Prominent Pseudoacini in Focal Nodular Hyperplasia

Abstract

Pseudoacini are generally a morphologic feature of hepatocellular carcinoma (HCC), being absent or rare in benign hepatocytic tumors, such as hepatocellular adenoma. However, rarely these can be seen in focal nodular hyperplasia (FNH) and may pose diagnostic challenges, especially when prominent. The study was aimed to evaluate the occurrence of pseudoacini in FNH and their clinicopathologic correlations. A total of 95 FNH cases diagnosed from 2005 to 2020 were included in the study. A pseudoacinus was defined as a circular arrangement of hepatocytes around a central dilated lumen present within the lobular parenchyma of the lesion with or without inspissated bile. Among the 95 FNH cases, 28 (29.5%) showed pseudoacini, which were prominent in 12 (12.6%) cases. Of these 3 occurred in patients above 50 years old. The pseudoacini were numerous in 3 cases, leading to an initial consideration of HCC in the differential diagnosis, and 1 case was diagnosed as well-differentiated hepatocellular neoplasm on initial biopsy. All 12 cases showed map-like staining pattern for glutamine synthetase. The hepatocytes forming the pseudoacini were positive for CK7 and HepPar1, while the inner lumina were highlighted by CD10 and bile salt export pump immunostains similar to adjacent canaliculi. The presence of prominent pseudoacini was not significantly associated with any clinical or pathologic features. The findings suggest that pseudoacini are likely manifestation of hepatocyte biliary transdifferentiation associated with chronic cholestasis in the lesion. This feature may pose a potential diagnostic pitfall especially on needle biopsies and awareness is needed to avoid misdiagnosing this as HCC.

Focal Nodular Hyperplasia in the Pediatric Population: A Multicenter Experience

“…19 Some of the atypical findings described in FNH include cytologic atypia, unpaired vessels, steatosis, and pseudoacini, among others. 6,[13][14][15]20 In our study, none of the cases showed cytologic atypia of hepatocytes. Unpaired vessels were common and present in 66% of cases which is like our cohort of adult patients (65%).…”

“…The classic pathologic features of FNH includes a benign hepatocellular proliferation containing a central scar from which multiple fibrous septa radiate and in which dystrophic vessels can often be seen; the fibrous septa usually have lymphocytic inflammation as well as a prominent ductular reaction. 6,[12][13][14][15] By definition, no portal tracts are identified within the lesion and the hepatic plates are 1-2 cell thick with an intact reticulin framework. Although FNH is usually a morphologic diagnosis, in biopsies lacking all the morphologic features immunohistochemical stains can be useful to confirm the diagnosis, particularly GS which shows overexpression in the lesion compared to the background liver in a map-like pattern on low-power examination.…”

“…Pseudoacini formation was defined as the arrangement of hepatocytes in a circular fashion with a central lumen with or without bile plug. 6 Medium to large sized vessels with a prominent muscular layer present within the fibrous septa and/or central scar were considered dystrophic vessels. Cholate stasis was defined as the presence of swollen hepatocytes with concentration of the cytoplasm in the perinuclear region resulting in a clear cytoplasm (hydropic change) in the other regions.…”

“…3 Regarding FNH, there are a limited number of studies with exclusively pediatric patients, and they are predominantly focused on the clinical and imaging features with very little, if any, pathologic characterization. [4][5][6][7][8][9] In these studies, FNH in pediatric patients were commonly associated with history of malignancy or hematopoietic conditions treated with stem cell transplantation (SCT). Additionally, pediatric patients with a history of malignancy tended to present with multiple FNHs which were asymptomatic and smaller in size.…”