Fig. 2

Morphological change of the tumor. a, Grossly, the mass was well circumscribed, with a firm and grey-white cut face. b, The tumor was encapusuled by the fibrous capsule. c, The tumor was composed predominantly of papillary structures with fibrovascular cores. d, The abundant hyalinized collagen with few cells was focally present in the core of the papillary structure. e, Numerous histiocytes was present in the outer spaces of papillary structures, which might cause a diagnostic confusion. f, The lining cells were columnar or cuboidal with mild atypia and extremely rare mitosis, and numerous nuclear inclusions