Excerpt from Renal Arteriovenous Malformation

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Renal arteriovenous malformations (AVMs) are abnormal communications between the intrarenal arterial and venous systems. These malformations are either congenital or acquired (often by iatrogenic means). Renal AVMs are usually identified during the evaluation of gross hematuria. Treatment can be tailored to the individual patient. Options for therapy range from observation to embolization to nephrectomy.

Renal AVM usually refers to the congenital type of malformation. Two types of congenital renal AVMs are described. The cirsoid AVM is the most common type, and the cavernous congenital AVM is less common. On the other hand, acquired renal arteriovenous anomalies are often termed renal arteriovenous fistulas. Idiopathic renal arteriovenous fistulas have the radiographic characteristics of acquired fistulas, but no cause can be identified. They may be associated with renal artery aneurysms.

History of the Procedure

Renal AVMs were described first in 1928 by Varela. Angiographic embolization is the preferred treatment for symptomatic AVMs and has been used since the mid 1970s. Nephrectomy and partial nephrectomy are more invasive treatment options. The first planned nephrectomy was accomplished in 1869 by Simon for the treatment of ureterovaginal fistula. The first partial nephrectomy was performed for a nonmalignant renal mass by Wells in 1884.

Problem

Renal AVMs and fistulas include various abnormal connections between the intrarenal arterial and venous systems. They cause hematuria and are associated with hypertension.

Frequency

Renal AVMs are uncommon. The estimated rate in large autopsy series is less than 1 case per 30,000 patients. In clinical studies, usually including patients undergoing evaluation with urologic or vascular imaging techniques, the incidence ranges from 1 case per 1000-2500 patients.

Congenital AVMs account for less than one third of renal AVMs. Most of these are the classic cirsoid type. Congenital cirsoid AVMs have a dilated, corkscrew appearance, much like a varicose vein. Cavernous AVMs, with single dilated vessels, account for the remainder of congenital malformations.

Acquired arteriovenous fistulas are the most common and represent as many as 75-80% of renal AVMs.

Idiopathic renal arteriovenous fistula represents less than 3% of renal AVMs.

The international incidence of renal AVMs is influenced by the prevalence of percutaneous renal surgery and biopsies because these interventions cause most of the acquired renal fistulas.

Etiology

The etiology of congenital AVMs is unknown. On the other hand, the cause of acquired AVMs is usually known.

Percutaneous renal biopsy is the most common known cause of acquired renal arteriovenous fistula. An estimated 15-50% of biopsies result in some degree of fistula formation. In one study in which arteriograms were performed after every renal biopsy, radiographic evidence of fistula was identified in 15% of patients.

Trauma is another important, although uncommon, cause of acquired renal fistulas. In patients with hypertension following renal trauma, renal AVMs may occur in one third of patients. In patients with penetrating trauma, arteriovenous fistulas may affect as many as 80% of patients with posttraumatic hypertension.

Idiopathic arteriovenous fistulas are thought to arise from the spontaneous erosion or rupture of a renal artery into a nearby renal vein.

AVMs may also occur in the setting of malignancy. Renal cell carcinoma has a vascular predilection, with renal vein extension and parasitic tumor vessels both being relatively common. Angiogenic tumor factors have been implicated and may explain the development of AVMs within renal tumors.

Pathophysiology

In the cirsoid congenital AVM, multiple communications exist between the arteries and veins. These communications develop multiple coiled channels, forming a mass within the renal parenchyma. The communicating vessels are tortuous, dilated, and located beneath the lamina propria of the renal urothelium. This cluster of vascular channels forms a mass, with the arterial supply arising from one or more segmental or interlobar renal arteries. Its nearness to the collecting system may explain the high prevalence of hematuria.

The less common cavernous congenital AVM is characterized by a single artery that feeds into a single cystic chamber, with a single draining vein.

Acquired AVMs result from traumatic disruption of renal vessels. A fistulous connection between the arterial and venous systems occurs as a result of the trauma.

Any renal AVM may result in renin-mediated hypertension.

Clinical

Gross hematuria is the initial sign or symptom in most (as many as 75%) patients with a renal AVM.

Renal colic may result from obstructing blood clots, which may be voided as vermiform (wormlike) masses.

Rarely, during the evaluation of asymptomatic microscopic hematuria, an AVM is found and presumed to be the cause of hematuria.

A significant percentage of patients with renal AVMs are hypertensive. Half the patients with acquired AVMs and a quarter of the patients with congenital renal AVMs have high blood pressure. Preexisting hypertension is thought to be a risk factor for developing a fistula following a renal biopsy. Conversely, hypertension that develops following a biopsy can be due to increased renin secretion that is caused by relative hypoperfusion distal to the AVM.

Cardiomegaly, congestive heart failure (CHF), or both also may be present among patients evaluated for renal AVMs.

Rarely, a patient may present with hypotension from hemorrhage caused by an AVM. This has been described in numerous settings, including during pregnancy.

A history of a previous renal biopsy or percutaneous renal surgery is an important risk factor for the development of an acquired arteriovenous fistula. A history of renal trauma, especially a penetrating injury, is also an important risk factor for developing a renal fistula.

A physical evaluation may demonstrate findings of a flank bruit. A palpable mass is usually present in those patients with renal tumors as the cause of the fistula.

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