Muscle tissue tumors
These neoplasms originate from striated muscle elements.
- Rhabdomyoma: A benign lesion macroscopically presenting as a dense grayish-white nodule up to 15 cm in diameter. Microscopically, the tumor consists of large spindle-shaped and round pale cells, in whose cytoplasm transverse (sometimes longitudinal) striation is clearly visible. Cellular atypia is completely absent, and the stroma is represented by a delicate argyrophilic network. The prognosis after removal is favorable.
- Rhabdomyosarcoma: A rare but extremely aggressive malignant tumor. Typically located deep within the muscles of the trunk and extremities. An atypical location—in the retroperitoneal tissue, mediastinum, or urogenital organs—is also possible. Histological preparations show sharp cellular polymorphism (cells mimic embryonic muscle tissue), marked nuclear atypia, and the presence of "monstrous" pathological mitoses. The tumor early gives extensive metastases and frequently recurs, which determines a poor prognosis.
Connective tissue tumors
This group is the most common among all soft tissue neoplasms.
- Fibroma: The most frequent benign connective tissue tumor. Grows as a well-circumscribed, encapsulated, dense gray nodule. Found practically everywhere, including the mammary glands, ovaries, and tissues along nerve trunks (neurofibromas). Consists of bundles of mature spindle-shaped fibroblasts surrounded by a fibrous stroma, which may undergo hyalinosis.
- Fibrosarcoma: A malignant counterpart, frequently affecting the retroperitoneum and lower extremity tissues (especially the thigh and knee joint). Lacks a capsule, grows infiltratively. On cross-section, the tissue is soft, resembling "reddish fish flesh," and contains foci of necrosis and hemorrhage. The cells are arranged haphazardly, nuclei are hyperchromatic, and there are many bizarre atypical cells and irregular mitoses. Recurs in more than 50% of cases.
- Fibrous histiocytoma: The benign variant (dermatofibroma) usually arises in the skin (size up to 1 cm), with spindle cells forming storiform ("whirled") structures. The malignant form grows up to 20 cm, infiltrates skeletal muscles, and is distinguished by marked polymorphism. Malignant histological variants include pleomorphic, giant-cell, angiomatoid, and myxoid types (with stromal mucinous change).
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Borderline and tumor-like lesions
This group includes processes that may clinically or morphologically resemble malignant tumors but have a different nature.
- Desmoid tumor (aggressive fibromatosis): Occupies an intermediate position between benign and malignant tumors because it is capable of destructive infiltrative growth. Consists of mature fibroblasts with rare mitoses. The abdominal variant frequently grows in women from the sheaths of the rectus abdominis muscles (especially actively during pregnancy).
- Pseudosarcomatous proliferations: Reactive lesions arising in response to trauma or ischemia. An example is nodular fasciitis. A rapidly growing lesion, frequently on the forearm. Consists of immature fibroblasts with high mitotic activity, but without signs of cellular atypia.
- Myositis ossificans (heterotopic ossification): The appearance of well-demarcated bone tissue (3–6 cm) near the periosteum or at a distance from it, frequently after trauma. The muscle fibers themselves are not affected. Frequent localization is the elbow joint region and the thigh.
- Fibromatoses: Local proliferation of fibroblasts and collagen fibers. Includes palmar fibromatosis (Dupuytren's contracture—flexion deformity of the 4th and 5th fingers), plantar (without contractures), and penile fibromatosis (Peyronie's disease, causing penile curvature).
Briefly: answers to topical questions
What are the histological variants of rhabdomyosarcoma?
Modern classification distinguishes the following histological variants of rhabdomyosarcoma:
- Embryonal — the most frequent variant, resembling primitive mesenchyme with myxoid edematous stroma.
- Botryoid (grape-like) — a subtype of embryonal, has a compact cambial layer of hyperchromatic cells beneath the epithelium.
- Spindle cell — a subtype of embryonal, forms bundles of elongated cells.
- Alveolar — divided into cellular clusters by stromal fibrovascular septa.
- Pleomorphic — distinguished in the nomenclature of malignant tumors.
What histological variants of liposarcoma exist?
The following histological variants of liposarcoma exist:
- Well-differentiated — includes lipoma-like, sclerosing, inflammatory, and spindle cell subtypes.
- Dedifferentiated — represents a mixture of atypical adipocytes with sarcomatous elements of a different structure.
- Myxoid — mentioned in the general histological classification.
- Round cell — distinguished among the tumor subtypes.
- Pleomorphic — also belongs to the histological variants of liposarcoma.
Which tumors develop from soft tissue blood vessels?
Vascular tumors develop from blood vessels, which in sources are classified as:
- Hemangiomas — tumors from blood vessels; benign angiomas are frequently congenital and grow slowly.
- Angiosarcoma — the malignant variant of a vascular tumor.
- Postradiation angiosarcoma — indicated among breast vascular tumors.
- Epithelioid hemangioma — an intermediate, locally aggressive vascular tumor.
- Epithelioid hemangioendothelioma — a malignant vascular tumor.
What are the microscopic signs of synovial sarcoma?
The microscopic picture of synovial sarcoma is distinguished by extreme polymorphism and the presence of biphasic, spindle cell, or epithelioid cell structure.
- The tumor consists of undifferentiated fibroblasts and atypical pale synoviocytes with hyperchromatic nuclei.
- Atypical synoviocytes are arranged in clusters, cell nests, and tubular structures.
- Atypical fibroblasts together with stromal tissue form strands that run in various directions.
- A characteristic feature is the biphasic structure of the tumor.
How to memorize
To memorize desmoid variants, use anatomical localization: abdominal — "female" (abdomen, pregnancy), extraabdominal — "general" (shoulders, chest, thighs in both sexes), intraabdominal — "deep" (mesentery, pelvis).
Class and exam questions
How do malignant soft tissue tumors differ from benign ones?
Benign tumors exhibit only tissue atypia. Sarcomas have both tissue and marked cellular atypia, infiltrate surrounding tissues, and metastasize predominantly via the hematogenous route.
What is Dupuytren's contracture?
This is a form of palmar fibromatosis characterized by local fibroblast proliferation with fascial thickening. The process leads to a slowly progressive flexion contracture of the 4th and 5th fingers of the hand.
Name the characteristic histological features of rhabdomyosarcoma.
It is characterized by marked cellular polymorphism (cells mimic embryonic structures), sharp nuclear atypia, and the presence of large cells with multiple "monstrous" mitoses.
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What else to study on this topic
- Morphological characteristics and pathways of metastasis of bone fibrosarcoma.
- Pathogenesis and classification of metabolic bone diseases (osteoporosis, rickets, osteomalacia).
- Causes, types, and morphological picture of aseptic osteonecrosis.
- Chronic hematogenous osteomyelitis: pathologic anatomy and main causes of death.
- Pathogenesis, morphological changes, and complications of deforming osteoarthritis.
- Duchenne muscular dystrophy: pathologic anatomy and most frequent causes of death.
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Other topics in the section "Chapter 22. Diseases of the Musculoskeletal System"
Bone tissue pathologyOsteomyelitisBone tumorsOsteoarthritisGoutSkeletal muscle pathologyArthritisPathogenesis and outcomes of diseasesInvasive tumor growthComplications of amyloidosisComplications of osteoporosisComplications of psoriasisComplications and outcomes of atrophy
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