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The Reliability of the “Absent Cistern Sign” in Assessing LP Shunt Function

  • Abhaya V. Kulkarni (a1), Mary Cheang (a1), Paul D. Chumas (a1), James M. Drake (a1) and Derek C. Armstrong (a1)...

Abstract:

Objective:

One of the difficulties with lumboperitoneal (LP) shunts has been non-invasively ascertaining shunt function. It has been previously reported that in the presence of a functioning LP shunt the perimesencephalic cisterns become obliterated – the “absent cistern sign”. In order to more rigorously test this association we performed a retrospective analysis of LP shunt patients at the Hospital for Sick Children, Toronto.

Methods:

The CT scans of all patients undergoing LP shunting over a 17 year period were reviewed. The “absent cistern sign” and ventricular size were compared against the results of either an isotope shunt study or surgical findings performed within 2 days of the CT.

Results:

There were 38 CT scans (27 patients) performed within 2 days of an isotope shunt study and 15 CT scans (14 patients) performed within 2 days of a surgical intervention. These results give the absent cistern sign a sensitivity of 75% and a specificity of 57% when compared to the shunt isotope findings and a sensitivity of 100% and a specificity of 50% when compared to the surgical findings. Over 30% of the CT scans showed ventriculomegaly in the presence of a functioning shunt and, conversely, nearly 45% of the CT scans had normal or small lateral ventricles in the presence of a malfunctioning shunt.

Conclusions:

The “absent cistern sign” appears to reliably rule out a completely blocked shunt, but is less reliable in detecting a normal or partially obstructed shunt. Ventricular size correlates poorly with LP shunt function.

Résumé: <span class='italic'>But:</span>

Une des difficultés associées aux dérivations lombopéritonéales (LP) est de s'assurer de façon non invasive que la dérivation fonctionne. On a rapporté antérieurement que les citernes périmésencéphaliques sont oblitérées en présence d'une LP fonctionnelle – le “signe de la citerne absente”. Nous avons effectué une analyse rétrospective des cas de patients ayant une dérivation LP au Hospital for Sick Children à Toronto afin d'évaluer de façon plus rigoureuse cette association.

<span class='italic'>Méthodes:</span>

Nous avons revu les tomodensitométries de tous les patients qui ont subi une dérivation LP sur une période de 17 ans. Le “signe de la citerne absente” et la taille ventriculaire ont été comparés aux résultats soit d'une étude isotopique de la dérivation ou aux observations chirurgicales obtenues dans les 2 jours suivant la tomodensitométrie.

<span class='italic'>Résultats:</span>

38 tomodensitométries ont été effectuées (27 patients) dans les 2 jours d'une étude isotopique de la dérivation et 15 tomodensitométries (14 Patients) dans les 2 jours suivant une intervention chirurgicale. Ces résultats confèrent au signe de la citerne absente une sensibilité de 75% et une spécificité de 57%, par rapport aux observations obtenues par l'étude isotopique et une sensibilité de 100% et une spécificité de 50% par rapport aux observations obtenues à la chirurgie. Plus de 30% des tomodensitométries montraient une ventriculomé-galie en présence d'une dérivation fonctionnelle et, à l'inverse, près de 45% des tomodensitométries montraient des ventricules latéraux normaux ou petits en présence d'une dérivation défectueuse.

<span class='italic'>Conclusions:</span>

Le “signe de la citerne absente” semble éliminer de façon fiable une dérivation complètement obstruée, mais il est moins fiable pour mettre en évidence une dérivation normale ou partiellement obstruée. La taille ventriculaire est faiblement corrélée au fonctionnement d'une dérivation LP.

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Copyright

Corresponding author

Division of Neurosurgery, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8

References

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The Reliability of the “Absent Cistern Sign” in Assessing LP Shunt Function

  • Abhaya V. Kulkarni (a1), Mary Cheang (a1), Paul D. Chumas (a1), James M. Drake (a1) and Derek C. Armstrong (a1)...

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