Ultrasound features of acinic cell carcinoma of the tongue: a rare case report.

Histopathological diagnosis should be considered mandatory in benign-appearing lesions, and the treatment choice should be surgical removal with adequate margins.

Introduction

In this study, a rare case is presented in which a tumor was found on the tip of the tongue. Ultrasound was performed on the lesion. Findings indicated a benign nature, but histopathological evaluation after surgical excision showed it to be a malignant minor salivary gland tumor of the tongue.

Salivary gland tumors represent a significant proportion of oral tumors and are the second most common neoplasm of the maxillofacial region after squamous cell carcinoma. The annual incidence of salivary gland tumors throughout the world ranges from about 1–6.5 cases per 100,000 people 1. About 73.8% of these neoplasms are located in the major salivary glands, and the remaining 26.2% are found in the minor salivary gland 2. About 88.2% of minor salivary gland neoplasms have been found to be benign in nature and about 11.8% are malignant 3.

In this study, we describe a rare case in which a nodular and freely movable tumor was found on the tip of the tongue; ultrasonographic (USG) findings indicated a round hypoechoic lesion without infiltration into the tongue musculature. These findings suggested that the lesion was benign. However, histopathological evaluation showed that the tumor was malignant acinic cell carcinoma. This case is notable because of the rarity of the tumor and its location. The use of ultrasound for such type of lesions is suggested as it is a readily available imaging modality as compared to MRI, and it enables to appreciate the pattern of the enlargement, the shape, border, and the vascularization and helps establish the exact location and relation with the surrounding structures. The aim of this study was to highlight the importance of histopathological analysis, regardless of the clinical and USG findings suggesting benign behavior.

Case History

A 42‐year‐old man presented with the chief complaint of swelling on the tip of his tongue, associated with mild discomfort when speaking. The swelling had been present for the past 4 months. It was not associated with numbness or discharge. He had noticed the swelling when it was about the size of a peanut and it had increased gradually.

Oral examination revealed a solitary, ill‐defined nodular swelling on the right ventral surface of the tongue, 1 cm from the tip and not crossing the midline (Fig. 1). The well‐demarcated swollen area was about 1.5 cm in diameter, with diffuse borders. The overlying mucosa was intact and normal in color. The swelling had caused elevation of the right dorsal surface of the tongue. Slight asymmetry of the tongue and widening of its right anterior third were observed in the relaxed state (Fig. 2). Palpation revealed a firm nodular mass, about 1 cm in diameter, beneath the submucosa; it was nontender and freely movable, with a positive slip sign. The patient had been edentulous for 6 months. His medical history was noncontributory, with no significant extraoral finding. Lymphadenopathy was not evident. A provisional diagnosis of a benign salivary gland tumor was made, and routine blood investigations, fine‐needle aspiration cytology (FNAC), and radiographic and USG examinations were performed. A mandibular occlusal radiograph did not show the presence of any foreign body. A B‐mode ultrasound examination of the tongue was performed; coronal and transverse sections confirmed the presence of a well‐defined, rounded, iso‐ to hypoechoic lesion measuring 9 mm at the tip of the tongue, slightly on the right side, with a relatively hypoechoic margin suggestive of a capsule but no infiltration into the tongue musculature or subepithelium (Figs 3 and 4). The gray‐scale examination was followed by the color Doppler sonography (CDS) examination. The lowest wall filter value and highest color sensitivity available on the machine were used to depict intratumoral blood flow. Doppler imaging showed the absence of intralesional blood flow. USG examination of the cervical nodes, carotid vessel, and parotid and submandibular salivary glands yielded normal findings. The diagnosis, based on USG examination, was a benign‐appearing semisolid lesion 1 cm posterior to the tip of the tongue.

Figure 1

A solitary, ill‐defined nodular swelling on the right ventral surface of the tongue.

Figure 2

Slight tongue asymmetry.

Figure 3

A well‐defined, rounded, iso‐ to hypoechoic lesion measuring 9 mm.

Figure 4

Doppler image showing the absence of intralesional blood flow.

Surgical treatment was planned, and preoperative FNAC yielded negative findings. Excisional biopsy was performed on a 1‐cm‐diameter encapsulated nodule with smooth, rounded borders, and firm consistency was removed. The ultrasound report was correlated with the histopathological report.

Considering the clinical presentation and localization of the lesion, we included minor salivary gland tumors such as mucoepidermoid carcinoma, Warthin's tumor, and clear cell carcinoma. Lesions such as giant cell fibroma, focal fibrous hyperplasia, deep‐seated mucocele and granular cell tumor, neurofibroma, neurilemmoma, subgemmal neurogenous plaque, intraoral rhabdomyoma amyloid tumor were also included in the differential diagnosis.

Histopathology

Grossly, the specimen measured about 1.7 × 1.7 cm; it was a well‐circumscribed, circular, soft gray/white mass (Fig. 5). Microscopically, a histopathological section showed a lobular pattern of partially encapsulated tissue composed of centrally placed cells, resembling acinar cells, with granular eosinophilic cytoplasm and basally placed nuclei. The central cells were arranged in sheets, whereas intercalated duct‐like cells with peripherally placed hyperchromatic nuclei predominated in surrounding tissue. The intercalated duct‐like cells were columnar to cuboidal, and some places showed small duct‐like spaces lined with cuboidal cells and mucous pools within the lumen. Clear cells with peripheral nuclei were present in many places; lymphoid aggregates were also noted in three or four places. Supporting stroma appeared to be scanty, with vascular proliferation (Fig. 6). Peripheral muscle infiltration was noted, and the lesion was diagnosed as solid‐variant acinic cell adenocarcinoma of low‐grade malignancy.

