Sebaceous lymphadenoma of the parotid gland

Sebaceous differentiation in normal salivary gland tissue is a well-recognized finding. It occurs as a metaplastic change of the salivary duct epithelium and is observed in 11 to 28% of normal parotid glands.1,2 Areas of sebaceous differentiation may be associated with salivary gland neoplasms1,3,4; however, primary sebaceous neoplasms of the salivary glands are extremely rare.47 Here, we present a case of sebaceous lymphadenoma in a 56-year-old female. We found 41 previously reported cases in the literature.1,4-13

Case Report

A 56-year-old female presented with a 2 1/2-year history of a painless swelling in her left upper neck. Clinical examination showed a well-circumscribed, firm, mobile, nontender mass at the left parotid region. A 0.5-cm cervical lymphadenopathy was palpable; facial nerve was intact. Axial computed tomography (CT) scan showed a solid mass with a low-density centre involving the inferior portion of the parotid gland (Fig. 1 ). The lesion was previously biopsied in another institution and branchial cleft cyst was suggested in the diagnosis. Reviewing the material from this biopsy revealed a multicystic lesion with areas of sebaceous differentiation and a prominent lymphoid stroma. Histopathologic findings were interpreted as sebaceous lymphadenoma, and left superficial parotidectomy was performed. The superficial lobe of the parotid gland with the overlying skin including the biopsy scar was removed. The lesion was found to be located in the tail of the parotid gland at the operation. The facial nerve branches were preserved. The patient is presently free of disease 12 months after surgery.

Figure 1

The parotidectomy specimen measured 6 x 3.5 x 2.5 cm. Its cut surface showed an encapsulated mass, measuring 3.5 x 2.5cm, surrounded by salivary gland tissue. It was a yellowish white, focally mucoid mass containing cystic spaces with a maximum diameter of 0.6 cm. Frozen sections were prepared from this specimen for lipid stains.

Microscopic examination revealed a neoplastic lesion composed of epithelial nests and variably sized cystic cavities lined by squamous or pseudostratified columnar epithelium (Fig. 2). In some areas, epithelial cells lining the cystic cavities and forming the nests showed differentiation into foamy sebaceous cells (Fig. 3). The cyst contents stained strongly positive with Oil-- Red-O, indicating the presence of lipid in the lumina. Mucin was also focally positive in the cystic cavities but not in the cytoplasm of the foamy cells. Stroma was composed of a dense lymphoid tissue showing follicular organization with germinal centres. Histiocytic infiltration was seen in the stroma, especially around the cystic cavities, presumably representing a reaction to the escaping cyst contents. A fibrous capsule was surrounding the neoplasm, but subcapsular sinuses were not identified.

Figure 2

Figure 3

Immunohistochemical studies were performed by using avidin-biotin complex system, and the antibodies included were anticytokeratin (pan-cytokeratin, Biogenex,1:40), antiepithelial membrane antigen (EMA, Novocastra, 1:200), anti-S 100 protein (S-100, Novocastra, 1:20), anti-B cell (CD 20, Biogenex, 1:40), anti-T cell (UCHL-1, Novocastra, 1:200), and antigranulocyte macrophage (Mac-387, Dako, 1:50). The epithelium lining the cysts and ductal structures showed strong positive staining for cytokeratin. Epithelial membrane antigen was positive in the luminal surfaces. No staining for S-100 protein was observed in the epithelial structures. The lymphoid component of the neoplasm consisted of small B lymphocytes around the lymphoid nodules in close apposition to the epithelia and larger cells within the follicule centres. T lymphocytes were mainly parafollicular and away from the epithelia. Few scattered macrophages were identified within the stroma by Mac-387; however, no structures resembling marginal sinuses were observed.

