Pleomorphic adenoma of submandibular gland: An uncommon occurrence.

Pleomorphic adenoma (PA) is the most common tumor of the benign salivary gland neoplasms, and the most common gland to be involved is the parotid gland. Its occurrence in the submandibular or the sublingual gland is uncommon. We present a case of a histologically proven PA involving the submandiblular gland.

INTRODUCTION

Salivary gland tumors are rare and make up to 3% of head and neck tumors.[1] Approximately 90% of the benign neoplasm of the major salivary gland is associated with the parotid gland. Pleomorphic adenoma (PA) comprises 80–90% of these benign parotid neoplasms. PA of the submandibular and sublingual gland is quite uncommon and comprises rest (8–10%) of the group.[2] In a recent Asian study, Subhashraj in his single institutional review of 422 benign cases of benign salivary gland tumors has reviewed 422 benign cases.[3] Out of these, 363 tumors were PA (86%). Of these 363 cases of PA, 203 involved the parotid (56%), 72 involved the submandibular (20%) and 1 involved the sublingual gland (0.2%). The rest had an origin from the minor salivary glands. This case report presents a case of a histologically proven PA involving the submandibular gland. The case was treated surgically and followed up for more than 2 years with no recurrence.

CASE REPORT

A 20-year-old male was referred to the maxillofacial out-patient department with a history of firm palpable mass in the left submandibular region [Figure 1]. The swelling was noticed a year back and was slow growing and painless in nature. On palpation, the mass was firm and non-tender. The mass was oval in shape and the clinically measurable dimension was 7 cm × 5 cm. The mass was freely movable and not attached with the surrounding tissue or the skin. Bimanual palpation was positive and there was no neuronal or functional disturbance in the adjacent tissues. Axial and coronal views of the computed tomography (CT) scan showed a well-defined radiolucent mass in the medial aspect of the left mandibular body covering its whole extent and extending inferiorly into the submandibular region [Figures 2 and 3]. A provisional diagnosis of PA was made and the patient was posted for explorative and excisional biopsy under general anesthesia. With a standard submandibular incision, the submandibular gland and the mass was excised and sent for histopathological examination [Figures 4 and 5]. Primary closure was done in a layer-wise manner with no drain attached. The histological examination was confirmatory of PA [Figure 6]. The patient is being followed up regularly for almost 4 years now, with no recurrence noted.

Figure 1

Facial profile showing swelling in the submandibular region

Figure 2

Coronal CT scan

Figure 3

Axial CT scan

Figure 4

Intraoperative photograph

Figure 5

Excised lobular tumor (8 cm × 5 cm × 4 cm)

Figure 6

Micropictograph showing darkly stained tumor cells lying in a predominantly mesenchyme like background (H and E, ×4)

DISCUSSION

PA is an epithelial tumor of complex morphology, possessing epithelial and myoepithelial elements intermingled with mucoid, myxoid, or chondroid tissue arranged in a variety of patterns and embedded in a mucopolysaccharide stroma.[4] It is the commonest benign tumor of salivary glands[5] and accounts for 90% of all salivary gland tumors. The submandibular gland is the second most common site of PA after the parotid gland.[6] It is also the most frequent benign tumor arising in submandibular gland.[7] The differential diagnosis should include basal cell adenoma, adenocarcinoma, mucoepidermoid carcinoma and lymphoma.

CT scan or magnetic resonance imaging (MRI) are the gold standard radiological tools for lesion arising from the major or minor salivary glands. Adjunctive procedures like ultrasound guided needle aspiration or fine needle aspiration are non-confirmatory. An incisional biopsy can be taken initially if the lesion is of large size. The recommended surgical approach is with a direct submandibular incision which provides an easy access. The excision of the tumor should also be accompanied by the removal of the submandibular gland in toto. Incomplete removal of the glandular tissue paves the way for a definitive recurrence. PAs are benign tumors with a well-documented transformation to malignancy (carcinoma ex pleomorphic adenoma). It is estimated that up to 25% of untreated PAs undergo malignant transformation.[8] Therefore, early definitive treatment is strongly recommended.