N AT U R E R E V I E W G E H ; M AY 2 0 1 4

PVT: IMAGING IN CLINICAL DECISION-MAKING

KURDISTAN BOARD GEH JOURNAL CLUB

PVT: ABSTRACT

A frequent & potentially life-threatening condition with various causes including liver cirrhosis, HCC, other solid tumours, abd septic foci, acute pancreatitis, haematological malignancies &congenital or acquired prothrombotic disorders.

Clinical decision-making is a particularly complex process owing to the heterogeneity of the population affected by this condition & the lack of high-quality evidence from RCTs for anticoagulation therapy.

A flowchart to use imaging in diagnosis based on current evidence is followed.

PVT: ABSTRACT

Non-malignant causes:Liver cirrhosis

Abdominal septic foci

Acute pancreatitis

Prothrombotic disorders (congenital or acquired).

PVT: ABSTRACT

Malignant causes:HCC

Other solid tumours.

Haematological malignancies.

PVT: INTRODUCTION

PVT indicates the presence of a clot in the PV lumen or a permanent obliteration of the portal vein as a result of prior thrombosis with replacement by numerous tortuous venous channels ( cavernoma).

PVT can be located in the intrahepatic&/or the extrahepatic venous tracts & can extend to the splenic & superior mesenteric veins.

Thrombosis can also be restricted to the SV&/ or SMV& altogether these conditions are known as ‘thrombosis of the portal venous system’.

PVT: INTRODUCTION

The prevalence of PVT in necropsy is 1%. Rare in the general population . > With pre-existing cirrhosis or neoplastic diseases, particularly HCC. >60% of cases of non-cirrhotic, nonmalignant PVT are associated with

congenital or acquired thrombophilic disorders, hypercoagulable states or prothrombotic diseases.

in 30% of cases an additional known risk factor (namely, a local factor, such as a septic focus) can be identified.

PVT prevalence in cirrhosis:10–25%,highest in advanced decomp cirrhosis.

Risk factors for PVT in cirrhosis partially known& the result of a complex interaction between the 3 factors of the Virchow’s triad—stasis, hypercoagulability &endothelial dysfunction.

PVT: INTRODUCTION

PVT clinical presentation is extremely variable:Asymptomatic: identified during imaging for an alternative

reason.To devastating episodes complicated by intestinal infarction. Acute PVT is often asymptomatic or paucisymptomatic in

patients without underlying liver diseases But can present as an acute process characterized by abdominal

pain, fever &/or features of intestinal venous ischaemia. In up to 30% of acute PVT cases, splenomegaly &minimal

ascites are already present.

PVT: INTRODUCTION

The effect of PVT on the clinical outcome of patients with cirrhosis is controversial, but at least in some patients, it can result in worsening of pre-existing portal hypertension with development of ascites or variceal bleeding.

It is an independent negative prognostic factor for post-transplantation survival in patients who are on a waiting list for liver transplantation.

In patients with cirrhosis& HCC, the onset of malignant PVT indicates an advanced stage of the disease in which locoregional therapy is no longer indicated.

PVT: INTRODUCTIONAnticoagulants are effective in recanalization in around 40% with

acute PVT.

Anticoagulants are safe in patients with a healthy liver & with cirrhosis.

A prompt & accurate diagnosis of prothrombotic disorders is always required.

Most patients with long-lasting chronic PVT, present with complications of portal hypertension (oeso varices, variceal bleeding&hypersplenism).

In these patients, surgical treatment or TIPS are often needed after meticulous evaluation by clinicians.

PVT: CIRRHOSIS VS NON

U/S is the best method to assess whether PVT has taken place on the background of a healthy or a cirrhotic liver.

The single most accurate sign of cirrhosis on U/S is liver surface nodularity, best by using high-frequency probes.

Changes in the morphology of the liver, such as caudate lobe hypertrophy & atrophy of the right liver lobe, can be seen by any of the 3( U/S, CT or MRI) ,but have poor specificity for cirrhosis, as they can be found in long-lasting no-ncirrhotic PVT as a consequence of lobar perfusion alterations&curling of hepatic veins cannot be considered specific for cirrhosis in patients with PVT.

PVT: CIRRHOSIS VS NON

In unclear cases, more specific signs of altered liver morphology should be analysed using CT or MRI.

The atrophy–hypertrophy complex (which includes atrophy of the right liver lobe &lateral segment of the left liver lobe, together with hypertrophy of the caudate lobe &the fourth liver segment) can be found in up to 91% of patients with non-cirrhotic cavernomatosis, usually absent in patients with cirrhosis.

Despite these different findings, long-lasting PVT, in particular that occurring in patients with idiopathic portal hypertension, is sometimes indistinguishable by standard imaging from the appearance of PVT in patients with cirrhosis.

PVT: CIRRHOSIS VS NON

In most patients in whom U/S & CT/ MRI cannot provide a conclusive answer regarding the presence of underlying cirrhosis, transient elastography can be successfully used.

