Without injection
Arterial phase
Parenchymal phase
Extravasation blush
Hematic hyperdensity
Extravascular contrast
Extension of the leak with persisting hyperattenuation
False aneurysm
Isodense
Contrast-enhanced outpouching without a delimiting wall
Persistent enhancement of the well-circumscribed outpouching
Arteriovenous fistula
Isodense
Early venous opacification
Washout
During arteriography, initial global injections allow the cartography of the afferent supplying vessels. Distal selective injections depict a low-flow extravasation or unmask one hidden by a vasospasm. High frame rate (6 frames/s) might be necessary so as not to ignore transient bleeding or to evaluate more precisely the hemodynamic features of arteriovenous communications.
If the morphological assessment is the radiologist’s responsibility, the embolization indication, however, as a rule, must be decided by a multidisciplinary team among which anesthesiologists, medical specialists, surgeons, oncologists, and radiotherapists, within a formalized framework (multidisciplinary meetings) or in an emergency setting. This multi-team decision as well as the other therapeutic alternatives should be reported in the medical file.
2.2 Embolization Techniques
The embolization target (truncal or parenchymal), the vessel size and the flow rate, the vascularization type (end artery or anastomotic), the catheterization pathway, and the occlusion type (permanent or temporary) are the parameters which condition the choice of the access (puncture site, catheters) and the choice of the occlusion agent. Three questions must thus be answered:
1.
What type of occlusion: a temporary or a permanent one?
2.
What is the target of occlusion: vascular truncal (vessels depicted on angiography) or distal parenchymal (vessels undepicted by angiography)
3.
How much parenchyma should be preserved? (The more distal is the embolization, the greater the risk of ischemia.)
When choosing an occlusion agent, it is necessary to put into the balance its safety with its effectiveness. The cost is also an essential parameter.
2.2.1 Truncal Embolizations
They are carried out to divert blood flow or to treat a vascular lesion (aneurysm, vascular injury, etc.). No matter what the initial clinical condition is, two situations are distinguished:
Preservation of the parent vessel patency (aneurysm, arterial rupture, etc.).
Vascular occlusion is the possibility of occluding the concerned segment (Table 2.2).
Table 2.2
Truncal embolization strategy
Vessel to be preserved: access?
Vessel to be excluded: caliber, flow, downstream parenchyma?
Covered stent
Gelfoam
Coils
Packing
Plugs
Liquid agents
In the first case, in order to preserve the parent vessel, according to the target size and its accessibility, a covered endoprosthesis can be used (endobypass), or a filling of the vascular cavity can be carried out (aneurysmal sac or false aneurysm).
Larguable balloons are no longer used and have been replaced by coils which can be deployed safely by using remodeling techniques should the collar be difficult to treat; the collar can thus be protected by a balloon or a stent during the coil delivery. In addition, in high-flow vessels, a balloon can be inflated upstream, thus reducing the flow and securing coils release. More recently, the use of Onyx® has been reported to treat visceral aneurysms.
In the second case, to exclude a vascular segment, a distal and proximal “sandwich” occlusion is the ideal solution in order to prevent a reinjection by anastomotic networks. When it is not possible to cross the lesion, liquid agents (glues, Onyx®) can in some cases be used, after assessing the risks of out of target embolization. In case of end arteries, a proximal embolization may be carried out. Occlusion agents are selected according to the caliber of the vessel and the type of embolization (permanent or temporary):
Absorbable gelatin sponge (Gelfoam) is very frequently used in a trauma context, allowing a temporary hemostasis, even in vessels of medium size. Vessel recanalization is generally observed 3 weeks post-procedure.
Coils ensure a mechanical occlusion. Their profile allows both distal and proximal occlusions.
AV plugs have considerably simplified the occlusion procedure for large vessels, with a controlled release, even in case of high flow.
A temporary upstream inflation of an occlusion balloon, before the delivery of embolic agent, can simplify the procedure by reducing the flow. In the event of arteriovenous communication, a balloon brought through the venous system can also be inflated downstream.
