AVOIDANCE OF BLOOD VESSELS

The most important use of colour Doppler ultrasound in interventional procedures is visualisation of blood vessels along the needle trajectory. This allows the vessels to be avoided as the needle is advanced, thereby minimising the risk of bleeding.³ Alternatively, in some situations such as arteriography or venography, colour may be useful to localise vessels for puncture. The focus of this chapter will be the use of colour Doppler for non-vascular interventional procedures.

The addition of colour Doppler to imaging guidance has been shown to reduce the risk of bleeding in both percutaneous liver and kidney biopsies.4–6 Good guidance technique routinely incorporates colour Doppler imaging immediately prior to needle placement anywhere in the body. Specific vessels (Table 16-1) should be identified during certain common interventional procedures (Fig. 16-1).

In fine needle aspiration of thyroid nodules and lymph nodes, colour Doppler is used to avoid the internal jugular veins and carotid arteries and their major branches (Fig. 16-2). In the chest, colour Doppler ultrasound has been shown to improve vessel visualisation during transthoracic needle aspiration biopsies.^7,8 During mediastinal biopsy, not only should the great vessels be visualised, but a specific search for the internal mammary arteries and veins must be performed. Intercostal vessels can be avoided by advancing the needle directly over ribs, as the vessels run along the inferior margin of the ribs. However, a search for intercostal vessels with colour Doppler is warranted, especially if the needle must be directed close to the inferior margin of the rib in order to target the lesion.

Ultrasound-guided percutaneous liver biopsy can be performed using a sub-xiphoid approach to access the left lobe, or an intercostal approach into the right lobe. Although both techniques are acceptable, some authors favour a sub-xiphoid approach to avoid damage to intercostal structures and avoid traversing the pleura.⁹ However, a recent study reported a 0.8% (6/776) rate of significant bleeding complications from percutaneous US-guided liver biopsy, all from the left lobe approach.¹⁰ Four of the six cases were attributed to superior epigastric artery injury. These vessels lie approximately 4 cm from midline at the level of the xiphoid process. Therefore the superior epigastric arteries must be identified and avoided during left lobe biopsies or any other procedure in the epigastric region. If they cannot be visualised, a midline approach is preferred in order to avoid these vessels. Likewise, the inferior epigastric arteries should be identified during any puncture in the lower abdomen or pelvis, such as paracentesis (Fig. 16-3). Additionally, as paracentesis is often performed in cirrhotic patients with portal hypertension, colour Doppler should be also used to identify enlarged abdominal wall varices.

During liver biopsy colour Doppler can decrease bleeding risk by visualisation and avoidance of major intrahepatic vasculature. Fine needle aspiration biopsy under US guidance is an established technique for distinguishing between bland and malignant portal vein thrombus. Colour Doppler improves visualisation of the thrombus by identifying flow surrounding it or within it, and can guide needle placement directly into the thrombus without traversing patent portions of the portal vein and helping avoid the adjacent hepatic artery.¹¹ Colour Doppler is useful to distinguish hepatic vessels from bile ducts when performing transhepatic cholangiography. Colour and spectral Doppler US can identify tumour neo-vascularity. It is important to avoid such vessels as they lack a normal coagulation response and have a higher propensity for bleeding (Fig. 16-4). Puncture of these vessels can result in aspiration of a large amount of blood during FNA which will degrade the specimen and reduce diagnostic yield.

IDENTIFICATION OF VASCULAR LESIONS

A less common but highly important use of colour Doppler ultrasound is the identification of vascular lesions such as pseudoaneurysms and arteriovenous fistulas (AVFs) prior to performing an intervention. On grey scale US, a pseudoaneurysm can appear to be a cystic lesion or fluid collection and aspiration or drainage may be requested. Puncture of such a lesion could result in a life-threatening haemorrhage. This scenario may be encountered in the setting of acute pancreatitis, where pseudocysts are common. However, splenic (or any branch of the celiac axis) artery pseudoaneurysm can mimic a pseudocyst and must be excluded before performing an intervention. Colour Doppler US can easily identify the vascular nature of these lesions by demonstrating the characteristic swirling blood in a ‘yin-yang’ pattern (Fig. 16-5). The use of colour Doppler in the treatment of pseudoaneurysms is discussed elsewhere in this book.

