What is the role of imaging in the diagnosis of portal vein (PV) complications following whole-liver orthotopic liver transplantation (OLTX)?

Updated: Mar 01, 2019
  • Author: Paul D Russ, MD; Chief Editor: John Karani, MBBS, FRCR  more...
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After aggressive percutaneous thrombolysis, balloo After aggressive percutaneous thrombolysis, balloon dilatation, mechanical thrombectomy, and systemic anticoagulation, patency of the portal vein has been restored. Follow-up portography shows that the portal vein is open. Competing collaterals communicating with the superior mesenteric vein (arrow) and the inferior mesenteric vein (arrowhead) were noted. Subsequently, the collateral gonadal vein draining the superior mesenteric vein to the inferior vena cava was embolized with coils to improve hepatopetal flow.
Transjugular portography demonstrates extensive po Transjugular portography demonstrates extensive portal vein thrombus in the whole-liver allograft of a 40-year-old woman whose clinical condition rapidly deteriorated on postoperative day 39.
Spectral Doppler ultrasonogram of the portal vein Spectral Doppler ultrasonogram of the portal vein was obtained at the onset of graft dysfunction. Compared with the baseline examination, markedly accelerated flow to 150 cm/s was documented. Subsequent catheter venography was performed that documented a high-grade venous stenosis. The stenosis was treated successfully by using balloon angioplasty and stent placement.
Early posttransplantation evaluation of the portal Early posttransplantation evaluation of the portal vein by using spectral Doppler ultrasonography depicts a normal waveform with peak flow velocity of approximately 31 cm/s.

US, CT scanning, MRI, and MRV can be used to detect PVS and PVT, as follows:

  • Short-segment PV narrowing can be depicted by using gray-scale US.

  • An abrupt 3- to 4-fold increase in velocity occurs within the PV, as documented with spectral Doppler US.

  • Aliasing on color Doppler US reflects turbulent flow associated with PVS.

  • PVS can be demonstrated by using conventional CT scanning or MRI; however, this finding is uncommon. Unlike US, conventional CT scanning and MRI are not routinely used to screen for postoperative vascular complications. CT scanning and MRI are more expensive modalities, and the findings can be suboptimal because the PV is oriented obliquely to axial sections, making stenoses and partial thromboses more difficult to appreciate. In addition, PV flow artifacts can be difficult to assess on routine MRI scans.

  • With state-of-the-art magnets and pulse sequences, PVS can be displayed by using a variety of coronal MRV techniques. MRV is usually reserved to confirm PVS suggested by findings on screening US scans.

  • Digital subtraction angiography (DSA) can ultimately be used to diagnose and treat PVS. Splenic, mesenteric, transjugular, and transhepatic portography can be employed. PVS can be successfully corrected in many patients by using percutaneous transluminal balloon angioplasty.

With noninvasive imaging, PVS must be diagnosed with caution. Hemodynamically significant PVS must be distinguished from PV pseudostenosis. Pseudostenosis results when the recipient PV is somewhat larger than the donor PV. The difference in caliber causes increased velocity and turbulence at the anastomosis that are not physiologically significant. If PV narrowing is associated with a velocity increase of less than 3- to 4-fold on spectral Doppler ultrasonographic analysis, the narrowing likely is pseudostenosis. Unlike PVS, pseudostenosis is not associated with impaired graft function or clinical signs of portal hypertension. In equivocal cases, DSA may be necessary to measure the actual pressure gradient across the anastomosis.

PVT also can be diagnosed noninvasively, as described below:

  • On gray-scale sonograms, a hypoechoic–to–mildly hyperechoic filling defect can be seen within the PV. Because a fresh clot can be anechoic and not perceptible on gray-scale US scans, all US examinations should include spectral and color Doppler ultrasonographic analysis of the PV to confirm vessel patency. In patients with complete PVT, no detectable flow is visualized by spectral or color interrogation. Partial PVT may appear as a nonocclusive filling defect on US. Resultant luminal narrowing can be mistaken for PVS with gray-scale, spectral, and color Doppler US. As previously noted, PVS can underlie PVT, which can be difficult to determine by using noninvasive imaging.

  • PVT can be diagnosed with the help of CT scans. The presence of a thrombus is diagnosed most accurately with the use of intravenous (IV) contrast material during the portal venous phase of dynamic scanning. Caution must be exercised not to mistake laminar flow artifact for PVT.

  • Conventional MRI can demonstrate PVT. The age of the clot can affect its signal intensity on T1- and T2-weighted pulse sequences. Because flow artifacts commonly occur in the PV on MRI images, an accurate diagnosis of PVT can be difficult using conventional sequences. A confident diagnosis of PVT often requires the use of robust, nonenhanced or IV contrast-enhanced MRV pulse sequences, usually obtained in the coronal plane.

  • DSA can be used to diagnose and treat PVT. Portography can confirm the presence and extent of a thrombus in the PV. Percutaneous intervention can be successful in restoring venous patency. Techniques include infusion of a thrombolytic (eg, recombinant tissue thromboplastin activator), angioplasty of associated PVS (if present), mechanical thrombectomy, and catheter embolization of competing collaterals.

  • Surgical options in PVT include thrombectomy, segmental PV resection, placement of a jump graft, or creation of a portosystemic shunt. PVT can necessitate retransplantation.

  • Occasionally, PVT is detected in patients with normal allograft function and without portal hypertension. In these patients, sufficient hepatopetal collateralization has developed to maintain adequate venous inflow.

In a study by Torres et al of off-label use of contrast-enhanced ultrasonography to identify circulatory complications after liver transplantation in children, positive predictive value for diagnosing arterial circulatory complications was 80%, and for diagnosing portal vein circulatory complications, 66.7%. [9]

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