British Medical Bulletin Advance Access published online on April 30, 2007
British Medical Bulletin, doi:10.1093/bmb/ldm006
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Modern trends in interventional radiology
Interventional Radiology Department, Guy's and St Thomas' Hospital, London, UK
* Correspondence to: Dr Tarun Sabharwal, Radiology Department, First floor Lambeth Wing, St Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK. E-mail: tarun.sabharwal{at}gstt.nhs.uk
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Abstract |
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Top
Abstract
IntroductionObjective: To review the current applications of Interventional Radiology (IR), outline newer technologies and techniques and emphasize the role of Interventional Radiologists as clinical practitioners.
Background: IR is a clinical modality that makes use of imaging guidance for the performance of minimally invasive treatment. The development of new imaging technologies and interventional devices has greatly increased the number of medical conditions that may now be treated by IR.
Promising new treatments in cancer therapy, the treatment of fibroids, venous access and spine interventions as well as advances in non-invasive vascular imaging, pharmacological therapies and peripheral arterial and venous interventions are providing exciting opportunities for IR, attracting significant patient interest and promising tremendous public benefit.
Keywords: Interventional radiology • minimal invasive • therapeutic treatment
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Introduction |
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Interventional radiology (IR) was developed from diagnostic angiography and the innovative minds and technical skills of many radiology-angiographers. Charles Dotter1 first discussed the idea of IR in June 1963, at a congress in Czechoslovakia, when he said that an angiographic catheter used with imagination may become an important therapeutic instrument.1 On January 16, 1964, he successfully demonstrated his vision by performing the first percutaneous angioplasty of a tight localized stenosis of the superficial femoral artery in an 82-year-old woman with painful leg ischaemia and gangrene of the toes.2 Since then, the emergence of this speciality has been made possible by enormous technological advances in catheter and instrument design and manufacture, imaging systems and radiological expertise. Advances in medical imaging has led to a decrease in diagnostic invasive procedures, like diagnostic angiography, while there was a significant increase in minimally invasive therapeutic techniques. Twenty years ago it was the angioplasties, thrombolysis, treatment of gastrointestinal (GI) bleeding and non-vascular procedures like biliary, urinary tract and abscesses drainages that contributed the main workload of IR. In the last decade, the development and evolution of arterial stents and stent grafts, percutaneous tumour ablation techniques, embolization procedures including fibroids and tumour chemoembolization, venous ablation, venous access and musculoskeletal interventions have exponentially expanded the therapeutic possibilities IR may offer. Nowadays, IR is a clinical-oriented speciality which uses imaging modalities for diagnosis, consultation and consent issues with patients, procedural guidance and follow-up of patients. This review offers a brief overview of some of the main current interventional procedures, and focuses on new developments and trends in IR.
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Angiography—non-invasive vascular imaging |
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Non-invasive imaging techniques have replaced the use of angiography for the diagnosis of most vascular diseases. Routinely, patients undergo a combination of ultrasound, computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) in the evaluation of vascular disease.
Today's interventionalist must have a fundamental knowledge of ultrasound, CTA and MRA, so that they can integrate these non-invasive modalities into daily practice for diagnosis and treatment planning. Non-invasive imaging benefits patient care, as vascular pathology is identified and treatment decisions are made with less risk to the patient and without unwarranted catheter angiography. It also affords more widespread vascular screening, allowing diagnosis to be made at an earlier stage.
Multi-detector CTA has greater spatial resolution than MRA, is quicker, has no venous contamination and has better acceptance from patients than MRA.3 Advantages of MRA are the lack of ionizing radiation, the non-nephrotoxic contrast, better diagnostic accuracy in heavily calcified vessel and the significantly reduced time taken for image reconstruction and post-processing.4
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Peripheral vascular interventions |
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Since percutaneous transluminal angioplasty (PTA) of peripheral vessels was first described by Dotter and Judkins2 in 1964, the procedure has been performed with increasing frequency. Today, angioplasty of iliac, superficial-femoral (SFA) and popliteal arteries is a widely accepted and commonly performed procedure.5,6 For iliac vessels, stenting seems to have long-term patency rates comparable with that of surgical aortoiliac by-pass grafts.7 Angioplasty of the infrapopliteal vasculature has gained increasing popularity over the past few years as technical advances, including low-profile ‘monorail’ balloons, and soft 0.014 inch radiopaque, steerable guidewires and ‘subintimal technique’ have made tibial PTA safer and more successful.8
Until recently, stenting of SFA has failed to show any advantage over PTA. In a randomized control study published in May 2006 in the New England Journal of Medicine,9 primary stenting of the SFA with self-expanding nitinol stents yielded superior results than those of the currently recommended approach PTA with optional secondary stenting. Further trials, with longer follow-up periods are required for a consensus on this issue.
