Primary carcinoid tumor of the parotid gland: a case report and review of the literature

Ear, Nose & Throat Journal, August, 2006 by Irvin M. Modlin, Michael D. Shapiro, Mark Kidd

Abstract

Salivary gland tumors account for 3 to 6% of all head and neck neoplasms in adults. Some 70 to 85% of these lesions are found in the parotid. Carcinoid tumors, which represent a distinct and relatively uncommon subset of neuroendocrine tumors, are most commonly found in the gastrointestinal tract, although in rare cases they are known to occur in extragastrointestinal locations, including the larynx, middle ear, and pancreas. Malignancies of the parotid gland are uncommon (approximately 25% of parotid neoplasms), and to the best of our knowledge, a primary carcinoid tumor of the parotid has not been previously described in the literature. Reports of parotid carcinoid tumors during the past 30 years have described the presence of nonparotid primary carcinoid tumors (usually gastrointestinal) that had been diagnosed and treated several years prior to the presentation of the parotid lesion. Under such circumstances, the parotid lesion may be assumed to have been a metastatic rather than a primary carcinoid. This report documents what we believe is the first case of a primary carcinoid tumor of the parotid gland. We detail the clinical, surgical, radiologic, immunologic, and histochemical findings associated with its diagnosis, and we describe our management of this case. Although a primary carcinoid in this location is exquisitely rare, knowledge of such lesions is important because their management is substantially different from that of other parotid tumors. In particular, it is important to differentiate them from metastatic tumors from other sites.

Introduction

Tumors of the salivary glands account for 3 to 6% of all head and neck neoplasms in adults. (1) Their clinical and histologic appearance varies markedly. Most of these tumors (70 to 85%) are found within the parotid gland. Among the parotid tumors, 25 % are malignant at diagnosis. (1) Carcinoid tumors are characterized by distinct biologic, histologic, and functional properties, and they represent a unique, relatively uncommon subset of neuroendocrine neoplasms. Although approximately two-thirds of carcinoid tumors are identified within the gastrointestinal tract, it is well known that carcinoid tumors may arise within any anatomic location that is populated with endocrine or endocrine-like cells. (2)

Carcinoid tumors are known to arise in extragastrointestinal locations in exquisitely rare cases, and such a finding in the parotid gland is among the very rarest. Scattered reports have documented the presence of parotid carcinoid tumors, but all such cases have been associated with a primary carcinoid tumor elsewhere in the body. (3-6) After conducting an extensive search of the world literature, we report what to the best of our knowledge is the first case of a primary carcinoid tumor of the parotid gland. We detail the clinical, surgical, radiologic, immunologic, and histochemical findings associated with its diagnosis, and we describe our management of this case.

Case report

In November 1992, a 40-year-old man presented with a painless enlargement of his left face. He reported no other symptoms or complaints. Incisional biopsy initially revealed the presence of a parotid tumor, and it was extirpated by superficial parotidectomy. On gross examination, the specimen was made up of two portions of firm, tan-to-pink tissue that measured 0.3 and 0.5 cm in their greatest dimension. The tissue had a firm, yellow-to-pink cut surface. The tumor was initially characterized as a ductal salivary gland carcinoma with solid and basaloid patterns. Light microscopy revealed nesting of the tumor cells into cohesive groups of various sizes, with large, pleomorphic nuclei and granular cytoplasm (figure 1, A). Further immunohistochemical analysis with neuroendocrine markers stained strongly positive for chromogranin A and neuron-specific enolase, and the lesion was designated as an atypical carcinoid tumor (figure 1, B). Electron microscopy further confirmed the diagnosis, demonstrating the presence of numerous neuroendocrine-type, dense-core, secretory granules that ranged in size from 350 to 400 nm and were mostly round in shape (figure 2).

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When the patient initially presented in 1992, he had no other significant medical history, and he was not taking any medication. His family history was notable for thyroid cancer in his mother that was treated successfully with surgery and radioactive iodine therapy. The patient denied any history of smoking or of radiation exposure during childhood. He did not have any symptoms suggestive of carcinoid syndrome, such as diarrhea, flushing, bronchospasm, or right-sided heart failure. Furthermore, he displayed no signs or symptoms of liver disease, such as pruritus, edema, or jaundice.

Two months postoperatively, in January 1993, abdominal computed tomography (CT) detected two contrast-enhancing hypodense lesions in the liver. Nuclear single-photon emission CT (using tagged red blood cells) and percutaneous liver biopsy of the lesions revealed no evidence of malignancy. As a result, both lesions were diagnosed as hepatic hemangiomas. At that time, a 24-hour level of urinary 5-hydroxyindole acetic acid (5-HIAA), an excreted by-product of serotonin degradation and a clinical marker of carcinoid disease, was within the range of normal (2.0 to 8.0 mg/24 hr). Normal levels were subsequently documented in March, June, and July 1994 (figure 3). Findings on chest x-ray, bone scan, small bowel x-rays, and upper and lower gastrointestinal series were normal, and no lesions suggestive of primary or metastatic disease were evident elsewhere. Serial CTs over the next few years revealed no change in the two liver masses, and annual urinary 5-HIAA levels remained within the normal range.