Arteriovenous fistulas have been reported as a complication of renal biopsies in 3–18%.¹² Although often asymptomatic, they are of particular importance in renal transplant recipients who often undergo multiple biopsies. These lesions must be identified and avoided prior to repeat biopsy in order to minimise the risk of serious bleeding. Arteriovenous fistulas are rarely seen on grey scale US but can be easily identified on colour Doppler. Tissues surrounding the fistula vibrate due to the high-velocity blood flow and may show a flash of colour noise – the equivalent of a palpable thrill or audible bruit. The feeding artery will demonstrate aliasing unless the pulse repetition frequency is increased. Spectral Doppler tracings show high-velocity, low-resistance waveform in the feeding artery, and high-velocity, arterialised flow in the draining vein (see Chapter 10, Fig. 10-19).

EVALUATING TISSUE PERFUSION

While it is important to avoid macroscopic blood vessels when performing an interventional procedure to minimise bleeding risk, it can be beneficial to identify perfusion within lesions in order to target these areas for biopsy. A common pitfall in image-guided percutaneous biopsy is the sampling of non-viable or necrotic tissue leading to non-diagnostic results. Colour Doppler US can be used to direct biopsy towards vascularised portions of lesions in order to increase diagnostic yield. Additionally, if a target lesion is difficult to visualise on grey scale ultrasound, colour Doppler US can identify neovascularity which may help localise the lesion. This is especially useful in hypervascular tumours such as hepatocellular carcinoma, and in cases of local recurrence after tumour resection or radiofrequency ablation as it may be difficult to distinguish post-surgical or post-RFA changes from recurrent tumour.

IMPROVED NEEDLE VISUALISATION

Real time visualisation of the needle tip is an advantage of US-guided intervention. Generally, the needle should only be advanced when the tip can be seen in order to ensure successful access to the target lesion and to avoid inadvertent puncture of adjacent structures. Unfortunately, it can be difficult to clearly delineate the needle tip and that is a common source of frustration when performing US guided interventions. Visualisation of the needle is particularly difficult when it traverses tissues that have high echogenicity similar to that of the needle (fatty livers), when the needle is advanced parallel to the insonating beam, and with small-gauge needles. Many techniques have been described to improve needle tip visualisation, such as roughening the surface of the needle tip, Teflon coating, and the so-called ‘pump manoeuvre’ where the needle stylet is gently moved back and forth within the needle. The addition of colour Doppler US is a useful adjunct to improve needle visualisation.^11,13 Colour Doppler detects motion of any kind and therefore the movement of the needle or inner stylet is more easily detected and the needle localised (Fig. 16-2).

As mentioned above, needle visualisation can be particularly difficult when the needle is advanced parallel to the insonating beam because the low angle of insonation causes the US waves to be reflected away from the transducer. Needle visualisation is best when it is as close to perpendicular as possible (90° to the US beam) on grey scale imaging. Conversely, the Doppler shift is greatest when the moving structure is parallel (0°) to the US beam. Therefore, colour Doppler US is of particular benefit when parallel needle trajectory is required.

If needle placement is performed using real-time colour Doppler, it is important to properly adjust the colour Doppler sensitivity in order to avoid a ‘snowstorm’ of colour signal with minor movement of the adjacent tissue or patient. Additionally, the temporal resolution (frame rate) will be decreased when colour Doppler is on and therefore should be turned off once blood vessels are identified and needle position is confirmed.

