PART TWO
Diagnostic Cytology
Syringocystadenoma Papilliferum
The aspirate from
syringocystadenoma papilliferum
shows
papilla-like clusters and dyshesive, monomorphic epithelial cells
in a background of inflammatory cells.215,216
Key features of syringocystadenoma papilliferum
• Papilla-like clusters and dyshesive, monomorphic
epithelial cells; and
• Inflammatory cells in background.
Eccrine Porocarcinoma (Hidradenoma)
Eccrine porocarcinoma is the most common of the sweat gland
adenocarcinoma types. The cytology specimens show two cell
types, irregularly dispersed or forming nests or cords, sometimes
harboring central necrosis. The larger cells have abundant clear
granular cytoplasm with small to large, occasionally multinucle-
ated nuclei and small nucleoli. The chromatin is finely granular
with smooth nuclear membranes. The smaller cells have scanty
cytoplasm and a round to oval nuclei with small but promi-
nent nucleoli. Aggregates of parakeratotic squamous cells and
necrotic debris are also present.217-219
Key features of eccrine porocarcinoma
• Presence of two cell types, irregularly dispersed or
forming nests or cords, sometimes harboring central
necrosis;
• Abundant clear granular cytoplasm with small to large,
occasionally multinucleated nuclei and small nucleoli
in larger cells;
• Finally granular chromatin and larger cells in smooth
nuclear membranes;
• Scanty cytoplasm and a round to oval nuclei with
small but prominent nucleoli in smaller cells; and
• Aggregates of parakeratotic squamous cells and
necrotic debris also present.
Merkel cell carcinoma
Merkel cell carcinoma is a rare tumor of the skin found in the
dermis of the elderly patient. This neoplasm is slightly more
common in women. Histologically, it is characterized by a
proliferation of small round cells with a granular chromatin
pattern and scant cytoplasm arranged in a trabecular pattern
(Fig. 18.50A). FNABs of Merkel cell carcinoma are usually cellu-
lar and composed of small to medium-sized cells in a predomi-
nantly single-cell pattern, with a few large clusters surrounding
segments of capillary-sized blood vessels. The nuclei are uni-
form, round to oval, with delicate nuclear membranes and
finely granular chromatin pattern. The cytoplasm is scanty (Fig.
18.50B). Rosette formation is very rare. Frequent mitotic figures
and individual cell necrosis are frequently noted.220-222 Immu-
nocytochemical studies show the cells to be positive for CK20,
which show a paranuclear "dot-like" pattern.223 Neuron-specific
enolase, epithelial membrane antigen, and S-100 protein are
positive in varying degrees. The main differential diagnosis
includes metastatic small-cell carcinoma and lymphoma, which
can be distinguished with immunocytochemical studies. Small-
cell carcinomas are immunoreactive for TTF-1, while negative for
CK20 and lymphomas are negative for small-cell carcinoma.
Fig. 18.50 Merkel cell carcinoma. (A) Histologic section. Proliferation
of small round cells with granular chromatin pattern and scant cytoplasm
arranged in a trabecular pattern (H&E x LP). (B) Smear. Small to medium-sized
cells with scant cytoplasm in a predominantly single-cell pattern. The nuclei
are uniform, round to oval, with delicate nuclear membranes and finely
granular chromatin pattern (H&E x MP).
Key features of Merkel cell carcinoma
• Cellular speciman with small to medium-sized cells in
a predominantly single-cell pattern;
• Uniform round to oval nuclei with delicate nuclear
membranes and finely granular chromatin pattern;
• Scant cytoplasm; and
• Frequent mitotic figures and individual cell necrosis.
Mucinous carcinoma
Primary mucinous carcinoma of the skin is a rare neoplasm of
sweat gland origin. It is slightly more common in men than
in women and typically affects people in the fifth to seventh
decades of life. The scalp and eyelids are the most commonly
involved sites. FNABs of mucinous carcinomas of the skin
are moderately cellular and composed of pools of metachro-
matic magenta-colored mucin containing islands and clusters
of bland-appearing epithelial cells. Some of the tumor islands
have distinctly round edges while others appear more irregular.
A prominent linear streaming pattern can be seen. Tumor cells
506
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