Central Mucoepidermoid Carcinoma (CMEC) of Maxilla – A Case Report and Review of Literature

INTRODUCTION

Mucoepidermoid tumour was first studied and described by Stewart, Foote and Becker in 1954 as separate tumor of the salivary glands. Rarely, it may occur intraosseously from the epithelial lining of the odontogenic cyst and/or epithelial remnants of ectopic salivary glands which is known as (CMEC) or (IMEC)^1-6. (MEC) is the most commonly occurring malignant salivary gland neoplasm, comprising 2.8%–15% of all salivary gland tumors. Aberrant salivary gland neoplasm's arising within jaws as primary central bony lesions are extremely rare with 2–4.3%of all being (MECs)^5,7 and (CMEC) is a rarest entity affecting the jaw bones. The pathogenesis, radiological and histopathological aspects have been extensively discussed. Most primary (CMEC) lesions occur in the mandible, but are rare in themaxilla⁵. 

CASE REPORT

A 53-year-old male patient of Indian origin reported to the Department of Oral Medicine and Radiology with the chief complaintof swelling and pain with left maxillary region since 6 months, which had initiated after a trauma to the left facial region, the swelling was initially of smaller size and had gradually increased to the present size. The patient also had a history of an extraction with the same region 3 months ago in a primary health center, after which the swelling increased with pain which, pain was dull and intermittent type. His habit history revealed that he was a beedi smoker and alcoholic since 30 years, with no other significant medical or family history.

Extraoral examination, revealed the presence of left facial swelling (Fig-1), extending horizontally from the ala of the nose to the zygomatic region and vertically from outer cantus of eye to angle of the mouth (3x4 cm) in its longest diameter. The skin over the swelling was normal. The swelling was soft in consistency, non-tender, without palpable regional lymph nodes like pre-auricular, post-auricular, sub-mandibular, sub-mental and deep cervical lymph nodes. Intraoral examination revealed solitary non tender swelling with left maxillary tuberosity extending antero posteriorly from left first premolar to the tuberosity and laterally from buccal vestibule to the mid palatal raphe (3.5x3 cm) with variegated consistency, mucosa over the swelling was ulcerated with lobular surface and mobility of 24, 25 and 26 teeth (Fig-2) with patent salivary flow from both the parotid ducts. Intraoral periapical radiograph of the left premolar-molar region showed an ill-defined diffused radiolucent lesion, extending from the distal surface of the left second premolar to maxillary tuberosity with loss of lamina dura and displacement of first molar (Fig-3). A panoramic radiograph showed a massive osteolytic lesion extending horizontally from distal aspect of second premolar to maxillary tuberosity and vertically from the crest of the alveolar bone to 0.5 cm away from the floor of the maxillary sinus approaching the nasal cavity in an upwarddirection displacing 25 and 26 teeth (Fig-4). An additional radiograph (PNS Para nasal sinus view) showed (Fig-5) diffused radiolucent lesion extending from posterior part of left maxillary tuberosity to lateral wall of the nasal fossa involving the maxillary sinus with ill defined borders.

Evaluating the clinical and radiographic findings, the working diagnosis of carcinoma of minor salivary glands involving palate was given. Subsequently incisional biopsy was performed. The gross examination of specimen revealed grey black soft tissue mass measuring 0.75mm x 1cm. The patient was adviced for computed tomography (CT) of the maxilla but not done, Histopathological examination revealed a neoplasm composed predominantly of acinar cells, mucussecreting epidermoid and intermediate type cells, islands of epithelial cells showing dysplastic features like nuclear hyperchromatism and pleomorphism with increased mitotic activity, fibrosis and chronic inflammatory infiltrate. Histopathological diagnosis of moderately differentiated (CMEC) of the left maxilla was made (Fig-6).

DISCUSSION

Intraosseous carcinoma arising in the jaw bones was describedas a central epidermoid carcinoma by Loos in 1913. Later, Pindborg coined the term "primary intraosseous carcinoma" (PIOC) in the first edition of the World Health Organization classificationfor the histopathological typing of the odontogenic tumors^4,5. 

In 1974, Alexander et al introduced the following clear-cut criteria, to establish a diagnosis of central origin MEC which were modified by bronwand and Waldron in 1975 and simulated to Kochaji et al guidelines^4,5 , using the published guidelines, knowledge about this rare entity will definitelyhelp the diagnosticians, radiologists, surgeons and pathologists all across the globe reach an accurate decision regarding best treatment and prognosis for each reported case^4,5.

