Cytology of Soft Tissue, Bone, and Skin
Palisading of the cells is frequent and in this way the aspirates
may resemble those of peripheral nerve sheath tumors.
Degenerative changes such as sclerosis, hemorrhage, cystic
change, and calcification can be present.
S-100 negativity can help differentiate the cells of benign
smooth muscle tumors from histiocytes; desmin is positive.
The presence of large pleomorphic, hyperchromatic cells
with multiple nuclei may be found in atypical leiomyomas, but
the lack of mitosis and necrosis should steer one away from the
diagnosis of malignancy.
Lymphangioleiomyomatosis (LAM) is found in the lung of
women of childbearing age and may be difficult to diagnose
on cytology. Groups of bland spindle cells intermixed with pul-
monary tissue and blood may be present.58 HMB 45 is positive
Key features of leiomyoma
• Pain on aspiration of superficial lesions;
• Cellular preparation with loose collections of bland
• Round to oval nuclei with nucleoli;
• Cytoplasmic vacuoles that indent the nucleus; and
• Degenerative changes expected.
This malignant smooth muscle tumor is found in adulthood,
most frequently in the retroperitoneum, but also in associa-
tion with blood vessels such as the pulmonary artery or vena
cava. It can be confused with leiomyoma when small or well
differentiated. Malignant smooth muscle tumors are characterized
by increased mitoses, cytologic atypia, and poor cohesion
(Fig. 18.6). Size also plays a role in malignancy with tumors
greater than 7 cm being more often malignant.59
Low-grade leiomyosarcoma may be less cellular and nuclear
atypia and coarse chromatin more difficult to identify. Cells may
palisade similar to neurogenic tumors. It may not be possible
to make a diagnosis of malignancy with accuracy in these cases,
which may have to be considered suspicious for malignancy or
labeled as atypical. High-grade leiomyosarcoma can be pleo-
morphic with necrosis and markedly abnormal-appearing cells
(Fig. 18.7). Multinucleation may be present. Leiomyosarcoma
may express SMA but not myoglobin.60 High-grade leiomyo-
sarcoma may show squamoid cytoplasm.61 High-grade smooth
muscle tumors may also resemble MFH (Fig. 18.8).
Metachromatic material may be found in the background of
any smooth muscle tumor.
Primary leiomyosarcoma of bone has been reported.62
Key features of leiomyosarcoma
• Cellular smears with many spindle cells;
• Atypical nuclei and multinucleation;
• Mitosis present;
• Desmin and SMA positive, myoglobin and S-100
• Palisading arrangement of nuclei possibly present.
Epithelioid Muscle Tum ors
Focal epithelioid or round cell features can be found in smooth
muscle tumors such as round or polygonal cell shapes63
(Fig. 18.9). Nuclear atypia is not common but intranuclear
cytoplasmic vacuoles as well as vacuolated cytoplasm may be
present64 (Figs 18.10, 18.11). Histology of this tumor does not
predict its behavior, but mitotic count is important. Both the
epithelioid appearance and the more classic appearance of
smooth muscle may coexist. The differential diagnosis is with
epithelial tumors, especially malignant ones.
Key features of epithelioid muscle tumors
• Round to polygonal cells;
• Nuclear atypia;
• Vacuolated cytoplasm; and
• Possible biphasic pattern.
Pericytic (Perivascular) T umors
Glomus Tum or
They are composed of cells that resemble the modified smooth
muscle cells of a glomus body. Most of these tumors are present
in the distal extremities, especially in subungual region, hand,
Fig. 18.6 Leiomyosarcoma. (A) FNA biopsy of a deep tissue leiomyosarcoma. This single cell is characterized by a spindle shape with a markedly abnormal
nucleus and prominent nucleoli (Papanicolaou x HP). (B) Corresponding tissue section of leiomyosarcoma with parallel bundles of elongate cells. Cells are
pleomorphic with eosinophilic cytoplasm (H&E x MP).