Distinction between inflammatory hepatocellular adenoma and mass effect on liver sampling

Inflammatory hepatocellular adenoma (IHA) is characterized by sinusoidal dilation, inflammation, and bile ductular reaction. However, these changes can also be seen in nonneoplastic liver tissue adjacent to a mass lesion. This differential may arise in biopsy tissue attempting to sample a liver mass. Serum amyloid A (SAA) immunostaining is useful for the diagnosis of IHA but is not entirely specific. In addition, the histologic pattern of mass effect (ME) has received little formal scrutiny. We compared the clinical, morphologic, and immunohistochemical findings in 18 IHA and 36 livers with ME. Several histologic findings were evaluated in all cases. SAA and CD34 staining were also performed. Patients with IHA were younger (P<.0001) and more often female (P=.0044) than patients with specimens showing ME, but lesions were multifocal on imaging in two-thirds of patients in each category. Unpaired arteries were only seen in IHA (P<.0001), whereas ductular reaction was more common in ME (P=.012). Strong SAA immunostaining was observed in 100% of IHAs and 56% of ME cases (P=.0004), and CD34 staining was seen in 95% of IHAs and 6% of ME cases (P<.0001). Unpaired arteries and staining for SAA and CD34 best distinguish IHA from ME. However, unpaired arteries may be absent because of sampling, and SAA is not available in all laboratories. Ductular reaction can occur in IHA but is more common in ME.