Bone Tumors

Abstract

Bone tumors are rare lesions affecting the skull and vertebral column. Benign bone-forming tumors include osteoma, osteoid osteoma, and osteoblastoma. Osteosarcoma is a malignant bone-forming tumor. Benign cartilage-forming tumors include osteochondroma, enchondroma, chondroma, and chondroblastoma. Chondrosarcoma is a malignant cartilage-forming tumor. Other bone tumors affecting the skull include fibrous dysplasia, chordoma as a notochordal tumor, giant cell tumor, and aneurysmal bone cyst.

Treatment includes depending on the diagnosis surgery, chemotherapy, and radiation.

Osteoma is composed of compact bone arising on the surface of the bone. It is made up of lamellar and woven bone with Haversian-like systems with a cortical-like architecture. Osteoma is a slow-growing lesion. Simple excision leads to excellent outcome with no recurrence.

Osteoid osteoma is characterized by small size (<2 cm), limited growth potential, and disproportionate pain, usually responsive to non-steroidal anti-inflammatory drugs. Radiologically, it presents as a lucent nidus (<1.5 cm) with surrounding sclerotic bone (lesions >1.5 cm are called osteoblastoma). The nidus (1–2 cm) is the central portion of the lesion with differentiated osteoblastic activity. Trabeculae of woven bone are rimmed by osteoblasts. Osteoid osteoma can be treated with radiofrequency ablation, curettage, or resection. Local recurrence rate ranges between 0 and 10%.

Osteosarcoma is a high-grade, intra-osseous, malignant neoplasm in which the neoplastic cells produce bone. Radiologically, it presents as an aggressive, ill-defined bone tumor with bone destruction and soft tumor mass. The neoplastic bone shows woven architecture, primitive disorganized trabeculae, and mineralized bone. Mutations in tumor suppressor genes, i.e., retinoblastoma gene (RB1) (66%) and TP53 gene, have been described. Wnt/catenin pathway, GSK-3ß/NF-κB, and cyclin-dependent kinases (CDKs) are involved. Osteosarcoma is treated by surgery, chemotherapy, and radiation.

Chondroma is a benign, well-circumscribed neoplasm composed of low-cellularity hyaline cartilage. The chondrocytes show fine granular eosinophilic cytoplasm, small round nuclei with condensed chromatin and are situated within sharp-edged lacunar spaces.

Chondrosarcoma is a malignant mesenchymal tumor with cartilaginous differentiation. Radiologically, it presents as a lytic tumor with chondroid calcifications. Histologically, neoplastic chondrocytes are of variable size with moderate amounts of eosinophilic cytoplasm showing cytologic atypia.

Molecular changes involve isocitrate dehydrogenase (IDH), tyrosine kinase, phosphoinositide 3-kinase/AKT/pathway, mammalian target of rapamycin (mTOR), tumor suppressor pathways: retinoblastoma and p53, and hedgehog pathway. Treatment: aggressive curettage to surgical resection followed by radiation.

Fibrous dysplasia is a benign, medullary, fibro-osseous lesion, which may involve one or more bones. Radiologically, it presents as tumor-like growth of fibrous tissue replacing normal bone and causing bone deformation. Molecular changes include the presence of stimulatory alpha subunit of G protein (Gs) in dysplastic bone lesions, mutations in Gsalpha, constitutive elevation in cAMP level induced by the Gsalpha mutations which lead to alterations in the expression of several target genes whose promoters contain cAMP-responsive elements, such as c-fos, c-jun, Il-6, and Il-11. Treatment ranges from observation to surgical removal. Malignant transformation is possible.

Chordoma is a malignant tumor showing notochordal differentiation. It usually arises within bones of the axial skeleton. Histologically, it consists of large epitheloid cells with clear eosinophilic cytoplasm or vacuolated cytoplasm, i.e., physaliphorous cells. The cells are arranged in small ribbons and cords embedded in abundant extracellular matrix. The tumor originates from remnants of embryonic notochord along the spine, more frequently at the skull base and sacrum. Treatment consists of surgery followed by radiation therapy. Prognosis is affected by tumor location, size, and resectability. Local progression is possible. Metastatic spread ranges between 5 and 43%. The tumor can resist chemotherapy and radiotherapy.

Giant cell tumor is composed of cytologically benign, oval, or polyhedral mononuclear cells that are admixed with numerous, evenly distributed, osteoclast-like cells. Radiologically, it presents as a well-defined osteolytic lesion usually without sclerotic margin. Molecular changes involve receptor activator of nuclear factor-κB ligand (RANKL) as well as proteases, including numerous matrix metalloproteinases. Giant cell tumor is treated by surgery, radiation, and RANK ligand inhibitors. Local recurrence rate is of about 25%.

Aneurysmal bone cyst is a destructive, expansile benign tumor with blood-filled cystic spaces. The blood-filled, cystic spaces are separated by fibrous septae which is composed of moderately dense, cellular proliferation of bland fibroblasts, multinucleated, osteoclast-like giant cells, and reactive woven bone rimmed by osteoblasts. Recurrence rate is low; malignant transformation possible (rare).