Table 1: Translation of the epidemiological questions into a query logic of operations of ICD and OPS codes.

No. Epidemiological Question Query logic using a logic operation of German-ICD-9 codes and German OPS codes
Q1 How many patients with any type of hydrocephalus underwent surgery in that year? a) G91* AND 5-023.00; b) G91* AND 5-023.10
Q2 How many patients with (idiopathic) normal pressure hydrocephalus underwent surgery in that year? a) G91.2* AND (5-023.00 OR  5-023.10)
b) G91.20 AND (5-023.00 OR  5-023.10)
Q3 How many patients with normal pressure hydrocephalus underwent revision surgery in that year? a) G91.2* AND 5-023.00 AND 5-024*
b) G91.2* AND 5-023.10 AND 5-024*
Q4 How many patients with normal pressure hydrocephalus underwent revision surgery in that year, but had undergone shunt implantation in another, earlier year? G91.2* AND 5-024* NOT (5-023.00 OR 5-023.10)
Q5 How many patients with normal pressure hydrocephalus underwent revision surgery in that year due to infectious complications? a) G91.2* AND 5-023.00 AND 5-024* AND (G00* OR G01* OR G02* OR G03* OR G04* OR G05* OR G06* OR G07* OR G08*)
b) G91.2* AND 5-023.10 AND 5-024* AND (G00* OR G01* OR G02* OR G03* OR G04* OR G05* OR G06* OR G07* OR G08*)
Q6 cross-check: How many patients with normal pressure hydrocephalus underwent revision surgery within that year due to infectious complications? a) G91.2* AND 5-023.00 AND 5-024* AND T85.72
b) G91.2* AND 5-023.10 AND 5-024* AND T85.72
Q7 2nd cross-check: How many patients with normal pressure hydrocephalus underwent revision surgery within that year due to infectious complications? a) G91.2* AND 5-023.00 AND 5-024* AND G04.9
b) G91.2* AND 5-023.10 AND 5-024* AND G04.9
Q8 How many patients with normal pressure hydrocephalus underwent revision surgery in that year due to mechanical complications? a) G91.2* AND 5-023.00 AND 5-024* AND T85.0
b) G91.2* AND 5-023.10 AND 5-024* AND T85.0
Q9 How many NPH patients underwent surgery due to over-drainage complications? a) G91.2* AND 5-023.00 AND 5-024* AND T85.0 AND G97.2
b) G91.2* AND 5-023.10 AND 5-024* AND T85.0 AND G97.2
Q10 How many patients with iNPH underwent ICP measurement within a diagnostic pathway? 5-029.10 AND G91.20
Q11 How many patients with iNPH underwent ICP measurement within a diagnostic pathway and underwent surgery? 5-029.10 AND c AND 5-023.10
Q12 How many patients with iNPH were coded? G91.20
Q13 How many patients were coded with iNPH and Parkinson's disease? G91.20 AND G20*
Q14 How many patients were coded with iNPH and Alzheimer's disease? G91.20 AND G30*
Q15 How many patients with iNPH and Parkinson's disease underwent vp shunt surgery? G91.20 AND G20* AND 5-023.10
Q16 How many patients with iNPH and Alzheimer's disease underwent vp shunt surgery? G91.20 AND G30* AND 5-023.10
Q17 How many patients hydrocephalus underwent endoscopic IIIrd venrticulostomy? G91* AND 5-022.20