A rare case of renal failure due to perianeurysmal retroperitoneal fibrosis – CT evaluation

Clinical History

A 71-year old male patient presented to our hospital with a 5-month history of low back pain, nausea and weight loss. Clinical examination revealed a prominent abdominal aorta, whereas laboratory examinations showed good haematological profile and high creatinine and urea blood levels, for which the patient was admitted in the renal dialysis unit.

Imaging Findings

A triple phase computed tomography (CT) examination of the abdomen and pelvis was performed (unenhanced, arterial and portal phase post-IV contrast administration), which showed a fusiform aortic aneurysm below the origin of the renal arteries. In addition, a concentric, lobulated, retroperitoneal soft tissue mass (mean attenuation:40 HU) surrounded the aortic aneurysm, from the level of the renal arteries till below the iliac bifurcation (Fig. 1). The aforementioned mass enveloped both ureters (Fig. 2), and therefore caused bilateral moderate hydronephrosis (Fig. 3). Post-contrast media injection phases revealed no active extravasation from the aneurysm, while there was no soft tissue enhancement demonstrated (Fig. 4). Bilateral hydronephrosis was treated with pigtail catheter placement in both kidneys (Fig. 5).

Discussion

Perianeurysmal retroperitoneal fibrosis (RPF) is part of the disease spectrum of chronic periaortitis (CP), an unusual fibro-inflammatory condition characterised by adventitial and periadventitial inflammation, medial thickening and advanced atherosclerosis. As a disease entity, it has the same histopathological findings as CP, in conjunction with inflammatory abdominal aortic aneurysm (AAA) existence [1-6]. The pathogenesis of the disease still remains unclear, with several pathogenic theories being proposed so far, including a) inflammatory reaction to antigens in the atherosclerotic plaques b) autoimmune systemic disease manifestation and c) IgG4-related systemic disease manifestation [4, 7, 8].

Clinical symptoms are nonspecific, including anorexia, weight loss, low-grade fever and dull pain over the flank, low back pain, or diffuse abdominal pain. As the disease progresses and the soft tissue encases proximal organs, symptoms may include renal colic pain (in case of ureter obstruction), lower extremity oedema and deep vein thrombosis due to extrinsic compression of lymphatic vessels and deep veins. Varicocele, scrotal swelling, and hydrocele may also occur because of obstruction of the lymphatics and venous drainage [9].

CT imaging is essential for the diagnosis and treatment of perianeurysmal RPF, as it can help determine the extent of the aneurysm and to assess possible adjacent organs encasement due to soft tissue mass existence. It can also help distinguish among the various pathological conditions included in the disease spectrum of CP. More precisely, unlike idiopathic RPF, in perianeurysmal RPF there is by definition aortic dilatation, and in contrast to inflammatory AAA there is usually entrapment of adjacent organs (most often ureters or venous and lymphatic drainage) [1-9]. In addition, perianeurysmal RPF differs from infected (mycotic) aneurysm as in the second case the aneurysm is saccular and not fusiform-shaped, with rupture risk and periaortic gas existing in some cases [10]. CT imaging may also help to evaluate the stage of the disease, as soft tissue mass enhances during the active phase, whereas chronic stages are characterised by absence or mild enhancement [11].

Histopathological examination of the surrounding soft tissue is needed for definite diagnosis. Steroids and immunosuppressive agents are used as first-line therapy, as they lead to restoration of pyeloureteral dilatation and regression of the fibrosis. Ureteral stenting and/or percutaneous nephrostomy is also required in order to relieve ureteral obstruction. Aneurysm follow-up and surgical intervention may also be needed [12-14].

Written informed patient consent for publication has been obtained.

Differential Diagnosis List

Final Diagnosis

Perianeurysmal retroperitoneal fibrosis with bilateral ureter obstruction.

URL:	https://eurorad.org/case/16056
DOI:	10.1594/EURORAD/CASE.16056
ISSN:	1563-4086