Innovative techniques used in peripheral vascular interventions, which may also play an important role in the future, include intravascular brachytherapy, cryoplasty, cutting balloon angioplasty and implantation of drug-eluting stents.
Carotid stenting Early results of two large recent randomized control studies have failed to prove non-inferiority of carotid artery stenting compared with carotid endarterectomy.10,11 Currently, carotid endarterectomy is the standard of care for treatment of carotid artery disease and stenting is justified only if the following conditions are met:
- Re-stenosis at a carotid endarterectomy site where a repeat carotid endarterectomy is associated with high risk of injury (e.g. facial nerve, etc.).
- A patient with severe carotid disease who has had prior radiation of the head and neck.
- Unfavourable anatomy (e.g. high-carotid bifurcation).
- Severe comobidities (advanced cardiac or pulmonary disease, etc.).
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Renal artery angioplasty and stenting There have been several favourable developments within IR technology to improve the outcome for renal interventions. These include contemporary low-profile (five French or even four French) balloons and balloon expandable stents, that tract over 0.014 or 0.018 inch steerable, floppy tip-stiff shaft, rapid exchange monorail guide wires, that have significantly decreased the morbidity and the duration of the procedure. In order to avoid contrast-induced nephropathy N-acetyl-cysteine is administered, good pre-hydration is required and the preferential use of iso-osmolar contrast media (Iodinaxol) instead of low osmolality contrast media. In cases of severe renal impairment, gadolinium or carbon dioxide angoiography can be used as an alternative to the conventional contrast medium.
There has also been stricter patient selection guidelines practiced widely within IR for renal intervention. It has been emphasized that patients should undergo evaluation for renal artery stenosis (RAS) only when the detection of RAS will alter the therapy. Three broad clinical situations have been identified in which patients should undergo evaluation and treatment for RAS:12
- Hypertension: Patients with the onset of hypertension before the age of 40, particularly those with no family history (possible fibromuscular dysplasia), patients with accelerated or resistant hypertension.
- Renal insufficiency: Patients with worsening renal function precipitated by an angiotensin-converting enzyme-inhibitor; patients beyond the age of 60 with coexistent diffuse atherosclerotic disease, especially with a normal urine sediment; and asymmetric kidney size or a decrease in the size of a solitary kidney.
- Cardiac disturbance syndromes: Patients with recurrent ‘flash’ pulmonary oedema not secondary to cardiac ischaemia.
- Prophylactic therapy is not justified. However, if the stenosis is severe enough to be considered ‘preocclusive’ revascularization, may be undertaken when there is a solitary kidney, severe RAS is present bilaterally, progression of RAS is documented, kidney size decreases, renal function deteriorates or blood pressure control becomes more difficult.
Covered stents Covered stents/peripheral endografts are now an integral part of every IR suite. These come in various diameters and lengths and it is essential that these are available. The primary indications are for post-angioplasty vessel rupture, for arterial trauma and pseudoaneurysm formation (Fig. 1), for degenerative aneurysms of peripheral vessels (iliac, popliteal aneurysms) and for treatment of recurrent intimal hyperplasia. (TIPS procedures, venous stenosis in dialysis outflow.)
