EUROPEAN JOURNAL OF RADIOLOGY

European Journal of Radiology 19 (1994) 43-49 ELSEVIER

Magnetic resonance angiography in transjugular intrahepatic portosystemic stenting: comparison with contrast hepatic

and portal venography

S. Eustace*, B. Buff, J. Kruskal, M. Roizental, J.P. Finn, H.E. Longmaid, K. Stokes, G.G. Hartnell

The Department of Radiological Sciences, Deaconess Hospital and Harvard Medical khool, 185 Pilgrim Road, Boston, MA 02215. USA

Received 9 May 1994; revision received 22 July 1994; accepted 26 July 1994

Abstract

In order to highlight the role of magnetic resonance angiography [MRA] in the assessment of patients pre-transjugular in- trahepatic portosystemic shunt (TIPS) stenting, the MRA images of portal and hepatic veins of 21 patients were compared with the images from contrast portal and hepatic venograms performed on the same patients at the time of TIPS stenting (20 patients). MRA enabled accurate, non-invasive, multiplanar imaging of portal and systemic venous anatomy in each of the patients studied. MRA facilitated accurate determination of vessel patency and flow direction, images correlating exactly with contrast venograms of hepatic and portal veins in each case. In one patient, identification of occult hepatocellular carcinoma extending to the portal vein lead to the postponement of the TIPS procedure.

Keywords: Liver, MRA; Magnetic resonance (MR), angiography; Magnetic resonance (MR), liver; Interventional radiology, TIPS; TIPS

1. Introduction 2. Patients and methods

The pre-operative assessment of portal and hepatic venous anatomy prior to the placement of a transjugular intrahepatic portosystemic shunt stent (TIPS) should be accomplished noninvasively and with great accuracy.

Twenty-one patients with end stage liver disease and variceal haemorrhage were referred for TIPS stent placement pre liver transplantation.

Previously, late phase contrast angiography, trans- hepatic portography and ultrasound (Fig. la,b) have been used in this regard but each has limitations [l-3]. ‘Time of flight’ magnetic resonance angiography represents a noninvasive method of assessing both por- tal and systemic venous anatomy [4-71. The value of this technique in assessing patients prior to TIPS sten- ting is not widely recognised. This study was undertaken to evaluate its utility prior to the placement of TIPS stents by comparing MRA images with those obtained at conventional hepatic and portal venography.

In each case pre-procedural magnetic resonance imag- ing was performed using a 1.0 Tesla superconducting magnet (Magnetom SP, Siemens Medical Systems, Iselin, NJ) with a maximum gradient of 10 mT/m.

* Corresponding author.

In each case, a parenchymal study using a Tl- weighted coronal turboflash sequence was performed prior to angiographic imaging. A saturation slab was then placed over the heart in the region of the ascending aorta to eliminate signal from arterial structures and then selective venographic imaging using a sequential time of flight technique was commenced (Fig. 2a). Sagit- tal, coronal and axial images were obtained using a flow compensated gradient echo sequence (TR = 32 ms, TE = 10 ms, flip angle = 30”, image matrix = 192 x

0720-048X/94/%07.00 0 1994 Elsevier Science Ireland Ltd. All rights reserved SSDI 0720-048X(94)00559-U

44 S. Eustace et al. /Eur. J. Radiol. 19 (1994) 43-49

a b Fig. I. (a,b) Axial 2-D ‘time of flight’ magnetic resonance angiogram demonstrating the hepatic venous confluence with corresponding axial section from doppler sonography examination. (linear bright signal coarsing between the IVC and aorta, Fig la, is due to the presence of an oesophageal porto-systemic venous collateral).

256, slice thickness = 5 mm). Each 2-D slice required 6-8 s of breathholding. The 2-D images were then pro- cessed using a maximum intensity projection algorithm to generate three dimensional projectional angiograms (Figs. 2a, 3a). Flow direction within the portal vein was determined using a pre-saturation pulse bolus tracking technique in each case (Fig. 3b,c).

