[Primary malignant bone tumours-part II]

Chondrosarcomas are tumours that typically occur in older adults. Although a few arise de novo, they often develop from pre-existing enchondromas, much more frequently from osteochondromas. In these secondary chondrosarcomas, the primary site of pre-existing chondrogenic lesion plays an important role (close to the trunk, centrally; appendicular skeleton, peripherally). Thus, low-grade chondrosarcomas in the periphery are referred to as atypical chondrogenic tumours (ACT), whereas tumours of the same histopathological type located close to the axial skeleton are called chondrosarcoma grade 1. Syndromal occurrence (Ollier's and Maffucci's diseases) carries a significantly higher risk of malignant transformation. Other malignant primary bone tumours being much less frequent exhibit an unspecific osteolytic morphology but sometimes at a typical location (chordoma: sacrococcygeal region; adamantinoma: tibial shaft; malignant giant-cell tumor [GCT]: epi-metaphyseal expansion). Subsequent histological evaluation frequently reveals the (unexpected) diagnosis. For this reason, one section will focus on tumour mimics and differentiation from benign bone lesions. In this respect, some associated aspects of the well-known Lodwick (Madewell) classifications are discussed in order to highlight three very peculiar bone tumour-associated imaging phenomena (periosteal reactions, aneurysmatic bone cyst-like changes, peritumoral reactive zones).