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 reported and are sometimes difficult to recognize. To characterize the morphologic spectrum of focal nodular hyperplasia, we studied 305 lesions surgically resected from 168 patients. Clinicomorphologic correlations were established by statistical analyses. The patients included 150 women and 18 men (sex ratio, 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 1 mm to 19 cm in diameter. Only 49% of these lesions had one to three macroscopic scars. Histologically, 245 (80.3%) lesions were of classical form, and 60 (19.7%) lesions were nonclassical. The latter were classified as focal nodular hyperplasia of telangiectatic form (47 lesions), of mixed hyperplastic and adenomatous form (five lesions), and with atypia of large 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 nonclassical forms. The absence of a central scar could explain the difficult preoperative diagnosis of some of the cases. The morphologic diagnostic criteria in this study require further prospective evaluation.