2.2.2 Parenchymal Embolizations
The goal here is to devascularize a tumor, a traumatic or hyperfunctioning tissue, in order to obtain hemostasis, ischemia, or tumor necrosis, to divert blood flow or to deliver cytotoxic drugs or radioactive particles. But whatever the aim, the main principles of embolization are common:
Preliminary assessment of the blood flow, afferent vessels and collaterals, and careful iterative reevaluations during embolization.
Choice of the occlusion agent accordingly to the need or not to preserve downstream tissues.
Additional proximal occlusion should be carried out only in specific cases (Table 2.3).
Table 2.3
Parenchymal embolization strategy
Initial assessment
Material
Associated measures
Afferent vessels
Gelfoam
Non-systematic proximal embolization
Collaterals
Particles
Protection of the collateral network
Flow
Glues
Analgesics and/or anti-inflammatory drugs
Access
Alcohol
2.2.2.1 Evaluation of Flow, Afferent Vessels, and Collateral Networks
A comprehensive assessment of the afferent vessels is a prerequisite: non-bronchial systemic arteries in case of hemoptysis, diaphragmatic or parietal arteries and hepatic tumors, polar renal arteries for kidney trauma, etc.
During embolization, this vascular reevaluation should be carried out whenever there is the slightest doubt, as vascular redistributions can unexpectedly occur.
In some indications (radio-embolization, chemoembolization, etc.), it can be necessary to carry out a truncal occlusion of the collateral network (i.e., gastroduodenal artery) to preserve the downstream parenchyma and to avoid off-target embolization.
When using particles or cyanoacrylate, the flow is a decisive factor in the progression of the occlusion agent. It will sometimes be necessary to withdraw the diagnostic catheter or the carrier catheter/sheath, to carry out a free-flow injection via a micro-catheter.
2.2.2.2 Choice of a Distal Embolization Agent
Particles, biological glues, sclerosing agents, and alcohol can be used. Particles are preferred when one wishes to avoid a complete downstream necrosis (uterine fibroids, hemoptysis, GI tract hemorrhages, etc.). Their diameter must be adapted to the target. Because of the intra-tumor shunts, particle diameters inferior to 300 μm are rarely used. The risk of parenchymal ischemia is inversely proportional to the size of the particles. Apart from tumor embolization, the size of the particles is usually gradually increased, in order to complete with a proximal exclusion.
Glues, alcohol, and sclerosing agents can be used to obtain tissue necrosis (superselective tumor embolization, etc.). Pure alcohol exposes to the risk of necrosis of adjacent and distal tissues. Systemic diffusion is its main pitfall, which makes it difficult to administer precisely.
Glues ensure exclusion of some distal targets, but their use requires considerable skill. Their association with Lipiodol enables the modulation of their viscosity.
2.2.2.3 Associated Proximal Occlusions
In inflammatory diseases or tumors, the reoccurrence of hemorrhages is possible: a prior proximal occlusion precludes other embolizations. So the proximal occlusion is in theory performed in specific situations (preoperative embolization, hemostasis embolization in traumatic context, etc.).
2.3 Adjuvant Medications
Vasoactive drugs, pro-thrombotic agents, and antiangiogenic agents have been proposed to complete and/or extend the duration of vascular occlusions.
In practice, their use remains limited. In specific chapters of this book, we shall describe the elective indications for each targeted zone (GI tract and postpartum hemorrhages, etc.).
Similarly we shall discuss the complementary prescription of hormones, growth factor inhibitors, and antimitotic agents.
Anti-inflammatory drugs will be detailed in the following paragraph (sedation).
2.4 Anesthesia and Sedation
If most of the simple procedures can be carried out under local anesthesia or conscious sedation, the use of major sedation or of general anesthesia is sometimes necessary. The collaboration with anesthesiologists is particularly helpful for the management of vulnerable patients with comorbidities: from our point of view, this collaboration is mandatory. Patient management is determined by initial clinical status, foreseeable pain, procedure duration, and required patient positioning. Ideally the clinical evaluation carried out during a pre-procedure consultation is standardized according to the scale of the American Society of Anesthesiology (Table 2.4).
Table 2.4
ASA physical status classification system
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