The field of radiology was once limited only to the diagnosis of the diseases. Nevertheless, the advances in the diagnostic imaging modalities over the last half a century have enabled the possibility of utilizing imaging in guiding real-time treatment of diseases. The minimally invasive interventional radiology has led to avoidance of surgery and its related complications in some patients, while in others IR-facilitated surgery by creating an avascular plane in patients with potential bleeding complications. The interventional radiology has now encompassed diseases from head to toe, involving all of the medicine. In this article, we will explore the journey of interventional radiology, with advances in imaging and the new sophisticated treatments.
The foundation
The root for the development of interventional radiology is innovation. It is innovation that has been used as a common thread in the techniques and the instruments involved in the field of interventional radiology. Innovation occurs when someone improvises a new tool or a technique or tries to create a tool to solve a clinical problem. The new technique or tool will be compared with the existing one in terms of clinical, safety, and cost parameters, thus having its role a defined one. Thus, innovation and creativity formed the basis for the practice of interventional radiology over the last 50 years.
History
The diagnostic angiography was the earliest breakthrough in 1953 by a Swedish radiologist, Sven Ivar Seldinger, who innovated and introduced his “Seldinger technique”, which allowed for the small-bore needle-guided catheter access, thus minimizing vascular trauma (1). Following this, diagnostic angiography became widely available in the “pre-CT” era where the diagnosis of many pathologic conditions was dependent on diagnostic angiograms. This led to the development of various tools like image intensifiers, digital subtraction cineangiography, rapid film changers, etc (2).
Subsequently, the dawn of interventional radiology occurred with the blocking or constricting the artery in case of bleeding disorders while dilating the arteries in case of stenotic disorders.
Interventional radiology today
Interventional radiology today has spread its branches widely to enable and provide service to all the fields of medicine. Although the interventional radiology has expanded itself enormously, this article will be limited to the utility of interventional radiology in neurology, neurosurgery, head and neck, and gastrointestinal system.
Neurointerventions:
The utility of interventional radiology has grown leaps and bounds in neurology and neurosurgery to provide important clues in diagnosing neurological disorders and treating various acute and chronic disorders. The major breakthrough in acute emergency came with treating acute stroke in 2015 with five landmark trials (MR CLEAN, EXTEND-IA, ESCAPE, REVASCAT, SWIFT PRIME) (3-7) establishing the benefits of stroke thrombectomy, within the window period. The Hermes metaanalysis, which comprised these major trials, has signified the incredibly smaller number needed to treat (NNT) with stroke thrombectomy, and NNT was only 2.6 (8). Currently, stent retrievers and aspiration catheters are the widely used instruments in stroke thrombectomy (6,7). The other causes of hemorrhagic stroke include aneurysms, arteriovenous malformations, and dural arteriovenous fistula. Endovascular therapy has spread its wings to provide treatment for these disorders.
Intracranial aneurysms are the major cause of subarachnoid hemorrhage. SAH has high mortality, and the mortality associated with rebleed increases up to 40%. Thus, ruptured intracranial aneurysms are of utmost importance to have them treated adequately to prevent them from rebleeding (9). Though surgery and endovascular coiling form the mainstay of definitive management, ISAT and BRAT trials advocated “coil-first” approach to reduce the morbidity associated with surgery (10,11). Presently, IR in intracranial aneurysms has increased its armamentarium from coils, stents, flow divertors and endosaccular devices (intrasaccular flow disruptors) like web device, medina, contour device (12,13). The requirement of dual antiplatelet therapy precludes usage of stents and flow divertors in ruptured intracranial aneurysms.
AVMs and dural AV fistula are anomalies that can lead to intracranial hemorrhage. AVMs refer to abnormal communication between intracranial arteries and pial veins. DAVFs refer to anomalous communication between extracranial arteries and dural venous sinuses. They are amenable to both surgery and endovascular therapy. Endovascular treatment will be done using permanent liquid embolic agents like onyx, squid, and n-butyl cyanoacrylate (NBCA) (14). Currently, interventional treatment for intracranial AVM is limited to ruptured AVM based on ARUBA trial (15).
Spinal vascular disorders include arteriovenous fistula and arteriovenous malformations. Advanced imaging techniques like 3D SPACE and time-resolved contrast-enhanced MR angiogram helps in localizing the AV fistula (16). These imaging techniques reduced the angiogram time and radiation dose for the diagnosis and facilitate endovascular treatment for the same. After analysing the angioarchitecture, liquid embolic agents are used in the embolization of spinal vascular malformations. Embolization of anterior or posterior spinal arteries is the dreaded complication that can lead to paraplegia or paraparesis. Superselective angiograms of intercostal arteries are required to evaluate the origin of anterior or posterior spinal arteries to avoid inadvertent embolization of these vessels(17).
