Incidental finding of left renal artery aneurysm from X-ray film

Clinical History

Lumbar spine X-ray examination in patient with back pain showed a thin sclerotic calcification at the left of L1, suspected to be a renal arterial aneurysm - renal arteries arise from the aorta at the level of the intervertebral space between L1 and L2 - soon confirmed by CT multislice.

Imaging Findings

Lumbar spine X-ray examination was performed in a 56 years old woman with chronic back pain. Radiography revealed multiple degenerative discopaties in arthrosis and reduced lordosis, and also, at the left of L1, a retroperitoneal round calcification with thin, sclerotic, discontinuous border, and approximately a 1,5 cm diameter: this finding brought doubt of arterial aneurysm. There was no systemic hypertension or history of trauma. Blood tests showed normal liver and kidney function, and electrolytic and glucose levels. The patient underwent a multislice CT exam of the abdomen: CT scans have been performed in basal conditions and in arterial contrastographic phases. Non-contrast axial CT scan demonstrated a low-density round focal lesion at the hilum of left kidney, laterally limited by a thin, discontinuous calcification. Contrast-enhanced CT scans showed an intralesional central vascular enhancement similar to and synchronous with arterial vessels. The MIP (Maximum Intensity Projection) and VR (Volume Rendering) reconstructions evidenced a mushroom-shaped lesion of 16 mm x 13 mm, with a collar of 5 mm, typical for aneurysm. The aneurysm was extrarenal, supplied by the left renal artery at the origin of its bifurcation, best proven by the MIP and VR reconstructions. Both kidneys had normal volume and cortical thickness.

Discussion

Based on autopsy studies, the incidence rate of renal aneurysms (RAA) is 0.01%. However, selected patients who undergo renal arteriography have an incidence rate of 0.3-1%. On average, these patients are aged 40-60 years. RAAs can affect the main renal arteries or their branches or they can even be intraparenchymal. Extraparenchymal aneurysms predominate, comprising approximately 85% of all RAAs: 70% are saccular, 20% are fusiform, and 10% are dissecting. The other 15% of RAA are intraparenchymal. 20% of patients with RAA presents bilateral pathology and 30% has multiple aneurysms. RAAs occur equally in men and women, although ruptures are more common in reproductive-aged women. In a large series of cases by Martin et al. and Ortenberg et al., they found that the aneurysms founded at the bifurcation of the main renal artery or its branches may be related to atherosclerosis, hypertension, fibromuscular dysplasia, arteritis and trauma. Intraparenchimal RAAs may be related to polyarteritis nodosa, tuberculosis and neurofibromatosis (in children). Regardless of etiology, the common factor in the pathogenesis of RAA is the compromission of one or more layers of the vessel wall. Common to saccular and fusiform aneurysms are degenerative fibroplasia-type changes in the tunica media associated with fibromuscular dysplasia (FMD). Although atherosclerotic changes are often observed in the aneurysm wall, this is believed to be secondary. Calcification is an usual feature, but thrombotic occlusion is rare. The causes include those mentioned above along with trauma or damage following kidney biopsy and renal carcinoma. Patients with extraparenchimal RAA are usually elderly and asymptomatic and found incidentally while investigating other intra-abdominal pathologies using diagnostic imaging studies. Others present with hypertension, flank pain or haematuria. The relationship between renal artery aneurysms and hypertension is still controversial. Majority believe that aneurysms are a result of hypertension and only rarely they produce hypertension. Patients do not usually present with rupture. Patients with aneurismal rupture typically have signs and symptoms of an abdominal catastrophe and may be in frank shock. The current trend in therapy of such aneurysms is to limit indications for surgery to certain specific cases: rupture, flank pain and/or abdominal pain that may be indicative of a rapidly expanding aneurysm or impending rupture, in females who are pregnant or in those contemplating pregnancy, large size (diameter greater than 2 cm). Diameters range from 1.5 to 3 cm, although most are approximately 2 cm. However, reports of aneurysm rupture at 1.5 cm diameter do exist. Complete calcification of the wall of the aneurysm sac is present in approximately 40% of patients. This was previously believed to confer protection against rupture, even for larger aneurysms; however, more recently, this theory has been questioned. Regular follow-up examination with ultrasound or CT scan is recommended in patients who are treated expectantly. CT scan is the most widely available and reproducible imaging modality and it is the test of choice for diagnosis and follow-up, but also MRI with gadolinium enhancement and 3D reconstruction can produce images similar in quality.

Differential Diagnosis List

Final Diagnosis

Aneurysm of the left renal artery.

URL:	https://eurorad.org/case/4576
DOI:	10.1594/EURORAD/CASE.4576
ISSN:	1563-4086