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Aortic stent grafts |
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It has been approximately 15 years since Parodi et al.13 reported the first successful clinical use of a stent graft for exclusion of an abdominal aortic aneurysm (AAA) in 1991. Endovascular aneurysm repair (EVAR) is now commonly used to treat patients with amenable anatomy.14 The justification for the use of such a technique relates to observed decreased short-term mortality and aneurysm-related mortality when compared with open surgical repair, although overall mortality is the same for both techniques and re-interventions are more common with EVAR.15 EVAR is related to significantly decreased hospital stay, less surgical morbidity and earlier return to preoperative levels of activity.16 Overall, the current status of EVAR continues to be exceptionally robust and promising. The introduction of new devices allows additional patients to qualify for the procedure, and this number continues to expand. Today's devices are smaller, better tapered and more durable.
Recently, fenestrated and branched customized stent grafts have been used successfully for the endovascular exclusion of juxtarenal and suprarenal aneurysms of surgically unfit patients.17 Even complex thoraco-abdominal aneurysm which involved the thoracic and visceral abdominal aorta, and are related to high surgical mortality and morbidity can be treated, nowadays, with a combination of endovascular exclusion and visceral revascularization. The key principle of this procedure called ‘hybrid operation’, is that retrograde revascularization of the visceral and renal arteries through an abdominal approach allows for endovascular stent grafts to exclude a thoraco-abdominal aneurysm that extends into the visceral aorta. Intermediate results are promising and these procedures are going to be developed further in the future.18
Key role in the success of EVAR is the multi-disciplinary approach and the team work. Following the early clinical experience with stent grafting of the abdominal aorta, this technique was used for the first time, in 1992, in the management of descending thoracic aortic aneurysms by Dake et al.19 Since then, a rapidly growing number of applications have been reported for a wide spectrum of thoracic aortic diseases. These include acute and chronic aortic dissection, penetrating atherosclerotic ulcer, traumatic injury, mycotic aneurysm, aortobronchial fistula, aneurysm after coarctation repair and rupture. Although the cumulative experience with thoracic stent graft repair is limited, studies to date have demonstrated promising preliminary results, supporting further evaluation of this technology.20
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Percutaneous biopsy and drainage procedures |
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Imaging advances have included CT fluoroscopy and better resolution and more readily available ultrasound machines. In addition, MRI is also being increasingly used for needle guidance and treatment. Most biopsy procedures may be performed on an outpatient basis. Even in patients with coagulopathy, techniques such as transvenous approaches and ‘plugged’ (where the percutaneous biopsy tract is occluded with embolic material) biopsies allow tissue samples to be obtained with relative safety.21
Urinary tract Percutaneous nephrostomy is the placement of a drainage catheter into the renal collecting system under imaging guidance. It is used in the management of renal obstruction, urinary leaks and as a prelude to percutaneous nephrolithotomy or ureteric stenting.
Biliary tree Biliary intervention is often carried out using endoscopic techniques. Biliary obstruction can be relieved by the insertion of an external drain into the dilated biliary system to allow decompression. However, external catheters are an unsatisfactory method of long-term relief from biliary obstruction, which is best managed by the insertion of an endoprosthesis. Plastic endoprostheses are of relatively small calibre and are prone to blockage; they have been replaced by metallic stents, which are much less likely to become occluded and can be inserted with less discomfort and risk.22 Mucocele or empyema of the gall bladder can be treated with percutaneous drainage in patients who are too frail for surgery.
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Gastrointestinal interventions |
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Oesophageal, duodenal and colonic stents Fluoroscopically guided balloon dilatations and stent insertions have been an established and successful service routinely provided for in IR.23,24 What is now new is the emergence of smaller introductory devices and more flexible stents and, in particular, the availability of retrievable stents. This is likely to increase the number of procedures such as the insertion of temporary stents in benign disease or in patients awaiting surgery but being downstaged with chemotherapy.
New advances in oesophageal stent technology include retrievable metallic stents for benign strictures refractory to balloon dilatation, as a bridge to surgery, or when complications occur24 and stents with an anti-reflux valve for stenting across the gastro-oesophageal junction.
Patients with gastro-duodenal obstruction and acute obstruction of the colon are often elderly and frail with dehydration and electrolyte imbalance. Self-expanding metallic stents rapidly relieve obstruction and improve clinical condition; they have a high success rate and low morbidity.