MONITORING ASPIRATION, INJECTION, AND CATHETER PLACEMENT

One of the main interventional applications of US is guidance for fluid collection aspiration or drainage. Examples include renal or liver cyst aspiration, pancreatic pseudocyst aspiration or drainage, and abscess drainage throughout the abdomen and pelvis. Additionally, US-guided percutaneous cyst sclerosis is a useful technique for treatment of symptomatic benign cysts. A wide variety of agents have been used for sclerosis including alcohol and doxycycline, and cyst sclerosis has been described in practically every organ in the body. Colour Doppler US can help visualise the moving fluid during aspiration or injection and can assist in determining catheter position and patency.

During aspiration of fluid collections, the moving fluid through the needle will produce a line of colour on colour Doppler which can aid in needle localisation. Likewise a line of colour will be seen with injection of fluid during cyst sclerotherapy. Colour Doppler has also been shown to be useful in evaluating drainage catheter position and patency after placement.¹⁴ Pigtail catheters can be surprisingly difficult to visualise with grey scale US. Improved detection can be obtained by aspirating the catheter or injecting sterile saline, both of which will lead to colour signal with Doppler imaging (Fig. 16-6). Visualising colour signal at the side ports when injecting saline or aspirating will also confirm catheter patency. Saline should be injected slowly to avoid the snowstorm pattern which will obscure the catheter.

POST-PROCEDURE BLEEDING

US-guided percutaneous liver and renal biopsies are widely established techniques for diagnosing both diffuse parenchymal disease and focal lesions. The rate of serious bleeding complications has been reported at 0.5% for liver biopsies and 0.7% for kidney biopsies.¹⁵ However, the risk may be increased in patients with abnormal coagulation parameters such as low platelets, prolonged bleeding time, or elevated INR. In fact, many patients referred for these procedures have such coagulopathies due to their underlying hepatic or renal disease. Although appropriate correction of such deficiencies will reduce the risk: when it occurs, bleeding from these procedures can be life-threatening. Therefore prompt detection of post-biopsy bleeding is of paramount importance.

Recently colour Doppler US has been shown to be useful in identifying bleeding after both US-guided liver biopsy and RFA. After needle withdrawal, colour Doppler evaluation of the needle tract can reveal a line of colour signal (‘patent track’ or ‘colour line sign’), indicating bleeding through the needle track^16,17 (Figs 16-7–16-9). This sign has been shown to indicate a significantly higher risk of clinically important post-procedure bleeding when it persists for five minutes after needle withdrawal following liver biopsy. The absence of this finding was predictive of a lack of significant bleeding with a negative predictive value of 99%.¹⁷ As this technique can be performed quickly and easily, we recommend using colour Doppler after all percutaneous biopsies of solid organs to assess for the line sign. If present, immediate pressure can be applied to the biopsy site to help tamponade the bleeding. The patient can be positioned with the biopsy site down forcing apposition of the biopsied organ against the body wall for five minutes. US can then be used to re-check for the absence or persistence of the line sign and further management decisions can be made at that point.

VASCULAR COMPLICATIONS

Arteriovenous fistulas are a known complication of percutaneous renal biopsy. The true incidence is unknown, with estimates ranging from 3–18%.¹² Although most are asymptomatic, some may cause complications such as hypertension or haematuria. Although these lesions are occult on grey scale imaging, colour Doppler US will easily identify these lesions as described above. One study found small localised flow disturbances consistent with AVFs in 12 of 77 patients using colour Doppler US immediately after renal biopsy.¹² Importantly, most of these lesions resolved by 24 hours and none were symptomatic, therefore routine treatment is not indicated. However knowledge of their presence is important in the rare patient that does become symptomatic.

