Benign Hepatic Lesions Arising in Accessory Hepatic Lobes

An accessory hepatic lobe is an uncommon hepatic congenital anomaly that can sometimes mimic a mass lesion clinically and radiologically. Because accessory hepatic lobes are only rarely resected, detailed descriptions of their histologic features are sparse. We report the histologic and immunohistochemical features of 3 cases of resected accessory hepatic lobes, all of which contained benign hepatic lesions (2 hepatic adenomas [HAs] and 1 focal nodular hyperplasia). All accessory lobes were connected to the liver by a pedicle. Histologically, all lesions demonstrated no cytologic or architectural atypia. Based on immunohistochemical analysis, 1 HAwas classified as inflammatory type (positive for C-reactive protein and serum amyloid A), and 1 was unclassified type (negative for C-reactive protein, serum amyloid A, glutamine synthetase, and beta-catenin and positive for liver fatty acid-binding protein); the focal nodular hyperplasia showed the typical map-like staining pattern with glutamine synthetase. Interestingly, multiple foci of myelolipoma were identified within the unclassified-type HA. Of note, in all cases, the nonlesional hepatic parenchyma featured structural vascular abnormalities of the hepatic artery branches, including abnormal thickening of arterial branches and multiple arterial branches per single portal tract. Our findings describe, for the first time, benign hepatic lesions arising in accessory hepatic lobes and suggest that accessory lobes are perhaps prone to such benign lesions because of structural abnormalities in their vasculature.