Year : 2009 | Volume
: 52 | Issue : 3 | Page : 379--382
Oncocytic sialolipoma of the submandibular gland with sebaceous differentiation: A new pathological entity
Teresa Pusiol1, Ilaria Franceschetti1, Michele Scialpi2, Irene Piscioli3,
1 Institute of Anatomic Pathology, S. Maria del Carmine Hospital, Piazzale S. Maria 6, 38068 Rovereto (TN), Italy
2 Department of Diagnostic and Interventional Radiology, University of Perugia, Via Brunamonti 51, 06100, Perugia, Italy
3 Department of Radiology, Budrio Hospital, Budrio (BO), Italy
Institute of Anatomic Pathology, S. Maria del Carmine Hospital, Piazzale S. Maria 6, 38068 Rovereto (TN)
Case Report: We report the case of an oncocytic sialolipoma of the submandibular gland with sebaceous differentiation in a 73-year-old man. The initial symptom was a right submandibular painless mass. Ultrasonography showed a hypoechoic oval mass posterior to the submandibular gland. The tumorectomy was performed with preservation of the salivary gland. The tumor was composed of mature adipose tissue surrounded by a thin fibrous capsule, multiple nodules of oncocytes, normal ductal-acinar units with focal ductal sebaceous differentiation. Discussion: We reviewed literature of the reported cases of mixed tumors of the salivary glands composed of mature adipose tissue with oncocytosis, salivary ducts, and acini with sebaceous differentiation. Conclusions: Sialolipoma and lipoadenoma with or without oncocytosis and/or sebaceous differentiation should be considered organ-specific tumors with a distinct histological appearance and specific terminology.
|How to cite this article:|
Pusiol T, Franceschetti I, Scialpi M, Piscioli I. Oncocytic sialolipoma of the submandibular gland with sebaceous differentiation: A new pathological entity.Indian J Pathol Microbiol 2009;52:379-382
|How to cite this URL:|
Pusiol T, Franceschetti I, Scialpi M, Piscioli I. Oncocytic sialolipoma of the submandibular gland with sebaceous differentiation: A new pathological entity. Indian J Pathol Microbiol [serial online] 2009 [cited 2021 Dec 5 ];52:379-382
Available from: https://www.ijpmonline.org/text.asp?2009/52/3/379/55000
Salivary glands are the anatomic site in which mixed tumor (pleomorphic adenoma) is the most common neoplasm representing from 45 to 74% of all neoplastic lesions.  Mixed tumor is a benign, epithelial-derived neoplasm composed of cells that demonstrate both epithelial and mesenchymal differentiation. Immunohistochemical and ultrastructural findings suggest that this tumor is entirely of epithelial origin and that mesenchymal areas are composed predominantly of cells that represent neoplastic modified myoepithelial cells.  The characteristic morphologic diversity occurs because the epithelial element expresses ductal and myoepithelial differentiation, produces matrix, and undergoes chondroid and osseous metaplasia. True benign mixed epithelial and mesenchimal tumor of the salivary glands may be considered as a lesion composed by an intimate admixture of predominant mature lipomatous tissue and salivary gland elements. These tumors have been described as single cases or small series. They have been considered as a "curiosity" and not regarded as a distinct entity. The recent world health organization classification of head and neck tumors described sialolipomas only in the soft tissue tumors of the salivary glands as "lipomas entrapping salivary glandular tissue," but not as mixed tumors. In the present paper we report the first case of oncocytic lipoadenoma of the submandibular gland with sebaceous differentiation and we discuss the terminology of similar neoplasms with the aim of proposing a new classification approach.
A previously healthy 73-year-old man was admitted to a tertiary case hospital because of a right submandibular painless mass.
Ultrasonography of the right submandibular region with a 7.5 MHz linear array probe showed a hypoechoic oval mass [Figure 1]a posterior to the submandibular gland. The lesion was not homogeneous, prevalently hyperechoic, and it extended externally to the gland [Figure 1]b.
The tumorectomy was performed with preservation of submandibular gland tissue. Postoperative ultrasonography showed normal morphology, size, and echogenicity of the right submandibular gland [Figure 2]. Currently the patient is well with no evidence of tumor recurrence.
The lesion was well circumscribed, capsulated, soft, yellowish, and its largest diameter measured 9 cm.
The histological features consisted of mature adipose tissue surrounded by a very thin fibrous capsule and multiple not encapsulated nodules of oncocytes. Phosphotungstic acid haematoxylin staining demonstrated strong and diffuse cytoplasmic granularity consisting with abundant mitochondria. Intense Ker 19 and focal p63 positivity were found in the oncocytic nodules, while Ki-67-labelled cells were absent in the normal ductal-acinar units of the salivary gland tissue. The ducts showed focal sebaceous differentiation. Both duct and acinar cells were positive for cytokeratins (AE1/3, CAM5.2). Ker 7 was positive in ductal cells and negative in acinar elements. The positivity for muscle-specific actin, a-smooth muscle actin, and p 63 suggest a myoepithelial origin of the cells that surround the acinar and ductal elements [Figure 3] and [Figure 4].