EQUIPMENT

While standard ultrasound probes are ideal for daily use in the ultrasound department, they are usually not suitable for intraoperative use. Specific probes are designed for both laparoscopic and intraoperative applications. These probes are typically small and are designed to gain access into tight anatomical regions during surgery. They are configured as end-fire or side-fire probes which are usually multi-frequency (ranging from 5–9 MHz depending on their particular use and manufacturer). The intraoperative abdomen transducers are usually small linear array probes, some with novel designs, including those that can be placed on the end of the user’s finger. These probes may have higher frequencies for increased resolution. However, for other surgical procedures including guidance of intraoperative spinal cord and/or the brain surgery, transducer frequencies usually range from 7–12 MHz. Laparoscopic ultrasound probes are designed to fit through different-size laparoscopic ports usually in the range of 1 cm in diameter. Also the shaft of laparoscopic probes is fairly long (usually 25–30 cm) so they can reach from the laparoscopic port to the target organ such as the liver.

Probe sterilisation for intraoperative use includes placing a sterile covering over the transducer and cable. Maintaining meticulous sterile technique is mandatory in the operating suite. Probes are usually soaked in sterilising solution before intraoperative use to minimise significant contamination if there is a break in the sterile covering.

Intraoperative ultrasound provides increased resolution compared to transcutaneous sonography as the signal degradation from overlying fat, muscle and bone is eliminated. For instance, with the increased resolution of intraoperative liver ultrasound additional small solid nodules which are not detected on transcutaneous ultrasound are often identified. It has been estimated that intraoperative ultrasound detects more focal liver lesions compared to preoperative ultrasound, CT or even MRI.¹⁸

USES OF INTRAOPERATIVE COLOUR DOPPLER ULTRASOUND

While this discussion will not go into great detail about specific parameters utilised for Doppler sonography in a target area, it will give an overview of intraoperative colour and/or Doppler ultrasound. For the exact parameters, such as predicting stenosis with Doppler in specific target areas, please consult other relevant chapters. The use of colour Doppler during surgical procedures can be classified into five different applications. These include the following:

Many times intraoperative Doppler is utilised more than once during the course of a surgical procedure.

PLANNING SURGERY

Intraoperative Doppler ultrasound is very helpful in planning surgery. Within the abdomen either laparoscopic or open ultrasound imaging and Doppler can be utilised for surgical planning of the liver, pancreas and kidney. Ultrasound is used for defining tissue planes, identifying anomalous vessels or demonstrating tumour invasion.^19,20 For instance, in surgical resection of the liver, identification of lobar and segmental anatomy is aided by the use of colour Doppler. Colour Doppler ultrasound is important to help define a plane for resection. Thus, colour Doppler may demonstrate major vessels to allow dissection in the most avascular plane in the liver or kidney. The middle hepatic vein is a critical landmark demarcating the plane between the right and left lobe of the liver (Fig. 16-10). Anomalous vasculature is readily identified by colour Doppler sonography. For instance, accessory arterial supply is frequently identified in the liver such as either a replaced right hepatic artery originating from the SMA or a replaced left hepatic artery from the left gastric artery. Intraoperative colour Doppler is also extremely helpful in predicting the extent of disease. For instance, while preoperative ultrasound or CT may not demonstrate vascular invasion by tumour, it can be precisely localised with colour Doppler ultrasound during surgery. Further research has shown added value of the use of contrast-enhanced intraoperative ultrasound in detecting increased number of colorectal liver metastases, as compared to preoperative imaging or intraoperative ultrasound.²¹

Colour Doppler ultrasound has utility in numerous other surgical applications. For instance, intraoperative Doppler can be used to precisely localise arterial venous malformation of the brain, identifying the least disruptive surgical approach. Doppler has now replaced intraoperative angiography for confirmation of successful resection by not only demonstrating absence of colour flow of the AVM after resection; but also by identifying normalisation of resistance index in the feeding arteries²² (Fig. 16-11). Likewise, neurosurgical resection of large intracavernous paraclinoid aneurysms can be evaluated to assess blood flow of the parent and branch vessel with microvascular Doppler sonography.²³ Colour Doppler ultrasound can be used in both preoperative and intraoperative planning and decision making in head and neck surgery.²⁴

USE OF ULTRASOUND DURING SURGERY

Intraoperative Doppler ultrasound is very helpful to demonstrate success of surgery by re-evaluating vessel patency during difficult surgical dissection (Fig. 16-10). Also intraoperative blood flow to solid organs can be evaluated with intraoperative sonography.^25,26 It can demonstrate ancillary findings, including critical vessel stenosis during surgery (Fig. 16-12).

