Figure 1. Diagram of the angiographic classification of AV malformations by Cho et al.11: Type I ...

Figure 2. Schematic drawing of Yakes classification. Source:Yakes et al.26: Type ...

Figure 3.

Figure 4.

Figure 5. Injection of n-butyl-cyanocrylate (Histoacryl) through the microcatheter into the ...

Figure 6. Post-embolization follow-up.

Figure 7. Four-month-follow-up with abdominal CT scan without IV contrast. Axial ...

Figure 8. Follow-up with IV contrast. Coronal view.

Introduction

Renal arteriovenous malformations (AVM) are abnormal communications between the intrarenal arterial and venous systems.¹

AVMs are categorized as congenital, idiopathic, and acquired. The first amount to 25% of the total.^3,4,5,7 They occur more often during the third and fourth decades of life mostly in women and in the right kidney.^1,4,6 Acquired AVMs are also called AVF (arteriovenous fistulae), they are the most common of all (75%) and are due to iatrogenic trauma like that caused by renal biopsies, extracorporeal lithotripsies or surgeries. The estimated prevalence of renal AVMs is <0.04%.^5,6

The clinical presentation is micro or macroscopic hematuria in 75% of the cases is due to the rupture of the dysplastic vessel inside the urine collection system. Hematuria is a common cause for consultation at the emergency room and urology offices.

 Hematuria can be due to different causes. For study purposes it is useful to divide them into nephrological: primary (glomerulopathies, glomerulonephritis) and secondary causes (systemic erythematosus lupus, Schonlein-Henoch purpura, Goodpasture syndrome, vasculitis, Fabry disease, thrombotic microangiopathy, endocarditis, sepsis, and amyloidosis) and non-nephrological (renal tumors, renal lithiasis, urinary tract infections, cystic processes, urological traumas, radiation, metabolic disorders, blood dyscrasias, vasculorenal processes, and ex vacum hematuria).⁹

Other forms of presentation of renal AVMs can be flank, colic backpain due to the accumulation of clots in the urinary tract, nausea, vomits, arterial hypertension (AHT), congestive heart failure, continuous murmur or, less specific, palpable flank mass.^1,3,4,5,7,8

The coronary computed tomography angiography (CCTA) is a sensitive imaging modality for the detection of renal AVMs while selective renal arteriographycan reveal the vascular architecture and hemodynamics in detail.^2,10,12 Therefore, treatment is etiology oriented.

Renal artery embolization (RAE) is the treatment of choice for the management of renal AVMswith different embolic materials and has given good results.

We present the successful management of hematuria through selective artery embolization in 2 patients with hematuria and no significant past medical history.

Review of the medical literature

Angiographic findings and embolization technique

Peripheral AVMs are classified according to the Cho et al. score¹¹ depending on the angioarchitecture formed among nutrient arteries, the nidus, and draining veins. This architecture seen on the angiographyis at the baseof the therapeutic and prognostic decisions made. Cho described 4 different architectures (figure 1) and proved thatAVMswith multiple arterial branches flowing towards a single vein, types #1 and #2, have a better response to therapy.AVMswith multiple entries and exits, types #3a and #3b, have a worse response to therapy.

Yakes²⁶ established a new classification (figure B) of the angioarchitecture of these lesions. This new AVM classification system is used to decide which endovascular approaches and embolic agents that will be able to eliminate these AVMs. Yakes classification included lesions that, according to the to theInternational Society for the Study of Vascular Anomalies (ISSVA) classification of 2018, are classified as arteriovenous fistulae (AVF) and not as AVMs.

Embolization technique

A 5-Fr introducer sheath is often inserted into the right common femoral artery. The selective catheterization of the renal artery was performed using a 5-Fr catheter (Cobra, Cook) for the renal arteriography. The contrast injection rate to perform the renal angiogram was established at 5 mL to 7 mL/s with a total volume ofbetween 10 mL to 15 mL. High-flow renal AVMs are defined as thedraining vein opacified before staining the renal parenchyma; on the contrary, they were defined as low-flow renal AVMs.

