Figure 22.1 Presenting symptoms in children with CPSSs.
Bernard et al. reviewed the world’s literature and summarised the presenting symptoms in 265 children with CPSSs. They found that 27 (10%) were discovered on prenatal US. Seventy-eight (30%) were identified during the neonatal period, including 55 (20%) due to an abnormal galactosaemia screening test, 12 (4.5%) during workup for congenital heart disease and 10 (4%) during evaluation of neonatal cholestasis. One hundred sixty (60%) were identified after the first month of life due to complications of the shunt in 117 (44%), incidental imaging findings in 29 (11%) and abnormal liver tests in 12 (4.5%) [6].
In their review of 316 published cases of CPSSs (a cohort which overlapped with Bernard et al.’s), Sokollik et al. reported that a majority of patients were symptomatic at presentation, including 23% with neurologic symptoms (including hyperammonaemia) and 14% with pulmonary symptoms [13].
Age at presentation has ranged from prenatal to 84 years, with 66% diagnosed before age 12 and 24% in adulthood [13]. Among patients who avoid detection until adulthood, encephalopathy is the most commonly reported presenting symptom [14,15].
22.5.1 Diagnostic evaluation
Evaluation of children with known or suspected CPSSs is aimed at
1. Defining shunt anatomy – including assessing the degree of atresia in the intrahepatic portal venous system
2. Determining suitability for operative or endovascular shunt closure
3. Searching for associated pathology
History and physical exam are focused on identifying sequelae of the shunt. While overt encephalopathy is rare in these children, subtle symptoms of neurocognitive dysfunction are often present. History should also investigate cardiopulmonary symptoms suggestive of pulmonary hypertension. The exam includes a neurologic assessment, inspection for jaundice, a cardiopulmonary exam and an abdominal exam palpating for masses and assessing the size of the liver and spleen.
Laboratory investigations should include a complete blood count, basic chemistry panel, liver function tests (including γ-glutamyl transpeptidase [γ-GT]), coagulation panel, serum ammonia level and fasting serum bile acid concentration. Serum α-fetoprotein (α-FP) concentration should be measured in children with concurrent liver mass. In their summary of the literature, Bernard et al. found that serum γ-GT was elevated in 50% of children, prothombin time in 40%, ammonia level in 79% and serum bile acid levels in 97% [6].
Duplex US is the initial imaging modality of choice, and in addition to visualising the actual portosystemic shunt, US may identify secondary signs of a CPSS, including enlargement of the hepatic arteries, absence of intrahepatic portal venous branches and regenerative liver nodules.
Cross-sectional imaging with computed tomography venogram (CTV) or magnetic resonance venogram (MRV) is the next test for children found to have a CPSS by US, and is important prior to surgical or endovascular intervention. CTV or MRV provides excellent detail of the shunt anatomy and can assess the extent of intrahepatic portal vein atresia. Furthermore, the cross-sectional imaging is the key modality for distinguishing shunts amenable to endovascular closure from those which require surgery. In general, longer and narrower shunts are suitable for endovascular techniques, while short and broad shunts require an operation. Figure 22.2 shows the typical CTV appearance of a CPSS between the main portal vein and IVC.
Angiography can be useful even for cases that are not expected to be suitable for endovascular shunt closure. With a trial of balloon occlusion of the shunt, angiography permits measurement of portal pressure and visualisation of the intrahepatic portal venous system. It is not uncommon for intrahepatic portal veins which appear absent on cross-sectional imaging to opacify when the shunt is occluded. As will be discussed in the next section, it is now apparent that the distinction between end-to-side and side-to-side shunts is actually more of a continuum. With shunt occlusion, distal branches of the portal vein can be visualised in virtually all cases.
Figure 22.2 Typical preoperative axial CTV imaging of two separate children (a and b) with a CPSS with the most common anatomic configuration requiring operative intervention – a fistulous connection between the main portal vein and IVC.
Additional studies should be tailored to the child’s clinical presentation. Per-rectal scintigraphy is an optional study which can be used to quantify the fraction of portal flow being shunted [6,16]. This shunt ratio has been shown to correlate with the serum ammonia level and clinical signs of encephalopathy [6]. Echocardiography is indicated for children with cardiopulmonary symptoms to screen for pulmonary hypertension. Formal neurocognitive (psychometric) evaluation can be useful for objectively assessing children with subjective learning deficits [10].