Head and neck interventions:
Hypervascular head and neck tumours have become amenable to surgery after the advent of preoperative embolization using liquid embolic agents. Various head and neck soft tissue vascular malformations have become easier to treat with sclerosant agents (sclerotherapy) and liquid embolic agents (18). Orbital vascular malformations also could be effectively treated endovascularly, with particular caution to be exercised with respect to the origin of the ophthalmic artery (19). The important complications associated with head and neck embolization are the inadvertent embolization of intracranial vessels due to presence of persistent fetal collaterals between the internal and external carotid arteries. The usual site of collaterals is seen at the ophthalmic artery, cavernous internal carotid artery, and vertebral artery (20). Superselective angiograms are required to prevent this avoidable complication.
Hepatobiliary interventions:
The important pathologies for which interventional radiology could offer solutions include hepatocellular carcinoma, obstructive jaundice, and liver metastases. The treatment for HCC includes ablation procedures and transarterial chemoembolization (TACE). The types of ablation procedures are thermal ablation, chemical ablation, and electrical ablation. The subtypes of thermal ablation are heat-based approaches (radiofrequency ablation, microwave ablation) and cooling based approaches (cryotherapy) (as shown in fig.1). Irreversible electroporation (IRE) is the electrical pulse-based ablation. Chemical ablation procedures include injection of ethanol and acetic acid into the lesion. Chemical ablation is not advisable due to its variable efficacy, though inexpensive. RFA and microwave ablation are the commonly used techniques due to their proven efficacy and their ease of use. The current indications for ablation procedures include smaller lesions (lesion <3 cm, or up to 5 cm), inoperable for surgery (21).
TACE involves selective cannulation of hepatic artery, and super-selective tumor angiograms will be taken. Following this, the chemotherapeutic agent (doxorubicin or epirubicin) will be injected into the selected vessel, and then embolization of the hepatic artery will be done using gelfoam beads. Thorough preprocedural investigations including the evaluation of liver function tests, ascites, prothrombin time, cardiac evaluation are to be done as the important complication of TACE is decompensation of liver failure and cardiac toxicity associated with the chemotherapy. Child–Pugh scoring and BCLC staging of liver disease are the important determinants of performance of TACE in a patient with HCC. Currently, TACE is the standard of care for patients with BCLC stage B disease (22).
Obstructive jaundice occurs due to obstruction of the bile duct at various levels ranging from hilum to distal common bile duct. The obstruction of bile ducts results due to malignancy arising from bile duct and stricture due to extrinsic compression. The interventional radiology treatment aims to relieve the obstruction by percutaneous transhepatic biliary drainage (PTBD). PTBD can be done in one of the three ways.A) Externalization: A pigtail catheter will be placed into the bile duct proximal to the stricture for external drainage. B) Internalization: The stricture is crossed, and a self-expanding metal stent will be placed across the stricture to relieve the obstruction (as shown in fig.2). C) Internal–external drainage: A special type of catheter (ring-biliary) catheter is placed distal to the stricture for both internal and external drainage of bile (23).
CONCLUSION:
Interventional radiology has evolved itself as an indispensable clinical subspeciality of radiology over the last fifty years to cater service to every speciality. The minimally invasive nature of the procedures helps patients to tolerate the procedure well with much-reduced morbidity and mortality associated with the procedure. This article covered the most important neurointerventions, head and neck interventions, and hepatobiliary interventions.
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FIGURES:
FIG.1: Microwave ablation of liver metastases: Image in (A)represent a small hypodense lesion is seen abutting middle hepatic vein in a patient with sigmoid colon primary neoplasm. Microwave antenna was placed in the distal end of the lesion as represented in (B). Image (C) exhibits the lesion clearly before embolization and image (D) shows post ablation effects with a clear 1 cm margin
FIG.2: PTBD in a patient with recurrent neoplasm: Image in (A) dilated intrahepatic biliary radicals in a patient who underwent right hepatectomy for intrahepatic cholangiocarcinoma.z Lesion around the duodenum in the tumor bed, as represented by arrow in (B). Image (C) exhibits the stent placement after crossing the lesion (stent is exhibited by red outline), and image (D) shows after stent placement and balloon dilation; the duodenal lesion is opacified by contrast (as marked by arrow in D). There was another fistulous tract noted in the stomach (as signified by arrowhead in D)
