An unusual case of posterior nutcracker syndrome

To the Editor Nutcracker syndrome commonly refers to left renal vein compression between aorta and superior mesenteric artery, resulting in increased venous pressure, kidney congestion and proteinuria. Posterior nutcracker syndrome is a rare variant, linked to retro-aortic position of the last tract of the left renal vein which remains compressed between aorta and spinal column. We report an unusual case of posterior nutcracker syndrome in a 22-year-old man with congenital solitary left kidney who was admitted to our department because of proteinuria of 700 mg/24 h and microhematuria. Upon admission, blood pressure was 120/70 mmHg. Mild pitting edema was present in his lower limbs. Laboratory workup showed a normal renal function with a creatinine of 1.1 mg/dl. Urinalysis revealed the presence of rare hyaline and granular casts and isomorphic erythrocytes. No previous episodes of left flank pain were reported. Ultrasonography was performed showing the absence of the right kidney, compensatory hypertrophy of the left organ and dilation of the left renal vein. After a few centimeters from the hilum, the left renal vein presented an abnormal course, addressed in cranio-caudal direction until merging into inferior vena cava just below common iliac arteries (Fig. 1a). Proximal venous dilation was also noted (antero-posterior diameter 13.8 mm in the hilar area, 1.6 mm in the narrow portion, ratio 8.6). Doppler peak velocities were 25 cm/s in the hilar area and 111 cm/s in the narrow portion (ratio 4.4). An abdomen contrast-enhanced computed tomography was then carried out, confirming the anomalous course of the vein. Compression of the vein was evident between left common iliac artery and a lumbar vertebral body (Fig. 1b, c). In order to confirm the diagnosis, a right femoral vein approach was performed, and the left renal vein was visualized in a contrast-enhanced phlebography (Fig. 1d). It was dilated, with a pressure gradient of 8 mmHg versus inferior vena cava. Endovascular stenting was then carried out and a self-expandable 14–40 mm stent made of nitinole was inserted where the vein narrowed. Post-procedural phlebography documented normal flow through the vessel, with no significant pressure gradient between the left renal vein and inferior vena cava. 24-h proteinuria promptly fell below 300 mg/day. Posterior nutcracker syndrome is characterized by the abnormal retro-aortic position of the left renal vein and its subsequent compression between aorta and spinal column [1–3]. Similar to the ‘‘anterior nutcracker phenomenon’’, this syndrome usually leads to renal venous hypertension and it should be considered among the causes of recurrent left flank pain, proteinuria and hematuria. A. Granata (&) A. Clementi Nephrology and Dialysis Unit, San Giovanni Di Dio Hospital, Agrigento, Italy e-mail: antonio.granata4@tin.it