Sialoblastoma of the parotid gland

Introduction 

Salivary gland tumors of epithelial origin are exceedingly rare in children. Fewer than 5% of all salivary gland tumors occur in childhood, account for 8% of all head and neck tumors [1], [2]. Most tumors of salivary glands are non-epithelial masses, usually hemangiomas or lymphangiomas [3].

Sialoblastomas have been reported to occur predominantly in the parotid gland [4]. To best of our knowledge, there are about fewer than 40 cases reported in the literature. Because of the rarity and aggressive character of sialoblastomas, it is important to diagnose early and treatment should be done immediately.

This article presents a sialoblastoma that occurred in a 3-year-old girl, including clinicopathologic characteristics and its treatment.

Case report 

A 3-year-old girl presented with a 6-month-history of facial swelling in the region of cheek. Her parents were concerned about the slow but progressive increase in the size of the mass over this time. Physical examination revealed a firm, non-tender, non-erythematous, mobile, 3cm×3cm mass in the right cheek. Cranial nerve examination demonstrated no deficits (Fig. 1). Her medical, surgical and family histories were unremarkable.

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Fig. 1. Swelling at the right cheek of the patient.

Ultrasonographic scan of the area showed mixed pattern nodular areas with well-defined margins and a predominantly hypoechoic pattern. Fine needle aspiration biopsy of the mass demonstrated significant mitotic activity, slight pleomorfism and atypical cells. For the reason of being unsure in deciding whether the mass is malign or benign, a transoral incisional biopsy was performed. Histologically, the tumor was made up of primitive basoloid cells arranged in nests and trabeculae that were separated by a fibromyxoid stroma. Focal evidence of duct differentiation and cribriform patterning was visualized. The tumor had high nucleus to cytoplasm ratios and round to oval nuclei with one to two nucleoli demonstrating high mitotic activity (Fig. 2, Fig. 3). Immunohistochemistry has demonstrated cytokeratin in the ductal components, vimentin in both the ductal structures and solid nests.

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Fig. 2. H&E (heamatoxyline–eosine) staining demonstrates high mitotic activity in the tumoral cells.

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Fig. 3. H&E (heamatoxyline–eosine) staining demonstrates high nucleus cytoplasma ratio and round to oval nuclei with one to two nucleoli.

The tumor was diagnosed as sialoblastoma and through a superficial parotidectomy, the tumor was excised with large margins. Postoperative course of the patient was uneventful.

Discussion 

Sialoblastoma which is also called embryoma, is a rare, aggressive and potentially malignant perinatal salivary tumor, that predominantly affects the parotid gland and appears to recapsulate the developing salivary anlage [1], [5]. Various alternative names such as congenital basal cell adenoma, monomorphic adenoma, basal cell adenoma, low-grade basal cell adenoma, congenital hybrid basal cell adenoma–adenoid cystic carcinoma have been proposed in the literature [4], [6]. It is usually diagnosed at birth or shortly thereafter.

Clinically, sialoblastoma typically presents as a slow growing, painless mass. Grossly, most tumors were tan-pinkish to yellow, firm and multilobulated [7]. In the present case, the tumor had increased progressively in a period of 6-months.

Radiologically, sialoblastoma have been reported in a limited number of cases. Computerized tomography appearance is a soft tissue mass hypodense to the brain and isodense to muscle. Magnetic resonance imagining of the tumor reveals low-intermediate signal intensity in T1 weighted images, and slightly higher intermediate signal intensity on T2 weighted images. The finding of mild hyperintensity on T2 weighted images proposes a high nucleus/cytoplasmic ratio belonging to blastoma and can be predictive for the diagnosis of the blastomas [8].

Histologically, sialoblastoma contains the presence of variably arranged, tight clusters of atypical appearing, basoloid like cells in a background of dispersed epithelial and myoepithelial cells separated by thin fibrous bands. The clusters contain admixed benign ductal cells and dens, metochromatic, hyaline globular material with smooth rounded outlines. Immunoperoxidase staining demonstrates the presence of cytokeratin in the ductal cells as well as the positive staining for vimentin, actin and S100 protein in the outermost layer of the ducts [9]. Differential diagnosis of the tumor includes pleomorphic adenoma, basal cell adenoma and adenoid cystic carcinoma [10]. Basal cell adenoma shows similarities to sialoblastoma but it does not contain myoepithelial cells [11]. Cribriform pattern developed within solid sheets of cells is different in adenoid cystic carcinoma to differ from sialoblastoma [12]. In the present case, firstly fine needle aspiration biopsy was performed on the patient and it demonstrated high nucleus cytoplasm ratios, high mitotic activity and atypical cells as seen in malignant tumors therefore we needed to do an incisional biopsy transorally on the patient and confirmed the diagnosis as sialoblastoma.

It is widely agreed that primary excision with negative margins is adequate with these tumors. Radiotherapy may be considered if lesions are not completely resectable, but the adverse effects of radiation therapy may be severe for growing facial structures. Chemotherapy may be chosen when the tumor is not completely resectable or in cases of persistent or recurrent tumor [10].

Biologically, sialoblastoma has a tendency for local invasion and recurrence after gross complete excision, occasionally metastases have been reported to occur in lymph nodes and lung [1], [7].

In the present case, after performing superficial parotidectomy, we reached to the tumor and excised it with large margins. Pathologic examination of the tumor demonstrated invasion to the adipose tissues by perforating the capsule around the tumor therefore it is important to resect the tumor with the surrounding tissues. No adjuvant treatment was given and no recurrence has been noted after 6-months.

Conclusion 

In conclusion, the present case is a sialoblastoma in the parotid region. Despite the rareness of the disease, pathologists and otolaryngologists should always consider the possibility of sialoblastoma of salivary glands in childhood and that can be best described as locally aggressive with malignant potential.