Table 1 Diagnostic criteria for columnar cell lesions without atypia (columnar cell change and columnar cell hyperplasia) and flat epithelial atypia^{11, 13}

TDLUs with variably dilated acini

TDLUs with variably dilated acini

TDLUs usually bluer than normal at low power

Acini lined by one to two cell layers

Acini lined by cells that show stratification (more than 2 cell layers); may form tufts, but complex architectural patterns (rigid bars, bridges, well-formed micropapillations) are absent

Acini lined by cells with low-grade (monomorphic type) cytologic atypia; cells most often resemble those seen in low-grade DCIS. Flat growth pattern (no complex architectural patterns). Features do not fulfill combined architectural and cytologic criteria for diagnosis of ADH or DCIS

Lining cells have uniform, ovoid to elongated nuclei oriented perpendicular to basement membrane; nucleoli absent or inconspicuous

Lining cells have uniform, ovoid to elongated nuclei oriented perpendicular to basement membrane; nuclei may appear crowded and overlap; nucleoli absent or inconspicuous; cells similar to those seen in columnar cell change

Lining cells have nuclei that are typically round, but may be ovoid in some cases; nucleoli may or may not be prominent. Cells typically lack polarity and are not regularly oriented perpendicular to basement membrane; in some cases, stratified, atypical, ovoid nuclei are arranged perpendicular to basement membrane (resembling the pattern seen in colonic adenomas)

Apical snouts may be present; usually not prominent or exaggerated

Apical snouts often present; may be exaggerated

Apical snouts often present; may be exaggerated

Luminal secretions may be present; usually not prominent

Luminal secretions may be present and prominent

Luminal secretions may be present and prominent

Calcifications may be present

Calcifications often present; may be psamommatous

Calcifications often present; may be psamommatous