Massive ossifying pleomorphic adenoma of the maxillary antrum: A rare presentation.

Pleomorphic adenoma is the most common benign neoplasm of salivary gland origin involving both major and minor glands. Though parotid is the most common site of origin, it has been reported to arise from various unusual locations. Incidence of its origin in the respiratory tract is extremely rare, and the occurrence is even lower in the maxillary sinus. We report a case of a huge antral pleomorphic adenoma in a 33-year-old male patient presented as a swelling in the maxilla which was mistaken of odontogenic origin. Histological findings showed extensive ossification and hyalinization of the stroma as a striking feature. The patient has undergone hemimaxillectomy and is in 8 months follow-up without any sign and symptom of recurrence.

Introduction

Pleomorphic adenoma is a frequent benign neoplasm in the head and neck region and accounts for 70% of all salivary gland tumors.[1] 65% of the tumors arise in the parotid gland, and only 35% involve the minor glands. Unusual locations comprising the cheek, lacrimal gland, external auditory meatus, etc., has been reported.[2] Its origin in the maxillary antrum is an extremely rare phenomenon as, involvement of the upper respiratory tract by it occurs almost exclusively in the nasal cavity.[3] The present article reports a unique case of antral pleomorphic adenoma with an extensive ossification accounting to be the second reported case.

Case Report

A 33-year-old male patient reported in our department with a swelling in the left upper jaw for a period of 9 months. The patient complained a sense of heaviness and occasional pain in the affected area. He was referred to us from a primary health care center to evaluate any possible odontogenic association to the swelling.

Extraoral examination of the patient revealed a diffuse swelling in the left middle third of the face, lateral to the nose with normal skin covering. It caused obliteration of the left nasolabial fold and slight rising of the left ala of nose. Intraoral observation showed smooth buccal and mild palatal cortical plate expansion in the left maxilla with no surface ulceration [Figure 1]. The regional teeth were not mobile and caries free.

Figure 1

Intraoral photograph of the patient showing buccal and mild palatal cortical plate expansion of the left maxillary bone

Computerized tomography scan of the face and the maxilla revealed the presence of a huge expansile mass in the left maxillary sinus measuring 47 mm × 43 mm that attenuates the antral walls with its expansion in the nasal cavity also [Figure 2]. With a provisional diagnosis of odontogenic neoplasm, incisional biopsy was performed via Caldwell-Luc procedure.

Figure 2

Axial computerized tomography scan demonstrating the huge mass in the left maxillary sinus

Histological evaluation revealed the presence of the tumor mass composed of overwhelming osteoid seams intermixed with small ducts, nests and strands like structures and some myxoid areas [Figure 3]. With the diagnosis of ossifying pleomorphic adenoma hemimaxillectomy was done. Multiple H and E stained sections of the resected specimen showed features consistent with that of the incisional biopsy, justifying our primary diagnosis.

Figure 3

Photomicrograph of H and E stained section (×40) showing the tumor mass with an extensive ossification abutting the peripheral fibrous capsule

Discussion

The term pleomorphic adenoma was first suggested by Wills, which designates the benign mixed tumor of the salivary gland, characterized by a combination of epithelioid and connective tissue-like growth. It is the most frequently encountered salivary gland tumor with the parotid being the most common site. Neoplasms of the minor salivary gland may occur at any location though the palate, upper lip, and buccal mucosa are the three most common sites comprising 82.2% of all minor salivary gland tumors.[4]

Pleomorphic adenomas of the upper respiratory tract have been rarely described in the literature and occurs almost exclusively in the nasal cavity with the nasal septum involving 82.5–90% of the reported incidences.[23] Involvement of the seromucous glands of the maxillary antrum by this tumor is even more rare with minimum reported cases. In a review of 2807 cases of salivary gland neoplasms by Spiro, no tumor of the maxillary and ethmoidal sinus was reported. Berenholz et al. and Ishikawa et al. described intranasal mixed tumors to have no primary involvement of the paranasal sinuses validating its rarity.[56] Facon et al. in the year 2002 reported a unique case of a pleomorphic adenoma of the nasal cavity arising and extending from the medial wall of the maxillary antrum.[7]

Pleomorphic adenoma of the sinonasal origin usually presents unilaterally as a nasal mass. The most common clinical presentations include nasal obstruction, discharge, epistaxis, or rhinorrhea.[56] The usual age of occurrence is between third to sixth decade of life. Few literature states slight female predilection of this tumor.[16] Radiological findings are nonspecific, generally presenting with a well-defined mass with features of bony remodeling rather than bone invasion.[56]

Histologically, the pleomorphic adenomas are limited by the outer connective tissue capsule which helps to distinguish the tumor from the surrounding normal tissue. The tumor comprises diverse patterns with three basic structures: Tubuloductal, solid and myxoid areas.[28] While the ducts are made up of cuboidal cells, spindle and myoepithelial cells comprise the solid areas. Myxoid areas are characteristically hypocellular in nature.[2] The tumor may show sheets and strands of cells in a mucoid or chondromyxoid background.

The pleomorphic adenomas of the minor salivary glands of aerodigestive tract demonstrate a high cellularity with paucity of stroma contrasting the histological findings of the major salivary gland tumors. The cellular preponderance may even mimic an aggressive tumor producing a diagnostic dilemma.[17] Careful monitoring of multiple sections must be done to differentiate it from squamous cell carcinoma, the most common sinonasal malignancy, affecting the maxillary sinus most frequently. The nonsquamous cell malignancy principally includes adenomatous tumors, chiefly the adenoid cystic carcinoma. It should be carefully excluded as it most commonly affects the maxillary sinus, accounting 47% to arise in it.[9] Farman et al. reported a rare case of carcinoma ex pleomorphic adenoma of the palate and maxillary sinus with features of adenoid cystic carcinoma and adenocarcinoma in the year 1985.[8]

In our case though marked myoepithelial cell proliferation was noted in some sections of the excisional sample, absence of cellular pleomorphism, mitotic activity, perineural invasion or squamous metaplasia, ruled out the possibility of the malignant counterpart [Figure 4]. The numerous mature osteoid islands abutting the intact peripheral fibrous capsule with intermixed myxoid areas further suggested that of a benign entity [Figure 5]. It is presumed that the myoepithelial cells undergo metaplasia to produce osteoid areas. The preponderance of osteoid tissue may produce confusion with fibro-osseous lesions arising in the maxilla. The presence of glandular elements in such instance is the key factor for diagnosis. Myxoid areas were inconspicuous as ill-defined fine basophilic regions produced by glycosaminoglycan-rich matrix.[10] Though the extensive ossification dominated the histological picture, the connective tissue stroma also showed extreme hyalinization producing cribriform-like patterns.

Figure 4

Photomicrograph of H and E stained section (×400) showing cellular elements in a chondromyxoid stroma

Figure 5

Photomicrograph of H and E stained section (×100) showing glandular elements intermixed with osteoid islands and myxoid areas

Considering the treatment part, complete surgical resection with histological clear margins produces satisfactory outcomes.[7] The risk factor for malignant transfer of pleomorphic adenoma varied from 6% to 10%. Routine postoperative follow-up is mandatory as some cases are reported with recurrences.[2]