INTRODUCTION
Normal pressure hydrocephalus (NPH) is characterized by abnormal cerebrospinal fluid (CSF) dynamics, often leading to cognitive decline, gait disturbances, and urinary incontinence [1]. Traditionally classified as communicating hydrocephalus, NPH is commonly treated with shunt surgery to redirect excess CSF and relieve symptoms. The standard treatment primarily involves CSF diversion procedures, with ventriculoperitoneal shunt (VPS) surgery being the most frequently performed technique. Additionally, ventriculoatrial and ventriculopleural shunt surgeries are alternative options in cases where peritoneal absorption is inadequate [31]. Conversely, endoscopic third ventriculostomy may also be considered, particularly in selected patients with obstructive components, although its efficacy in NPH remains limited [25].
Lumboperitoneal shunt (LPS) surgery is favored over VPS surgery in elderly patients with NPH due to its minimally invasive approach and a complication profile compatible with that observed in VPS procedures [12,21]. Previous literature has shown that LPSs reduce the need for intracranial procedures, thereby minimizing surgical risks such as intracranial hemorrhage and infection associated with VPSs [15,29]. Additionally, LPS surgery has demonstrated comparable, if not superior, clinical efficacy in improving gait disturbances, cognitive function, and urinary incontinence, which are hallmark symptoms of NPH [2,15]. The procedure’s effectiveness in restoring CSF dynamics, along with its lower morbidity and reduced hospital stay, makes it a favorable option for elderly patients who may have increased surgical risks [26]. These advantages have contributed to the growing preference for LPS surgery as a surgical intervention for NPH in the elderly population.
In the Republic of Korea, VPS surgery remains the primary surgical intervention for NPH. Although LPS surgery was introduced in the late 1990s, its adoption was limited due to the absence of programmable valves, leading to challenges such as overdrainage and difficulties in assessing shunt function [14,15]. However, in February 2020, the Strata valve (by Medtronic Neurologic Technologies, Medtronic Inc., Goleta, CA, USA), a programmable valve system for LPS surgery, received approval from the Ministry of Food and Drug Safety in Republic of Korea. Since then, LPS surgery has been increasingly performed in many hospitals across the country.
Although numerous studies from other countries have demonstrated the effectiveness of LPS surgery in patients with NPH, large-scale research in Republic of Korea remains scarce. This study primarily aimed to evaluate the functional outcomes and complication profile of LPS surgery in NPH, with specific attention to the impact of anesthesia type and valve pressure management protocol on outcomes.
MATERIALS AND METHODS
This study was approved by the Institutional Review Board of Kyungpook National University Chilgok Hospital (KNUCH 2025-02-020). We conducted a retrospective analysis of LPS surgeries for NPH from February 2020 through February 2025.
Diagnosis of NPH
Fig. 1 illustrates the NPH diagnostic algorithm employed at our institution. All patients were evaluated according to the Japanese NPH guidelines [9,22]. Inclusion criteria required the presence of clinical triad symptoms, ventriculomegaly (Evans’ index >0.3), and either improvement following a CSF tap test or progressive clinical and radiological findings. Exclusion criteria included secondary hydrocephalus, severe neurodegenerative diseases, prior CSF diversion procedures, or inadequate follow-up. The presence of disproportionately enlarged subarachnoid‑space hydrocephalus [9] was independently assessed by two specialists (K.K. and K.S.P.). Additional PET imaging was selectively performed to identify comorbid Alzheimer’s disease or Parkinson’s disease.
Preoperative evaluation for LPS surgery
Preoperative magnetic resonance imaging (MRI) evaluates the entire spine, from cervical to lumbar regions, to identify spinal stenosis. Particular attention is paid to the puncture level—typically L2-3 but sometimes L1-2. To minimize spinal cord injury risk, degenerative changes at this level and the conus medullaris position are assessed. Because the spinal needle is inserted via a paramedian approach, the interlaminar space must also be evaluated. X-ray and computed tomography (CT) imaging assess bony anatomy and interlaminar spacing.
Anesthesia
LPS surgery was performed under three different types of anesthesia over time. Initially, general anesthesia was used (period 1), followed by spinal anesthesia (period 2), and later transitioned to local anesthesia with mild sedation using agents such as propofol and midazolam (period 3). General anesthesia provided excellent surgical conditions but carried risks like postoperative cognitive dysfunction, especially in elderly patients, and required longer recovery [5,10]. Spinal anesthesia, involving injection into the subarachnoid space, avoided systemic effects but sometimes caused hypotension and discomfort during prolonged procedures [7]. In the most recent phase, local anesthesia with mild sedation was associated with reduced anesthetic risk and allowed intraoperative neurological monitoring, as also reported in prior studies [5,8,11]. Currently, local anesthesia with mild sedation is predominantly used as the standard approach, given its safety, effectiveness, and patient-centered benefits, particularly for elderly patients with NPH.
