Oncocytomas may be confused with non-neoplastic oncocytic
nodular hyperplasia, acinic cell carcinoma, and Warthin's tumor.
A precise cytologic distinction between various benign lesions
containing oncocytic cells does not seem important because all
are cured by simple surgical excision. It is more important to dif-
ferentiate between a benign oncocytic lesion and a malignant
tumor, which may require a different type of treatment. In the
malignant variant of oncocytic origin mitotic figures are often
seen as well as necrosis. In aspirates from acinic cell carcinoma,
the cells tend to a more poorly outlined cytoplasm which is more
granular and finely vacuolated than typical cells from oncocy-
toma. In May-Grunwald-Giemsa stain, the cytoplasm of cells
from acinic cell carcinoma usually appears slate-gray and may
contain a fine red granulation not seen in benign oncocytic cells.
Pleomorphic adenoma and mucoepidermoid carcinoma
may have focal oncocytic changes. This is, however, seldom
a diagnostic problem if adequate sampling of material from
different parts of these tumors has been carried out.
Basal Cell Adenoma
Basal cell adenomas account for about 2% of all primary tumors of
the major salivary glands and are mostly seen in elderly patients.30,34
The term basal cell adenoma is used to identify a neoplasm with
a single, well-defined, basaloid histologic pattern, which can have
a diverse architecture such as trabecular, tubular, papillary, and
solid patterns.30,35 Cystic changes may be superimposed on these
patterns. The mesenchymal chondromyxoid elements of the type
encountered in pleomorphic adenomas are generally lacking.
The FNA features of basal cell adenoma have been described by
several investigators.11,36 Smears are cellular and show cohesive
solid groups and irregularly branching cords (Fig. 22.18). The
individual cells are uniform, with scant poorly defined cytoplasm,
oval nuclei with finely granular chromatin (Fig. 22.18). Nucle-
oli may be seen in occasional cells. Single cells usually appear
as naked nuclei, and small amounts of fibrous to amorphous
material may be seen at the edges of cell clusters. This matrix
is homogeneous, stains bright red with May-Grunwald-Giemsa
stain, and is almost translucent in Papanicolaou-stained slides.
Key features of basal cell adenoma
Small clusters of branching cords composed of small
uniform cells with round or oval nuclei;
Sparse homogeneous background material; and
Individual cells appear as naked nuclei or have a
scant amount of cytoplasm.
FNA from basal cell adenomas and from the solid form of
adenoid cystic carcinomas have similar cytologic features. The
size and configuration of cell groups, as well as the individual
cell morphology and the presence of single cells, are virtually
identical. The solid adenoid cystic carcinoma is lacking the
metachromatic globules or cylinders that characterize cribri-
form adenoid cystic carcinoma.
The distinction between these two prognostically quite differ-
ent tumor entities is very difficult.11,36-38 Clinically, pain or nerve
damage indicates malignancy.
The cytologic differentiation from pleomorphic adenoma is
sometimes difficult but myoepithelial cells are never seen. The
distinction between these two entities seems to be less impor-
tant because the management is similar.
Fig. 22.18 Basal cell adenoma. Irregular tumor fragments with
monomorphic tumor cells mixed with some amorphous matrix material
(May-Grünwald-Giemsa x HP).
Clear Cell Adenoma
Clear cell adenomas are composed of prominent clear cells that
form tubular structures. The differential diagnosis in tissue sec-
tions includes nodular clear cell/oncocytic hyperplasia, acinic
cell tumor, and mucoepidermoid tumor.39 Although we have
not encountered this uncommon tumor, we believe that the
same differential diagnostic problem would occur in FNA.
Sebaceous Cell Adenoma
Sebaceous cell adenoma is a very rare solid or sometimes cystic
neoplasm made up of flat polygonal cells similar to the sebaceous
cells usually seen in smears from epidermoid cysts (Fig. 22.19).11
Sebaceous cells are occasionally seen in tissue specimens
from major salivary glands and within neoplasms such as
pleomorphic adenoma and Warthin's tumor.30
Key features of sebaceous cell adenoma
Tumor cells often in dense clusters;
Few dispersed cells; and
Monomorphic cells with round nuclei and a rich
Fig. 22.19 Sebaceous cell adenoma. Tumor cells with rich vacuolated
cytoplasm (May-Grunwald-Giemsa x HP).