World Health Organization Classification of Tumours Pathology and ...

Table 1.08Histologic criteria for focal anaplasia.- Anaplasia must be circumscribed and itsperimeter completely examined(May require mapping of anaplastic foci thatextend to the edge of tissue sections)- Anaplasia must be confined to the renalparenchyma- Anaplasia must not be present within vascularspaces- Absence of severe nuclear pleomorphismand hyperchromasia (severe "nuclearunrest") in non-anaplastic tumour.loose fibromyxoid stroma.An epithelial component of differentiationis present in most nephroblastomas. Thispattern may be manifested by primitiverosette-like structures that are barely recognizableas early tubular forms; othernephroblastomas are composed of easilyrecognizable tubular or papillary elementsthat recapitulate various stages ofnormal nephrogenesis. Heterologousepithelial differentiation may occur, themost common elements being mucinousand squamous epithelium.A variety of stromal patterns may occurand may cause diagnostic difficultywhen blastemal and epithelial differentiation,are absent. Smooth muscle, skeletalmuscle and fibroblastic differentiationmay be present. Skeletal muscle is themost common heterologous stromal celltype and large fields of the tumour oftencontain this pattern. Other types of heterologousstromal differentiation includeadipose tissue, cartilage, bone, ganglioncells, and neuroglial tissue.Post-chemotherapy changesChemotherapy induces necrosis, xanthomatoushistiocytic foci, haemosiderindeposits and fibrosis. Other chemotherapy-inducedchanges include maturationof blastema, epithelial, and stromal components,with striated muscle being themost frequent. Remarkable responsivenessto chemotherapy has resulted incomplete necrosis in some tumours;such cases are considered to be low riskand may receive minimal treatment aftersurgery {259}. In contrast, those tumoursthat do not show response to therapyhave a reduced prognosis and increasedrequirement for therapy.AnaplasiaApproximately 5% of nephroblastomasare associated with an adverse outcomeand are recognized pathologicallybecause of their "unfavourable" histologydue to the presence of nuclear anaplasia{194,318,2952}. Anaplasia is rareduring the first 2 years of life, andABFig. 1.69 Nephroblastoma. A Primitive epithelial differentiation. B Serpentine blastemal pattern.ABFig. 1.70 Nephroblastoma. A Skeletal muscle differentiation. B Cytologic appearance of blastemal cells.50Tumours of the kidney