Contrast studies were performed on 20 of 21 patients by injection of 40 ml of ionic contrast to a hepatic catheter pre TIPS (hepatic venography) and by injection of 40 ml of ionic contrast to the portal vein having bridged the transhepatic tract at the time of the TIPS procedure (Fig. 2c,d). Images from MRA and contrast studies were subsequently reviewed independently by two radiologists and evaluated to determine portal and hepatic vein position and patency and the proximity of hepatic and portal venous pathways. The level of in- terobserver agreement was calculated using the Kappa statistic [8]. In addition, the liver size (grade 1, small; grade 2, normal; grade 3, enlarged) and the presence or absence of hepatic and perihepatic occult pathology were recorded following review of MR images. MRA post TIPS stenting was performed in four patients to confirm positioning and patency using the same tech- nique (Fig. 4a,b).

3. Results

Magnetic resonance angiograms were performed on

21 patients (18 males, three females) of mean age 51.5 years. Contrast venograms were performed on 20 pa- tients. Contrast venography was postponed in one pa- tient following the demonstration of hepatoma exten- ding to the portal vein at MRA (Table 1).

In 20 cases, an exact correlation was observed be- tween the MRA study and the contrast hepatic and por- tal studies, specifically hepatic and portal vein patency was observed by both imaging modalities in each case (Fig. 2b-d). Exact correlation was observed between size, position and proximity of vessels identified at MRA and at contrast venography (Kappa = 0.97).

In each of 20 cases, MRA facilitated pre-operative lo- calisation of the portal and hepatic veins in three planes and allowed identification of the largest and nearest communication between the two venous pathways (Figs. 2b, 3a).

In addition MRI facilitated evaluation of hepatic size (shrunken/grade 1,13 cases; grade 2, seven cases) in each case and enabled the detection of incidental perihepatic pathology in 16 of 2 1 cases (ascites identified in 14 cases, pulmonary basal atelectasis and effusion in seven pa- tients).

MRA accurately predicted the direction of portal venous flow in each case correlating with flow direction observed at contrast venography (antegrade flow observed in all cases by both modalities) (Fig. 3b,c).

The identification of signal within the stent lumen (despite susceptibility effects from the metallic stent

S. Eustace et al. /Eur. J. Radiol. 19 (1994) 43-49 45

a b

d Fig. 2. (a) ‘Time of flight’ magnetic resonance venography following elimination of arterial signal by ascending aorta saturation band (arrow), demonstrating patent portal vein and splaying of inferior vena cava and superior mesenteric vein due to presence of retroperitoneal adenopathy. (b) 3-D magnetic resonance angiogram (maximum intensity projection) demonstrating proximity of patent right hepatic and portal veins (open arrow demonstrates the coronary vein). (c) Hepatic venogram following injection of 40 cc of contrast to TIPS catheter (in right hepatic vein) demonstrates distal right hepatic venous radicles corresponding to findings at MRA. Metallic coils medial to the hepatic vein, placed at the time of TIPS, mark the position of the portal vein. (d) Contrast injection to the portal vein having bridged the transhepatic tract demonstrating portal vein patency and position corresponding to 3-D magnetic resonance angiogram. Large coronary vein, (open arrow) is identified on both the magne- tic resonance angiogram and contrast study, superior mesenteric vein (closed arrow) is out of plane on 3-D MR angiogram.

46 S. Eustace et al. /Eur. J. Radio/. 19 (1994) 43-49

a b

Fig. 3. (a) Maximum intensity projection (patient 3) demonstrating proximity of the right hepatic vein (RHV) and the right portal vein (RPV). (b,c) Pre-saturation pulse (black band) bolus tracking of the portal vein demonstrating advancement of saturated spins towards the liver (progres- sion of black band, arrow) indicating hepatopedal flow.