A 2.8-Fr microcatheter was inserted. Catheter insertion (Progreat catheter, Terumo, Japan) was performedinthe identifiable target vessels for the transarterial embolization.

Several embolic materials have been used for the embolization of renal AVMs including particles (gelatin sponge particles), polyvinyl alcohol (PVA) particles, metallic coils (detachable and pushable), vascular plugs, detachable balloons, and liquid materials (absolute ethanol, NBCA, and ethylene-vinyl alcohol copolymer) (Onyx). The right selection of the embolic material to use will be based on the type of renal AVM and the size and flow of the fistula.

A final renal angiography was performed after the procedure to assess the target vessel occlusion and the infarcted renal area of the damaged kidney.

Technical success was defined as the complete occlusion of the nutrient arteries and the nidus of the renal AVM with a greatest preservation possible of normal renal arterial branches. Clinical success was defined as the resolution of hematuria or the disappearance of relevant symptoms for renal AVMs.

Case report

Clinical case #1

Forty-three-year-old male patient, athlete (cyclist) from Paraná city (Entre Ríos) without a significant past medical history. Three months ago, macroscopic hematuria started suddenly after performing water ski. No hospitalization or transfusion was required at the time. Afterwards, the patient showed asthenia, lack of energy and repeated episodes of hematuria. The lab tests performed show these values: hematocrit, 31.2; hemoglobin, 11.9 with normal remaining parameters. The renal ultrasound, abdominal and pelvic CT scans, and abdominal NMRI (nuclear magnetic resonance imaging) performed show an image that is consistent with a renal AVM located in the upper portion of the left kidney. A selective renal arteriographyis performed that confirms the presence of a renal AVM with high-flow fistula (figure 1 and figure 2). The multidisciplinary team recommends selective renal arterial embolization.

Afterwards, the patient was referred by his company to our center. There he was treated with super-selective embolization of the renal AVM with a mixture of n-butyl-cyanocrylate (NBCA, Histoacryl) and iodized oil (Lipiodol; Guerbet) (figure 3). For the total occlusion of the nidus, the segmental artery was sacrificed, which induced a small renal infarction (figure 4). The only procedural complication reported by the patient was mild discomfort in the region of interest that would away within 3 days.The patient was released from the hospital 2 days after the procedure and after the control CT scan performed confirmed the embolization of the AVM and the renal infarction region in the upper portion of the kidney. The lab test confirmed the presence of a normal renal function.

Abdominal and pelvic Uro-CT scans were performed at the 3-and-6-month follow-up (figure5, axial view without IV contrast and figure 6, coronal view with IV contrast) followed by lab tests of the renal function. The patient’s general state of health was good, and no hematuria relapses were reported.

Clinical case #2

Twenty-five-year-old woman who presents to the ER with clinical signs of hypogastric pain of 1-day duration and overt hematuria with sudden-onset clots. The patient has no significant past medical history; the physical examination conducted revealed a good general state of health, the patient remained hemodynamically stable with pale mucosa, soft, depressible and painless abdomen, and no masses or signs of peritoneal irritation. The results of the remainder of the physical examination were within normal limits.The patient was hospitalized, and the lab tests gave the following results: hemoglobin, 12.7; hematocrit, 37; leukocytes, 6800; platelets, 301000; normal coagulation times; cytochemical testing with urine pH 7; density, 1015; erythrocyte sedimentation rate >20; proteins, 500; creatinine, 0.7; negative PCR; normal electrolyte levels, renal and urinary tract ultrasound with intravesical clots. The CT urogram performed revealed the presence of intravesical clots and upper calyceal cluster images of heterogeneous densities that were consistent with a clot and late contrast clearance in the right kidney; the urology unit performed a diagnostic flexible uretero renoscopy that confirmed the presence of right lateralizing hematuria, multiple clots in the renal pelvis, and upper calyx; in the latter, erythematous, flat lesions of vascular appearance were seen. Also, another cribriform lesion was seen through which pulsatile blood was flowing out. A JJ catheter was inserted.

