The hepatic sinusoid is the smallest caliber blood vessel in the liver, and much of end stage liver disease is based on sinusoidal pressures. Portal hypertension can be divided into pre-sinusoidal (portal vein thrombosis), sinusoidal (hepatic fibrosis) and post-sinusoidal conditions (Budd-Chiari Syndrome).
Whenever sinusoids are dilated, you should consider post-sinusoidal conditions. In addition to Budd-Chiari syndrome, cardiac causes like constrictive pericarditis and severe tricuspid regurgitation (right-sided heart failure) are all possible. Abdominal imaging and echocardiography can be helpful with these diagnoses.
Notice in the histology above the wide, dilated sinusoids (the white spaces are prominent on the right side of the biopsy). Early stages of fibrosis is seen in blue.