Intracranial pressure monitoring in patients with spontaneous onset of orthostatic headache

Abstract

Background

Spontaneous intracranial hypotension (SIH) is a debilitating disorder, with an estimated annual incidence of 3.7 per 100,000. Diagnosing SIH can be challenging for clinicians, as patients frequently present with normal investigation findings. Intracranial pressure (ICP) monitoring has been proposed as a valuable tool for patients with orthostatic headaches that are highly suggestive of SIH but have inconclusive investigation results. The primary objective of this study was to determine the proportion of patients with spontaneous orthostatic headaches and normal diagnostic work-up who exhibited abnormal ICP monitoring results.

Methods

This single-centre, retrospective observational study was conducted at a tertiary referral centre specialising in SIH and CSF dynamics disorders. Consecutive patients with spontaneous orthostatic headaches and inconclusive diagnostic work-up who underwent 24-hour ICP monitoring were considered eligible. The 24-hour ICP monitoring followed a standardised protocol, measuring median ICP and pulse amplitude (a marker of brain compliance) during the daytime, nighttime, and over the entire 24-hour period. Specific cut-offs for low and high ICP states were predetermined based on the best available current evidence.

Results

Thirty-eight patients (23 females, mean age 41 years ± 14SD) were identified. All patients had orthostatic headaches with a spontaneous onset. The mean duration of symptoms was 46 months ± 36SD. ICP monitoring identified 3 patients (7.9%) with low ICP (mean of the median 24-hour ICP − 2 mmHg ± 2SD) and 6 patients (15.8%) with high ICP (mean of the median 24-hour ICP 9 mmHg ± 3SD). Obvious CSF dynamics disturbances were excluded in the remaining 29 patients (76.3%, mean of the median 24-hour ICP 3 mmHg ± 3SD). The only clinical feature that was more common in patients with abnormal ICP compared to patients with normal ICP results was audiovestibular disturbance, namely aural fullness or muffled hearing (67% versus 17%, p = 0.015). There were no complications from the ICP monitoring procedure for any patient.

Conclusions

When appropriately selected, patients with a clinical picture highly suggestive of SIH, who have a negative diagnostic work-up, may benefit from consideration of invasive ICP monitoring. Moreover, a significant minority of patients with orthostatic headache may paradoxically have a high CSF pressure state, which can be detected using ICP monitoring.

Meeting presentations

Portions of this work were presented in abstract and oral presentation form at the Twenty-eighth Anglo-Dutch Migraine Association meeting (08/06/2018), the Tenth Meeting of the International Society for Hydrocephalus and Cerebrospinal Fluid Disorders (20/10/2018; Bologna, Italy), the Society of British Neurological Surgeons 2018 Autumn Meeting (19/09/2018; London, United Kingdom), and the European Association of Neurosurgical Societies 2023 congress (27/09/2023; Barcelona, Spain). This work is also part of the doctoral thesis of one of the authors (LD).

Background

Spontaneous intracranial hypotension (SIH) is a disorder characterised by orthostatic headache secondary to the spontaneous occurrence of a spinal cerebrospinal fluid (CSF) leak. According to current International Classification of Headache Disorders (ICHD-3), SIH can be diagnosed when the headache has developed spontaneously and in temporal relation to a low CSF pressure state or CSF leakage, or has led to its discovery [1]. To meet the ICHD-3 diagnostic criteria patients also have to show evidence of either CSF leak on imaging or low CSF opening pressure (< 60 mm CSF) [1]. Diffuse pachymeningeal enhancement, brain sagging, cerebellar tonsillar descent, subdural collections, venous engorgement, pituitary enlargement and spinal longitudinal epidural collection (SLEC) are typical signs of SIH on brain and spine MRI [2,3,4,5]. A variety of spinal imaging techniques can be used to identify the spinal CSF leak and to guide targeted treatment [2, 3]. Epidural blood patches are often successful in the treatment of SIH (64% success rate for the first patch) especially if large volume patches are employed [2, 6].

