Nodular hyperplasia (proliferative hepatocytes maintaining single-celled hepatic cord architecture with normal reticulin support) occurs as a benign, age-related microscopic or grossly apparent small mass lesion in dogs. It is often associated with a vacuolar hepatopathy (VH), lacks a defining remodeled border (as characterizes regenerative nodules), and may be confused histologically with adenomatous hyperplasia or hepatic adenoma (demonstrating proliferative disorganized hepatocytes forming thick hepatic cords with diminished reticulin support).
Although nodular hyperplasia does not cause clinical signs of disease, it can be accompanied by increased liver enzyme activity, particularly alkaline phosphatase. Unless the liver is diffusely remodeled with nodular lesions (secondary to degenerative VH), total serum bile acid concentrations remain normal. Ultrasonographically, nodular hyperplasia is associated with hypoechoic hepatic nodules set against a hyperechoic background (if associated with glycogen-like VH).
Cytology of an aspirate may discriminate dysplastic, neoplastic, or inflammatory cells but cannot exclude any of these disorders. Biopsy is necessary to differentiate between nodular hyperplasia, dysplastic microscopic nodules, regenerative nodules, cirrhosis, and neoplasia.