Interventional radiology techniques

In the context of expanding the role of NOM of abdominal trauma interventional radiology is used to control haemorrhage, either acutely or to prevent re-bleeding from pseudo aneurysms or in a post surgical patient.

The use of modern low osmolar contrast media (LOCM) for MDCT or angiography carries a small risk; mortality of 1 in 170,000 and severe or life threatening reactions of 1 in 40,000. In addition, if a patient has existing acute renal failure or severe chronic renal insufficiency, there is a risk of contrast induced nephropathy (CIN) of 5 to 50%. CIN is usually transitory and its significance is uncertain [20]. In the context of life threatening haemorrhage and in comparison to surgical morbidity for these patients, the risk of CIN would appear to be acceptable.

Occlusion balloons placed selectively and temporarily within internal iliac arteries, main visceral vessels or even within the aorta can be useful temporising measures. If there has been direct arterial trauma then assuming suitable anatomy stent graft or covered stent placement can provide a means to control the haemorrhage whilst preserving end organ blood supply. However, for solid organ haemorrhage embolisation is the most frequently used interventional technique.

Many different types of embolic materials are available (Table 1). Microcoils, delivered through coaxial microcatheters are the agents of choice if it is safe to effect permanent occlusion of a vessel and it has been possible to superselectively get close to the point of haemorrhage. In the renal circulation the vessels are end arteries and so it is usually sufficient to block the branch feeding the bleeding site. In the liver a rich collateral circulation means that this approach may not be ideal and embolising the vessels on both sides of the bleeding, so called 'closing the front and back door!' might be better. This can sometimes be achieved by passing beyond the bleeding point with the microcatheter and deploying a coil, then withdrawing proximal to the haemorrhage and deploying a second coil.

Table 1. Embolic materials

If it proves impossible to obtain a superselective position close to the bleeding site then the choice is between proximal vessel embolisation with an occlusion device or larger coil to decrease haemostatic pressure at the bleeding site (good for splenic bleeding but prevents a second embolisation attempt if bleeding recurs) or the use of particles or gel foam to pass into the distal circulation, blocking smaller vessels. Use of particles runs a higher risk of ischaemic damage than superselective coil embolisation and therefore a temporary agent is often preferable. If using particles then larger sizes (500 μm diameter) are preferred as this leaves the capillary bed the potential to revascularise later from collaterals.

Onyx (ev3, Irvine, California, USA) is a polymer dissolved in dimethyl sulphoxide (DMS0) which is delivered as a liquid but becomes solid when in contact with blood. It takes time to prepare and deliver and is therefore less useful in the acute situation, but in the context of prevention of delayed haemorrhage it can be extremely useful as it can be deployed from a microcatheter proximal to a target. From the point of injection it will follow even tiny vessels distally to fill a pseudo aneurysm and continue on beyond, shutting both front and back doors without necessitating manipulation through the lesion with a microcatheter and wire. Figure 2 demonstrates embolisation of multiple hepatic artery aneurysms with onyx.

Figure 2. a) A patient with vasculitic hepatic artery aneurysms presented following minor trauma. Axial contrast enhanced CT demonstrates haematoma around a pseudoaneurysm (arrow) indicating that this is the likely cause of recent haemodynamic instability. b)3D volume rendered reconstruction demonstrates 3 aneurysms arising from a branch of the left hepatic artery (arrows). The right hepatic artery arose from the SMA. c)Selective arteriogram of the coeliac axis with standard catheter after 2 aneurysms had been embolised with onyx (ev3, Irvine, CA, USA). The cast of the onyx is demonstrated, and some distal embolisation (arrow) of onyx. d)A microcatheter is demonstrated within the final bleeding aneurysm (arrow). e)A selective angiogram demonstrates onyx filling all aneurysms and maintained patency of the gastroduodenal artery.

In practice, coils, microcoils and gelfoam slurry are the most common agents employed but availability of the full range of techniques is necessary in the delivery of an interventional trauma service.

Splenic injuries

The spleen is the most commonly injured organ in severe abdominal trauma [21,22] particularly following blunt trauma [23]. To preserve immunological and haematological function and reduce the risk of post-splenectomy sepsis all attempts should be made to preserve the spleen. Following the acceptance of NOM in paediatric surgical practice the indications for NOM in adults have increased over the past 2 decades in an attempt to avoid the morbidity of surgery.