LPS surgery for NPH
After induction of general, spinal, or local anesthesia, the patient was placed in the left lateral decubitus position. Initial dermal marking was made at the L3-4 interspinal space on the right side of the patient’s back. A Tuohy needle was inserted 1 cm lateral to the midline at the L3-4 level and advanced cephalad toward the L2-3 interspinal space under fluoroscopic guidance. When the Tuohy needle reached the CSF space, the spinal catheter was inserted. A Strata adjustable programmable valve (Medtronic Neurologic Technologies, Medtronic Inc.) was connected to the spinal catheter and secured to the fascia of the erector spinae muscle using a fixation tab located at the distal end of the spinal catheter, which corresponds to the proximal portion of the shunt valve. This fixation tab, included in the commercially available LPS surgery kit, was wrapped around the catheter and anchored to the underlying fascia to prevent catheter kinking and displacement along the course of the shunt. Subsequently, the distal catheter was connected to the valve and inserted into the abdominal cavity using a standard technique.
Postoperative clinical and radiological evaluation
Postoperative follow-up assessments were conducted at 1, 3, 6, and 12 months after surgery, and annually thereafter. During each outpatient visit, the modified Rankin scale (mRS), timed up and go (TUG), 10-m gait test, and Mini-Mental State Examination (MMSE) were performed. However, the second postoperative year onward, MMSE administration was not uniform across patients. Many elderly patients reported fatigue and psychological discomfort during cognitive testing, prompting a selective approach aligned with ethical research considerations. When rapid cognitive decline was suspected or clinically indicated, MMSE was administered selectively. This strategy minimized patient burden while still enabling meaningful evaluation of cognitive changes.
Radiological assessments were also performed during outpatient visits to monitor for postoperative complications. Brain CT imaging was obtained to evaluate ventricular changes and to identify any subdural fluid collections or chronic subdural hematoma (CSDH). Lumbar spine and abdominal X-rays were also performed to assess for potential displacement of the spinal or distal catheters.
In the early phase of LPS surgeries, initial valve pressure settings were determined based on the patient’s opening pressure, height, and weight. However, because a notable number of patients experienced headaches suggestive of intracranial hypotension after surgery, the strategy was later modified. Currently, the valve is initially set to the highest-pressure setting (2.5), followed by stepwise reductions based on clinical and radiological assessments. In cases where stepwise reduction was performed, follow-up imaging was conducted 1 month later to assess for subclinical overdrainage. If subdural fluid collections or findings suggestive of subclinical CSDH were identified, the valve pressure was subsequently adjusted upward to prevent further complications.
Definition of clinical improvement following LPS surgery
Clinical improvement was assessed annually after LPS surgery and defined as meeting at least one of the following criteria : 1) a reduction of ≥1 point on the mRS; 2) more than 10% improvement in TUG test time or 10-m gait test time; 3) an increase of more than 3 points on the Korean version of the K-MMSE. All clinical evaluations were performed independently by a board-certified neurologist (K.K.). For gait assessment, each test was measured two to three times to ensure reliability and accuracy, and the mean value was used in analysis.
Statistical analysis
All statistical analyses were performed using SPSS Statistics for Windows, version 29.0.1.0 (IBM Corp., Armonk, NY, USA). Continuous variables were presented as mean±standard deviation. Categorical variables were summarized as frequencies and percentages. The Shapiro-Wilk test assessed normality. Paired t-tests or Wilcoxon signed-rank tests compared pre- and postoperative values, while independent t-tests, Mann-Whitney U tests, or Kruskal-Wallis tests were used for between-group comparisons. Chi-square or Fisher’s exact tests were applied for categorical variables. Univariate and multivariate analyses identified factors associated with clinical improvement (≥1-point mRS reduction). Variables with p<0.1 in univariate analysis were included in multivariate logistic regression. Statistical significance was set at p<0.05.
RESULTS
Demographic and clinical characteristics of the patients
Table 1 shows the demographic and clinical characteristics of the 244 patients with NPH who underwent LPS surgery between February 2020 and February 2025.