Discussion

Sebaceous lymphadenoma is a benign neoplasm first described in 1950 by Rawson and Horn.l2 The name "sebaceous lymphadenoma" was given to this rare entity by McGavran et al, 10 years after its first description.ll It is nearly exclusively confined to the parotid glands; only one case arising in the anterior midline of the neck has been reported.8 The age of presentation ranges from 25 to 89 and more than 70% of the patients are over the age of 50.1,4,8 It occurs equally in both sexes and has a favourable prognosis without recurrence after total excision.4,8 A single case for which the initial excision technique has not been specified is known to recur among 22 cases with available follow-up information.8

Sebaceous lymphadenoma is a neoplasm containing an epithelial component and a prominent lymphoid stroma.4,8,10 Epithelial cells forming nests and ductal structures show sebaceous differentiation. Lipoid material is demonstrated in these areas with special stains and occasionally mucin is present in the ductal lumina.6,7,9,12 This well-circumscribed and frequently multicystic neoplasm rarely presents as a unilocular cyst.1,5

Sebaceous lymphadenoma shares some morphologic and histogenetic features with Warthin's tumour (papillary cystadenoma lymphomatosum).3,6,9 Both of these neoplasms occur mainly in the parotid glands. Their lymphoid stroma contains well-developed follicules with germinal centres, and the origin of both sebaceous and oncocytic differentiation is the salivary ducts.5,6,13 By evaluating 106 Warthin's tumours, Bernier and Bhaskar concluded that they are salivary gland neoplasms arising in lymph nodes.14 Their conclusions are based on several factors: (1) ectopic salivary gland tissue is commonly found in intro- and periparotid lymph nodes and may form simple cysts in clearly identifiable lymph nodes, (2) Warthin's tumours in their early stages of development are observed in lymph nodes with only partial replacement of the nodal architecture, and (3) in many of the Warthin's tumours, it is possible to demonstrate subcapsular and/or medullary sinuses representing a lymph node. Neoplasms with coexisting areas of Warthin's tumour and sebaceous lymphadenoma have been described, supporting the theory of a common histogenesis for these neoplasms,3,12,13 Subcapsular sinuses have been identified in sebaceous lymphadenomas,3,4,6 and the presence of normal sebaceous glands intermixed with ectopic salivary gland tissue in periparotid lymph nodes have been demonstrated.1,5 According to these findings, sebaceous lymphadenoma seems to be a neoplasm arising from ectopic salivary gland tissue found in lymph nodes. The presence of lymph nodes within salivary gland tissue is a feature described for parotid glands,10,14 so nearly exclusive limitation of sebaceous lymphadenoma to the parotid glands is another supporting finding for this theory. However, there are contradictory opinions. Auclair argued that the prominent lymphoid stroma observed in some salivary gland neoplasms including sebaceous lymphadenoma represents a reactive proliferation of lymphoid tissue rather than a lymph node.ls They suggest that neoplastic epithelial cells stimulate this florid lymphoid proliferation and the interactions between a possible irritant and the neoplastic cells might be the reason of this process.

In this case, histopathology and immunohistochemical staining for Mac-387 failed to demonstrate subcapsular sinuses. This observation supports the salivary gland origin; nevertheless, the arguments about the histogenesis of this rare entity remain controversial.

Sidebar

Rced 1/5/99. Received revised 21/9/99 Accepted for publication 21/9/99

References

References

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2. Mesa-Chavez, L. Sebaceous glands in normal and neoplastic parotid glands. Am J Pathol 1949;25:627-645.

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4. Gnepp DR, Brannon R. Sebaceous neoplasms of salivary gland origin. Report of 21 cases. Cancer 1984; 53:2155-- 2170.

References

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6. Fleming KA, Morrice I. Sebaceous lymphadenoma of the parotid gland: a report of a case. J Pathol 1973; 110:259-261. 7. Tschen JA, McGavran MH. Sebaceous lymphadenoma.

Ultrastructural observations and lipid analysis. Cancer 1979; 44:1388-1392.

8. Auclair PL, Ellis GL, Gnepp DR. Sebaceous lymphadenoma. In: Ellis Gl, Auclair PL, Gnepp DR, eds. Surgical pathology of the salivary glands. Philadelphia: WB Saunders, 1991: 263-268.

References

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12. Rawson AJ, Horn RC. Sebaceous glands containing of the salivary gland. Surgery 1950; 1954:93-101.

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15. Auclair PL. Tumor-associated lymphoid proliferation in the parotid gland. A potential diagnostic pitfall. Oral Surg Oral Med Oral Pathol 1994; 77:19-26.