Several historic predictors of failure of conservative management, including complex splenic injuries [24], older age [25], pre-existing splenic pathology [26] or blood transfusion requirement are no longer universally accepted as reasons to avoid NOM of splenic trauma.

NOM has become the standard of care for haemodynamically stable patients, with failure rates of observational treatment reported as low as 5% [27]. Techniques include radiological intervention and careful monitoring.

i) CT imaging and classification of injury

CT is the imaging modality of choice in the evaluation of splenic injuries. With continued technical advances of CT scanners the CT can no longer be perceived as the 'doughnut of death' engendered by slower 1^st and 2^nd generation scanners. MDCT scanners have rapid diagnostic capability with increased spatial and temporal resolution [28] and should be considered a crucial step in the diagnostic pathway for stable patients.

CT has an accuracy of up to 98% in diagnosing acute splenic injuries [29]. CT grading correlates strongly with the actual injury seen at operation [30]. A recent study correlating MDCT with splenic arteriography noted an overall accuracy at detecting vascular injury of 83% [31]. Importantly, not all vascular injuries were detected prospectively on MDCT imaging and so angiography may still be necessary in high-grade injuries.

The American Association for the Surgery of Trauma organ injury scale (OIS) for the spleen, based on surgical appearance is widely referred to in the literature and clinical practice (Table 2).

Table 2. Spleen organ injury scale. [75]

The accuracy of CT diagnosis depends on technique, and problems can arise with misdiagnosis and misgrading. Some patients with apparently low grade injury will still fail NOM, and CT is a morphological snapshot at a certain point in time and not an accurate predictor of subsequent haemorrhage [21]. Hence methods of grading the injury cannot be accurately used to distinguish patients at risk of delayed complications [32] and the use of splenic injury grade as the sole criterion for determining management strategy remains controversial [31].

CT grading systems incorporating MDCT findings of vascular lesions and active bleeding when assigning grade of injury have been suggested [33,34] and may be better than the AAST system for predicting which patients need angiography or intervention after blunt splenic trauma [35]. To date these are not in widespread use.

Indicators of the need for intervention in the form of transarterial embolisation or surgery include active contrast extravasation from the splenic parenchyma and vascular injuries such as pseudoaneurysm or arteriovenous fistula. At CT, these are demonstrated as an intraparenchymal contrast blush - a focal hyperdense collection of contrast. The presence of haemoperitoneum can also suggest vascular injury [31]. If the patient is hypotensive, parenchymal enhancement is often delayed and heterogenous and so appropriate CT technique with plain, arterial and delayed (2-3 minutes) phases of examination is necessary to achieve optimum sensitivity.

ii) Conservative management

The majority of blunt splenic injuries can be managed safely with observation, even in centres with a low incidence of trauma [36]. Embolisation is required in only 7% of patients [37] and conservative treatment of low grade injuries is successful in over 90% of patients [26,38].

Patients with a high grade injury are at greatest risk of failure of observational management (up to 70%) [25,26,30,38] and are at greatest risk of delayed operative intervention [14]. The need for transfusion of greater than 1 unit of blood is another independent risk factor for failure of observation [27,30] and haemodynamic instability will also determine further treatment as is discussed later.

Vascular injury (haemorrhage, haematoma, pseudoaneurysm or arteriovenous fistula) at CT is also associated with failure of observational treatment [26,32,39]. A contrast blush at CT scanning is associated with failure of observational treatment in up to 80% [32,39].

iii) The role of embolisation

Surgery is necessary if there is parenchymal destruction and injury to hilar vessels [40] an injury involving multiple vessels, associated hollow viscus injury or other injuries requiring operative intervention.

There are no set criteria to select patients for angiography and embolisation. If there is active bleeding (contrast blush) or non-bleeding vascular injury such as pseudoaneurysm, high grade injury or haemoperitoneum on CT, angiography is indicated [29,41,42]. Patients undergoing standard NOM in one study had volumes of haemoperitoneum approximating to blood in the perisplenic and/or perihepatic region and/or Morrison's pouch, whereas those undergoing angiography and embolisation had larger volumes with blood tracking down one or both paracolic gutters and in some patients into the pelvis [41]. Arterial extravasation detected by MDCT is present in between 13% and 17.7% of patients [21,22]. Extravasation has a high sensitivity in predicting the need for angiography and subsequent endovascular treatment or splenic surgery[21,29].