CPSSs can often be identified on prenatal US. Achiron et al. reported on nine cases of prenatally diagnosed CPSSs [17]. Anomalies were detected at a mean gestational age of 20 weeks and as early as 14 weeks. In all cases, the abnormal shunt was visualised, and they were able to distinguish Type I from Type II shunts by assessing portal flow in the fetal liver. Absence of the DV on prenatal US should prompt a search for an abnormal portosystemic shunt. Acherman et al. reported on six cases of absent DV among 990 fetuses who underwent fetal echocardiography due to cardiomegaly, a dilated umbilical or systemic vein, or extracardiac anomalies [9]. They found that all had an abnormal connection from the umbilical vein to the right atrium, IVC or iliac vein. After birth, only one of six children required shunt closure.
22.6 ANATOMY AND CLASSIFICATION
The basic classification was published in 1994, by Morgan and Superina, and was determined on whether there was any preservation of intrahepatic portal venous flow [18].
1. Type I shunts (end to side), that is, no portal venous flow to the liver.
a. Superior mesenteric vein (SMV) and splenic vein do not join to form a confluence – that is, true congenital absence of the portal vein.
b. SMV and splenic vein form a confluence.
2. Type II shunts (side to side) preserve some portal blood flow.
It follows that Type II shunts can be considered amenable to surgical or endovascular closure, while Type I shunts can only be managed symptomatically or referred for transplantation.
Since then, it has become apparent that the distinction between Type I and Type II shunts is really more of a continuum. With modern imaging utilising shunt occlusion, diminutive intrahepatic portal venous branches can be visualised in almost all cases. Furthermore, staged approaches allow for shunt closure even in children who develop acute portal hypertension with initial shunt clamping.
A number of other classification systems with variable clinical utility have been described, although none have gained widespread usage. Some authors have made a distinction between intrahepatic and extrahepatic shunts [3,13,19]. The rationale for this distinction related to the finding that some intrahepatic shunts may close spontaneously, while extrahepatic shunts do not. However, we have found that this distinction can be excessively subjective, such as in the case of a predominantly extrahepatic shunt which traverses a short segment of caudate lobe or a PDV which cannot truly be classified as intrahepatic or extra-hepatic. We believe that the most useful way to subclassify CPSSs is based on the section of the mesenteric or portal system from which they arise [20]. In predicting the likelihood of spontaneous shunt closure, a finding that the shunt arises from a branch of the portal vein has greater prognostic significance than identifying an intrahepatic course. The most complete description of a shunt includes
1. Anatomic location of the afferent portal or mesenteric connection (e.g. splenic vein, main portal vein, or left portal vein)
2. Anatomic location of the efferent systemic connection (e.g. renal vein, IVC, or left hepatic vein)
3. Type of communication (end to side or side to side)
4. Number of communications (single or multiple) [6]
There are a number of papers which try to categorise the anatomy of CPSSs reported in the literature [3,6,11,13,20–22]. Sokollik et al. reviewed 316 cases of CPSSs from the literature and found that 185 (58%) were extrahepatic and 131 (41%) were intrahepatic [13]. Among the extrahepatic shunts, 103 (56%) were classified as Type I and 82 (44%) as Type II. However, the vast majority of cases classified as Type I never underwent imaging with temporary shunt occlusion or attempted staged closure and are therefore probably misclassified by current standards. In a previous review of 96 cases of Type II CPSSs, we found that 56 (58%) arose from a branch of the portal vein, 26 (27%) arose from the main portal vein and 14 (15%) arose from a mesenteric, gastric or splenic vein [20].