Figure 5

A well‐circumscribed, circular, soft gray/white mass.

Figure 6

Lobular pattern of partially encapsulated tissue composed of centrally placed cells, resembling acinar cells, with granular eosinophilic cytoplasm and basally placed nuclei.

Discussion

Acinic cell carcinoma is a malignant epithelial neoplasm of the salivary glands in which the neoplastic cells show acinar cell differentiation. It is classified as a low‐grade malignant neoplasm 3. Most authors have agreed that tumors with infiltrative borders or local invasion are more likely to behave aggressively 4, 5. Acinic cell carcinoma is defined by cytological differentiation toward serous acinar cells, the characteristic feature of which is cytoplasmic periodic acid–Schiff‐positive zymogen‐type secretory granules 6.

In the Armed Forces Institute of Pathology (AFIP) data for salivary gland neoplasms, acinic cell carcinoma represented 17% of primary malignant salivary gland epithelial neoplasms, after mucoepidermoid carcinomas and adenocarcinomas. In these data, acinic cell carcinoma comprised 6% of all salivary gland tumors 3, 6. However, some studies have shown the occurrence to be 2.7–4.6% of all salivary gland neoplasms 5, 7. Although this tumor has been reported to occur chiefly in the parotid gland (80–97% of cases), it occasionally occurs in other major salivary glands and about 0.2–8% of cases have been reported in the minor salivary glands 6, 7, 8, 9, 10; about 0.6% of cases occur in the minor salivary glands of the tongue 6. Acinic cell carcinoma occurs primarily in middle age (average, 44 years), but it can occur at virtually any age; it has been found in children up to 11 years and adults up to 77 years. Women are affected more often than men (ratio, 3:2) 10, 11. In the present case, the lesion originated in the minor salivary glands of the tongue tip of a 42‐year‐old male patient, which makes it a rare occurrence.

The tumor usually arises as a slowly enlarging, asymptomatic, fixed mass. In about 78% of cases, it appears as a painless mass 12. Most untreated patients had been aware of the lesion for <1 year, and 5–10 years had elapsed before a physician was consulted in about 7% of cases 8. Tumors of this type are fairly well circumscribed and encapsulated, with some degree of microscopic invasion in 56% of cases. About 8% of cases show facial paresis. Tumor size ranges from 0.7 to 7 cm, with a firm rubbery consistency and a tan–gray cut surface. Lymph node involvement has been observed rarely 10, 11, 12, 13, 14, 15.

Histologically, acinic cell carcinoma is composed mainly of differentiated glandular cells bearing secretory granules identical to those of the normal serous salivary acinus 16. Tumors in the minor salivary glands are histologically similar to those arising in the major salivary glands 10. Four growth patterns have been described: solid, papillary cystic, follicular, and microcystic. The solid variant is characterized by numerous well‐differentiated acinar cells arranged in a pattern resembling normal parotid gland tissue 6, 12, 13, 15, 16. A solid growth pattern is the most easily recognized and dominant (38% of cases) morphological variant of acinic cell carcinoma; it is considered to be the “classic” pattern because it is typified by numerous well‐differentiated acinar cells and closely resembles a normal parotid gland 6. Findings in our case were consistent with this classic solid variant. In the differential diagnosis, we considered clear cell carcinoma, mucoepidermoid carcinoma, Warthin's tumor, and oncocytoma.

In the present case, it was useful in determining the tumor site and size; the sharp borders and homogeneity suggested the noninvasive nature of the lesion. Sharp borders have also been noted in other acinic cell carcinomas. The echostructure of the tumor is not an indicator of malignancy. Whether a tumor is homogeneous or not, on the whole, gives no indication of its nature, as around 50% of both benign and malignant tumors have been found to be nonhomogeneous, which means that the echostructure of the tumor is not an indicator of malignancy. It was also concluded that vascularisation alone cannot determine the benign or malignant nature of a tumor 17. In such cases, elastography could provide useful information in differentiating benign and malignant behavior. Considering the apparently benign nature of the tumor, our patient underwent surgical enucleation and was followed closely. Surgical resection is the treatment of choice for acinic cell carcinoma 18.

Conclusion

This case is notable because of the rarity of the tumor and its location. The use of ultrasound for such type of lesions is suggested as it is the more easily available imaging modality as compared to MRI and it enables us to appreciate the pattern of the enlargement, the shape, border, and the vascularisation and helps establish the exact location and relation with the surrounding structures. Considering the clinical and ultrasound correlation, the malignant tumor in this case was initially diagnosed as benign. We suggest that no lesion should be underestimated; histological diagnosis should be considered mandatory, and the treatment of choice in benign‐appearing malignant lesions should be surgical removal with adequate margins.

Conflict of Interest

None declared.