If angiography confirms active bleeding, embolisation should be performed. Dent et al expanded the role of embolisation to include significant haemoperitoneum, grade 4 or 5 splenic injury, decreasing haematocrit not explained by other injuries, and persistent tachycardia [37].

Whilst haemodynamic instability is difficult to define, it has historically been an indicator for surgical intervention [30]. This is now controversial with some studies demonstrating safe effective use of embolisation in unstable patients. In one study, patients with a systolic blood pressure of <90 mmHg and shock index (heart rate divided by systolic blood pressure) of >1.0, and a transient response to fluid resuscitation underwent angiography [15]. Whilst only 15 patients were included (mean systolic blood pressures of 84.2 mmHg), embolisation was successful in all, with no reported complications. Other studies demonstrate rapid normalisation of haemodynamic status as would be expected in haemodynamically unstable patients following embolisation [41]. Ultimately the decision will depend on local experience and service availability.

Many authors have used embolisation as an adjunct to NOM [42-44]. Success rates of NOM in high grade injuries of 95% have been documented with this strategy [45]. Splenic artery embolisation in selected patients without evidence of active bleeding is a safe and useful adjunct to NOM[37,41]. Some authors have expanded the indication for angiography to include some patients without contrast blush on CT. Gaarder et al., demonstrated increased success rates of NOM from 79% to 96% when mandatory angiography (and embolisation if indicated) was performed on all high grade injuries (with a high rate of failure of NOM and risk of delayed bleeding) regardless of the presence of contrast blush [46]. The splenic salvage rate increased with fewer complications of delayed bleeding compared to historical controls when mandatory angiography was not performed on all high grade injuries.

Superselective embolisation of the bleeding segmental artery using microcatheter techniques when possible may ensure a greater likelihood of the immune function of the spleen remaining uncompromised [47] though may be associated with increased complication rates [48]. Benefits of preserving splenic function must be balanced against the risk of delayed haemorrhage even in patients with low grade injuries [29,32]. CT reconstructions as shown in figure 3 can help to guide catheter selection by providing a 'roadmap' of the splenic artery [49].

Figure 3. a) Axial CT of a 73 year old man with iatrogenic splenic injury following chest drain insertion. An active bleeding point in the spleen (arrow) with surrounding haematoma was demonstrated. b)Coronal CT reconstruction showing a tortuous splenic artery and bleeding point (arrow). These allowed optimal catheter choice for arteriography. c)A Tracker-18 microcatheter system with a Fasdasher 0.014 in wire (Boston Scientific, Maple Grove, MN, USA) were used to achieve access distally within the splenic circulation. After several unsuccessful attempts at superselective catheterisation of the branch supplying the bleeding point, 4 platinum Vortex-18 diamond-shaped coils (Boston Scientific) were deployed sequentially in the main splenic artery distal to the dorsal pancreatic branch. 2 initial coils migrated past the required branch and there is ongoing bleeding from the spleen (arrow). d)The next 2 coils achieved occlusion of the main splenic artery with preservation of branches to the dorsal pancreas and upper pole of the spleen. e)Axial CT at 1 week showed a small splenic infarct where the initial coils had migrated distally. Arterial supply to the spleen was preserved with some flow through the main splenic artery coils.

iv) Complications of embolisation

Recent studies report failure rates for embolisation as low as 2.7% to 4% [41,46] after proximal embolisation for high grade lesions, active contrast extravasation or haemoperitoneum. However, proximal rather than selective embolisation may result in fewer complications [48] and other studies have recorded a higher overall complication rate for embolisation of around 27% [50,51]. Patient selection is therefore considered crucial and the authors highlight the necessity for a low threshold for further intervention if there are signs of continued bleeding post-embolisation.

A retrospective study comparing embolisation to operation demonstrated a significantly lower number of complications in the embolisation group (13%) than the operative group (29%) [27]. The complications attributed to embolisation are generally minor and need to be viewed in the context of having avoided an operation with its attendant morbidity.

Minor complications can be expected in up to half if fever is included [45] and fever and reactive pleural effusion can be considered as a form of mild post-embolisation syndrome. Infarcts may occur in up to 20% of patients (more so with distal embolisation) but usually resolve without clinical sequelae [52]. Recurrent haemorrhage can occur in up to 11% and abscess in 4%. Coil migrations and splenic artery dissections are potential but rarely encountered complications [41].