22.7 MANAGEMENT ALGORITHM AND SURGERY
Type I CPSS is a diagnosis of exclusion which should only be considered following a comprehensive evaluation as though for a Type II shunt, which includes temporary occlusion via an operative or endovascular approach. Figure 22.3 illustrates our management approach for children with Type II CPSS [20]. Evaluation includes history and physical exam, laboratory studies and initial duplex US followed by cross-sectional imaging with CTV or MRV as detailed above. All cases are reviewed in a multidisciplinary conference with our interventional radiology colleagues. Children who are <1 year of age with an incidentally discovered CPSS, normal ammonia level, normal liver function tests and no liver mass may be observed. Families are counselled on the likelihood of spontaneous closure based on imaging of the shunt. We advise families that >85% of reported cases of spontaneous closure of a CPSS occurred in shunts located between a portal branch and a hepatic vein [6]. Those managed nonoperatively are asked to return in 6 months for repeat physical exam, laboratory studies and US.
Figure 22.3 Management algorithm for children with CPSSs.
Children with symptomatic shunts are first considered for endovascular closure. Factors associated with a decreased likelihood of successful endovascular closure include
1. Shorter length of shunt
2. Increased shunt diameter
3. Shunt arising from the main portal vein
4. Shunt draining into the IVC
5. Diminutive intrahepatic portal venous branches
When endovascular intervention is considered, the approach is dictated by the child’s anatomy. For many shunts, such as a PDV, the portal vein can be accessed using a transjugular approach via the shunt [10] or alternatively via a direct puncture of the portal vein. Options for endovascular shunt closure include placement of an Amplatzer* device [23–25] or coils [26,27] in the shunt (Figure 22.4). An alternative is to place a covered stent in the IVC across the location where the shunt terminates [28].
If an endovascular option is not considered viable, then an open surgical approach should be used. Although laparoscopic shunt closure has been reported in a small number of cases with favourable anatomic features, this approach remains experimental [29]. If cross-sectional imaging fails to demonstrate intrahepatic portal venous branches, we prefer to perform preoperative portal venography with balloon occlusion of the shunt. The balloon can be positioned within the shunt (e.g. in cases of PDV) or in the IVC for cases with a large portal vein–IVC shunt. Figure 22.5 shows how temporary shunt occlusion dictates patient management; if the intrahepatic portal venous system does not opacify well when the shunt is occluded, then a staged approach to shunt closure is usually required (as detailed below). Nowadays, in the rare instance where the shunt can be classified as Type I after balloon occlusion, an operation can be avoided and the patient is considered for transplant if symptomatic. Preoperative angiography also permits measurement of mesenteric venous pressures before and after shunt occlusion. This information is predictive of the likelihood that a staged approach will be necessary.
Figure 22.4 Endovascular closure of CPSSs. Patient 1: (a) Venogram demonstrated a large fistula between the portal vein and right atrium. (b) With balloon occlusion of the shunt, intrahepatic branches of the portal vein are visualised. (c) Postoperative CT demonstrates an Amplatzer plug which successfully occluded the shunt. Patient 2: (d) An alternative endovascular modality for shunt closure is coil embolisation.
Shunts arising before the confluence of the portal vein or from an intrahepatic branch of the portal vein can typically be isolated and divided with impunity. For large shunts arising from the main portal vein, especially those with diminutive intrahepatic portal vein branches, we adhere to the algorithm shown in Figure 22.3, as previously described [20].
Box 22.2 illustrates the operative steps in surgical closure of the typical Abernethy Type II side-to-side portocaval shunt.
Liver transplant is reserved for patients with a true Type I CPSS who fail nonoperative management. Both living donors and deceased donors can be utilised [30–33]. Depending on the anatomy of the shunt, the proximal portal anastomosis must often extend to the mesenteric vein, which necessitates a considerable venous conduit. When living-donor transplants are performed for this indication, conduit options for the portal vein reconstruction include (1) ‘spare’ deceased donor vessels, (2) recipient jugular vein grafts or (3) polytetrafluoroethylene (PTFE) grafts.
22.8.1 Hepatic encephalopathy
Perhaps the defining feature of a symptomatic CPSS is hepatic encephalopathy, which can often remain occult until much later in life [14,15]. In children, overt encephalopathy is rare, but elevation of serum ammonia levels may be associated with more subtle evidence of neurocognitive dysfunction [10,16,20]. MRI findings on T1-weighted images, including abnormal signals in the globus pallidus, and on MR spectroscopy are comparable to changes seen in patients with encephalopathy from cirrhosis [6,34].
