Focal nodular hyperplasia of the liver - A comprehensive pathologic study of 305 lesions and recognition of new histologic forms

Atypical histologic variants of focal nodular hyperplasia have been reporte d and are sometimes difficult to recognize. To characterize the morphologic spectrum of focal nodular hyperplasia, we studied 305 lesions surgically r esected from 168 patients. Clinicomorphologic correlations were established by statistical analyses. The patients included 150 women and 18 men (sex r atio, 8:1; median age, 38 years). One hundred twenty-eight (76.2%) patients had solitary lesions, and 40 (23.8%) had 2 to 30 lesions. All 305 lesions measured I mm to 19 cm in diameter. Only 49% of these lesions had one to th ree macroscopic scars. Histologically, 245 (80.3%) lesions were of classica l form, and 60 (19.7%) lesions were nonclassical. The latter were classifie d as focal nodular hyperplasia of telangiectatic form (47 lesions), of mixe d hyperplastic and adenomatous form (five lesions), and with atypia of larg e cell type (eight lesions). Several benign or malignant tumors were found in association with these lesions. This large retrospective series of focal nodular hyperplasia shows the relative incidence of its classical and nonc lassical forms. The absence of a central scar could explain the difficult p reoperative diagnosis of some of the cases. The morphologic diagnostic crit eria in this study require further prospective evaluation.