AVFs, first described by Varela in 1928 , are relatively uncommon lesions with considerable clinical impact. They may cause hypertension, local thrombosis, peripheral embolization, high-output cardiac failure, and hematuria .
AVFs can be congenital, acquired, or idiopathic. About 70% to 80% of all AVFs are acquired and may occur as a result of renal biopsy, blunt or penetrating trauma, inflammation, malignancy, or renal surgery [11, 12].
AVFs are a congenital condition in 20% to 30% of cases. It is usually located on the kidney upper pole (45%), but it also can be detected in the mid-point or in the kidney lower pole in an equal ratio . The left kidney is more frequently involved, and women are affected twice as often as men. The peak incidence is in patients ages 30 to 40 years, and AVFs are rare in the pediatric population .
Acquired fistulas are usually caused by iatrogenic injuries. A fistula can appear after renal needle biopsy, often in kidney transplant patients, and sometimes these fistulas are a post-operative complication after nephrostomy or nephrectomy, particularly in cases of intra-operative injuries of the renal pedicle [14, 15].
A fistula caused by angioplasty in a segmental renal artery branch has also been reported in the literature . Malignant tumors of the kidney and metastases can cause fistulas as a result of vein erosion. Other possible causes are penetrating or blunt abdominal trauma, fibromuscular dysplasia, and aneurysm of the renal artery [3, 4].
Congenital renal arteriovenous fistulas are the most uncommon form, but their incidence may be underestimated because patients are usually asymptomatic [5, 6]. There are two types of congenital AVMs: (1) crisoid, a malformed lesion characterized by multiple varix-like vascular communications and a major incidence of gross hematuria , and (2) aneurysmal, which typically occur in elderly patients when a pre-existing arterial aneurysm erodes into an adjacent vein .
This kind of malformation has been treated to date with surgical therapy, such as nephrectomy, which is still considered as the first-choice treatment by some authors for patients who present with alterations in the cardiovascular system, such as renin-mediated hypertension caused by fistula-related relative ischemia or high-output cardiac failure caused by an increase in venous return . Endovascular approaches to treating AVMs are now increasingly performed .
In our patient, typical diagnostic criteria of the disease were met. The patient was immediately referred to the Department of Radiology for imaging assessments because of her age; moreover, she had received only liquid re-infusions, and neither plasma nor solution of succinylated gelatine (Gelofusine Braun Medical, Milan, Italy) had been administered. It is remarkable that our patient had not undergone any surgical intervention before her presentation to our hospital, which is in contrast to what has been presented in the literature .
Our aim was to immediately treat the AVM by performing endovascular embolization to stop the bleeding, preserve renal parenchymal function, and eradicate the symptoms and hemodynamic effects associated with the abnormality that we have seen in our patient, who had a reduction in hemoglobin and an increase in heart rate. It is truly important to preserve renal function in patients who have just one functioning kidney or renal insufficiency . Indications for treating an AVM are a progressive increase in the size of the fistula, recurrent or persistent hematuria, and hemodynamic effects associated with the abnormality, especially decompensation, hypertension, and high-output cardiac failure. Recently, endovascular techniques have also been used to treat giant aneurysms with AVFs. For small renal AVFs, macroparticles or methyl cyanoacrylate glue should be used [5–7]; for larger fistulas, however, coils or detachable balloons are preferable. If there is concern regarding systemic and pulmonary emboli, a high-flow AVF should be managed by performing an open resection or ligation [5–7].
The benefits of percutaneous treatment are avoidance of nephrectomy, reduction of peri-operative risk and post-operative morbidity, reduced surgical time and hospital stay, and decreased incidence of renal ischemia .
Post-embolization syndrome (PES) may occur sometimes after transcatheter arterial embolization. PES consists of fever, loin pain, nausea, and vomiting, but selective embolization of renal AVMs allows for the preservation of the renal parenchyma and therefore leads to minimal PES .