Fig. 4 (a,b) Coronal section from magnetic resonance angiogram and corresponding contrast study following placement of the TIPS stent demonstrating intraluminal signal due to venous flow (arrows). Circumferential signal degradation around the tract is due to magnetic susceptibility effects from the metallic stent.

S. Eustace et al. /Eur. J. Radio/ 19 (1994) 43-49 41

Table 1 Summary of patient data, patient age, sex, diagnosis, and findings at both magnetic resonance angiography and at contrast studies

Sex Age (years) Diagnosis MR angio findings Other findings Contrast findings

patent pv, others (patent hv pv,hv)

M 36 M 56 M66 M 70 M 45 M 82

M 51

M 51

M 37 M 70

F 46

M 67

M 48

M 65

M 42 M 62

M 73 F 35

M46

F 33

M 54

C2Hs

C2Hs

C2Hs

C2H5

Hepatoma C2I-G

C2I-h

C2I-b

Hp B/C2H5 C2H5

1” biliary cir- rhosis

C2H5

C2H5

C2H5

C2H5

C2H5

C2H5

1” biliary cir- rhosis

C2H5

C2H5mp B

C2H5

+ + + +

+

+

+

+ +

+

+

+

+

+

+ + +

+

+

+

Antegrade flow, varices Antegrade flow, varices Antegrade flow, varices Patent umbilical vein Tumour invasion of pv Antegrade flow pv, gastric vatices Antegrade flow pv

Antegrade flow

Antegrade flow

Antegrade flow

Antegrade flow

Antegrade flow Antegrade flow Antegrade flow

Antegrade flow

Antegrade flow

Splenectomy, small liver Splenomegaly, small liver ascites Ascites Ascites, rt basal consolidation Cirrhosis splenomegaly Haemangiomas in cirrhotic liver and

spleen Cirrhosis, rt basal infiltrate, It basal ef-

fusion Cirrhosis, splenectomy; ascites,

paraoesophageal varices Cirrhosis splenomegaly Ascites, gastric varices, patent shunt

post TIPS

Gastric, paraoesophageal, splenic, retroperitoneal vat-ices

Cirrhosis, cholecystectomy, ascites, gas- tric, paraoesophageal, retroperitoneal varices

Normal liver and spleen size/ patent shunt post TIPS

Cirrhosis, gastric, splenic, paraoesophageal varices

Minimal ascites, paracesophageal varices, patent shunt post TIPS

Pericardial effusion Cirrhosis, ascites, gastric varices Cirrhosis, gastric, umbilical,

retroperitoneal vat-ices Splenomegaly ascites, splenic, gastric

varices, rt basal consolidation Cirrhotic liver, gastric, paraoesophageal

varices Splenomegaly splenic, retroperitoneal

vat-ices, rt basal effusion, patent shunt post TIPS

+ + + + a

+

+

+

+

+

+

+ +

+ +

+ + +

+

+

+

M, male; F, female; C2H5, alcohol cirrhosis; pv, right and left portal veins; Hp B, hepatitis B; hv, right middle and left hepatic veins. *Postponed following liver biopsy.

resulting in marked circumferential signal loss) (Fig. 4a,b) in four patients post TIPS stent placement con- firmed stent patency and position following the pro- cedure.

4. Discussion

Portal decompression through a percutaneously es- tablished communication between the hepatic and por- tal veins was first described by R&h and colleagues in 1969 [9]. Following their initial work, Colapinto and colleagues performed the first successful percutaneous

shunt procedure on a human subject in 1982 [lo]. It was not until the introduction of metallic stents, providing long term porto-systemic shunt patency and tamponade of the trans-hepatic parenchymal tract that the proce- dure gained widespread acceptance in the late 1980s. TIPS now provides a successful minimally invasive treatment of portal hypertension which does not miti- gate against subsequent orthotopic liver transplantation and represents a vital option for the 1520% of patients with acute variceal haemorrhage in whom conventional treatments fail [ 1 l-141. Despite technical advances, the procedure is still fraught with difficulties; in particular,

48 S. Eustace et al. /Eur. J. Radio/ I9 (1994) 43-49

atraumatic puncture of the portal vein may only be achieved by accurate and detailed pre-procedural imaging.

