A 2 month baby presents with history of jaundice, turmeric colored urine and pale stools since birth. Examination reveals liver span of 10 cms. The most specific investigation for establishing the diagnosis would be –
The given clinical picture is suggestive of either of the following diagnosis:

Neonatal hepatiits
Extra hepatic biliary atresia

"Percutaneous liver biopsy is the most valuable procedure in the evaluation of neonatal hepatobiliary disease and provides the most reliable discriminatory evidence".
Biopsy findings of biliary atresia

Bile ductular proliferation                        
Portal or perilobular edema and fibrosis.
Bile plug               
Intact basic hepatic lobular architecture.

Biopsy findings of Neonatal hepatitis

Severe, diffuse hepatocellular disease
Focal hepatocellular necrosis.
No alteration in bile ductules.
Distortion of lobular architecture.
Marked infiltration with inflammatory cells.

Giant cells are seen in both.
Liver function tests
Ultrasound abdomen
Peroperative cholangiogram
Liver biopsy