| Abstract|| |
Neoplastic lipomatous lesions of the salivary glands constitute ≤0.5% of all the salivary gland tumors. Oncocytic sialolipoma of the parotid glands is extremely uncommon. We report a case of oncocytic sialolipoma of the parotid gland in a 59-year-old male who presented with a gradually increasing swelling of the right parotid. Excisional parotid biopsy performed in view of possible pleomorphic adenoma as suggested on ultrasonography showed histological features consistent with oncocytic sialolipoma. We also described the characteristics of 24 previously reported cases of oncocytic sialolipoma of the parotid gland. The median age of the patients including the present case was 56 years (range 7–89), and 14 were male. The largest and the least reported sizes of the tumor were 7.0 and 1.4 cm, respectively. The left-sided parotid gland was more commonly involved (14/23). Despite its rarity, oncocytic sialolipoma should be considered in lipomatous parotid lesions showing epithelial components with oncocytic changes.
Keywords: Oncocytic lipoadenoma, oncocytic sialolipoma, parotid gland, sialolipoma
| Introduction|| |
Neoplastic lipomatous lesions of the salivary glands are uncommon, and constitute ≤0.5% of all the salivary gland tumors. Based on the histology, these lesions are divided into monophasic lesions (lipoma) containing only adipose tissue, and biphasic lesions (where salivary epithelial components are seen in addition to the adipose tissue). The latter group is further categorized based on the type of epithelial components such as sialolipoma and oncocytic sialolipoma (also known as oncocytic lipoadenoma). Oncocytic sialolipoma of the parotid glands is extremely uncommon with only 24 cases reported.,,,,,,,,,,, Histopathology plays an important role in the diagnosis of these benign lipomatous lesions and differentiating them from malignant tumors. Here, we report a case of oncocytic sialolipoma of the parotid gland.
| Case Report|| |
A 59-year-old hypertensive male presented with gradually increasing, painless swelling below the right ear for 6 months. The patient did not have fever, cold, cough, hemoptysis, xerostomia, odynophagia, dysphagia, weight loss, oral pain, facial weakness, or other symptoms of immunodeficiency.
The examination revealed a freely mobile, non-tender swelling of size 5 cm × 3 cm in the right parotid region. There was no cervical lymphadenopathy, and the rest of the physical examination was normal. The ultrasonography of the swelling suggested the possibility of pleomorphic adenoma. Based on these clinical and radiological findings, the patient underwent right superficial parotidectomy with facial nerve preservation. A well-circumscribed specimen of 5.5 cm × 3 cm × 2 cm was received for histopathological examination, which was yellow and tan-brown on cut section [Figure 1]a. The microscopic examination revealed a well-circumscribed encapsulated mass composed of mature adipose tissue admixed with epithelial components of the salivary gland [Figure 1]b and [Figure 1]c which constituted around 60% of the lesion. Around 80% cells of the epithelial component showed oncocytic differentiation [Figure 1]c and [Figure 1]d, having round to oval nuclei, prominent nucleoli, and eosinophilic granular cytoplasm. Periductal lymphocytic infiltrate [Figure 1]e and focal sebaceous differentiation of the ductal epithelium [Figure 1]f were also seen. There was no evidence of cellular pleomorphism, atypia, or mitotic activity. Lymphovascular, perineurial, or extracapsular invasion was not seen.
|Figure 1: Oncocytic sialolipoma of the parotid gland. (a) Cut section of gross specimen. Histopathology showing (b and c) well circumscribed lesion with mature adipose tissue admixed with epithelial components of the salivary gland (c and d) oncocytic differentiation of the epithelial component (e) periductal lymphocytic infiltrate, and (f) focal sebaceous differentiation of the ductal epithelium|
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| Discussion|| |
Although lipoma is a very common soft-tissue tumor, salivary gland lipomatous lesions are uncommon. There is no general agreement on the nomenclature and histologic classification of these lesions. Sialolipoma was not regarded as a separate entity until 2001 when Nagao et al. proposed this term after studying seven cases of salivary gland lipomatous lesions. In contrast to lipoma (which contains only adipose tissue), sialolipoma additionally contains an epithelial component within the lesion. The pathogenesis of sialolipoma remains unclear. It is suggested that the normal salivary gland component becomes entrapped within the proliferative adipose tissue. Based on the presence of oncocytic changes (cells having eosinophilic granular cytoplasm) in the epithelial component of sialolipoma, these lesions are further categorized as “oncocytic lipoadenoma” by a few authors,, and “oncocytic sialolipoma” by others. Although it remains controversial, the latter terminology sounds more appropriate for these lesions as the epithelial component is non-neoplastic. The recent World Health Organization classification of head and neck tumors has not yet adopted these terms, and irrespective of oncocytic epithelial changes, all the lesions are classified under sialolipoma. The distribution of the adipose tissue and oncocytic epithelial component within a lesion greatly varies. Some lesions show intermingling of both the tissues, whereas circumscribed oncocytic nodules within the adipose tissue background are seen sometimes. Although a few foci of oncocytic cells can also be seen in sialolipoma, it usually lacks a significant oncocytic component. Periductal inflammation and foci of sebaceous metaplasia are common features of both sialolipoma and oncocytic sialolipoma.
Oncocytic sialolipoma of the parotid gland is extremely uncommon. PubMed search with terms “sialolipoma,” “lipoadenoma,” “oncocytic sialolipoma,” and “oncocytic lipoadenoma,” identified 24 cases of parotid gland oncocytic sialolipoma published in the English literature with adequate data.,,,,,,,,,,, The characteristics of these cases including the present case is summarized in [Table 1]. The median age of the patients was 56 years (range 7–89), and 14 were males. The largest and the least reported size of the tumor were 7.0 and 1.4 cm, respectively. The left-sided parotid gland was more commonly involved (14/23).
The differential diagnosis for sialolipoma includes salivary gland lesions containing adipose tissue. Interstitial lipomatosis is an age-related change where the lesion is uncircumscribed as opposed to an encapsulated lesion in the sialolipoma. In fibrolipoma, mature adipose tissue is seen interspersed by dense connective tissue without a capsule. Spindle cell lipoma is composed of a well-circumscribed lesion containing bland spindle cells, collagen, and adipocytes. Pleomorphic adenoma can be identified by the proliferation of both the epithelial and stromal components and chondromyxoid stroma.,
Despite the rarity of lipomatous lesions of the salivary gland, oncocytic sialolipoma should be considered in patients with parotid lesions having adipose tissue and epithelial components with oncocytic changes. Further studies are warranted to enhance the knowledge regarding the appropriate nomenclature/classification, clinical profile, pathogenesis, and prognosis of this uncommon entity.
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Venu Patel Sureja,
Department of Pathology, Star Hospitals, Banjara Hills, Hyderabad - 500034, Telangana
Source of Support: None, Conflict of Interest: None