Page 885 - Textbook of Pathology, 6th Edition

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Figure 29.11 Classic synovial sarcoma, showing characteristic biphasic cellular pattern. The tumour is composed of epithelial-like cells lining
cleft-like spaces and gland-like structures, and spindle cell areas forming fibrosarcoma-like growth pattern.

ALVEOLAR SOFT PART SARCOMA the skin and subcutaneous tissues as a small swelling. The
tumour is slow growing but metastasising.
Alveolar soft part sarcoma is a histologically distinct, slow-
growing malignant tumour of uncertain histogenesis. The Grossly, the tumour is somewhat circumscribed and has
tumour may occur at any age but affects children and young nodular appearance with central necrosis. CHAPTER 29
adults more often. Most alveolar soft part sarcomas occur in Microscopically, the tumour cells comprising the nodules
the deep tissues of the extremities, along the musculofascial have epithelioid appearance by having abundant pink
planes, or within the skeletal muscles. cytoplasm and the centres of nodules show necrosis and
Grossly, the tumour is well-demarcated, yellowish and thus can be mistaken for a granuloma.
firm.
Microscopically, the tumour shows characteristic alveo- CLEAR CELL SARCOMA
lar pattern. Organoid masses of tumour cells are separated Clear cell sarcoma, first described by Enginzer, is seen in
by fibrovascular septa. The tumour cells are large and skin and subcutaneous tissues, especially of hands and feet.
regular and contain abundant, eosinophilic, granular Soft Tissue Tumours
cytoplasm which contains diastase-resistant PAS-positive Microscopically, it closely resembles malignant
material. This feature distinguishes the tumour from melanoma, and is therefore also called melanoma of the
paraganglioma, with which it closely resembles. soft tissues.

GRANULAR CELL MYOBLASTOMA TUMOUR-LIKE LESIONS
Granular cell tumour is a benign tumour of unknown histo- Besides the soft tissue tumours, there are some proliferative
genesis. It may occur at any age but most often affected are conditions of the soft tissues which resemble clinically and
young to middle-aged adults. The most frequent locations morphologically with soft tissue tumours. Important
are the tongue and subcutaneous tissue of the trunk and examples are nodular fascitis (pseudosarcomatous fascitis)
extremities. and myositis ossificans. The former condition has already
been described under fibromatous lesions while the latter is
Grossly, the tumour is generally small, firm, grey-white discussed below.
to yellow-tan nodular mass.

Histologically, the tumour consists of nests or ribbons of MYOSITIS OSSIFICANS
large, round or polygonal, uniform cells having finely
granular, acidophilic cytoplasm and small dense nuclei. Myositis ossificans is a benign, tumour-like lesion
The tumours located in the skin are frequently associated characterised by osteoid and heterotopic bone formation in
with pseudoepitheliomatous hyperplasia of the overlying the soft tissues. It is a misnomer since the lesion neither occurs
skin. exclusively in the skeletal muscle as the name leads one to
believe, nor are the inflammation or ossification always
essential.
EPITHELIOID SARCOMA
Myositis ossificans is generally preceded by history of
This soft tissue sarcoma occurring in young adults is peculiar antecedent trauma to a skeletal muscle or its tendon. The
in that it presents as an ulcer with sinuses, often located on trauma may be minor and repetitive e.g. to the adductor