Prevalence of left renal vein compression (nutcracker phenomenon) signs on computed tomography angiography of healthy individuals

Abstract

Objective: We evaluated the frequency of significant left renal vein (LRV) compression, also called the nutcracker phenomenon (NCP), in a normal asymptomatic population.

Methods: The present retrospective descriptive anatomic study analyzed the data from high-definition renal computed tomography (CT) angiography of living kidney donors. A total of 324 CT examinations were evaluated for signs of LRV compression, including the beak sign, aortomesenteric angle <41°, LRV diameter ratio ≥4.9, and beak angle ≥32°. The presence of pelvic varicose veins and the left gonadal vein in the proximal and mid-portion (considered dilated if >0.5 cm) were also evaluated. Anthropometric and laboratory (urine erythrocyte count) data were collected from the medical records. Statistical inference was calculated using Fisher's exact test and Student's t test.

Results: The mean aortomesenteric angle was 53.1° in women and 58.7° in men (P = .044). The beak sign and beak angle were present in 15.3% and 9.8%, respectively, and both had a greater prevalence in the women (P = .01). An aortomesenteric angle <41° was identified in 30.5%, with a greater prevalence in women (P < .01). The diameter ratio was positive in 0.7% of the cases, with no difference between the sexes. A left gonadal vein >0.5 cm was more prevalent in women in both the proximal and the mid-portions (P < .01). Although analysis stratified by positive criteria (3 or 4) showed no difference between the sexes, a positive correlation was found with younger age (P < .01). The limitations included the absence of a nutcracker syndrome (NCS) population; the lack of a renocaval pressure gradient, because of the need for intervention; the absence of other types of imaging studies, such as duplex ultrasound scan; and the absence of female parity data.

Conclusions: The NCP and NCS CT criteria were present with a high frequency in healthy individuals. Women and younger individuals showed a greater prevalence of compression findings in the aortomesenteric axis. Revision of the current NCP and NCS criteria with a distinct categorization between sex, age, and body mass index is recommended to better evaluate LRV compressive events.

Keywords: Kidney transplantation; Nutcracker phenomenon; Nutcracker syndrome; Renal vein entrapment syndrome.