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Background
Hematuria is a relatively common presenting symptom most often this is attributable to urinary system calculi, however, a myriad of other pathologic entities may lead to the presence of blood in the urine. One rare entity which can lead to hematuria is renal arteriovenous malformations (rAVM). It is important for the radiologist to recognize this vascular anomaly which may predispose patients to clinically significant hematuria. Here, we present a case of a patient who experienced months of hematuria without a clear diagnosis on computed tomographic urogram who was eventually diagnosed with a rAVM. The relevant cross-sectional, sonographic, and fluoroscopic imaging correlates are shown, and the potential treatment options for this condition as described in the literature are discussed.

Educational Goals / Teaching Points
Review the pathophyisology of renal arteriovenous malformations. Describe the imaging findings of rAVM across multiple imaging modalities. Identify potential treatment options for rAVM.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Renal arteriovenous malformations are a rare pathologic vascular anomaly. This clinical entity is a vascular anomaly most often formed following iatrogenic or penetrating trauma. Rarely these lesions may form as the result of an adjacent invasive renal neoplasm or form as a congenital anomaly as well. The pathology of these anomalies lies at the level of the capillary vessels, which create dysplastic connections between the feeding artery and draining vein. These dysplastic vessels are prone to rupture; when ruptured into the urinary collecting system, hematuria becomes the evident presenting symptom for patients. Proper selection of imaging modality may lead to an accurate diagnosis in patients. On noncontrast CT, these lesions may be undetectable. Even on CT urogram protocols with 100 second and 8 minute delayed abdominopelvic CT performed after intravenous contrast administration, these lesions may be difficult to detect. CT angiogram will clearly delineate these lesions, which may be identified as a web of arterially enhancing vessels with early contrast opacification of the renal vein, demonstrating an underlying arteriovenous connection. Ultrasound (US) may be utilized for diagnosis as well, which would reveal tubular hypoechoic structures on B-mode imaging with evidence of turbulent internal flow when color doppler technique is utilized. On magnetic resonance imaging (MRI), these lesions present as T2-hypointense flow voids secondary to the high velocity of blood flow through the rAVM. The gold standard in diagnosis and treatment is via catheter directed angiography and catheter directed embolization.

Conclusion
rAVMs are a very rare cause of hematuria which may be radiographically occult on noncontrast enhanced CT and on CT urogram studies. Contrast-enhanced arterial phase CT is the recommended diagnostic modality for these lesions; US and MRI may serve as useful adjuncts. The gold standard diagnostic examination is catheter based angiography, at which time therapeutic actions such as embolization may be taken.