ABSTRACT
Extraarticular diffuse tenosynovial giant cell tumor is an unusual lesion the cytologic picture of which has not been discussed much in the literature. Fine needle aspiration biopsy of a nonpainful mass in the right shoulder in an 18-year-old woman revealed a highly cellular lesion consisting of polygonal cells and multinuclear giant cells with scant nuclear pleomorphism and a marked tendency toward xanthomization. Electron microscopy identified two basic cell populations among many intermediate forms: cells with scant filopodia and abundant ribosomes and cells with well-developed prolongations and numerous mitochondria, lysosomes and lipid drops. The karyotype of the tumor cells obtained from a surgically excised specimen showed a clonal population with 45, XX, t(1;2) (pter->p22::q24->pter), t(1:14)(qter->p13::q13->ter). The cytologic differential diagnosis included other tenosynovial lesions containing xanthomatous cells. Cytogenetic findings are discussed in relation to chromosomal alterations previously found in related lesions (nodular tenosynovitis and pigmented articular villonodular synovitis).
