Liver cysts are thought to arise from malformation of the ductal plate during embryonic liver development. Normal bile ducts arise from the ductal plate through growth and apoptosis. In polycystic liver disease, complexes of disconnected intralobular bile ductules are retained- these complexes are termed von Meyenburg complexes.
The cysts of polycystic liver disease are fluid filled, epithelial lined cavities. They should number > 20 before the PLD label is given. Elevations in alkaline phosphatase and GGT are common (reflecting the activation of cholangiocytes); if bilirubin is elevated it is probably from compression of the common bile duct. CA 19-9 is elevated in 45% of cases; it is produced by cyst epithelium, though does not reflect an underlying malignancy.
In the biopsy shown above, note the complex of tiny cystic structures. This is considered a benign finding. For an interesting review titled ‘Medical and surgical treatment options for polycystic liver disease’, refer yourself to the Drenth JP et al. article in Hepatology, December 2010 (p.2223-30).