Interventional Radiology



Interventional Radiology


J. Scott Williams



I. Introduction

Interventional radiology is an important part of trauma management across many types of injury. While CT has become the dominant modality in the imaging evaluation of the trauma patient, conventional angiography remains the standard method for definitive vascular diagnosis and guidance during interventional procedures. The most common interventional procedure in the acute setting of trauma is embolization of vascular injuries.


II. The Special Procedures Environment



  • The angiography/interventional suite is best constructed, equipped, and staffed as a modified intensive care unit. All nursing staff should have ICU skills and radiologic technologists should be able to meet the demands of the emergency environment. Respiratory technologists and trauma ICU nursing staff should be accessible to assure continuity of emergency trauma care during transfer and intervention.


  • The modern angiography suite uses digital acquisition and is integrated with the hospital radiologic archiving system and the hospital information systems to facilitate the rapid availability of angiographic images and radiologic documentation. While single plane systems are adequate for most trauma applications, intervention in the head and neck and brain is facilitated with biplane technology. Comprehensive bedside imaging system controls, including control of post-processing is required.


III. General Vascular/Interventional Techniques



  • Access



    • Prompt uncomplicated access, usually transfemoral, is a key initial step to angiographic intervention. A variety of techniques are available to the operator for reliable safe access, including the Seldinger technique, single wall puncture, and micro-access technique. Use ultrasound guidance, particularly when pulses are difficult to palpate or in those with indistinct landmarks.


    • For suspected unilateral pelvic injury or lower extremity injury, use the contralateral femoral site.


  • Diagnostic angiography



    • Principles and planning



      • Indications for angiography include extravasation or pseudoaneurysm on CT, resuscitation without expected response, and difficulty identifying or controlling hemorrhage.


      • The approach to angiography begins with the review of prior imaging, particularly CT. Identification of likely sources of bleeding, which may be multiple, permits injured anatomy to be targeted first in the angiographic sequence.


      • Marking entrance and exit wounds with radio-opaque markers aids care.


      • A general operational principle of trauma angiography is to start with the least selective angiogram, usually an aortogram. If an embolization target can be localized on the aortogram, proceed with maximal selectivity without wasting time. The offending vessel should be embolized to occlusion, and then complete regional angiography completed.



      • Optimal aortography requires the use of a flush catheter and a power injector, injecting at about 20 mL/s for 2 seconds. Thoracic aortography requires at least three imaging projections.


      • Pelvic arteriography



        • Abdominal aortogram—power injected through flush catheter at 15 mL/s for 2 seconds.


        • Selective internal iliac arteries, even if aortogram is normal.


        • Care not to miss external iliac branches that may contribute to pelvic hemorrhage.


    • Angiographic equipment



      • Catheters—Three general categories:



        • Flush catheters have multiple side holes in addition to the end hole, have a circular shape at the end, and support high injection rates. These are used for thoracic and abdominal aortography as well as pulmonary arteriography. They should be used through an access sheath and advanced and removed over a guidewire.


        • Simple curve catheters are angulated near the tip with less than 90-degree angulation. They generally have only one hole, an end hole. They may be used without a sheath and be used to navigate simple branching patterns of anatomy without a guidewire.


        • Reverse curve catheters. Reverse curve catheters have a shape angle that exceeds 90 degrees; many have 180-degree shapes and multiple additional curves. Once placed through a sheath over a diagnostic guidewire, a reverse curve catheter must be shaped, a process that converts the catheter, initially extended, to its native unconstrained reverse curve shape. This may be carried out either in the aorta primarily or by advancing the catheter into a side branch of acceptable geometry, withdrawing the supporting guidewire and pushing the catheter forward in the parent vessel as to form the curve.


      • Guidewires: There are a variety of diagnostic guidewires, commonly 0.035 in. in diameter, appropriate for arteriography. The wires may be generally categorized as those that may be torqued with precision and those that may not be. Shaped tip nitinol wires are examples of the former while outer wire wrap over stainless steel core wires are examples of the latter. Operator preference is the key factor in choosing a guidewire.


      • Tools for super-selective catheterization



        • Microcatheters are small diameter catheters passed through diagnostic or guide catheters to selectively catheterize small (1 to 4 mm) vessels. Microcatheters are extremely flexible and generally may not be advanced without guidewire support. They vary in inner diameter from 0.010 to about 0.027 in. and have one or two radio-opaque markers to facilitate fluoroscopic visualization and assist coil positioning and detachment.


        • Micro-guidewires are small diameter guidewires varying in diameter from 0.008 to 0.018 in. The most commonly used size is 0.014 in. matched to a 0.021 in. inner diameter microcatheter. Micro-guidewires are made of stainless steel or nitinol and may have a shapeable platinum coil over the distal several cm, outer polymer, and/or hydrophilic coatings.


    • Angiographic findings pertinent to vascular injury



      • Direct observations include extravasation of contrast material, stenosis, intraluminal filling defect, extension of contrast material outside the expected vascular boundary, and abrupt cut-off of contrast material (“stump”).


      • Seek functional consequences of injuries during angiography. These include identification of important collateral pathways (i.e., vertebral artery occlusion and ipsilateral PICA supply), dynamics over time that may distinguish vasospasm or dysplasia from structural injury, and arteriographically out-of-phase structures that confirm the presence of abnormal arteriovenous shunt. Washout distinguishes intra- from extraluminal contrast material.


      • Indirect findings such as displacement of otherwise normal vascular structures or organs or segments of organs.



    • The spectrum of arterial dissection

      The value of grading dissection is questionable, since the grading system does not reliably predict a continuous spectrum of structural or clinical outcomes. The range of findings includes the following but do not suggest a stepwise progression per se:



      • Stenosis



        • Vasospasm—no structural injury, but structural injury may be masked. Consider repeat examination.


        • Mural thrombus/thrombosis of the false lumen—“subintimal dissection.”


      • Filling defect



        • Linear filling defect: Intimal flap


        • Bulky intraluminal filling defect: Thrombus


      • Abnormal extension of contrast beyond expected vascular boundaries with washout: Pseudoaneurysm (if there is no washout, then this is extravasation).


      • Occlusion—“stump” appearance.


      • Opacification of a vein early in the angiographic sequence: The sine qua non of arteriovenous fistula is an arteriovenous shunt.


    • Complications of angiography

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Oct 17, 2016 | Posted by in CRITICAL CARE | Comments Off on Interventional Radiology

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