Lymphadenomas: sebaceous and non-sebaceous

 Definition

 Sebaceous lymphadenoma is a rare, well-circumscribed to encapsulated tumour composed of variably sized and shaped nests of sebaceous glands without atypia often intermixed with different proportions of variably sized ducts, within a background of lymphocytes and lymphoid follicles. Lymphadenoma is a similar tumour lacking sebaceous differentiation.

 ICD-O code Sebaceous lymphadenoma 8410/0

Epidemiology

Approximately 75% of sebaceous lymphadenomas are first diagnosed in the 6- 8th decades of life (25-89 years). There is no sex predominance. Lymphadenoma is a rare tumour, with only 5 cases having been reported in the literature {83,1399,1591}. From the limited available data, all patients are male ranging in age from 17-57 years.

Localization

 Well over 90% of sebaceous lymphadenomas occurred in or around the parotid gland with one tumour arising in the anterior midline of the neck {896}, and two tumours occurring in the oral region {1393,1654}. All cases of lymphadenomas reported so far have occurred in the parotid gland {83,1591}.

Clinical features

 Patients typically present with a painless mass.

Macroscopy

Tumours have ranged from 1.3-6.0 cm in greatest dimension. They are usually encapsulated, solid, multicystic, or unicystic masses that range from yellow to grey. Sebum is commonly found in many of the cysts.

Histopathology

Sebaceous lymphadenoma.

 The majority of sebaceous lymphadenomas are composed of variably sized sebaceous glands admixed with salivary ducts in a diffuse lymphoid background. Others consist mainly of lymphocytes and lymphoid follicles surrounding ductal structures with only occasional sebaceous glands. All tumours have a lymphoid background, and about one half have well-developed lymphoid follicles. In addition, tumours may contain small areas of identifiable residual lymph node and focal necrosis has rarely been observed. Occasional tumours may also contain or be intermixed with components of a Warthin tumour or membranous basal cell adenoma {896,901}. Histiocytes and foreign body giant cell inflammatory reactions secondary to extravasated sebum are commonly observed. This foreign body reaction can be helpful in differentiating these tumours from mucoepidermoid carcinoma (MEC). Unlike MEC, which contains a variety of cell types; mucin positivity is never found in the clear sebaceous cells. However, intracellular and extracellular mucin may be occasionally found within ducts adjacent to sebaceous cells.

Lymphadenoma

It can take the form of anastomosing trabeculae or solid tubules surrounded by basement membrane-like material, or cystically-dilated glands filled with proteinaceous materials. Papillary structures can be found in some cases. The lining cells are cuboidal to columnar and show no significant cytologic atypia or mitotic activity. Basal cells can be identified in some areas. However, the epithelial component can be obscured by abundant admixed and intraepithelial lymphocytes; the diastase-peroxidase acid Schiff stain can help in highlighting the basement membrane around the epithelial nests. The lymphoid stroma comprises dense populations of lymphoid cells with lymphoid follicle formation. The lymphoid component is generally considered to represent tumour-associated lymphoid proliferation {83,604}, hence conventional salivary gland adenomas occurring within intraparotid or cervical lymph node are excluded.

Differential diagnosis

 The most important differential diagnosis of lymphadenoma is lymphoepithelial carcinoma; distinguishing features of lymphadenoma are lack of mitotic activity, lack of invasive growth with desmoplastic stroma, presence of subtle or overt ductal differentiation, and absence of EBV association. Metastatic adenocarcinoma in lymph node is characterized by recognizable nodal structures, definite nuclear atypia and invasive growth. Lymphadenoma can be distinguished from lymphoepithelial sialadenitis by the circumscribed borders as well as a more proliferative epithelial component.

Treatment and prognosis

 Treatment consists of complete surgical excision. These tumours rarely recur.