Following are the published criteria for the diagnosis of (IMEC)^4,5:

1. Presence of an intact cortical plate

2. Radiological evidenceof bone destruction

3. Histological confirmation

4. Positive mucinstaining

5. Absence of primary lesion in the salivary gland 6. Exclusionof an odontogenic tumour. 

All this criteria were positive in our case too. Later Waldron and Mustoe suggested that (IMEC) should be included in the primary intraosseous carcinomas (PIOC) of the jaws as type 4.⁵ 

Classification of (PIOC)^5,8 

• Type 1 (PIOC) ex odontogenic cyst 
• Type 2a Malignantameloblastoma 
• Type 2b Ameloblastic carcinoma arising de novo, ex ameloblastoma or ex odontogenic cyst 
• Type 3 (PIOC) arising de novo: (a) keratinizing type; (b) non-keratinizing type 
• Type 4 (IMEC) 

(IMEC) or (CMEC) affects females twice more frequently than males and involves the mandible twice more often than the maxilla, exception being our case. It has been reported in all ages ranging from 10 to 78-years, with the overwhelming majority occurring in 4th and 5th decades of life with the mandible to maxilla ratio being 1:1 and showing main symptoms like swelling, pain with trismus, paraesthesia and tooth mobility.⁹

The pathogenesis of the (CMEC) has been discussed extensivelyand various possible origins have been considered, including: ^5,10,11

1. Entrapment of the retromolar mucous glands within the mandible,which later undergo neoplastic transformation.

2. Embryonic remnants of the submandibular and sublingual glands trapped within the mandible during development.

3. Neoplastic transformation and invasion from the lining of themaxillary sinus.

4. Neoplastic transformation of the mucus-secreting cells from the epithelial lining of the dentigerous cyst associated withimpacted thirdmolars.

However, (CMEC) of the maxilla is a rare lesion and the pathogenesis is not extensively discussed. The possibilities of the origin of the (CMEC) in maxilla may be:

1. Neoplastic transformation of entrapped minor salivary glandswithin themaxilla.

2. Neoplastic transformation and invasion from the lining of themaxillary sinus

Histopathological criteria for (MEC) diagnosis

According to the criteria of Seifert, Sobin and Auclairet al the tumours are graded for malignancy as follows^5,12,13

1. Low grade: highly differentiated neoplasia with a predominance of macro- and microcysts. Presence of intermediate and mucin-producingcells

2. Intermediate grade: predominance of intermediate cells and afew cysts. Presence of mucin-producing cells and islands ofepidermoid cells

3. High grade: poorly differentiated neoplasia with predominance of intermediate and epidermoid cells in solid blocks. Mucin-producingcells are present.

Radiographic examination is important to know the diagnosis, categorization as a central jaw lesion and the extent of the lesion with involvement or encroachment of adjacent vital structures. Brookstone and Huvos suggested a three-grade classificationfor (IMEC).^4,5

Grade 1, without expansion and ruptureof cortical plate;

Grade 2, with expansion but without ruptureof cortical plate;

Grade 3, with rupture of cortical plates or presence of regional metastasis;

Grade 2 involvement was noted our case and appreciated in OPG. The primary treatment modality for patients with (IMEC) is surgery, including curettage, enucleation, marsupialization and wide local excision. As a rule, even as low-grade (MEC) should be managed by wide local resection, en bloc resection, or hemimandibulectomy or hemimaxillectomy. Neck dissection is usually part of the treatment in cases where metastasis to the cervical nodes is suspected⁵ . The epidermal growth factor receptor protein is over expressed in approximately 70% of mucoepidermoid carcinoma patients and may represent a therapeutic target; hence treatment with anti-epidermal growth factor receptor 14 agents (anti-EGFR) has also been tried .Radiotherapy is recommended for high-grade (MEC) cases. These tumors usually show a good overall prognosis, but (CMEC) cases should be followed-up for a longer period due to the possibility of late recurrence or regional metastasis. In addition to high tumor grade, other predictive factors that have been associated with poor 5-year survival include bone invasion, age beyond 60 years, pain, positive cervical nodes and facial palsy^15,16 . However, death may occur as a result of extension into vital structuressuch as the base of the brain.⁵

But because of poor economic status and lack of major facilities in rural India, our patient expired after 7 months of diagnosis with (CMEC).

CONCLUSION

Although (CMEC) in maxilla are relatively uncommon; their importance should not be minimized. Clinically and radiographically, these lesions mimic other osteolytic and odontogenic tumors. A prompt biopsy is always indicated for such intraosseous, radiolucent lesions. After the surgical procedure, the high rates of local recurrence and late distant metastasis suggests the need for postoperative radiotherapy, semiannual clinical and radiographic examination for 5 years and then annual follow-up examinations. When managed appropriately, the 5-year survival rate in most cases is excellent, and overall prognosis is good.