In an attempt to localise the portal vein for tran- shepatic puncture, previous workers have advocated performing a transhepatic portogram at the time of TIPS. This may be hazardous in haemodynamically unstable patients with complicating ascites and coagulopathy [ 151. Such a procedure adds to the time re- quired to place the stent and where undertaken may in- volve a 2-day two-stage operation. Aware of this limitation, Richter et al. have attempted portal vein puncture without guidance [ 151. While often successful, this can result in puncture of peripheral low flow portal venous radicles which can predispose to post procedural stent thrombosis and occlusion [15]. Blind puncture of a shrunken cirrhotic liver may be hampered by paren- chymal fibrosis or lead to inadvertant puncture of the inferior surface of the liver with resultant life threaten- ing haemorrhage [ 161.

Alternative methods of portal vein localisation have been sought to negate these problems. It is well recognis- ed that late phase coeliac or mesenteric angiography may outline the portal vein. Nevertheless this procedure is invasive and a ‘steal phenomenon’ due to variceal col- laterals may lead to underfilling of portal segments and an incorrect diagnosis of thrombosis. Retrograde flow or selective flow to an enlarged spleen may result in the same phenomenon. Duplex ultrasound enables the iden- tification of both the portal vein and its flow direction and enables the identification of hepatic parenchymal pattern and size. However it represents an operator dependant investigation, it lacks reproducibility and in many cases is limited by the presence of bowel gas and patient obesity [6]. While the widespread availability and economic advantages offered by ultrasound make it the favoured modality in many centres, our experience suggests that pre-procedural MRA is of greater value 161.

In this study, we have documented excellent correla- tion between the findings at MRA and subsequently performed contrast studies of the hepatic and portal venous systems at the time of the TIPS procedure. Unlike contrast studies where the ‘steal phenomenon’ may be a problem, flowing blood is bright at MRA ir- respective of the flow direction and as it involves tomographic imaging, it is not hampered by overlying bowel gas.

The multiplanar imaging facility of MRA with selec- tive maximum-intensity processing enables the visualisa- tion of enhanced portal and hepatic venous anatomy pre-TIPS in both axial, coronal and sagittal planes (Figs. lb, 2b, 3a). In doing so, MRA allows the identili- cation of the largest and nearest communication be- tween the hepatic and portal veins and provides an accurate roadmap aiding portal vein puncture. In such

a way the problems inherent in blind puncture of small peripheral venous radicles may be avoided.

The value of selective bolus tracking using a pre- saturation pulse to determine flow direction has been previously reported [ 171. As in previous studies, this technique accurately determined flow direction in each of the patients in our study in concordance with direc- tion observed at contrast portography.

In four cases MRA repeated following the placement of the TIPS stent demonstrated satisfactory stent posi- tion. Accurate pre-procedural imaging, facilitating stent positioning, should theoretically decrease the likelihood of TIPS stent extension to either the extra-hepatic portal or hepatic veins, both of which complicate subsequent transplantation [ 121. Identification of signal within stents implies patency or vascular flow. As signal within TIPS stents is degraded due to metallic susceptibility ef- fects (Fig. 4a,b), duplex ultrasound appears to be a more valuable imaging modality in this regard.

In conclusion, we have observed excellent correlation between findings at MRA and contrast angiography of portal and hepatic veins in patients prior to TIPS, MRA allows noninvasive determination of portal vein position and patency, it provides some information concerning hepatic parenchymal patterns and size, and can show the largest and nearest communication between the hepatic and portal venous systems prior to TIPS stent placement.

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f81

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