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Reply:
======

* A. Scollato
* P. Gallina
* N. Di Lorenzo

We thank Dr Oktay Algin for his insightful comments on our article.1

We agree that the relationship between ischemia and idiopathic normal pressure hydrocephalus (INPH) is not well understood. It still remains unclear if ischemia induces INPH or if INPH induces ischemia or if both take place. We also agree that there is no consensus on the role of stroke volume (SV) in the selection of patients to undergo shunt treatment.2(#ref-3)(#ref-4)(#ref-5)(#ref-6)–7 As previously reported,8,9 the value of SV is of little importance if it is not correlated with clinical findings for each patient and with the timing of symptom onset.

In our experience, it is clear that patients with high a SV and a short time of onset of symptoms have a higher probability of improvement with shunt treatment, compared with patients with lower SV and a longer time of symptom onset.1 Although currently SV cannot be used as an absolute tool for selection of patients who will be shunt responders, our study shows promising results in the potential utility of SV and may encourage additional studies.

Even with our data, it is hard to predict a given patient's response to shunt surgery on the basis of the SV versus time-of-symptom-onset curve because the response changes with the progression of the disease and the timing of the shunt therapy. We agree with Dr Algin that we cannot delay treatment to obtain a series of SV controls before shunt therapy. Studies comparing SV with other selection tests are currently being performed at our institution.

Currently, in our clinical practice, after submitting the patient to a baseline SV study, we select patients with INPH by a prolonged spinal drainage (PSD) of CSF. PSD is considered the present criterion standard for shunt selection in patients with INPH.10 Moreover, the immediate benefit offered by the PSD, though temporary, is encouraging for the patient and may help him or her to pursue definitive treatment with the shunt. Furthermore, for those patients for whom SV data suggest a possible irreversible state of the disease, we can give them a choice of undergoing the PSD procedure or pursuing further treatment with shunt surgery on the basis of the results from the PSD.

We hope that our study contributes to the knowledge of the etiology of this complex disease process. In addition, we hope to have contributed to a more standardized approach in the selection of patients for shunt therapy.

## References

1.  1. Scollato A, Gallina P, Gautam B, et al. Changes in aqueductal CSF stroke volume in shunted patients with idiopathic normal-pressure hydrocephalus. AJNR Am J Neuroradiol 2009;30:1580–86. Epub 2009 May 20 
    
    [Abstract/FREE Full Text](http://www.ajnr.org/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiYWpuciI7czo1OiJyZXNpZCI7czo5OiIzMC84LzE1ODAiO3M6NDoiYXRvbSI7czoxOToiL2FqbnIvMzEvMi9FMjguYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

2.  2. Kahlon B, Annertz M, Ståhlberg F, et al. Is aqueductal stroke volume, measured with cine phase-contrast magnetic resonance imaging scans useful in predicting outcome of shunt surgery in suspected normal pressure hydrocephalus?. Neurosurgery 2007;60:124–30 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=17228260&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

3.  3. Dixon GR, Friedman JA, Luetmer PH, et al. Use of cerebrospinal fluid flow rates measured by phase-contrast MR to predict outcome of ventriculo-peritoneal shunting for idiopathic normal-pressure hydrocephalus. Mayo Clin Proc 2002;77:509–14 
    
    [CrossRef](http://www.ajnr.org/lookup/external-ref?access_num=10.4065/77.6.509&link_type=DOI) 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=12059119&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 
    
    [Web of Science](http://www.ajnr.org/lookup/external-ref?access_num=000176018900003&link_type=ISI) 

4.  4. Bateman GA, Levi CR, Schofield P, et al. The pathophysiology of the aqueduct stroke volume in normal pressure hydrocephalus: can co-morbidity with other forms of dementia be excluded? Neuroradiology 2005;47:741–48 
    
    [CrossRef](http://www.ajnr.org/lookup/external-ref?access_num=10.1007/s00234-005-1418-0&link_type=DOI) 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=16021440&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

5.  5. Bradley WG Jr., Scalzo D, Queralt J, et al. Normal pressure hydrocephalus: evaluation with cerebrospinal fluid flow measurement at MR imaging. Radiology 1996;198:523–29 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=8596861&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 
    
    [Web of Science](http://www.ajnr.org/lookup/external-ref?access_num=A1996TR36300042&link_type=ISI) 

6.  6. Kim DS, Choi JU, Huh R, et al. Quantitative assessment of cerebrospinal fluid hydrodynamics using a phase-contrast cine MR image in hydrocephalus. Childs Nerv Syst 1999;15:461–67 
    
    [CrossRef](http://www.ajnr.org/lookup/external-ref?access_num=10.1007/s003810050440&link_type=DOI) 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=10502007&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

7.  7. Mase M, Yamada K, Banno T, et al. Quantitative analysis of CSF flow dynamics using MRI in normal pressure hydrocephalus. Acta Neurochir Suppl 1998;71:350–53 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=9779227&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

8.  8. Scollato A, Tenenbaum R, Bahl G, et al. Changes in aqueductal CSF stroke volume and progression of symptoms in patients with unshunted idiopathic normal pressure hydrocephalus. AJNR Am J Neuroradiol 2008;29:193–98 
    
    

9.  9. Scollato A, Gallina P, Di Lorenzo N, et al. Is aqueductal stroke volume, measured with cine phase-contrast magnetic resonance imaging scans useful in predicting outcome of shunt surgery in suspected normal pressure hydrocephalus? Neurosurgery 2008;63:E1209, author reply E1209 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=19057297&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

10. 10. Marmarou A, Bergsneider M, Klinge P, et al. The value of supplemental prognostic tests for the preoperative assessment of idiopathic normal-pressure hydrocephalus. Neurosurgery 2005;57(3 suppl):S17–28, discussion ii–v 
    
    [CrossRef](http://www.ajnr.org/lookup/external-ref?access_num=10.1227/01.NEU.0000144844.72403.7B&link_type=DOI) 
    
    [PubMed](http://www.ajnr.org/lookup/external-ref?access_num=16160426&link_type=MED&atom=%2Fajnr%2F31%2F2%2FE28.atom) 

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