Salivary Gland




(1)
Department of Pathology, Sinai Hospital of Baltimore Pathology, Baltimore, MD, USA

 



Keywords
Pleomorphic adenomaAcinic cellAdenoid cysticMucoepidermoidSjögrenSialadenitisMammary analogueParotidSubmandibularSublingualWarthin tumor


With the exception of pleomorphic adenoma , salivary gland neoplasms are rare, so you may not see many during residency training. To make matters worse, there is a great deal of morphologic overlap in some of the tumors, and immunostains are not usually helpful in distinguishing them. Your goal, early in your training, should be to recognize the more classic forms of the major tumors and also to be able to create a short differential diagnosis for any given tumor. In this organ, with all the mimics and variants, it is extremely important to approach a specimen with the question, “What else could this be?”

Biopsies of the salivary gland are occasionally performed in search of Sjögren syndrome ; this is a complex diagnosis with specific criteria that must be met (see your favorite pathology textbook for that). Inflammatory lesions can also create a mass, such as chronic sialadenitis or a lymphoepithelial cyst . Necrotizing sialometaplasia is a known pitfall in the salivary glands, as this reactive condition shows intense inflammation, squamous metaplasia, and reactive atypia in the salivary ducts and may form a mass. The key to recognizing this condition is that, like chronic pancreatitis, the low-power architecture retains lobular contours and normal anatomic organization, with large ducts at the centers of the lobules.


Anatomy and Histology


There are three major and innumerable minor pairs of salivary glands. The largest, on the cheek, is the parotid, where most neoplasms arise. The smaller major glands are the sublingual and submandibular , under the tongue and jaw. In general, the smaller the gland, the higher the proportion of its neoplasms that are malignant. Salivary neoplasms can arise in virtually any part of the sinonasopharyngeal system .

The first major cell type is the secretory cell . The salivary glands are composed of serous and mucinous secretory units and ducts (Figure 25.1). Serous cells are wedge-shaped (like pie slices) and arranged in acini around ducts. They are full of blue to purple granules. Mucinous cells have basal nuclei and apical mucin, like goblet cells; these are also arranged in acinar formations. The parotid is primarily serous, the submandibular is mixed, and the sublingual is primarily mucinous.

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Figure 25.1.
Normal salivary gland. In this example of mucinous salivary gland, the columnar secretory cells (arrowhead) form acini arranged around salivary ducts (arrow). Myoepithelial cells are not particularly visible on H&E stain.

The second major cell type is the duct cell . The duct system has three types of ducts: the terminal or intercalated ducts, the intermediate-sized striated ducts, and the interlobular large ducts . Each has a different epithelium and is theoretically associated with different tumor types. The intercalated ducts are small profiles with low cuboidal epithelium, similar to a bile ductule (Figure 25.2). Striated ducts are more proximal and are larger, with pink columnar cells full of mitochondria and striated basal borders (hard to see). Interlobular or excretory ducts have pseudostratified columnar epithelium with or without goblet and squamous metaplasia. Different tumors have some morphologic similarity to these different ducts, which may help you keep the neoplasms straight.

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Figure 25.2.
Types of ducts . (a) In the parotid, which has mainly serous glands, the terminal or intercalated ducts are visible as small tubules lined by cuboidal epithelium (arrowheads). The medium-sized striated ducts are more oncocytic in appearance, with abundant pink cytoplasm (arrow). (b) The large interlobular ducts have pseudostratified columnar epithelium (arrow), with occasional goblet cells, and become squamous at their junction with the gingival mucosa.

The third major cell type is the myoepithelial cell . These cells, as in breast, surround acini and ducts. They are normally pale stellate cells with small nuclei and are very hard to identify in normal salivary gland. However, many neoplasms arise from the epithelial–myoepithelial cell line or, more specifically, from cells that can differentiate into either line. This creates a diagnostic nightmare, because the myoepithelial cells alone can take four different forms: spindled, plasmacytoid, epithelioid, and clear. Therefore, you must recognize any of these variants as myoepithelial (their immunologic profiles change with their form, unfortunately) and lump some very different-looking tumors into the same basket. Table 25.1 lists the most common neoplasms.


Table 25.1.
Basic categories of the most common neoplasms.



































Common neoplasms

Probable cells of origin

Benign adenomas

Pleomorphic adenoma (mixed tumor) and its end-of-the-spectrum variant, myoepithelioma

Epithelial–myoepithelial

Basal cell adenoma

Epithelial–myoepithelial

Warthin tumor and oncocytoma

Striated duct cells

Low grade, malignant

Mucoepidermoid carcinoma (low grade)

Interlobular duct cells, translocation related

Polymorphous adenocarcinoma

Epithelial–myoepithelial

Acinic cell carcinoma

Serous acinar cells

Secretory carcinoma

Terminal duct cells, translocation related

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Jan 30, 2018 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Salivary Gland

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