Percutaneous gastrostomy Nutritional support is indicated for patients who cannot eat normally and can be enteral or parenteral; the former is preferable whenever possible. In patients with impaired swallowing (e.g. after a stroke, in patients with tumours of the head and neck), the placement of a gastrostomy tube under fluoroscopic guidance can greatly improve well-being and ease of management. Often, the need for uncomfortable and distressing nasogastric tubes and intravenous lines is avoided. Gastro-jejunostomy tubes are preferred if there is gastric outlet obstruction or gastro-oesophageal reflux.
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Tumour ablation |
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Oncological interventions are one of the fastest growing fields within IR. Tumour ablation is now being performed widely. Percutaneous techniques of local tumour ablation may be categorized into three major groups:
- injection (ethanol, acetic acid, hot saline);
- heating (radiofrequency, electrocautery, interstitial laser therapy, microwave coagulation therapy, high-intensity focused ultrasound);
- freezing (cryotherapy).
Advantages of the ablative therapies compared with surgical resection include reduced morbidity and mortality, low cost and the ability to perform procedures on an outpatient basis. All these techniques induce cell death by coagulative necrosis.
Percutaneous liver tumour ablation The liver is the organ with the greatest number of patients eligible for treatment with percutaneous tumour ablation given the large number of patients with primary or secondary hepatic malignancies, and the low number eligible for surgical resection. Multiple minimally invasive techniques have been developed including percutaneous ethanol injection (PEI), interstitial laser photocoagulation, microwave, cryotherapy, focused ultrasound and radiofrequency ablation (RFA).
PEI has proven to be clinically effective in the treatment of hepatocellular carcinoma (HCC). Long-term survival rates of PEI-treated patients with HCC are similar to those of patients treated surgically.25,26
RFA is now the preferred modality for treatment of HCC, as experience with PEI shows similar results but with more sessions required for small tumours (<2 cm) and worse results for tumours larger than 2 cm.
Cryoablation has been used for many years during open surgery and is an effective method of tissue destruction. Currently, small size probes for effective percutaneous therapy are not widely available.27 Microwave ablation may have theoretical advantages over RFA (if technical difficulties can be overcome) regarding uniformity and shape of thermal lesion. The thermal lesion heats up more uniformly, and is less dependent upon thermal conduction and surrounding blood flow than RFA.
PEI and RFA work better for HCC than for liver metastases. Possible dielectric differences allow large HCC to be more effectively and completely treated than large colorectal metastases to the liver, regardless of the ablation method. However, there is evidence that there is a survival benefit for RFA treatment of unresectable liver metastases (Fig. 2).28
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Renal tumour ablation Experience with percutaneous RFA and cryoablation of renal tumours continues to increase. Indications remain limited to those patients with known contraindications to partial or complete nephrectomy due to cormorbid conditions or advanced age, and small tumour burden. Von Hippel Lindau and hereditary RCC may also be successfully treated with RFA, which preserves kidney function. Small and exophytic tumours are best suited for treatment with RFA, but selected patients with larger or central tumours may be successfully treated. Centrally located masses are harder to treat and the complication rate may be higher. This is likely related to the higher blood flow in the renal hilum that prevents complete thermocoagulation due to a heat-sink-effect. Also, thermal injury to the central collecting system can cause urinoma or fistula.29
Intermediate results of renal tumour RFA are excellent, with very few complications30 but long-term results are awaited to allow comparison of 5- and 10-year survival rates with partial and radical nephrectomy.
Lung tumour ablation Worldwide experience with lung RFA is increasing for both primary and metastatic lung tumours. The surrounding air in adjacent normal lung parenchyma may provide insulation for the thermal lesion, making burning of the tumour easier and faster than in the well-vascularized liver.
Initial experience shows that lung RFA yields high local tumour control rates and is associated with acceptable morbidity.31 Current indications include Stage I, small non-small cell lung cancers in inoperable patients and small limited metastases.
Ablation of benign and malignant bone tumours RFA has been applied to both benign and malignant bone tumours. The first use was for small painful benign osteoid osteomas with excellent results.
