liver transplantation postoperative assessment
Ultrasound plays a key role in the postoperative monitoring of liver transplant patients. Numerous complications are possible and many of these can be diagnosed with ultrasound. The operation is generally followed by ciclosporin immunosuppression. Blood levels of ciclosporin are a closely monitored balancing act; too low and the graft may reject, too high and the toxic effects of the drug may affect the kidneys. Liver function is biochemically monitored for early signs of complications. Elevated serum bilirubin, alkaline phosphatase and/or aminotransferase levels are present with most types of graft dysfunction or complication and are investigated first with ultrasound. Renal dysfunction is a further recognized complication following transplant. This can be due to various causes, including ciclosporin nephrotoxicity, intraoperative hypotension or preoperative renal failure.
liver transplantation postoperative ultrasound appearances
The vessels and vascular anastomoses
These are potential sites of complication in terms of thrombosis, stenosis, occlusion or leakage. The hepatic artery is vital to graft success as it is the sole vascular supply to the biliary system. Most hepatic artery occlusions occur relatively soon after operation, before a good collateral supply is able to be established. A blocked hepatic artery quickly results in ischaemia with resultant hepatic necrosis and is therefore treated as an emergency requiring surgicalintervention and, frequently, retransplant. Taken in context with the clinical picture, the patient may proceed immediately to surgery if the ultrasound diagnosis of occlusion is confident. If doubt exists, MRI or X-ray angiography may be performed. Ensure the artery is scanned intercostally to maintain a low vessel-to-beam angle, and that the Doppler sensitivity and filter controls are set for low velocities if arterial flow is not found. Hepatic artery thrombosis or stenosis can lead to bile duct necrosis, causing bile leaks and abscesses, or areas of infarction within the liver tissue. Hepatic artery stenosis/thrombosis is still a relatively common post-transplant complication in up to 12% of adult patients.
Colour Doppler ultrasound detects between 50% and 86% of total occlusions35 and angiography is still considered the gold standard although ultrasound continues to increase its clinical value here. The administration of ultrasound contrast media, whilst potentially useful for detection of flow, is rarely necessary in practice. Stenosis of the artery at the site of anastomosis is detected by examining the Doppler spectrum. The systolic upstroke tends to be delayed (?tardus parvus pattern) downstream of the stenosis;37 the acceleration time is increased (over 0.08 seconds) and the resistance index decreased (less than 55) in many cases. Both or either of these indices may be affected, giving a sensitivity and specificity of 81% and 60% for the diagnosis of hepatic artery stenosis with Doppler. The appearance of the hepatic artery waveform immediately postoperatively is often one of a small spike with no EDF. This is not a significant finding and will usually develop into the more familiar waveform with forward EDF by 48 hours after transplantation.
The PV anastomosis is readily demonstrated at the porta. The waveform invariably shows turbulence associated with the anastomotic site, as the diameters of the donor and recipient veins invariably differ. This is not significant in itself but can indicate a clinically significant stenosis when accompanied by high velocities of greater than 100 cm/sec.
PV stenosis also causes a steadily increasing spleen size, which is why it is important to have a baseline measurement of the spleen. PV thrombosis should only be diagnosed using the correct Doppler settings (low pluse repetitions frequency and optimum colour gain) and at an angle as near parallel to the beam as possible. In the absence of colour flow, power Doppler may be helpful in confirming thrombosis, as it is less angle-dependent, and contrast may be used to increase the level of confidence. It is also possible to have a blocked main PV with patent intrahepatic PVs, due to collateral formation. The IVC infrahepatic anastomosis is also readily seen on ultrasound (Fig. 4.32). Because of the near-perpendicular angle of the IVC to the beam it is difficult to assess blood flow velocity in the IVC. Power Doppler is helpful in confirming patency in technically difficult cases as it is angle-independent. Thrombosis in the IVC is a relatively rare complication of transplants, accounting for fewer than 3% of patients. If the transplant has been performed for BCS, pay particular attention to the hepatic veins, which show a tendency to re-thrombose in some patients.
The common bile duct
This should be carefully monitored postoperatively. A measurement serves as a baseline from which to detect small degrees of dilatation which may imply stenosis or obstruction. Even relatively minor dilatation can be significant in the transplant patient; cholestasis can precipitate ascending biliary infection which may subsequently form liver abscesses, a process which may be aggravated by immunosuppression. Biliary complications occur in up to 15% of transplants and most biliary complications become evident during the first 3 months, although late stenosis can occur after this. Strictures commonly occur at the anastomosis due to scar tissue, but other, non-anastomotic strictures can result from hepatic artery insufficiency causing ischaemia. Leakage is a comparatively rare event.
Focal lesions
Focal lesions within the parenchyma of the transplant liver are usually a poor prognostic indicator. Hepatic abscesses may be multiple and are often acoustically subtle in the early stages, with echo patterns closely similar to normal liver tissue. Other causes of focal lesions in the early postoperative period may be due to infarction and are associated with interruption of the arterial supply. These can be hyper- or hypoechoic, have welldefined borders and do not exert a mass effect. The longer the interval between removing and transplanting the donor liver, the greater the likelihood of ischaemic patches forming. In patients who have been transplanted following cirrhosis with malignancy, recurrence of HCC may also be a serious complication. Post-transplant lymphoproliferative disorder may also demonstrate hypoechoic focal lesions within the liver, occasionally also involving the spleen and kidneys.
Fluid collections
These can frequently be demonstrated and monitored with ultrasound. These may represent haematoma, seroma, loculated ascites or biloma. It is not possible to differentiate different types of collection with ultrasound alone. The appearances are taken in conjunction with the clinical features and the role of ultrasound is primarily to monitor the gradual resolution of the collection. It is important to determine if a collection is infected in a clinically ill patient. This cannot be done on the ultrasound appearances alone and guided aspiration is usually required. Haematomas frequently resolve if left untreated. However, a large haematoma could result from an anastomotic leak requiring surgical intervention. A leaking bile duct anastomosis is potentially a serious complication which could cause peritonitis. Drainage under ultrasound guidance is a temporary option but surgical repair is invariably necessary. Recent recipients of liver transplants will often have some free intraperitoneal fluid and a right pleural effusion, which resolve spontaneously.
Rejection
Rejection episodes are common in the first 2 weeks after transplantation. Graft rejection may be acute, in which case the immunosuppression is increased, or chronic following several acute episodes. Chronic rejection can only be treated by retransplantation. Rejection does not have any specific ultrasound features on either conventional imaging or Doppler, and the diagnosis is made from a liver biopsy following clinical suspicion.
Post-transplant malignancy
Because of the immunosuppression, patients are at greater risk than normal for developing malignancy. Most of these manifest as post-transplant lymphoproliferative disorder (similar in appearance to non-Hodgkins lymphoma) which can affect the lymphatics, gastrointestinal tract or other organs, including the transplanted liver. The most commonly found ultrasound appearances include focal, hypoechoic liver lesions and lymphadenopathy. Patients with malignant lesions pretransplant, such as HCC or cholangiocarcinoma, have a significant risk of recurrence after transplantation.
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