2022 Volume 59 Issue 1 Pages 125-131
As the imaging technology progresses, some new circulatory dynamics of cerebrospinal fluid (CSF) has been clarified. At the same time, the pathophysiology of idiopathic normal pressure hydrocephalus (iNPH) has been actively studied; however, many points in the study have not yet been elucidated. This is the main reason why definite diagnosis of iNPH before surgery is still difficult. In secondary normal pressure hydrocephalus (sNPH) patients requiring shunt surgery, none of them showed dilatation of Sylvian fissure or disproportionately enlargement of subarachnoid-space hydrocephalus (DESH) on preoperative imaging, which are the characteristic imaging findings in iNPH. Postoperatively, all sNPH patients demonstrated improvement in imaging findings and recovery of clinical symptoms, whereas some iNPH cases showed regaining of clinical symptoms despite no obvious improvement on imaging findings. Based on these facts, it is considered that the pathophysiological mechanisms in iNPH are significantly different from those in sNPH, although both iNPH and sNPH are caused by dysfunction of CSF absorption. In sNPH, the absorption of CSF is impaired by a high protein level in CSF due to leakage of blood, bacteria, or tumor cell components into entire CSF circulation. On the other hand, in iNPH, CSF glucose and protein were close to normal levels, suggesting that CSF absorption disorder occurs in the absorption mechanism itself. It is speculated that a scattered dysfunction of CSF absorption systems might lead to asymmetric CSF absorption deficits.
