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Asymptomatic nutcracker phenomenon: entrapment of the left renal vein shown by CT without left flank or pelvic pain, or macroscopic haematuria
  1. Masaki Tago,
  2. Naoko E Katsuki,
  3. Yuka Hirakawa and
  4. Shu-ichi Yamashita
  1. General Medicine, Saga University Hospital, Saga, Japan
  1. Correspondence to Dr Masaki Tago; tagomas{at}cc.saga-u.ac.jp

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Description

A 65-year-old woman presented with a 6-month history of mild epigastric pain without weight loss, left flank pain, pelvic pain, or macroscopic haematuria. Previously, during a routine medical check-up, she had been shown to have liver dysfunction. Subsequent abdominal ultrasonography incidentally revealed dilatation of the left renal vein. At the present evaluation, urinalysis showed no microscopic haematuria. Corticomedullary phase images of abdominal contrast-enhanced CT (CE-CT) revealed dilatation of the left renal vein in the upper stream of the region compressed between the superior mesenteric artery (SMA) and the aorta (figures 1 and 2). They also showed a dilated left lumbar vein with possible collateral circulation (figure 3), suggesting a diagnosis of the asymptomatic nutcracker phenomenon (NCP).

Figure 1

Corticomedullary-phase, axial, contrast-enhanced CT image shows the beak sign and a dilated left renal vein that is compressed between the superior mesenteric artery and the aorta (arrowhead).

Figure 2

The reconstruction contrast-enhanced CT image reveals that the left renal vein is entrapped between the superior mesenteric artery and the aorta (asterisk).

Figure 3

Corticomedullary-phase, axial, contrast-enhanced CT image shows that the left lumbar vein is dilated to 4.2 mm diameter with signs of reflux (arrows).

NCP is defined by its imaging findings, that is, entrapment of the left renal vein between the SMA and the aorta, regardless of the presence of symptoms.1 2 Among its presentations, symptomatic NCP, identified by such symptoms as haematuria or left flank or pelvic pain, has been designated the nutcracker syndrome (NCS). Its clinical features are thought to be caused by dilatation of the renal veins or formation of varices in the testicular or ovarian veins that flow into renal veins due to obstruction of their normal venous return.3 In contrast, NCP without any symptoms, despite displaying typical imaging findings, is called the asymptomatic NCP.3

Useful CE-CT clues for diagnosing NCP include (1) the beak sign, (2) a hilar diameter-to-aortomesenteric diameter ratio of ≥4.9, or (3) a combination of the SMA—aortic angle of <25° and visualisation of a dilated collateral vein with signs of reflux. The sensitivity and specificity of these three diagnostic clues are 91.7% and 88.9%; 66.7% and 100%; 80.0% and 88.2%, respectively.3–5 Our patient exhibited the beak sign (figure 1) and the combination of an SMA—aortic angle <25° (figure 4) and visualisation of a dilated collateral vein with signs of reflux (figure 3). The large diameter ratio was not present.

Figure 4

The sagittal reconstruction contrast-enhanced CT image shows an superior mesenteric artery—aortic angle of 20° (arrows).

Epigastric pain is not a typical symptom of NCS, although a patient with NCP and epigastric pain due to a complicated SMA syndrome has been reported.6 CE-CT revealed no findings of SMA syndrome in the present patient.

Learning points

  • Asymptomatic nutcracker phenomenon may be diagnosed despite CT images typical of the nutcracker syndrome (NCS). Careful follow-up and observation of such patients are essential for applying timely treatment for possible emerging symptoms.

  • The (1) beak sign, (2) a hilar-to-aortomesenteric diameters ratio of ≥4.9 or (3) the combination of a superior mesenteric artery—aortic angle <25° and visualisation of a dilated collateral vein with signs of reflux were reported to be useful CT imaging clues for diagnosing NCS.

References

Footnotes

  • Contributors MT: involved in literature search, study conception and manuscript drafting. NEK: involved in study conception and manuscript drafting. YH: involved in manuscript drafting and clinical care of the patient. S-iY: involved in study conception and manuscript revision.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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