Patients were excluded from the analysis if they met one or more of the following criteria : lost to follow-up (n=36), presence of comorbid neurodegenerative disorders such as Alzheimer’s disease or Parkinson’s disease (n=74), postoperative cerebrovascular accident resulting in severe disability (n=13), or LPS combined with unilateral biportal endoscopy decompression due to severe lumbar spinal stenosis (n=2) (Fig. 2).
After applying the exclusion criteria, 119 patients were included in the final analysis. The distribution of patients by follow-up duration was as follows : 1) 1 year or more : 119 patients; 2) 2 years or more : 79 patients; 3) 3 years or more : 24 patients; and 4) 4 years or more : 11 patients.
Clinical outcomes at 1 year following surgery during a 5-year follow-up
Among the 119 patients who were followed for at least 1-year, functional improvement was observed in various clinical parameters (Table 2). The mRS showed significant improvement in 64 patients (53.8%), with scores decreasing from 2.84±0.94 preoperatively to 2.33±1.08 at follow-up (p<0.001). In the TUG test, 79 patients (66.4%) showed improvement, with mean times reducing from 20.76±8.98 seconds to 18.42±6.78 seconds, although the change did not reach statistical significance (p=0.068). Similarly, the 10-m gait test improved in the same 79 patients (66.4%), with a significant reduction in walking time from 17.40±7.29 seconds to 15.68±5.02 seconds (p=0.043). In contrast, K-MMSE scores showed no significant change, with 57 patients (47.9%) showing improvement, but the mean score slightly decreased from 20.21±6.41 to 19.76±7.51 (p=0.468).
In addition to gait-related outcomes, focusing specifically on mRS improvement, clinical stability at 1 year was notable. A total of 93.3% of patients either showed improvement (53.8%) or maintained stable function (39.5%) at the 1-year follow-up (Table 3). To identify demographic factors associated with better outcomes, univariate and multivariate analyses were performed; however, no significant factors were identified.
Subgroup analysis by anesthesia type and valve pressure strategy
To assess the impact of changes in anesthesia type and valve pressure strategy on clinical outcomes, we conducted a subgroup analysis across three time periods based on the type of anesthesia administered : 1) period 1 : general anesthesia (n=21, 17.6%); 2) period 2 : spinal anesthesia (n=16, 13.4%), and 3) period 3 : local anesthesia with mild sedation (n=82, 69.0%) (Table 4).
In addition to anesthesia type, we also analyzed outcomes before and after the implementation of a revised valve pressure strategy. In the earlier phase, valve pressure settings were determined by patient height and weight in accordance the previous literature [18]. In the later phase, this protocol was modified to begin with the highest-pressure setting (2.5), followed by stepwise reductions based on clinical response and neuroimaging findings. Due to limited overlap between the strategies and potential confounding variables, the analysis related to valve pressure was described narratively rather than in tabular format.
Each anesthesia group was evaluated for clinical outcomes at 1 year, including the mRS, TUG test, and the 10-m gait test. Although no statistically significant differences were observed among the three groups, patients in period 3 exhibited trends toward shorter operative time, faster recovery, and a reduced length of hospital stay. Furthermore, while not statistically significant, the implementation of a high-initial-pressure valve strategy was associated with a measurable reduction in overdrainage-related complications and the need for revision surgeries, including burr-hole drainage for CSDH secondary to overdrainage.
Complication profile over the 5-year follow-up period
Over the 5-year follow-up period, among the 244 patients, 41 (16.8%) experienced complications related to LPS surgery (Table 5). Fourteen cases (5.7%) were managed conservatively (intracranial hypotension and CSDH), both resolving after increasing valve pressure. Twenty-seven cases (11.1%) required surgical revision, most commonly for catheter dislodgement, valve malfunction, or CSDH requiring burr-hole drainage.
No surgery-related mortality occurred. However, three patients (1.2%) with marked postoperative gait improvement suffered accidental falls resulting in traumatic brain injury and died.
DISCUSSION
Clinical outcomes and interpretation of follow-up data
The clinical outcomes following LPS surgery in our cohort demonstrate favorable functional improvement, particularly when assessed using the mRS. At 1 year postoperatively, 53.8% of patients showed improvement in mRS, which is slightly lower than the 60% reported in the SINPHONI-2 (Study of Idiopathic Normal Pressure Hydrocephalus on Neurological Improvement-2) trial [13]. However, including patients who maintained stable mRS—an aspect not addressed in SINPHONI-2—the proportion with stable or improved functional status reached 93.3%, indicating broader clinical benefit. Similarly, Toma et al. [28] reported improvement rates of 50-60% in their meta‑analysis, albeit with substantial variability. These findings collectively suggest that our results are generally aligned with prior studies on LPS surgery (Table 6) [3,4,6,16,17,19-21,27,30], thereby supporting the reliability of our data. Additionally, our study showed that 66.4% of patients improved in both TUG and 10-m walk tests, indicating meaningful functional recovery.
