Small for size (SFS) syndrome is a condition which causes considerable confusion partly because the term has been extended beyond its original meaning. It was initially used to describe the situation in liver transplantation where a patient develops liver dysfunction and ascites because the donated organ is too small for the recipient. It is now used variably to describe any circumstance where there is post operative liver failure or dysfunction in a patient who has had liver resection or partial or small graft liver transplantation.
I think the key to simplifying SFS syndrome is to think of the cause of the liver dysfunction and the circulation of the patient.
High flow small volume SFS syndrome.
This is the archetypal small for size syndrome. This occurs in the setting of liver transplantation with partial liver transplants or small grafts transplanted into a recipient. The key contributing factors are that the recipient has a high portal vein blood flow commensurate with cirrhosis and a hyperdynamic visceral circulation and the graft recipient weight ratio is small. It is thought that small for size syndrome in this context is driven by endothelial activation and shear stress causing release of RAGE and other molecules. SFS in this setting does not present immediately but may take several days to develop.
Clinical symptoms include the development of large volume ascites and deterioration in liver function tests with or without encephalopathy. Treatment focuses on attempts to reduce portal vein flow. Medical management with terlipressin, beta blockers or somatostatin analogues has been attempted (these drugs are used to reduce portal hypertension). Splenic artery embolization has also been used and can produce a rapid resolution in SFS syndrome. Surgical modification of portal inflow has also been used either by splenic artery ligation or portocaval venous diversion to reduce liver inflow. The latter procedure is easier to draw than to do!
Reduction of portal flow can reverse SFS but in resistant cases liver failure may ensue requiring urgent retransplantation.
(Hepatic vein outflow can also produce high volume ascites and deterioration of liver function and although this usually presents later it is an important differential diagnosis to exclude).
Poor function small volume small for size syndrome
When a patient is left with a small functional liver volume after resection they may also develop liver dysfunction or failure. This too has been termed small for size syndrome although it used to be termed simple post operative liver failure. The important difference here is that portal hypertension is not an issue and the patient does not have a hyperdynamic cirulation. The problem is that the residual functional liver volume is too small for the patient in terms of its metabolic and detoxifying functions.
Factors predisposing to this kind of liver dysfunction include, preoperative chemotherapy associated changes such as sinusoidal obstruction syndrome, steatosis or steatohepatitis. Previous studies including our own have shown that in healthy liver a cut off future liver remnant volume of approximately 25% is necessary to avoid the risks of postoperative liver failure and infection. This minimum volume may need to be increased where there is underlying liver disease secondary to chemotherapy, obesity or chronic inflammation.