Metastasis of Acinic Cell Carcinoma of the Parotid Gland to the Contralateral Orbit

Acinic cell carcinoma is an uncommon low-grade malignant tumor of the salivary glands, in which some cells resemble normal acinic cells.¹ Most of these tumors occur in the parotid gland.^1,2 Women are affected more often than men, and the age at occurrence is earlier than in other salivary gland cancers.² Most cases are unilateral, and bilateral involvement has rarely been reported. Conversely, an unusual case of synchronous acinic cell carcinomas of the left parotid and right submandibular glands has previously been described.³

Although acinic cell carcinomas rarely metastasize, they have a high tendency to recur locally if they are incompletely excised. We describe a patient with acinic cell tumor arising in the parotid gland, with metastases to the contralateral orbit, submandibular salivary gland, and submandibular lymph node.

A 54-year-old white woman came to the Maxillofacial Department with a right parotid mass of 2 months' duration. Results of a fine-needle aspiration biopsy suggested an epithelial neoplasm, and ultrasonography of the neck showed an unusual appearance of the superficial portion of the parotid and submandibular glands, and an enlarged submandibular lymph node. In January 2002, a right partial parotidectomy with sampling of the right submandibular lymph node was performed. Histologic examination showed that the parotid gland contained acinic cell carcinoma (Figure 1)extending to within 0.2 mm of the surgical excision margin, with a possibility of incomplete excision. Four mitoses in 40 high-power fields were noted in the tumor cells. The right submandibular lymph node contained a tumor growing in nests of large tumor cells showing vesicular nuclei with prominent nucleoli and granular cytoplasm, suggesting metastatic acinic cell carcinoma.

A magnetic resonance image of the head and neck was performed 3 weeks after the surgery and could not exclude residual tumor in the parotid gland because of postoperative changes in the parotid area. Incidentally, the image demonstrated a lesion approximately 1 cm in diameter in the left orbit that was intraconal, lying between the medial rectus muscle and the optic nerve, and that did not appear to arise from either structure (Figure 2).

Initially, the orbital lesion was not thought to be related to the salivary gland tumor, as an early metastasis with contralateral spread from the acinic cell carcinoma was believed to be very unlikely. It was therefore decided to monitor the orbital lesion with repeat magnetic resonance imaging at a later date. A right total parotidectomy with sacrifice of a part of the facial nerve, excision of contents of the right submandibular triangle, and supramental node sampling were performed. Histologic examination demonstrated complete excision of the residual tumor in the parotid bed. There was an island of tumor within the excised right submandibular gland that was believed to be either metastatic or a synchronous tumor.

Postoperative adjuvant radiotherapy was carried out, during which time the patient visited her optometrist with symptoms of blurred vision and diplopia. The latter was controlled with the addition of a 10–prism diopter Fresnel prism base out to the distance segment of the spectacle.

In June 2002, the patient was referred to and seen in the Ophthalmology Department for consideration of eyelid surgery to reduce the exposure of the right eye that resulted from the surgically induced facial nerve palsy. By this time, however, her diplopia had also increased.

Examination demonstrated 10– and 12–prism diopter esophoria for near and distance, respectively, with slight left proptosis. The previously arranged follow-up magnetic resonance imaging was done 2 weeks later and showed enlargement of the orbital lesion with displacement of the optic nerve (Figure 3). The diplopia was worse, with considerable limitation of elevation, depression, and adduction of the left eye.

Excision biopsy of the orbital mass was performed. At surgery the mass was found to lie between the medial rectus muscle and the eye. The lack of a capsule and its gelatinous consistency prevented excision in toto, with the posterior portion in particular requiring piecemeal removal. Histologic examination showed the mass to be acinic cell carcinoma (Figure 4), compatible with the primary tumor previously excised. After exclusion of any other distant metastasis with a computed tomographic scan of the abdomen and chest, radiotherapy to the left orbit was performed.

On follow-up in December, 11 months after the initial diagnosis of acinic cell carcinoma of the parotid gland, the patient had no evidence of tumor and had left convergent squint causing intermittent diplopia.

We found 2 reported cases of distant metastasis from parotid gland tumor to the orbit^4,5 in the English-language literature. The primary tumors were mixed parotid tumor⁴ and polymorphous low-grade adenocarcinoma.⁵

Acinic cell carcinoma represents approximately 5% to 17% of all salivary gland cancers^1,2 and can very rarely arise from the lacrimal gland.⁶ Spiro et al⁷ reported a distant metastasis rate of 12%, mainly to lung, bone, and brain. On gross pathological examination, acinic cell carcinoma is fairly well circumscribed and may appear encapsulated. Four histopathologic patterns have been described: solid, microcystic, papillary-cystic, and follicular.¹ It is not uncommon for these patterns to coexist in the same tumor. Batsakis et al⁸ categorized acinic cell carcinoma into low-grade and high-grade neoplasms. Low-grade tumors are broadly interpreted as those most closely resembling the architecture of a normal salivary lobule. High-grade tumors are poorly differentiated and resemble the early phases of embryonic development of acini.

Controversy persists regarding the prognostic value of assigning grade by histologic analysis of acinic cell carcinoma.² In a recent report by Hoffman et al, ² the high-grade cancers were significantly associated with age of more than 30 years, advanced stage, and distant metastasis at initial manifestation.

In our case, the acinic cell tumor was found in the parotid gland, the submandibular gland, and a lymph node. The primary tumor seemed to be partially encapsulated, but mitotic figures were seen, suggesting malignant potential. Metastasis to the orbit occurred very early in the disease process and was discovered only incidentally. The metastatic tumor in the orbit had grown considerably in 5 months, causing proptosis and diplopia.

We thank David Turner, FRCPath, PhD, Department of Pathology, Taunton and Somerset Hospital, Taunton, England, for his advice.

Corresponding author: Tarek A. Saleh, FRCSEd, Eye Department, Taunton and Somerset Hospital, Musgrove Park, Taunton, Somerset TA1 5DA, England.