DIVERSE HISTOMORPHOLOGY OF OSTEOSARCOMA; ILLUSTRATION OF TWELVE CASES

Abstract

<h3>Background</h3> Head and neck osteosarcomas are rare and comprise less than 1% of tumors of the head and neck. Their management is relegated to specialist head and neck centers, which means that only a small team of head and neck pathologists analyzes the resected tumors. Their rarity and the need to identify malignant osteoid in biopsies makes their diagnosis challenging. <h3>Objective</h3> To highlight the varied histomorphology of head and neck osteosarcoma through a pictorial presentation of 12 cases. <h3>Methods</h3> The histology database at University College London Hospital recorded 124 cases of osteosarcoma in 15 years. Histology reports were reviewed to identify cases with varied histomorphology. <h3>Results</h3> Twelve osteosarcomas were selected, 3 of surface origin and 9 of intramedullary origin. Three were chondroblastic, 7 osteoblastic, and 2 fibroblastic. Seven of the medullary tumors and 2 of the surface tumors were high grade, and 2 medullary and 1 surface tumors were low grade. Diverse features seen in these cases were psammomatoid calcifications, ganglion-like cells, osteosclerosis, osteoclast-like giant cells, and areas resembling benign fibro-osseous lesions, chondromyxoid fibroma, osteochondroma, aneurysmal bone cysts, and osteoblastoma. <h3>Conclusions</h3> Diagnosis of intramedullary and surface osteosarcoma relies on identification of malignant osteoid produced by atypical mesenchymal cells. Other features such as myxochondroid stroma, sclerotic bone, pseudocystic spaces, psammomatoid calcifications, fibroblastic proliferation, chondroblastic tissue, epithelioid osteoblastic population, osteoclast-like giant cells, and osteochondroma-like presentation can be misleading, leading to aberrant diagnosis such as benign fibro-osseous lesion, aneurysmal bone cyst, osteoblastoma, and osteochondroma.