Musculoskeletal Tumors

10.1055/b-0034-92253

Musculoskeletal Tumors

Histopathologic Classification

The World Health Organization (WHO) published a revised version of the histopathologic classification of bone and soft-tissue tumors in 2002.

Bone Tumors

Bone tumors are classified either by their tissue of origin (e.g., cartilage and osteogenic tumors) or by their characteristic cell type (e.g., giant cell tumor) ( Table 10.1 ). Exceptions are tumors of the Ewing group and “miscellaneous tumors” whose origin is uncertain. The classification also includes miscellaneous tumorlike (nonneoplastic) lesions, omitting some typical entities in this category such as nonossifying fibroma. Synovial osteochondromatosis is listed as a joint lesion that, although it may cause secondary bone involvement, primarily represents a soft-tissue process.

Soft-Tissue Tumors

The WHO classification of soft-tissue tumors ( Table 10.2 ) lists more than 120 different entities in its original version, including many rare lesions and subtypes. The tumors are classified on the basis of histologic differentiation and are divided into benign, intermediate, and malignant subgroups. Intermediate lesions are benign tumors with locally aggressive behavior such as desmoid-type fibromatosis or low-grade malignancies such as well-differentiated liposarcoma. The classification also includes soft-tissue tumors of unknown origin. Neurogenic soft-tissue tumors have been disregarded in the WHO classification of soft-tissue tumors because they are classified as tumors of neural origin. Entities in this category that are relevant to soft-tissue imaging were adopted from Enzinger and Weiss and added to Table 10.2 .

Fletcher CDM, Unni KK, Mertens F, eds. Pathology and genetics of tumours of soft tissue and bone. In: World Health Organization Classification of Tumours. Lyon: IARC Press; 2002 Weiss SW, Goldblum JR, eds. Enzinger and Weiss′s Soft Tissue Tumors. 4th ed. St. Louis: Mosby; 2001

Staging

Staging of Malignant Bone Tumors

In Europe the clinical staging of a malignant bone tumor is usually based on the classification of the American Joint Committee on Cancer (AJCC) adopted by the Union internationale contre le cancer (UICC) ( Table 10.3 ). This is a TNM system that has been expanded by adding the grade of histologic tumor differentiation (G), which is a key determinant of prognosis. Only the tumor diameter (T1/T2) and the presence of skip lesions (T3) are relevant for describing local tumor extent. Skip lesions, which are bony metastases occurring in the same bone as the primary tumor, are best detected or excluded by magnetic resonance imaging (T1-weighted spin-echo sequence). Regional lymph node metastases (N1) are very rare with bone tumors. Distant metastasis occurs predominantly to the lung (M1a) and rarely to other organs (M1b).

Staging of Soft-Tissue Sarcomas

As far as local tumor extent is concerned, the staging system for soft-tissue sarcomas ( Table 10.4 ) differs only in its designation of tumor size (T1/T2) and lesion location relative to the muscle fascia (a/b). Superficial tumors are subcutaneous lesions that are entirely superficial to the muscle fascia and show no fascial invasion. Deep tumors may be entirely beneath the fascia, above the fascia and invading it, or both above and beneath the fascia. Retroperitoneal, mediastinal, and pelvic soft-tissue sarcomas are classified as deep tumors.

Lymph node metastases (N1) are rare with soft-tissue sarcomas. Distant metastasis (M1) occurs predominantly to the lung.

