KLINIKINIS ATVEJIS Aorto-caval fistula clinically presenting as left renal colic Findings of multislice computed tomography

Summary. Spontaneous aorto-caval fistula is a rare complication of abdominal aortic aneurysm. A definitive diagnosis is sometimes difficult, as the classic diagnostic signs (pulsatile abdominal mass with bruit, high-output hearth failure, and acute dyspnea) are present in about half of the patients. Diagnosis may be suspected from clinical symptoms, but sometimes atypical clinical features may obscure the actual situation. Computed tomography findings include early detection of contrast medium in the dilated inferior vena cava, which is isodense with the adjacent aorta, an associated aortic aneurysm, loss of normal anatomic space between aorta and vena cava, and rarely one can even visualize the abnormal communication between aorta and vena cava. Prompt radiological diagnosis is of key importance in the management of these patients. We describe findings of multislice computed tomography of the patient with dissecting aortic aneurysm and aortocaval fistula, clinically presenting as left renal colic. Multislice computed tomography is the imaging modality of choice for diagnosis of abdominal vascular pathology as it is noninvasive, fast and demonstrates a high diagnostic accuracy.

Classical clinical signs of ACF are pain in the abdomen/flank, palpable aneurysm, and abdominal bruit (2), though the specific "triad" is not always present. Before wide implementation of spiral and multislice computed tomography (CT), some studies reported about 75% of preoperatively undiagnosed cases of ACF (1). Specific signs of ACF on CT enable the prompt and accurate diagnosis (2)(3)(4)(5).
We report a unique to our knowledge case of combination of dissecting infrarenal aortic aneurysm with aorto-caval fistula and ischemic injury of the left kidney, clinically presenting as left renal colic, and detected by means of multislice CT.

Case report
A 62-year-old male was admitted to the hospital with acute abdominal and lumbar pain. At the initial examination, left renal colic was suspected, and the patient was admitted to the emergency department for ultrasound examination and deeper evaluation. Auscultation abnormalities or sensible pulsatile mass were not detected. Neither history of blunt abdominal trauma nor former iatrogenic impact was detected. There was no history of chronic abdominal aortic aneurysm, hypertension, signs of heart failure, as well. Laboratory findings of cholesterolemia and anemia were absent; serum creatinine and urea levels were in normal range. In the emergency department, the syndrome of ischemia of lower extremities developed, while abdominal and lumbar pain increased. Thus, the patient was referred to urgent abdominal CT scanning, without initial ultrasound examination.
A total of 120 mL of non-ionic contrast medium (300 mg I/mL; injection rate, 3.0 mL/s; scan delay, 18 s) was injected via an 18-G standard intravenous catheter into the antecubital vein of the patient. No oral contrast material was given.
CT demonstrated a large infrarenal aortic aneurysm with slightly calcified walls, involving both iliac arteries. Mural thrombus of about 2 cm in thickness was evident. Signs of intra-aneurismal dissection were apparent in the aneurismal sack (Figs. 1A, 1B). Fistula to inferior vena cava (IVC) arising from the pseudolumen and situated beneath the left renal vein was possible to identify (Figs. 1A, 1B). Slight infiltration of periaortic fat was observed at the level of fistula.
In the arterial phase of enhancement, vivid retrograde opacification in both renal veins (especially in the left one) was obvious ( Figs On delayed venous phase scanning, the left kidney showed poor enhancement, as well (Fig. 3).
The patient was transferred to the Department of Surgery. During laparotomy, aorto-iliac synthetic graft was tailored into the aorta and iliac arteries, as well as suture of IVC was performed. Suspected thrombosis of IVC was not detected at surgery.
After the operation, the patient was moved to the intensive care unit. Unfortunately, the outcome was unfavorable. The patient developed hypovolemic shock, acute renal insufficiency, and pulmonary infection and died 14 hours after operation.

Discussion
Aorto-caval fistula uncommonly arises from ruptured atherosclerotic aortic aneurysm (6). It can also result from blunt abdominal trauma and iatrogenic injury (7). Rare causes include mycotic aneurysm,

Fig. 1 A. Contrast-enhanced computed tomography through the lower aorta, axial slice
Aneurysm with dissection is apparent, as well as aorto-caval fistula (solid arrow). lues, connective tissue disorders, such as Ehlers-Danlos syndrome and Marfan syndrome (6). Clinical symptoms are nonspecific; small aorto-caval fistulas may be with no symptoms present (5). In general, aorto-caval fistulas may manifest with increased pulse pressure, venous congestion, and congestive heart failure (7-9).
in the assessment of patients with abdominal aortic aneurysm (2-4). Spiral and especially multislice CT enables short acquisition time, thin collimation, and sufficient scan volume in addition to multiphase scanning, i.e. all that is of key importance in order to rule out all possible complications of abdominal aortic aneurysm (3,4). Typical findings of ACF on CT are as follows: early contrast enhancement of the dilated IVC (earlier than renal and hepatic parenchyma), which is isodense

Fig. 2 B. Contrast-enhanced computed tomography at the level of renal veins, axial slice
Left renal vein is in retroaortic position (dashed arrow).
Before wide penetration of helical and multislice CT technologies, the condition remained undetected in 25-75% of cases (1) and thus increased risk and death rate at surgery (6,7,10). Computed tomography is well determined as the first-choice imaging modality   (11). Fifteen of these patients had retroaortic left renal vein, as well. In this review, CT was performed in three patients only.
Knowing all the possible signs of ACF presentation on CT may help the radiologist to make a definite diagnosis when it is not suspected from clinical examination.
with the adjacent aorta, retrograde enhancement of dilated renal and/or iliac veins, an associated aortic aneurysm, loss of normal anatomic space between aorta and IVC (4,5,8). In some cases, it is possible to visualize the leak itself, though reports on direct fistula visualization are rather rare (2,3,9). In addition, sometimes it is possible to track delayed opacification of the renal cortex on CT, probably due to reduced renal perfusion, decreased arterial pressure associated with venous hypertension (2,4,9).