Monomorphic adenomas of the salivary glands. A clinico-pathologic study of 12 cases with immunohistochemical observation

Canalicular adenoma with unicystic morphology. A rare entity

Background

Canalicular adenoma (CA) is a benign salivary gland tumor (SGT) almost exclusively affecting the minor salivary glands, predominantly of the upper lip, and exhibiting characteristic histopathologic features. As observed in several other SGTs, a commonly encountered finding is the presence of prominent cystic morphology. Even though a multicystic appearance is usually noticed, solitary cystic CAs may rarely occur.

Case Report

Two female patients (74 and 78 years old respectively) presented for the evaluation of submucosal asymptomatic masses of the oral cavity. In the 1st case a solitary nodule was noticed in the upper lip, while the 2nd patient exhibited two symmetrical lesions of the buccal mucosae. All three excised specimens displayed cystic morphology upon gross examination. Histopathologically, a solitary cystic formation lined by monomorphic cuboidal or basaloid cells arranged in solid or trabecular patterns was observed in the 1st case. With a differential diagnosis of CA vs basal cell adenoma immunohistochemical examination was performed. Positivity for S-100, CK7 and CD117 (c-kit) and negative reaction for GFAP, p63 and SMA rendered the diagnosis of CA. In the 2nd case both lesions displayed well-circumscribed proliferations by monotonous cuboidal or columnar cells arranged in single cords and occasionally forming beading patterns, while central solitary areas of marked cystic degeneration were noticed. Diagnosis of multifocal unicystic CA was disclosed.

Discussion

To our knowledge, only 11 additional cases of unicystic CA have been reported in the English-language literature. Although the exact clinical significance of unicystic morphology in CA is unknown, a tendency for occurrence within the context of multifocal tumors has been detected.

Key words:Canalicular adenoma, monomorphic adenoma, unicystic morphology, multifocal tumors, minor salivary glands.

S100 protein in oral biology and pathology

The demonstration of S100 protein is used extensively for both research and diagnostic purposes in oral biology and pathology. This article reviews the structure and putative function of S100, technicalities of S100 immunohistochemistry, the cells of the oral and perioral tissues which express S100 and the possible significance of S100 expression in disease.

Immunohistochemistry of basal cell adenoma of the major salivary glands

An immunohistochemical study of basal cell adenoma of the major salivary glands was performed. All basal cell adenomas showed similar staining patterns. Carcinoembryonic antigen was expressed in the apical portions of luminal cells, in the luminal secretions, and in the duct-lining cells. Epithelial membrane antigen showed a similar pattern of expression but was less frequently present in duct-lining cells. Keratin expression was found in all epithelial cells but not in stromal cells. S-100 protein was strongly expressed in stromal cells, with focal positivity of cells in epithelial nests. Vimentin expression was noted in stromal cells and the outer layer of epithelial nests. Staining for muscle-specific actin was negative in both stromal cells and epithelial nests. Thus, there appears to be evidence of myoepithelial cell participation in the histogenesis of basal cell adenomas, and at least some basal cell adenomas appear to be closely related to pleomorphic adenomas.

Pathology of the salivary glands: the contribution of electron microscopy

Electron microscopy has a limited role in the diagnosis of primary salivary gland tumors, although it can be helpful in metastatic lesions of possible salivary gland origin. The diversity of subtypes in salivary gland tumors, as well as the range of histomorphology within any one subtype, is unparalleled in any other human tumor. This and their relative infrequency causes diagnostic problems for pathologists. Ultrastructural techniques have been of major importance in determining the inter-relationship of these tumors for classification purposes, revealing the subtle variations in common cellular differentiation pathways, determining the organization of tumor cells, and displaying the importance of extracellular matrix materials in establishing diagnostic criteria for each of the many subtypes. Electron microscopy has also been valuable in non-neoplastic salivary gland disease and has an increasing role in experimental studies involving tissue from human and animal salivary parenchyma.

Myoepithelioma of the lacrimal gland: report of a case with spindle cell morphology

The case is described of a 23-year-old female patient presenting with unilateral proptosis, headaches, and transient epiphora. Surgery revealed an encapsulated tumour composed exclusively of spindle-shaped cells within a richly vascularised myxoid stroma. Immunohistochemical staining showed focal positivity for smooth muscle actin, vimentin, and glial fibrillary acidic protein. These combined findings are interpreted as providing evidence of a myoepithelioma, which may be regarded as a monomorphic adenoma consisting solely of myoepithelial cells. To our knowledge this is only the second report of such a tumour in the lacrimal gland.

Trabecular and solid-cribriform types of basal cell adenoma. A morphologic study of two cases of an unusual variant of monomorphic adenoma

Monomorphic adenomas are a morphologically complex group of salivary gland tumors. Two unusual examples, one a trabecular and the other a solid form of basal cell adenoma, reveal the development of a cribriform growth pattern focally in the former example and diffusely in the latter. They illustrate the potential for cellular differentiation within this subgroup, organization of synthetic products by the tumor cells, and the histologic criteria useful for the distinction of basal cell adenoma from adenoid cystic carcinoma.

Basaloid salivary carcinoma

The basaloid salivary carcinoma is proposed as the malignant counterpart of the basal cell or basaloid monomorphic adenoma. The carcinoma can arise de novo or by evolution from a maternal monomorphic adenoma. Particularly at risk for the latter sequence is the dermal analogue monomorphic adenoma. Preponderantly a parotid gland neoplasm, the basaloid carcinoma appears to be a biologically low-grade carcinoma with a low mortality but with a respectable local aggressiveness and recurrence rate.

Basaloid monomorphic adenomas

Monomorphic adenomas can be divided into basaloid and nonbasaloid type. With the exception of the canalicular adenoma, the basaloid monomorphic adenomas are preponderantly tumors of the major salivary glands, most often the parotid gland. The dermal analogue monomorphic adenomas, so named because of their histologic similarity to eccrine tumors of the skin, are a unique subset of the basaloid adenomas. They are often multifocal, recur frequently, may undergo malignant change, and can be part of a salivary-cutaneous tumor diathesis.