AJCC. Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010 Peabody TD, Gibbs CP Jr, Simon MA. Evaluation and staging of musculoskeletal neoplasms. J Bone Joint Surg Am 1998; 80(8):1204–1218

World Health Organization classification of bone tumors (Fletcher et al 2002)
Classification
Cartilage tumors Osteochondroma Chondroma Enchondroma Periosteal chondroma Multiple chondromatosis Chondroblastoma Chondromyxoid fibroma Chondrosarcoma Central, primary and secondary Peripheral Dedifferentiated Mesenchymal Clear cell
Osteogenic tumors Osteoid osteoma Osteoblastoma Osteosarcoma Conventional Chondroblastic Fibroblastic Osteoblastic Telangiectatic Small cell Low-grade central Secondary Parosteal Periosteal High-grade surface
Fibrogenic tumors Desmoplastic fibroma Fibrosarcoma
Fibrohistiocytic tumors Benign fibrous histiocytoma Malignant fibrous histiocytoma
Ewing sarcoma and PNET Ewing sarcoma
Hematopoietic tumors Plasma cell myeloma Malignant lymphoma, NOS
Giant cell tumor Giant cell tumor Malignancy in giant cell tumor
Notochordal tumors Chordoma
Vascular tumors Hemangioma Angiosarcoma
Smooth muscle tumors Leiomyoma Leiomyosarcoma
Lipogenic tumors Lipoma Liposarcoma
Neural tumors Neurilemmoma
Miscellaneous tumors Adamantinoma Metastatic malignancy
Miscellaneous/Tumorlike lesions Aneurysmal bone cyst Simple bone cyst Fibrous dysplasia Osteofibrous dysplasia Langerhans cell histiocytosis Erdheim–Chester disease Chest wall hamartoma
Joint lesions Synovial chondromatosis
NOS = Not otherwise specified PNET = Primitive neuro-ectodermal tumor

World Health Organization classification of soft-tissue tumors (Fletcher et al 2002)
Classification
Adipocytic tumors Benign • Lipoma and variants Intermediate Well-differentiated liposarcoma Malignant Liposarcoma (subtypes)
Fibroblastic and myofibroblastic tumors Benign • Nodular fasciitis • Proliferative fasciitis • Proliferative myositis • Myositis ossificans • Ischemic fasciitis • Elastofibroma • Fibrous hamartoma • Fibromatosis (subtypes) • Fibroma, fibroblastoma (subtypes) Intermediate (locally aggressive) • Superficial fibromatosis • Desmoid-type fibromatosis • Lipofibromatosis Intermediate (rarely metastasizing) • Solitary fibrous tumor and hemangiopericytoma • Inflammatory myofibroblastic tumor • Low-grade myofibroblastic sarcoma • Myxoinflammatory fibroblastic sarcoma • Infantile fibrosarcoma Malignant • Fibrosarcoma (subtypes)
Fibrohistiocytic tumors Benign • Giant cell tumor of tendon sheath (GCTTS) • Diffuse giant cell tumor (PVNS) • Deep benign fibrous histiocytoma Intermediate (rarely metastasizing) • Plexiform fibrohistiocytic tumor • Giant cell tumor of soft tissues Malignant • Malignant fibrous histiocytoma (MFH; subtypes)
Neurogenic tumors* Benign • Neuroma and variants • Neurofibroma and variants • Benign schwannoma (neurinoma) and variants • Perineuroma and variants Malignant • Malignant peripheral nerve sheath tumors (MPNST) and variants
Smooth muscle tumors • Angioleiomyoma and variants • Leiomyosarcoma (excluding skin) • Pericytic (perivascular) tumors • Glomus tumor and variants • Malignant glomus tumor • Myopericytoma
Pericytic (perivascular) tumors • Glomus tumor and variants • Malignant glomus tumor • Myopericytoma
Skeletal muscle tumors Benign • Rhabdomyoma and variants Malignant • Rhabdomyosarcoma (subtypes)
Vascular tumors Benign • Hemangioma and variants • Angiomatosis • Lymphangioma Intermediate (rarely metastasizing) • Hemangioendothelioma and variants • Kaposi sarcoma Malignant • Epithelioid hemangioendothelioma • Angiosarcoma of soft tissue
Chondro-osseous tumors • Soft-tissue chondroma • Mesenchymal chondrosarcoma • Extraskeletal osteosarcoma
Tumors of uncertain differentiation Benign • Myxoma and variants • Pleomorphic hyalinizing angiectatic tumor • Ectopic hamartomatous thymoma Intermediate (rarely metastasizing) • Angiomatoid fibrous histiocytoma • Ossifying fibromyxoid tumor • Mixed tumor/myoepithelioma/parachordoma Malignant • Synovial sarcoma • Epithelioid sarcoma • Alveolar soft part sarcoma • Clear cell sarcoma of soft tissue • Extraskeletal myxoid chondrosarcoma • Extraskeletal Ewing tumor/PNET • Desmoplastic small round cell tumor • Extrarenal rhabdoid tumor • Malignant mesenchymoma • Intimal sarcoma
* From Enzinger and Weiss classification of neurogenic tumors, simplified.