SIH can pose an arduous diagnostic challenge. According to a recent patients’ survey by Cheema et al., the median time between symptoms onset and diagnosis of SIH was two months [7]. In addition, 45% of SIH patients had to see more than one specialist to receive the correct diagnosis [7]. The cause of these suboptimal findings is multifactorial but includes deficiencies within the most commonly utilised diagnostic criteria for SIH in the form of ICHD. ICHD-2 criteria for diagnosis of SIH required response to epidural blood patch. It is well recognised that a significant proportion of patients with SIH do not respond to an epidural blood patch and therefore should not form the diagnostic criteria. The revised version, ICHD-3, addresses this and it is no longer a prerequisite when diagnosing SIH. However, the latest version is also not without its limitations. ICHD-3 necessitates either a low CSF opening pressure (< 6 cmH2O) or imaging features of CSF leakage for the diagnosis of SIH. Given our knowledge that up to 19% of patients with SIH can have normal brain imaging, spinal imaging being negative for extradural CSF in 24–52%, and 32–61% of SIH patients do not have a low CSF opening pressure, use of current diagnostic criteria risks underdiagnosis of the condition [2, 8]. Furthermore, until recently, no evidence-based consensus guidelines existed on how to best manage SIH; leading to significant heterogeneity in the diagnostic work-up between different specialists and thus further exacerbating the aforementioned issues.

Despite the recent publication of international guidelines on the management of SIH, there remains a lack of consensus on how to identify and manage SIH patients with normal neuroimaging [9]. The study of CSF dynamics in patients with SIH has the potential to help delineate the pathophysiology of this disease and identify patients who present with atypical features. Current CSF pressure measurement practices for CSF hypovolemia syndromes rely almost entirely on snapshot measurements of lumbar puncture opening pressures. Lumbar punctures have limited utility due to the dynamic nature of CSF pressure changes and the fact that these measurements are performed in the lateral decubitus position, which does not account for the postural symptoms observed in SIH. Previous studies have highlighted the utility of lumbar infusion testing, while isolated case reports have documented the potential role of intracranial pressure (ICP) monitoring in patients with SIH [10,11,12,13,14,15]. This study reports the use of ICP monitoring in a series of patients with longstanding orthostatic headache, strong clinical suspicion of SIH, normal investigation findings, with or without a lack of response to epidural blood patches. The aim of the study was to identify the proportion of patients with orthostatic headache and diagnostic uncertainty for SIH who have confirmed CSF dynamics abnormalities identified with ICP monitoring.

Methods

This is a single-centre retrospective observational study conducted at the National Hospital for Neurology and Neurosurgery (London, UK). The data collection period was between January 2006 and June 2020.

Standard protocol approvals, registrations, and patient consents

This study has been approved by the North-East Newcastle and North Tyneside 2 Research Ethics Committee and the Health Research Authority (20/NE/0127). Due to its retrospective nature, written consent to take part in this study was waived. All patients provided written consent to undergo the ICP monitoring procedure as part of their standard clinical care.

Participants

Patients meeting all the following inclusion criteria were selected:

a. orthostatic headache,

b. negative results of brain MRI with contrast for features of CSF hypovolaemia,

c. negative results of spinal investigations (CT myelogram or MRI with contrast) and lumbar puncture opening pressures (≥ 6cmH₂O) if performed,

d. failure to respond to epidural blood patches if performed,

e. postural tachycardia syndrome (PoTS) was excluded with tilt-table/active stand test; when PoTS was present then cardiovascular parameters were optimally treated,

f. cervicogenic headache excluded clinically and with neuroimaging,

g. investigated with 24-hour ICP monitoring.

Patients were excluded if their orthostatic headache was secondary to significant trauma, surgery, shunt placement/overdrainage and/or lumbar puncture.

Eligible patients were identified through the screening of two sources: the clinical letters database and the ICP monitoring clinical database. The clinical letters database is prospectively built; every letter is written in a standardised and systematic fashion that allows access to a complete clinical summary of the patients’ management history. Clinical letters including the terms “ICP”, “leak” or “orthostatic headache” were identified using the Microsoft Word search within the document function. Each patient was then tested for eligibility against the predetermined eligibility criteria. The ICP monitoring results clinical database was also screened to identify patients who met the inclusion criteria but were not identified with the previous screening method.

Intracranial pressure monitoring methods

The National Hospital for Neurology and Neurosurgery (London, UK) is a tertiary referral centre for patients with CSF dynamics disturbances. Patients with ongoing orthostatic headaches who are referred to our centre would only undergo ICP monitoring for diagnostic purposes when there is a strong clinical suspicion for SIH (orthostatic headache not better explained by any other diagnosis), but with diagnostic uncertainty, due to the inability to identify obvious signs of SIH on imaging and the lack of response to empirical treatment with epidural blood patches. Each patient’s case is discussed in a multidisciplinary meeting during which potential benefits and risks of ICP monitoring are discussed. The multidisciplinary meeting is composed of neurologists, neurosurgeons, neuroradiologists and ophthalmologists with an interest in CSF dynamics disturbances. The decision to perform ICP monitoring is based on the consensus of this multidisciplinary team.