The patient remained with macroscopic hematuria and hemoglobin levels dropped to 7.8 with clinical signs of dizziness and adynamia. Therefore, 3 red blood cell units were transfused. Upon suspected arteriovenous malformation, an arteriography was performed without any significant findings. Then, a magnetic resonance angiography was performed that ruled out vascular malformations or other lesions in the renal parenchyma. Given the persistence of the clinical signs, a new arteriography was performed again without any significant findings. Therefore, it was decided to proceed with selective embolization with polyvinyl alcohol (PVA) particles (Contour 500–710 microns, Boston Scientific) and resorbable particles (Gelfoam, Pfizer) in the lobar and interlobal arteries of the upper pole of the right kidney. The hematuria was solved, and hemoglobin levels went back to normal. The patient was discharged after 5 days. Laboratory tests were conducted to assess the renal function at the 15-day follow-up. Renal function was looking good and the JJ catheter was removed.

Discussion

Renal AVMs often present with hematuria, which poses a therapeutic challenge because of their deep location in the renal parenchyma.¹⁴

Physicians have several diagnostic tools available for the study of hematuria: urine cytological-chemical test, urine culture, urine cytology, plain abdominal x-ray, renal and urinary tract ultrasound, computerized tomography urogram (Uro-CT scan), excretory urography, magnetic resonance imaging, and cytoscopy. The latter and urine cytology are probably the most important ones in elderly adults. It is in these patients that neoplastic disease should be ruled out as the first cause of the bleeding. Also, they have high-sensitivity and are cost-affordable.¹ However, we should remember the importance of the clinical history to be able to detect risk factors of neoplastic disease like smoking, occupational exposure to chemical materials, age > 40, recurrent urinary tract infections, abuse of analgesics, and pelvic irradiation.^5,6

Lateralizing essential hematuria, also known as chronic unilateral hematuria or benign lateralizing hematuria, is defined by the cytoscopic finding of macroscopic hematuria in a single meatus even with all diagnostic imaging tools looking normal as it was the cases of the patient of clinical case #2. Some patients can have a colic as a consequence of the passage of the clots, and even anemia, but for the most part the patient will remain asymptomatic; it is more common in young patients and its prevalence is the same regardless of sex and side it occurs on. A complete study should include renal function tests, peripheral blood tests, hemograms, coagulation tests, urine cultures, urine cytologies, cultures for fungi and tuberculosis.⁷

There is still no consensus on whether to perform an arteriography in all patients with essential hematuria because spontaneous AV malformationsare a rare entity. Therefore, the arteriography should be limited to patients previously treated with renal biopsy, surgery or with renal trauma or tumors;it is also acceptable to perform an echo-Doppler ultrasound, contrast CT scan or CCTA; if an AV malformation is highly suspected a selective arteriography with embolization should be suggested;^8,13 congenital or idiopathic AV malformations are rare since they are often due to percutaneous renal procedures like renal biopsies or renal traumas, situations where the most common malformation are pseudoaneurysms.¹⁰

AV fistulae are an abnormal communication between the arterial and venous circulation without a capillary bed. They can be congenital, idiopathic or iatrogenic. In most cases, fistulae go misdiagnosed. However,they can cause anemizing macroscopic hematuria, abdominal pain, hypertension and, in extreme cases, heart failure and even death. Fistulae and aneurysms can present simultaneously, which is something that can happen when the periarterial hematoma of the aneurysm penetrates the vessel wall and establishes communication between these 2 types de circulation.¹¹ AV fistulae are often acquired due to traumas or percutaneous procedures. However, they can be idiopathic, often solitary, and due to renal artery congenital aneurysms that develop at the sides ofa venous vessel; their diagnosis is often an incidental finding in an imaging study or as part of the diagnostic algorithm of hematuria.^15,16

