Biopsy procedure and immunohistochemistry

At surgery, three cylindrical cortical brain biopsies of 2–5 mm in diameter and 3–7 mm in length, were acquired preceding the insertion of CSF shunt proximal catheter, using biopsy forceps (until 2010) or disposable Temno Evolution^R TT146 biopsy needle (Merit Medical Systems Inc., South Jordan, UT, USA) (since 2010). The insertion point for the catheter was approximately 3 cm from the midline and anterior to the coronal suture. From all samples, a neuropathologist graded the presence of the immunoreactivity for amyloid-beta (Aβ) and hyperphosphorylated tau (HPτ) using light microscopy [23]. Patients were then further divided by the presence of pathology of any kind, the Aβ or HPτ observed in the frontal cortical biopsy (Table 2).