Preliminary studies in malignant bone tumour RFA is showing promise.32 Previously irradiated foci of tumour can be treated locally. Pain reduction, control of haemorrhage and local tumour eradication can be attained. In areas where tumour abuts, vital structures such as the spinal cord, RFA may not be effective since local thermal injury may not be desirable and in such cases cryotherapy can be used. RFA can be performed in conjunction with vertebroplasty. In larger tumours, a combination of RFA and external beam radiotherapy may improve local recurrence rates. In theory, thermocoagulation of the central, less vascular tumour (often not effectively treated with radiation) with RFA may make the peripheral well-oxygenated tumour more effectively treated with radiation.
Early reports show promise for RFA of painful soft tissue tumours that are recalcitrant to conventional radiation and pharmacological therapies.32
RFA of nerve ganglia has been effective in the treatment of multiple pain syndromes including trigeminal neuralgia, celiac ganglion pain, cluster headaches, chronic segmental thoracic pain, cervicobrachialgia and plantar fascitis. RFA has also been used for inflammatory, idiopathic and tumour-related pain. Multiple minimally invasive neurodestructive techniques have been safely applied for pain control, including RFA, cryoanalgesia and chemical neurolysis with agents such as phenol, alcohol and hypertonic saline. Neurodestruction, decreased interstitial or intra-tumoural pressure or decreased pressure upon adjacent structures may be the mechanism of pain relief in patients with focal tumour pain.32
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Embolizations |
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Arterial embolization is one the major therapeutic applications of IR and has been performed with great success for more than 20 years for GI bleeding, pelvic and abdominal trauma, massive haemoptysis/bronchial artery embolization, post-partum haemorrhage and preoperative embolization of hypervascular tumours. Advances in microcatheter technology and evolution of embolic materials including microcoils and particles (bead block, embospheres), have significantly increased the efficacy of the aforementioned procedures which nowadays are not only performed in tertiary centers, as they used in the past, but also in every district hospital which offers IR services.
Uterine fibroid embolization An embolization procedure which has emerged the last decade and is one of the main areas of interest of interventional radiologists nowadays, with major impact on public health is uterine fibroids embolization (UFE).
At the present time, UFE is the most appropriate procedure for pre-menopausal patients, with no plans of childbearing in future, and have uterine fibroids that are documented definitively with imaging studies and reasonably correlate with the presenting symptoms (given their size and position within the uterus). Presenting symptoms typically include menorrhagia (with or without anaemia), chronic pelvic, back, or leg pain, significant abdominal distension, ureteral compression causing hydronephrosis or urinary symptoms due to bladder compression. Although opinions differ regarding the appropriateness of offering this procedure to post-menopausal patients and patients with future plans of childbearing, counseling is mandatory to make sure that these patients undergo appropriate diagnostic testing and be certain that they are aware of the potential risks and benefits in this setting.
UFE appears to be effective, both in terms of symptom control and also in improving the health-related quality of life. Complications are infrequent and usually minor, including post-embolization syndrome, non-target embolization and infectious complications (
1%).33
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Venous access |
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The indications for the placement of central venous catheters are continually expanding because of the rapid growth of haemodialysis services, oncological centers and transplantation programmes. Traditionally, central venous catheters for long term use have been inserted by surgeons using a cutdown technique in the operation theatre under general anaesthesia.
