Renal Artery Embolization



Renal Artery Embolization


Dierk Vorwerk




Indications


Tumor Embolization


Total renal embolization is indicated for inoperable hypernephromas in patients with persistent hematuria or severe paraneoplastic symptoms such as hypercalcemia (Stauffer syndrome). In these patients, complete embolization of the tumor-bearing kidney is indicated if a functioning contralateral kidney is still present. Some groups prefer tumor embolization even without symptoms to reduce tumor bulk in combination with immunostimulating therapies. In total embolization not followed by nephrectomy, embolization should be performed by particles of small diameters or bucrylate–ethiodized oil mixed in a ratio of 1 : 3 to 1 : 5 to allow deep deposition into the tumor tissue.


Preoperative embolization is still indicated in a small subset of tumors, especially those that have developed extensive venous involvement. Preoperative embolization may be indicated as a safety procedure in patients who refuse blood transfusions, such as Jehovah’s witnesses. In preoperative embolization, the technique is modified because only occlusion of the main renal artery is necessary. This can be achieved by coils, Amplatzer plugs, or bucrylate–ethiodized oil mixed in a ratio of 1 : 1 to 1 : 3 to achieve rapid occlusion of the main renal artery.


Partial tumor ablation by embolization (Fig. 60-1) is preferred in patients who have a tumor in a single functioning kidney. Partial embolization has also been used as a preparation for thermal ablation of a circumscribed peripheral malignant tumor to reduce the risk of postprocedural bleeding after radiofrequency ablation or to enhance its efficacy.1



There is more published experience of renal artery embolization for ruptured or bleeding benign renal tumors such as angiomas and particularly angiomyolipomas.2 The latter have a tendency to grow during pregnancy, and prophylactic embolization may be performed in women who wish to become pregnant to prevent major bleeding during pregnancy. In benign lesions, a partial embolization is preferable whenever possible.


As an alternative to partial embolization, advanced surgical techniques such as partial nephrectomy—either open or laparoscopic—and radiofrequency ablation have been described.




Bleeding Control


Blunt or direct trauma may cause renal bleeding due to renal laceration or renal artery rupture. Trauma may also cause renal artery pseudoaneurysms, arteriovenous (AV) fistulas combined with hematuria, direct hemorrhage into the pelvicalyceal system, or development of perirenal hematomas.


Unfortunately, the main causes of traumatic renal hemorrhage are iatrogenic in origin and represent the majority of cases of traumatic renal hemorrhage in Europe. They include renal biopsies in native and transplant organs, percutaneous techniques such as percutaneous nephrostomy (Fig. 60-2), nephrolithectomy, and percutaneous transluminal renal angioplasty (PTRA), where direct arterial perforation by the guidewire tip has been described.5 Also, indirect methods such as shockwave lithotripsy can lead to renal trauma requiring embolotherapy.



Although iatrogenic hemorrhage is relatively common, few cases require treatment (0.3%-1% of percutaneous renal interventions6 and 0.5% of percutaneous biopsies7). Moreover, although hemorrhage that requires treatment is unusual, temporary and self-limiting bleeding or AV fistulas occur in up to one third of percutaneous renal procedures.7 Since the introduction of partial nephrectomy techniques, bleeding after partial surgery has become a significant cause of iatrogenic hemorrhage. Approximately 2% of patients who undergo partial nephrectomy develop postsurgical bleeding, and most of them require percutaneous embolization.8


Direct stab wounds, bullet wounds, and motor vehicle accidents are other traumatic causes of renal injury. Embolotherapy is the treatment of choice in patients who are (1) not controlled by conservative management and (2) do not have complete central laceration of the renal arteries, which requires surgery.


Rarely, benign tumors such as angiodysplasias, angiomas, or angiomyolipoma (Fig. 60-3) may cause spontaneous—sometimes substantial—bleeding (Wunderlich syndrome)9 and may undergo embolization. In a few cases, they may also develop hypertension.




Renal Artery Aneurysms


As a special problem, true and false aneurysms of the mainstem renal artery10 may occur that may be prone to rupture or serve as an embolic source for renal infarction. There is a general consensus that a diameter of 20 mm is a threshold for treatment; smaller aneurysms may undergo treatment if severe hypertension is present and difficult to treat. Central renal artery aneurysms require treatment by coil placement or, if possible, exclusion by the use of stent grafts. Peripheral (pseudo)aneurysms may be due to trauma or systemic diseases such as polyarteritis nodosa. Peripheral aneurysms are best treated by exclusion, coil placement, or medical adhesive (cyanoacrylate, “glue”) deposition. The most difficult location for treatment of renal artery aneurysms is at the site of a renal artery bifurcation (or trifurcation), because exclusion of the aneurysm may require occlusion of one or more segmental arteries. A combination of bare metallic stents with coils, glue, Onyx (ethylene vinyl alcoholic copolymer [ev3/Covidien, Plymouth, Minn.]), or flow-diverting stents may be an option in these challenging locations.1014





Technique


Anatomy and Approaches


Depending on the underlying disease, a complete or partial embolization is performed. Classical indications for complete renal embolization are embolotherapy before tumor nephrectomy, total renal ablation in tumors where there is a contraindication to surgery, or defunctionalization for benign causes either in native kidneys or transplants.


Partial embolization is performed to preserve renal function when it is possible to treat a localized lesion, and can be used in traumatic or iatrogenic lesions as well as in single kidneys with renal artery tumors. Whereas in total renal artery embolization, complete destruction of functioning renal tissue is the aim of treatment, when partial renal embolization is performed, the aim is to minimize loss of normal renal parenchyma.



Technical Aspects


Many materials have utility for renal arterial embolization. For total renal embolization, absolute ethanol is a common embolic agent used. Other liquid embolics such as glue (bucrylate [Histoacryl; Braun, Melsungen, Germany]) may be used after mixing with ethiodized oil (Ethiodol, Lipiodol [Guerbet USA, Bloomington, Ind.]). Total embolization with embolic microspheres (e.g., polyvinyl alcohol [PVA] particles), using a small particle size between 20 and 500 µm, has also been described.


In partial embolization, the choice of embolic agent depends on the purpose of treatment. In selective tumor embolization, the tumor bed is preferentially embolized using small particles after superselective catheterization of the tumor-feeding renal artery branches. Alternatively, embolization with glue mixed with ethiodized oil may be performed. If the main feeding branch can be identified, it can be additionally occluded by coil placement or a bucrylate–ethiodized oil mixture. If the patient is being treated for a vascular complication such as AV fistula, pseudoaneurysm, or blunt traumatic hemorrhage, a very localized embolization is desired, either by coil embolization or local application of glue (bucrylate–ethiodized oil).


Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Renal Artery Embolization
Premium Wordpress Themes by UFO Themes