Benign Tumors of Salivary Glands
Pleomorphic adenoma, also referred to as a mixed salivary gland
tumor, is the most frequently seen benign salivary gland neoplasm,
accounting for 60% of such tumors. The most common site of origin is the
parotid, followed by the minor salivary gland and submandibular gland. It has a
female predominance in adults and a male predominance in children. The tumors
are indolent, slow-growing, typically asymptomatic lesions. Most often, a tumor
begins in the lower portion of the gland and gradually enlarges to present as
an ovoid or rounded well-circumscribed mass that is typically encapsulated.
When expanding into the depth of the parenchyma, the tumor tends to be hard and
lobulated, causing thinning of the overlying skin. Facial nerve involvement may
result from direct infiltration or through external pressure on the neural
tissue. The tumor is composed of ductal epithelial and myoepithelial cells with
morphologic features of spindle, plasmacytoid, epithelioid, stellate, or basaloid cells residing most often in a
mucochondroidal mesenchymal stroma. Recurrent lesions following surgical
excision are typically multinodular.
Basal cell adenoma is a result of a proliferation of basaloid
cells in a solid, tubular, trabecular, or membranous pattern. The tumors are
typically solitary, asymptomatic, and slow growing and arise from the parotid
gland. Lesions are well circumscribed and can grow to 3 cm in diameter. The
recurrence rate following surgical excision for all but the membranous variant
is quite low.
Papillary cystadenoma
lymphomatosum, typically
referred to as a Warthin tumor, is the second most common salivary gland
neoplasm, occurring primarily in the parotid gland. Warthin tumors, unlike
other salivary gland lesions, have a strong association with tobacco use. These
lesions are most often seen in white men in the sixth or seventh decade. The
tumor is frequently multilobular and bilateral, and like other salivary tumors,
it is slow growing, reaching 4 cm in diameter. It consists of a double layer of
oncocytic epithelium within a dense lymphoid stroma arranged in a papillary and
cystic pattern. The lesions likely develop from salivary tissue intertwined
with lymph nodes draining the parotid gland. The recurrence rate is up to 25%
with surgical excision. Although malignant transformation is rare, squamous
cell carcinoma or B-cell lymphoma may develop from the tumors.
Canalicular adenoma accounts for 1% of benign salivary gland
tumors, with a preference for the minor salivary gland, specifically, the upper
lip. It is most commonly seen in African American women in their seventies. The
lesions are typically firm, slow growing, and solitary, reaching up to 2 cm in
diameter. On gross inspection, the lesions are well-circumscribed, solid, or
cystic pink/tan nonencapsulated masses. Histologically, the tumor consists of
long, single-layered strands or tubules of cuboidal to short columnar cells
within a loose, lightly collagenous stroma. Treatment is surgical excision of
the lesion. Recurrence is rare.