Patients with hematuria due to vascular malformation should be managed according to their hemodynamic stability bearing in mind that this entity can lead patients to death; therefore, in unstable patients or patients with active bleeding, the proper resuscitation techniques should be used followed by an urgent procedure. However, in stable patients these procedures can be delayed, and if necessary other diagnostic tools can be used for clarification purposes.¹⁷ Endovascular techniques and open-nephron sparing surgeries are elective in this second group of patients, that is, in stable or even asymptomatic patients; regarding unstable patients or patients with vascular anatomies non eligible for endovascular treatment, simple nephrectomy is the only therapeutic option here.¹⁶ However, we should not forget that some AV malformations can resolve spontaneously without adding extra mortality to the patients. It is unknown as why this happens, but it has been suggested that the hematoma induced lesion compression, vasospasm, perilesional edema, and turbulent flow may contribute to solve this condition, something even more feasible in small single lesions.¹⁸

Although the digital subtraction angiography is the gold standard for the diagnosis of vascular disease,¹⁹ there are some thin nutrient arteries of renal AVMs that cannot be identified clearly in the early arteriography. However, they become more evident after the occlusion of nutrition arteries. Therefore, an early renal arteriography should be performed carefully to reveal the details of the vascular structure. Also, the embolization protocol should be modified based on the arteriography performed during the procedure.

Arterial embolization has been used as a minimally invasive technique since 1973. Before this time, the only therapeutic option was open surgery with its multiple morbidities and complications; currently, most patients are treated percutaneously with high rates of success and low morbidity rates. Complications are rare including post-embolization syndrome, renal artery dissection, and loss of renal function due to ischemia in the renal parenchyma, which is sometimes more extensive than expected.^20,21 The latter is the most significant complication of all because itimpacts the patients’ quality of life and requires the use of iodinated contrast and post-embolization devascularization; however, super-selective embolization can reduced this as the loss of renal tissue is minimized to the fullest.²²

During arterial embolization different materials can be used such as metallic coils, sclerosing agents, and particulate matter; choosing one material over the other depends on the anatomy, vascular hemodynamics, condition, and targets set by the operator.

In the patients of the afore mentioned 2 clinical cases, embolization was performed with polyvinyl alcohol (PVA), resorbable particles (gelfoam), and a mixture of butyl-cyanocrylate (NBCA, Histoacryl) and iodized oil (Lipiodol; Guerbet) since the goal here was to fully obliterate the blood flow.

Embolization should be performed selectively, as in the patients mentioned, because that is how the renal parenchyma sacrificed by ischemia after the catheterization of a specific lobar artery can be reduced. By doing this, the infarctions caused are segmental and limited; arteries can also be embolized supra-selectively by causing the specific occlusion of miniscule arterial branches, preserving the normal surrounding vasculature, and causing infarctions in <10% of the parenchyma, which is associated with a scarce reduction of renal function.²³

Chatziioannou et al.²⁴ presented a series of 6 patients with renal vascular malformations who underwent a renal arteriography with selective embolization and a 23-month follow-up. The percentage of loss of renal parenchyma was estimated through an arteriography performed before and after the embolization and based on the creatinine levels measured before and after the procedure. All patients had good outcomes and required one session only; in all the patients urine cleared after 4 days. All of them had normal creatinine levels on day 5 when they were released from the hospital, except for one patient with underlying renal damage. None of the patients had complications, the resulting ischemic area in all the patients was between 0% and 30%, with an average 12%,²⁴ a percentage that can be reduced between 0% and 15% when supra-selective embolizations are performed.²⁵

Conclusions

Patients with macroscopic hematuria should be studied in detail because, although it is evident that the first cause that should be ruled out is neoplasms, there are other significant causes like vascular malformations that, if not diagnosed in a timely manner or treated inadequately, can lead to the patient’s death or loss of his kidneys. It is obvious that the best option for the management of these patients should be the one that benefits them the most with the fewest adverse events possible. Therefore, selective arterial embolization is a very good option because it solves hematuria and preserves a significant percentage of renal tissue.

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