New sonoelastography, which can be applied in real-time to both the liver & spleen (including acoustic radiation force-impulse imaging &shear wave elastography), might represent an important advance in the near future, but no study data are available so far.

Liver biopsy remains the gold-standard technique in patients who cannot be classified by noninvasive methods&further investigation is needed to better define imaging surrogates of diagnosis.

PVT:PANCREATITIS & SEPTIC FOCI

Pancreatitis cause PV system thrombosis in up to 2%.

The patency of the portal, splenic & mesenteric veins should be assessed by imaging.

Septic foci that increases the risks should be actively searched.

CT & MRI are more accurate than U/S for assessing the presence of abd septic foci such as diverticulitis or abd abscesses.

CT should be considered the method of choice in patients with fever or symptoms suggestive of infection.

PVT: HEPATIC & EXTRAHEPATIC CANCER

U/S is the screening method of choice to identify potentially malignant nodules in cirrhosis.

The presence of hepatic metastasis or extrahepatic malignancies (sp pancreatic cancer) causing direct invasion of the portal vein should be carefully evaluated during U/S performed for PVT.

U/S alone is not accurate enough to characterize nodules in cirrhosis&is insufficiently sensitive to rule out intrahepatic metastasis or extrahepatic abdominal tumours in cases of negative findings.

CT or MRI should be used to accomplish a comprehensive abdominal assessment in patients with newly diagnosed PVT.

PVT: BENIGN VERSUS MALIGNANT THROMBOSIS IN HCC

Malignant invasion of PV occurs in 12–30% with HCC.

Nonmalignant PVT described in in HCC &cirrhosis.

Presence of malignant PVT contraindicates locoregional therapies&liver transplantation,so an accurate, extensive imaging work-up is needed in any case of PVT arising in patients with cirrhosis& HCC, including those patients in whom the tumour has been treated by curative therapies.

PVT: BENIGN VERSUS MALIGNANT THROMBOSIS IN HCC

Specific signs of malignant (neoplastic) PVT include:

Expansive (enlargement of PV due to mass-forming thrombus).

Disruption of the vessel’s walls.

Intrathrombus arterial neovascularization , by CDUS or PWUS&much better by contrast-enhanced imaging.

Hyperenhancement in the arterial phase & wash-out in the late phase are typical features of HCC & HCC-related PVT invasion on CEUS, CECT& CEMRI.

Abnormal enhancement due to malignant thrombosis in HCC can also be identified by arteriography in early phases by thread &streak sign(thin linear or chainlike opacification in the portal vein after the injection of contrast, reflects neovessels within the tumour cast.

Diffusion-weighted MRI & dual-energy CT is helpful to diff between benign& malignant thrombus.

Finally biopsy of the thrombus should be considered for conclusive diagnosis.

PVT: THE EXTENT

The chance of achieving recanalization by anticoagulant therapy in patients with acute noncirrhotic PVT decrease:

In patients who have complete PVT compared with those who have mural PVT.

Involvement of >one vessel, or complete thrombosis of the whole portal venous system.

The presence of abdominal fluid.

PVT: THE EXTENT

In chronic PVT the extent of thrombosis is also central to planning treatment strategies to decompress the portal system in case of complications.

Derivative surgery for portal hypertension & liver transplantation are only feasible if at least one of the main vessels of the portal venous system is patent; for example, PV or SMV in liver transplantation.

U/S not accurate enough for excluding thrombosis extension to the SV or to the SMV ,so CECT or CEMRI is indicated to evaluate thrombosis extent after PVT diagnosed by U/S & the number, position, size of abdominal portosystemic collaterals.

PVT: THE EXTENT

Common collaterals include those arising from left & short gastric veins usually feeding GE varices& spleno-renal collaterals& ectopic collaterals(outside the EGJ)

Ectopic collaterals are more common in patients with PV system thrombosis(up to 40% ) &include vessels in the gallbladder wall, transparietal hepatic vessels, at site of biliary–enteric& entero-cutaneous surgical anastomosis.

Collaterals can be of importance for planning effective trt programmes & large collaterals might be used in selected patients with a complete thrombosis of PVS to attempt surgical shunting or portal reconstruction on liver transplantation.

PVT: PORTAL HYPERTENSIVE BILIOPATHY

Abno of biliary system&GB due to extrinsic vascular compression by collats

ERCP or MRI show some degree of portal cholangiopathy in >80% with portal cavernoma.

Few develop symptoms & labo tests are not useful to predict symptoms.

MRC is the noninvasive procedure of choice &findings correlate with the risk of developing clinical symptoms, which are limited to patients showing dilatation of the biliary tree (grade 3 portal cholangiopathy).

MRC should be performed at the time of diagnosis in chronic PVT & after 9–12 months of acute PVT if anticoagulants does not achieve recanalization to assess the presence of portal cholangiopathy at risk of later complications.

if grade 3 portal cholangiopathy has not developed at the 12 month follow-up, no further MRC exam is needed, as no progression is expected to occur.