Nowadays, it is a routine practice of interventional radiologist to insert the tunneled lines and portcaths, safely and accurately, using ultrasound and X-ray guidance, under local anaesthesia in a minimally invasive way. The scope of line insertions extends to end-stage venous access and IRs are more frequently being asked to place inferior vena cava or hepatic vein access lines. Interventional radiologists are trained to cope with post-procedural catheter care, patient follow-up and management of long-term complications.34
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Inferior vena cava filters |
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Although systemic anticoagulation remains the cornerstone of venous thromboembolism treatment, not all patients are candidates for this therapy; some fail the therapy, and some patients on anticoagulation suffer complications from the treatment. Fortunately, inferior vena cava (IVC) filtration is available for these selected patients as an adjunctive treatment for venous thromboembolism, or as an effective prophylactic measure in selected high-risk patients.35
Currently available devices could be classified as ‘optional’ filters, since they can function as permanent or temporary filters. A retrievable IVC filter, that is optional as a permanent or temporary filter, is an attractive alternative for patients with a time-limited necessity for IVC filtration, such as severely injured trauma patients at high risk for pulmonary thromboembolism and patients with venous thromboembolism and a temporary contraindication for anticoagulation who subsequently undergo anticoagulation.35
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Spine interventions |
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Vertebroplasty/kyphoplasty Vertebroplasty is a radiological procedure for the treatment of intense pain caused by vertebral compression fracture in patients whose pain has been refractory to medical management or bracing. It uses the US Food and Drug Administration (FDA) approved intraosseous injection of acrylic cement, under local anaesthesia and fluoroscopic guidance to control the pain of vertebral fractures associated with osteoporosis, tumours and trauma (Fig. 3). Pain reduction or elimination is immediate (85–90%), and the risk of complications is low.36
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This procedure is associated with a low morbidity rate. Less than 1% of patients with non-neoplastic lesions and only 5–8% of patients with neoplastic lesions have morbidity, which may include local pain, rib pain, spinal stenosis, nerve root compression and intravascular extension of acrylic.36
Kyphoplasty is a refinement of the vertebroplasty procedure. In this procedure, the additional step involves the insertion of two high-pressure balloon tamps that create a cavity prior to the injection of a more thicker prepared cement. However, there is no clear evidence that kyphoplasty is associated with better results than vertebroplasty, and is a much more expensive procedure.
Other minimally invasive radiological techniques for percutaneous treatment of back pain include facet joint injections of corticosteroids and long-acting local anaesthetics, synovial cyst injections, sacroiliac joints injection, selective nerve route injection and percutaneous nucleotomy and nucleoplasty. All of these procedures may be performed under X-ray and CT guidance, with local anaesthesia, effectively and safely.
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Varicose veins ablation |
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Venous insufficiency is a widespread health problem affecting many people. Operating for varicose veins is the commonest vascular surgical procedure and approximately 30% of these patients will have a recurrence of symptoms. Minimally invasive ways to treat varicose veins include the long-standing injection sclerotherapy and the newer techniques of endovenous thermal ablation including radiofrequency and laser. Percutaneous ablation for varicose veins was first carried out by an IR in United States and since then has now become the more popular treatment option for varicose veins among surgeons and IRs worldwide. Using ultrasound guidance and local anaesthetic, in an outpatient setting, the great saphenous vein is punctured lower down in the leg and the laser fibres or RFA probes are advanced towards the sapheno-femoral junction. Thermal therapy is then carefully delivered while the probe/fibres are slowly withdrawn.37
Procedure time for RFA is approximately an hour, with rapid recovery after 1–3 days and rare complications (bruising 5–10%, skin burn, DVT, paresthesia 1%. Results are excellent having 90–95% of veins initially closed. Recanalization and reccurence of symptoms is reported in 5–10% within the first 2 years.36
Laser ablation can treat larger veins than RFA (RFA theoretically limited to 12 mm diameter). The procedure time is shorter (30–30 min per vessel), however, the recovery time is slightly longer. Complication rate is low with minor (bruising) somewhat more than RFA, but with similarly low incidence of major complications. Technical results are excellent with 95% of veins closed initially. Recanalization rates are probably lower than RFA.38
The initial start-up costs of laser and RFA are similar but consumable cost of laser is approximately one-third of RFA.
Patients and doctors should be aware that almost every patient will require adjunctive therapy, phlebectomy and/or injection slerotherapy. Patient's compliance post-procedure compression is critical.37
Cosmetic IR As more and more interventional radiologists are entering into the minimally invasive management of varicose and spider veins, we can expect to come across more patients with an interest in cosmetic treatment. IR is well suited to expand into this emerging field; most interventional radiologists will have the manual dexterity, anatomical knowledge and image guidance necessary to perform excellent cosmetic injections.
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Conclusion |
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In the years to come IR will be the leader in providing the most innovative, non-surgical, high-tech, cost-effective, image-guided diagnosis and treatment.
Accepted for publication February 21, 2007.
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