Sinusoidal obstruction syndrome

Sinusoidal obstruction syndrome (SOS), previously known as hepatic veno-occlusive disease (VOD), is a condition arising from occlusion of hepatic venules.

Clinical presentation

• right upper quadrant pain

• painful hepatomegaly

• ascites

• abnormal liver function tests

Pathology

Toxic injury to liver sinusoids causes sloughing of endothelial cells that embolise to hepatic venules and cause eventual fibrosis of the venules. This results in hepatic congestion (similar to Budd-Chiari syndrome) and post-sinusoidal portal hypertension.

Aetiology

• bone marrow transplantation

• chemotherapeutics ⁶

  • gemtuzumab, inotuzumab ozogomicin

  • bleomycin, carmustine

  • 6-thioguanine, vincristine

  • oxaliplatin, carboplatin

• immunomodulators

  • azathioprine

  • sirolimus

• pyrrolizidine alkaloids

  • plant-derived toxins, common sources of exposure include ⁷:

    • comfrey tea (Symphytum species)

    • ragwort (Senecio species)

    • bush tea (Crotalaria species)

• oral contraceptives

• chronic ethanol use

• radiation exposure

Radiographic features

Ultrasound

The imaging modality of choice, which may show:

• hepatomegaly 

• splenomegaly

• portal venous abnormalities:

  • portal vein dilatation

  • portal venous pulsatility

  • decreased portal venous flow velocity

    • may progress to hepatofugal flow

• hepatic arterial abnormalities

  • elevated hepatic artery resistive index (> 0.8)

  • elevated peak systolic velocities in the common and left hepatic arteries ⁸

• hepatic venous abnormalities

  • loss of characteristic triphasic hepatic venous flow

  • decreased venous diameter (< 3 mm, measured 2 cm from the IVC)

• gallbladder wall thickening (> 6-8 mm)

• ascites

CT

• hepatomegaly

• nutmeg liver

• portal vein dilatation

• ascites

MRI

MRI studies with hepatocyte-specific contrast agent show a diffuse hypointense reticular pattern on post-contrast T1 delayed hepatobiliary phase as a highly specific sign for the diagnosis.

Treatment and prognosis

There is no standard treatment regimen but options include:

• anticoagulation

• vasodilators

• defibrotide

• supportive care

Preoperative planning for hepatic metastasectomy should include exclusion of SOS after the use of chemotherapy as there is an increased risk of postoperative liver failure.

Approximately half resolve but high mortality in severe cases (up to 90%).

Complications

• hepatic failure

• portal hypertension

• death