Valve pressure management protocol comparison with previously published LPS practices
Our current approach to LPS surgery closely aligns with the prevailing Japanese technique, particularly in terms of the location of valve placement, initial valve pressure settings and puncture site selection [8,21,23]. In line with recommendations from Japanese experts such as Professor Nakajima et al. [21], we routinely begin with a highest-pressure setting to minimize the risk of intracranial hypotension, gradually lowering it based on clinical and radiologic response. Earlier in our experience, we used simplified pressure-setting tables [18], however, this led to complications such as postural headaches due to intracranial hypotension and subdural fluid collections—findings that parallel those reported in early Japanese series. Nakajima et al. [21] have emphasized that individualized valve pressure should be considered based on patient factors like body mass index and preoperative mobility, as patients with low body mass or better gait function tend to be more susceptible to overdrainage. This patient-tailored approach is now widely adopted not only in Japan but also in European centers such as those in Germany and Sweden, reflecting a global trend toward precision adjustment rather than one-size-fits-all protocols.
While our valve pressure management strategy is increasingly refined and aligned with global trends, the hardware itself remains a challenge. Unlike Japan, where valves with siphon guards and magnetic-resistant technologies are commonly used, our current system lacks sufficient postural adaptation and remains vulnerable to MRI-induced setting changes. Future improvements should focus on finer pressure adjustments, magnetic-resilient valves, and anti-siphon features to enhance safety and optimize long-term outcomes.
Avoiding general anesthesia : enhancing acceptance and efficiency in LPS surgery for NPH
Avoiding general anesthesia in LPS surgery for NPH offers distinct advantages, particularly in elderly patients. Studies quantifying anesthesia refusal rates are limited, but cultural factors in East Asian countries (Korea and Japan) influence surgical decision‑making. Older adults in these regions often express apprehension toward general anesthesia due to fears of postoperative cognitive decline, respiratory complications, and loss of autonomy—concerns echoed in family-involved medical decisions and institutional surveys [5,24,29,32]. These fears can delay or prevent necessary surgical intervention.
To overcome these barriers, alternative methods such as local anesthesia with mild sedation or spinal anesthesia have been increasingly adopted and improve patient acceptance. A Japanese study demonstrated that LPS surgery under spinal anesthesia was associated with fewer respiratory complications and shorter hospital stays versus general anesthesia, enhancing its safety profile in elderly patients [8]. Similarly, a Taiwanese study reported successful non‑intubated anesthesia use in frail patients undergoing LP shunting [11]. These findings support the consensus that less invasive anesthesia approaches reduce perioperative risks and overcome psychological and cultural resistance, ultimately expanding access to surgical care for NPH in elderly patients.
Limitations
This study has several limitations inherent to its retrospective, single-center design. The absence of a control group and the non-randomized nature of treatment introduce potential selection bias, particularly as patients with more favorable recovery profiles may have been more likely to continue long-term follow-up. Although we included a relatively large cohort with up to 4 years of follow-up, a considerable proportion of patients were only followed for 1 year.
Cognitive outcomes were assessed using the MMSE, but data were limited in both duration and sensitivity. The lack of long-term, comprehensive cognitive testing prevents definitive conclusions regarding sustained neurocognitive benefits of LPS surgery. Future studies should incorporate tools such as Montreal Cognitive Assessment or Consortium to Establish a Registry for Alzheimer’s Disease to better evaluate cognitive trajectories.
In addition, surgical techniques and valve-setting strategies evolved over the course of the study, introducing heterogeneity in practice. Our institution did not utilize advanced programmable valve systems (e.g., siphon guards, gravitational valves, or MRI-resistant technologies), which may have contributed to valve malfunctions and pressure instability.
Comparisons with VPS surgery were not feasible in this dataset. Given the rising interest in LPS as an alternative, future prospective, case-control studies directly comparing LPS and VPS in terms of efficacy, complications, cognitive outcomes, and patient-reported measures are needed to better define the role of LPS in managing NPH, particularly in elderly or high-risk populations.
CONCLUSION
A retrospective study showed that LPS surgery with local anesthesia is effective for NPH patients, demonstrating favorable functional outcomes and acceptable complications, consistent with existing research. Using higher initial valve pressures significantly decreased the need for revision surgeries and complications related to overdrainage. To further improve safety and long-term results, future large-scale studies and advancements in programmable valve technology are recommended.
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