Figure 22.5 Decision making based on temporary shunt occlusion. Patient 1: (a) Preoperative endovascular balloon occlusion of the fistula demonstrates excellent opacification of the intrahepatic portal veins in this child, who tolerated single-stage operation to divide his portocaval shunt. Patient 2: (b) Intraoperative venogram performed with temporary shunt occlusion shows minimal opacification of the intrahepatic portal veins. This child required a two-stage procedure with initial partial shunt banding. (c) Repeat venogram 2 days later demonstrated an improved intrahepatic portal venous system, and the child then tolerated definitive shunt division.
22.8.2 Benign or malignant liver tumours
These are reported to occur in about a quarter of children with CPSSs [13]. The most common tumours are focal nodular hyperplasia (FNH), followed by nodular regenerative hyperplasia (NRH). Such liver tumours are multiple in the majority of cases [6]. The association between CPSSs and FNH is not surprising since the pathogenesis is believed to be a hyperplastic response to altered blood flow secondary to a vascular abnormality [35,36]. Children with CPSSs may have multiple small lesions or a single, massive tumour [13,37,38]. Hepatoblastoma has been reported in at least nine cases, and the diagnosis is often delayed because of an assumption that all liver nodules in these children are regenerative or benign [13,39]. There should be a low threshold for obtaining a biopsy in any child with an elevated α-FP level or if the tumour is >5 cm, has imaging findings which are atypical for FNH or enlarges on serial US.
22.8.3 Portopulmonary hypertension
This has been reported in at least 30 children with CPSSs and can occur at any age and in patients with all types of shunt anatomy [6,12]. Symptoms can range from mild dyspnoea to sudden death. Portopulmonary hypertension may occur simultaneously with or be preceded by symptoms of chronic hypoxaemia, similar to hepatopulmonary syndrome – a condition that can also occur in CPSSs without ever progressing to pulmonary hypertension [6,13,40–42]. Hepatopulmonary syndrome is postulated to be caused by exposure of the pulmonary vasculature to intestinal vaso-active mediators that have bypassed the liver [13,43]. Signs and symptoms of portopulmonary hypertension are identical to those in idiopathic pulmonary hypertension, except for the requirement for coexisting portal hypertension (cirrhotic or noncirrhotic). Primary screening for the diagnosis is via echocardiography, but definitive diagnosis requires the patient to meet stringent criteria for mean pulmonary artery pressure, pulmonary vascular resistance and mean pulmonary artery occlusion pressure during right heart catheterisation [44]. After medical optimisation, early intervention for shunt closure is indicated to prevent the child from developing irreversible changes in the pulmonary vasculature [11,28].
Neonatal jaundice may also occur in children with CPSSs and manifest as jaundice or hypergalactosaemia [6]. Neonatal jaundice may be associated with coagulopathy or hypoglycaemia. It is believed that disruption of normal portal venous flow to the liver parenchyma causes alterations in its synthetic function.
22.8.4 Metabolic associations
A number of metabolic syndromes have been described in association with CPSSs. These include hyperinsulinaemic hypoglycaemia in a child with Down’s syndrome which resolved on surgical closure of the shunt [45], and was possibly due to reduced hepatic degradation of secreted insulin. A similar mechanism was put forward for two females with primary amenorrhoea and virilisation due to hyper-androgenism and hyperinsulinaemia. Bas et al. reported on two girls who presented with early puberty at 7 years of age [46]. They were found to have elevated testosterone and androstenedione and hyperinsulinaemia. Again, the proposed mechanism was that there was decreased hepatic sulfation of androgen precursors due to shunting, allowing an elevation of more potent circulating androgens.
Important outcome measures following endovascular or operative intervention for CPSSs include procedural morbidity and mortality, as well as resolution of associated conditions.
While no deaths directly related to intervention for CPSSs have been reported, there have been five deaths during follow-up after shunt closure [13]. Furthermore, multiple complications have been reported, including two in our patients: one child who developed a haemorrhagic stroke while receiving thrombolytic therapy for portal thrombus following shunt banding, and another who developed stenosis of the IVC requiring stent graft placement [20]. Kamimatsuse et al. similarly reported a case of postoperative portal vein thrombus following PDV ligation [47].
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