PREDICTING OUTCOMES

Microemboli can be a potential problem with any vascular surgical procedure. For example, small deposits of debris can develop at the surgical site during carotid endarterectomy or thoracic endovascular aortic repair (TEVAR) and may embolise to the brain. Intraoperative detection of these microemboli is critically important to the surgical outcome since microembolism during surgery increases the risk of perioperative stroke. Intraoperative Doppler ultrasound is used to monitor the signal from within the middle cerebral artery during the vascular surgery. A transcranial Doppler probe is placed on the thinnest portion of calvarium in the region of the temporal bone. The identification of increased spectral reflection from the microemboli, mimicking turbulence, guides intraoperative decision making, specifically increasing the use of platelet antagonists or anticoagulation.27–29

CONFIRMING SUCCESS OF SURGERY

Intraoperative Doppler sonography may be used in a number of different circumstances to confirm an appropriate surgical outcome. For instance, after clipping of cerebral aneurysm, evaluation of the aneurysm and associated vessel after clip positioning is enabled by Doppler sonography. Doppler sonography, however, is limited in some cases especially when multiple clips are placed due to acoustic shadowing from them.³⁰ Intraoperative Doppler sonography has been applied for surgical treatment of the median arcuate ligament syndrome. It can be utilised to demonstrate stenosis of celiac artery and post-stenotic dilatation before the release of the median arcuate ligament; and, afterwards, it can be used to confirm decompression of the celiac artery.³¹ It is used to predict success of vascular surgery, such as bypass grafts that may connect to vessels beyond an area of stenosis. Intraoperative confirmation of appropriate flow profiles and lack of flow restriction in the bypass graft is critical to successful surgery (Fig. 16-13).

IDENTIFYING COMPLICATIONS OF SURGERY

Probably the most important role of intraoperative colour Doppler is the timely identification of potential complications or inadequate outcomes. Identification of a critical arterial stenosis, an internal flap or a continued area of narrowing, allowing immediate surgical correction, is important to the success of carotid endarterectomy (Fig. 16-14). It obviates the need for reoperation. In one series 11% of cases of carotid endarterectomy were immediately revised because of persistent stenosis demonstrated with intraoperative duplex sonography.³²

Another major role for intraoperative Doppler sonography is identifying either arterial or venous thrombosis immediately before operative closure. This is especially important in the area of transplantation. For instance, intraoperative Doppler ultrasound can detect hepatic artery thrombosis allowing immediate revision of the anastomosis.³³ Likewise, in renal transplantation, intraoperative colour duplex scanning can detect vascular complications such as renal vein thrombosis, arterial dissection, vasospasm, or arterial occlusion^34,35 (Fig. 16-15).

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31. Tsujimoto, H., Hiraki, S., Sakamoto, N., et al. Laparoscopic treatment for median arcuate ligament syndrome: the usefulness of intraoperative Doppler ultrasound to confirm the decompression of the celiac artery. Surg Laparosc Endosc Percutan Tech. 2012; 22(2):e71–e75.

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33. Gu, L. H., Fang, H., Li, F. H., et al. Prediction of early hepatic artery thrombosis by intraoperative colour Doppler ultrasound in pediatric segmental liver transplantation. Clin Transplant. 2012; 26(4):571–576. [Feb 13].

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35. Thalhammer, C., Aschwanden, M., Bilecen, D., et al. Intraoperative colour duplex ultrasound during renal transplantation. Ultraschall Med. 2008; 29(6):652–656.