American Joint Committee on Cancer/Union internationale contre le cancer 2010 staging system for bone tumors
Stage	T (primary tumor)	N (regional lymph nodes)	M (distant metastasis)	G (grade)
IA	T1	N0	M0	G1–2 low grade, GX
IB	T2 T3	N0 N0	M0 M0	G1–2 low grade, GX G1–2 low grade, GX
IIA	T1	N0	M0	G3–4 high grade
IIB	T2	N0	M0	G3–4 high grade
III	T3	N0	M0	G3–4
IVA	Any T	N0	M1a	Any G
IVB	Any T	N1 Any N	Any M M1b	Any G Any G
Primary tumor: T1 = Tumor 8 cm or less in greatest dimension T2 = Tumor more than 8 cm in greatest dimension T3 = Discontinuous tumor(s) at the primary bone site, skip lesion(s) Regional lymph nodes: N0 = No regional lymph node metastasis N1 = Regional lymph node metastasis Distant metastasis: M0 = No distant metastasis M1 = Distant metastasis M1a = Lung M1b = Other distant sites Histologic grade: G1 = Well-differentiated, low grade G2 = Moderately differentiated, low grade G3 = Poorly differentiated, high grade G4 = Undifferentiated, high grade

American Joint Committee on Cancer/Union internationale contre le cancer 2010 staging system for soft-tissue sarcomas
Stage	T (primary tumor)	N (regional lymph nodes)	M (distant metastasis)	G (grade)
IA	T1a T1b	N0 N0	M0 M0	G1, GX G1, GX
IB	T2a T2b	N0 N0	M0 M0	G1, GX G1, GX
IIA	T1a T1b	N0 N0	M0 M0	G2, G3 G2, G3
IIB	T2a T2b	N0 N0	M0 M0	G2 G2
III	T2a, T2b Any T	N0 N1	M0 M0	G3 Any G
IV	Any T	Any N	M1	Any G
Primary tumor: T1 = Tumor 5 cm or less in greatest dimension T1a = Superficial tumor T1b = Deep tumor T2 = Tumor more than 5 cm in greatest dimension T2a = superficial tumor T2b = Deep tumor Regional lymph nodes: N0 = No regional lymph node metastasis N1 = Regional lymph node metastasis Distant metastasis: M0 = No distant metastasis M1 = Distant metastasis Histologic grade (National Federation of French Cancer Centers [FNCLCC] system preferred): G1–G3.

Staging system for musculoskeletal tumors of the Musculoskeletal Tumor Society (source: Enneking et al 1980)
Stage	G (grade)	T (primary tumor)	M (distant metastasis)
IA	1	1	0
IB	1	2	0
IIA	2	1	0
IIB	2	2	0
III	1 or 2	1 or 2	1
Grade: G1 = Low grade G2 = High grade Primary tumor: T1 = Intracompartmental (intra-articular/superficial to deep fascia/paraosseous/intrafascial compartment) T2 = Extracompartmental (soft-tissue extension/intrafascial extension/intraosseous or extrafascial extension/extrafascial compartment) Distant metastasis: M0 = No distant metastasis M1 = Distant metastasis