The amount of fatty tissue was about 80%.
Because this lesion is well circumscribed by thin fibrous capsule and shows intimate growth of prevalent adipose tissue, not encapsulated oncocytic nodules, islands of glandular tissue consisting of acinar elements, myoepithelial component and ductal structures with sebaceous differentiation, we propose the term of oncocytic sialolipoma with sebaceous differentiation.
Lipomatous tumors admixed with salivary gland tissue attracted interest in recent years and include neoplastic and tumor-like lesions [Table 1].
Sialolipoma is a proliferation of mature adipose tissue, surrounded by a very thin fibrous capsule and glandular components consisting of ductal, acinar, basal, and myoepithelial cells. 
Lipoadenoma is composed of an intimate admixture of adipose tissue and ducts containing eosinophilic proteinaceous material which may show cystic dilation but in contrast to sialolipoma lacks of acinar differentiation and myoepithelial component.  Hirokawa et al .  reported a parotid lipoadenoma with sclerotic and polycystic changes. The tumor was composed of cystically dilated glands, fibrous connective tissue, and mature adipose tissue.
In the parotid lipoadenoma with probable striated duct differentiation the glandular tumor components were described as tubules showing a sertoliform pattern without myoepithelial cells and acinar differentiation.  Hirokawa et al .  described an oncocytic lipoadenoma of the submandibular gland. The tumor was composed of an intimate admixture of mature fat cells and oncocytes without glandular component. We think that the term lipoadenoma is inappropriate because the denomination "lipoadenoma" implies the presence of a ductal component that was absent in the case of Hirokawa et al .  The term oncocytic lipoma is more appropriate for this lesion.
The oncocytic lipoadenoma of the parotid gland with sebaceous differentiation described by Klieb et al .  was composed of a mixture of oncocytes, with "light" and "dark" cells intimately associated with mature adipose tissue. There were scattered mature sebaceous glands admixed with the oncocytes. We believe that the term lipoadenoma is inappropriate because the lesion lacked of the ductal component. The mature sebaceous glands were admixed with oncocytes. The absence of ductal component is in contrast with the diagnosis of lipoadenoma. We think that the term oncocytic lipoma of the parotid gland with sebaceous differentiation is more appropriated for the lesion.  The present case may be considered the first case of oncocytic lipoadenoma of the salivary glands. The histogenesis of the various components is unclear.
The origin of the lipomatous proliferation is controversial. In the original description of seven cases, Nagao et al .  believed that sialolipomas were lipomas with secondary entrapment of salivary gland elements. We think that the term sialolipoma implies a definite origin from the salivary gland mesenchimal tissue as reported by Ponniah et al .  The residual salivary gland parenchyma is compressed at the periphery of the lipomatous proliferation. According to present histogenetic hypothesis, we believe that the islands of epithelial salivary glands should be considered as secondary entrapment and not as a neoplastic proliferation of the lesion.
The World Health Organization Classification of Head and Neck tumors defines three categories of oncocytic neoplasms of the salivary glands: o0 ncocytoma, nodular oncocytic hyperplasia (or oncocytosis), and oncocytic carcinoma. It has been hypothesized that the presence of oncocytes with their characteristic mitochondrial hyperplasia and pleomorphism is the result of mitochondrial dysfunction causing defective cellular metabolism. Oncocytosis (nodular oncocytic hyperplasia) occurs as a multifocal nodular collection and proliferation of oncocytes with diffuse or focal replacement of the salivary gland tissue with oncocytic lobules and intervening small foci of residual normal serous glands and ducts. The formation of oncocytic micronodules has been considered as a result of oncocytic metaplasia and hyperplasia of small and large ducts.  In the present case, oncocytic nodules were adjacent to ductal structures and isolated in the fatty tissue. These sites confirm the ductal origin by oncocytic metaplasia and hyperplasia and in a second time by the separation from the ducts of origin by adipose tissue proliferation. In the series of seven cases, Nagao et al .  reported focal sebaceous metaplasia in two sialolipomas of the parotid gland. But this finding was not reported in the final diagnosis of sialolipoma. In benign salivary gland tumors sebaceous differentiation has been described in pleomorphic adenoma, oncocytoma, sialoblastoma, Warthin tumor other than sebaceous adenoma and sebaceous lymphadenoma. Consequently, the presence of sebaceous differentiation in sialolipoma may be considered uncommon but not unexpected. In our opinion, this histological feature should be reported in the final diagnosis of mixed epithelial and adipose tumor of the salivary glands according to the case reported by Klieb and Perez-Ordonez. 
Sialolipoma and lipoadenoma with or without oncocytosis and/or sebaceous differentiation should be considered organ-specific tumors with a distinct histological appearance and specific terminology.
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