Liver Pigmentation
Various substances and conditions can cause pigmentation of the liver.
Congenital melanosis
Can occur in calves and lambs at birth. It is not related to clinical disease. Black discolouration occurs in the capsule and stroma of the liver and these are an abnormal accumulation of melanin pigments.
Haemosiderin
Acuumulation of this pigment occurs in chronic passive congestion and surrounding areas where there has been prior necrosis and haemorrhage. The pigment is found within the Kupfer cells (macrophages of the liver) and this can be visualised using Perl's Prussian Blue stain.
The condition does not cause clinical signs alone, but is the consequence of haemorrhage so this will cause clinical signs. Deposition of large amounts of haemosiderin may result in liver failure.
Lipofuscin
Is a pigment of cellular ageing (it is also names the 'senility pigment') and is insoluble and golden brown in colour.
It occurs within heptatocytes and can be identified using Schmorl's stain where the pigment will appear dark blue. It is commonly seen in hepatocytes near to the centrilobular vein in older cats and is of no clinical significance.
Bile
Bile pigment discolours tissues green and therefore is very noticeable at necropsy. Often, intrahepatic bile caniculi are distended with a greenish pigment and are known as 'bile lakes'. Larger foci are seen in long standing cases when the hepatocytes rupture: the discharged bile is then surrounded by macrophages and perhaps giant cells.
Bile can be stained with Fouchet stain - and appears green.
Bile pigmentation is especially prominent in obstructive jaundice. Underlying causes must be addressed for treatment of this condition.
References
Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science.
Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2), W.B. Saunders Company.
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition), Mosby Elsevier.
Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition), Mosby Elsevier.