Abstract
Heterotopic salivary gland tissue is salivary tissue located outside the sites generally known to accommodate major and minor salivary glands. Although heterotopic salivary tumors were reported in various regions of the head and neck, they are seldom found in the superio-posterior neck region and can be confused with other neck masses. Herein, we present a rare case of a heterotopic pleomorphic adenoma in the postauricular area and remind clinicians that heterotopic salivary tumors should be in the differential diagnosis of neck masses.
Keywords: heterotopic salivary tissues, neck mass, pleomorphic adenoma
Introduction
Heterotopic salivary gland tissue (HSGT) is salivary tissue located outside the sites generally known to accommodate major and minor salivary glands. Tumors arising from ectopic salivary tissues are rare. Although heterotopic salivary tumors were reported in various regions of the head and neck, they are seldom found in the superio-posterior neck region. Herein, we present a rare case of a heterotopic pleomorphic adenoma in the postauricular area.
Case presentation
A 32-year-old healthy woman was referred for an evaluation of a painless, slowly growing mass behind her right ear, which she first noticed 3 years before. She denied a history of using cigarettes, alcohol, or betel nuts. A physical examination revealed a painless, firm, well-defined, 3 × 2-cm mass with intact overlying cervical skin in the postauricular region (Fig. 1). The patient's neck could move freely in every direction. No other head or neck abnormalities were noted.
Figure 1.
Painless mass measuring 3 × 2 cm with intact overlying cervical skin in the postauricular region.
The preoperative differential diagnosis included a heterotopic salivary gland tumor, neck lymphadenopathy, a cyst, and, less likely, a malignant tumor. An excisional biopsy was planned and was carried out under general anesthesia. Intraoperatively, the skin flap was elevated along the posterior border of the mass. The lesion was found to be solitary and deep in the investing layer of the deep cervical fascia without sinus tract formation. The mass was easily dissected from the surrounding fascia and was completely excised from the neck (Fig. 2). The specimen was a firm, well-encapsulated tumor, measuring 2.5 × 2 × 2 cm. A microscopic analysis of the tumor revealed a combination of glandular epithelium and mesenchyme-like tissues without malignant change (Fig. 3). The diagnosis was a heterotopic pleomorphic adenoma in the postauricular area. The patient was followed-up for 1 year without recurrence.
Figure 2.
Encapsulated mass with a well-defined margin was identified and excised from the posterior neck.
Figure 3.
Hyperplasia of the glandular epithelium and mesenchyme-like tissues without malignant change (hematoxylin and eosin stain; magnification, 200×).
Discussion
HSGTs are rare and should be distinguished from accessory salivary gland tissues. Accessory salivary glands are ectopic salivary gland tissues with a duct connecting them to the main salivary duct system, whereas heterotopic salivary glands have acini without a duct system.1 An accessory parotid gland is not uncommon, and has an incidence rate of approximately 21–56% reported in adults.2 In our case, the lesion was isolated from the parotid gland, and there was no duct system connecting the lesion to the parotid duct. Therefore, this lesion can be regarded as heterotopic to the salivary gland.
Theories of development of ectopic salivary tissues in the head and neck area were proposed in the literature, including entrapment of salivary tissues in lymph nodes, dislocation of a normal salivary gland, abnormal differentiation of local tissues, and abnormal migration of normal salivary tissue; among these, entrapment of salivary tissues in the developing cervical lymph nodes during embryogenesis is widely accepted.3 The entrapment theory can be explained by the presence of normal salivary tissue next to tumors occluded in cervical lymphatic tissues.4
Neoplasms originating from heterotopic sites are infrequent. The incidence, types, and diagnostic and therapeutic methods of tumors arising from normally positioned salivary gland tissue can be applied to tumors developed from HSGTs.5 Approximately 80% of HSGT tumors are benign.6 Fine-needle aspiration cytology (FNAC) is a simple, economic, and sensitive diagnostic tool, but it is problematic for a surgeon to decide whether performing an FNAC of a neck mass, especially one that is clinically benign looking, for a preoperative histopathological diagnosis is necessary. Tumor metastasis along the needle track after an FNAC procedure was reported in the literature. Although the majority of reported cases were related to malignant lesions, seeding of a benign parotid tumor was also described.7 According to history taking and a physical examination, we believed that the neck mass in our case was most likely a benign lesion. Thus, an excisional biopsy was carried out for diagnosis and treatment, and to avoid the risk of tumor seeding via the FNAC procedure.
Although pleomorphic adenomas are the most common salivary gland tumor, Warthin's tumor is the most frequent heterotopic salivary gland neoplasm.8 Heterotopic salivary tumors are predominantly found in the anterior triangle of the upper neck.6 A review of the literature revealed a small number of heterotopic pleomorphic adenomas noted in the neck.4, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Tumor locations of the presented cases were mainly in the upper neck and anterior to the sternomastoid muscle (Table 1). To the best of our knowledge, the present case is the first heterotopic pleomorphic adenoma found in the postauricular area.
Table 1.
Reports of heterotopic pleomorphic adenoma in the neck published in the English literature.
| Age/gender | Location of tumor | Authors | Year |
|---|---|---|---|
| 36/F | Below mandibular angle | Pesavento and Ferlito | 1976 |
| 50/F | Lower third of neck, lateral to SCM | Bothra et al | 1977 |
| 41/F | Below mandibular angle | Hulbert | 1978 |
| 40/M | Jugulodigastric area | Mair et al | 1978 |
| 61/M | Below mandibular angle | Singer et al | 1979 |
| 32/F | Jugulodigastric area | Zajtchuk et al | 1982 |
| 30/F | Submandibular area | Zajtchuk et al | 1982 |
| 35/F | Unknown | Zajtchuk et al | 1982 |
| 22/M | Upper neck, anterior border of SCM | Cotelingam and Gerberi | 1983 |
| 11/F | Below mandibular angle | Evans and Rubin | 1991 |
| 15/M | Below mandibular angle | Evans and Rubin | 1991 |
| 14/M | Upper neck, anterior border of SCM | Rodgers et al | 1991 |
| 9/F | Jugulodigastric area | Surana et al | 1993 |
| 12/F | Jugulodigastric area | Surana et al | 1993 |
| 50/M | Middle neck, anterior border of the trapezius muscle | Tay and Howitt | 1995 |
| 40/M | Right neck | Baldi et al | 2003 |
| 8/M | Upper neck, anterior border of SCM | Arunkumar et al | 2011 |
SCM = sternocleidomastoid muscle.
Surgical excision of the lesion with close follow-up is the best way to treat benign HSGT tumors. With adequate surgery, the prognosis is excellent.8 We present this unusual postauricular pleomorphic adenoma to remind clinicians that a heterotopic salivary tumor should be included in the differential diagnosis of superio-posterior neck masses.
References
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