but spontaneous resolution occurs within 2 months without any treatment. In contrast, there is a greater concern for those lesions that appear small and asymptomatic yet relate to a much more malignant disease.
IMAGING
Aside from routine dental radiography — periapicals, panoramic and possibly cephalometrics, medical grade CT scanning (not cone beam) and MRI remain the gold standards for most of these lesions. Both have the ability to show bony and soft tissue involvement with MRI preferable for soft tissue masses and CT often preferred for assessing bony involvement.
ARRIVING AT A DIFFERENTIAL DIAGNOSIS
Once the more common odontogenic lesions, mucosal and bony abnormalities have been ruled out, it is incumbent upon us to ensure that all of the more serious pathologies have been thought of and ruled out as well. As with any lesion, the definitive diagnosis is achieved once there is histological examination of a sample of the tissue; a biopsy must be performed which will either be excisional for a small lesion not believed to be malignant or incisional for a presumed malignant lesion or one that is larger.
As with any presumed malignant lesion, it is best to be biopsied by the surgeon that will be performing the definitive ablative surgery. If there is an oral and maxillofacial surgeon who performs cancer surgery, that will likely be the best referral since there is a natural connection between the ablative surgery and the reconstructive component that includes coordination of the dental rehabilitation usually with a maxillofacial prosthodontist.
In consideration of the potential neoplasms native to the palatal tissues we can think of the various tissue types in the region. While it is certainly possible to have a neoplasm arising from any tissue type such as nerve, lymphoid, bone, epithelium, smooth muscle, striated muscle, blood vessels, fibrous connective tissue and others, there are more common neoplasms with more serious consequences including malignancies that need to be susp
ected and subsequently ruled out as part of the work up.
The more common neoplasms include: those arising from the alveolar or maxillary bone such as the full list of odontogenic lesions, salivary gland tissue, lymphoid tissue (lymphoma), squamous cell carcinoma arising from either the antral or oral mucosa. For a comprehensive review of all of these lesions please refer to the text by Neville et al on Oral and Maxillofacial Pathology.1
Both benign and malignant conditions may present as a palatal mass. Fortunately, the majority of these are benign and, due to the location, are recognized and subsequently managed early.
Several benign conditions that affect the osseous hard palate may present as a palatal mass. These include both the nasopalatine duct cyst and torus palatinus. The most common is the torus palatinus, which is a hamartoma that nearly always presents as a firm palatal mass located in the midline. It is important to consider many palatal tori are often secondarily traumatized and may have associated ulceration of the overlying mucosa. Thankfully, in the majority of these cases the patient will offer a history of such and if they are re-evaluated two weeks later, the mucosa should be healing.
Tori are diagnosed through clinical examination and radiographic examination if need be. They are located in the middle of the palate and are firm to palpation. They can be identified dental radiographs such as a panorex or lateral ceph. They require no treatment unless they interfere with denture fabrication.
Several benign soft tissue conditions also present on the palate. These include benign salivary gland tumors, fibromas (including leaf fibromas), hemangiomas, neurofibromas, odontogenic abscesses and benign salivary gland tumors.
Benign salivary gland tumors commonly present as a palatal mass at the junction of the hard and soft palate off of the midline. They are often asymptomatic but like tori, may be secondarily traumatized.
There are a number of different benign minor salivary gland tumors including pleomorphic adenoma, papillary cystadenoma lymphomatosum, oncocytoma and canalicular adenoma to name a few.
Several malignant conditions may also present as a palatal mass including malignant minor salivary gland tumors, lymphoma, squamous cell carcinoma and Kaposi’s sarcoma. Fortunately, malignant conditions presenting as palatal masses are much less frequent than benign conditions with the exception of malignant minor salivary gland tumors.
It is generally stated throughout the literature that approximately half of minor salivary gland tumors occur on the palate and of those, approximately half are malignant. The most common malignant minor salivary gland tumor which presents on the palate would be adenoid cystic carcinoma followed by mucoepidermoid carcinoma.
Adenoid cystic carcinoma is an aggressive malignant salivary gland tumor with a propensity for perineural invasion. It is unique in that it often causes skip lesions along the course of the affected nerve. This complicates treatment in that a histopathologically negative margin may not necessarily be truly negative if there is a skip lesion more proximal to the surgical margin. This is the most likely cause for its high recurrence rate and extremely poor long-term survival. Figure 5 shows one that has just undergone incisional biopsy and aside from that does not appear any more ominous than the palatal swelling in Figure 3.
Treatment involves wide surgical excision of the primary with a 1.5 to 2 cm margin with post-operative radiation therapy. Peripheral nerves at risk should be followed as far proximally as possible and sacrificed. Neck dissection is usually not indicated as it metastasizes hematologically rather than via lymphatics. Patients require close follow up to assess for local-regional recurrence as well as for distant metastases to the lungs. OH
Archie Morrison, DDS, MS, FRCD(C), Associate Professor Oral and Maxillofacial Surgery, Dalhousie University, Halifax, NS
Curtis Gregoire, BSc, DDS, MD, MS, FRCD(C), Assistant Professor Oral and Maxillofacial Surgery, Dalhousie University, Halifax, NS
Oral Health welcomes this original article.
REFERENCES
1. Neville, Damm, Allen, Bouquot. Oral and Maxillofacial Pathology, Third edition. WB Saunders Publishing, 2008.
2. Shen C, Xu T, Huang C, Hu C, He S. Treatment outcomes and prognostic features in adenoid cystic carcinoma originated from the head and neck. Oral Oncol. 2011 Dec 29. (Epub ahead of print).
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