An intraparenchymal ICP probe is inserted in the operating theatre under local anaesthetic (with/without sedation). The probe is connected to a recording ICP monitor and continuous data on ICP (approximately 100 Hz) is recorded for a period of 24 h. The patients are encouraged to mobilise, sit up and stand as much as possible during the daytime and to lie supine in bed during the nighttime. This protocol allows for the recreation of conditions similar to the patients’ daily life, enhancing the likelihood of capturing their ICP when they are symptomatic; the upright position in this case. The continuous ICP monitoring data are then analysed through a specialised software (ICM+©, University of Cambridge, UK). The ICP monitoring results are summarised in terms of 24-hour, daytime and nighttime median ICP and pulse amplitude (PA). The PA is considered a marker of brain compliance, with the pulse amplitude being inversely correlated with brain compliance [16]. The percentage of time spent in negative ICP territories was also calculated. Further details on these ICP monitoring methods have been previously published [17, 18].

Data extraction

Information on the following variables was collected: age, sex, duration of orthostatic headache, intensity of orthostatic headache (verbal reporting scale for both supine and upright position), comorbidities, headache phenotype (location, quality, radiation), associated symptoms, precipitants, features on MRI head/spine and outcomes of epidural blood patch (if performed). All patients’ clinic letters and electronic records were reviewed.

Interpretation of ICP monitoring results

A recent systematic review and meta-analysis has provided reference values for normal ICP, the 95% confidence interval for normal daytime ICP is between − 2.27 and 2.05 mmHg, while the 95% confidence interval for normal nighttime ICP is between 2.85 and 9.78 mmHg [19]. The present study used the above reference values to classify the patients’ ICP monitoring results as ‘low’, ‘high’ or ‘normal/borderline’ ICP:

i. patients with ‘low’ ICP had daytime ICP < -2.27 mmHg and nighttime ICP < 2.85 mmHg;

ii. patients with ‘high’ ICP had daytime ICP > 2.05 mmHg and nighttime ICP > 9.78 mmHg;

iii. patients with ‘normal/borderline’ ICP did not meet the criteria for high or low ICP.

Statistical analysis

Continuous variables were summarised as means (standard deviation) and categorical variables as percentages. The clinical characteristics of the patients in the 3 groups were compared through Kruskal-Wallis H Test (for continuous variables) and Fisher’s exact test (for categorical variables). A significance level 0.05 was used. Microsoft^® Excel for Mac (version 16.25), Stata© (version 15.0) and GraphPad Prism for macOS (version 8.4.1) were used for the data collection and statistical analysis.

Results

The clinic letters database identified 4,397 clinic letters (out of a total of 38,240 letters) in which the terms “ICP”, “Leak” or “Orthostatic Headache” were used. The letters belonged to a total of 828 patients. Only 37 of these patients met the inclusion criteria for the study. The screening of the ICP monitoring database (including a total of 799 records) identified one extra patient meeting the inclusion criteria for the study.

Thirty-eight patients were included in the study, 23 were female (61%) and the average age was 41 years (SD ± 14 years). All patients had orthostatic headaches with spontaneous onset. Twenty-seven patients (71%) had at least another headache diagnosis: 18 patients had chronic/episodic migraine, 7 patients had medication overuse headache and 6 patients had another type of headache. Other common comorbidities were Ehlers-Danlos syndrome or hypermobility spectrum disorder (14 patients, 37%), anxiety and depression (9 patients, 24%), PoTS (9 patients, 24%) and asthma (4 patients, 11%).

The mean duration of orthostatic headache at the time of ICP monitoring was 46 months (± 36 SD). The headache was most commonly bilateral (32 patients, 84%). The site of the orthostatic headache was occipital (21 patient, 55%), frontal (12 patients, 32%), cervical and/or neck (9 patients, 24%), vertex (7 patients, 18%), temples (5 patients, 13%), retro-orbital (5 patients, 13%), parietal (4 patients, 11%), holocranial (3 patients, 8%), peri-auricular (2 patients, 5%) or temporal (1 patient, 3%). The pain quality was most commonly described as throbbing (18 patients, 47%), pressing (18 patients, 47%), aching (9 patients, 24%) or sharp (8 patients, 21%). In addition to the upright posture, 20 patients (53%) reported that Valsalva manoeuvres were triggers or exacerbating factors for the headaches. The headache intensity in supine and upright posture are displayed in Fig. 1. The most frequently reported associated symptoms were motion sensitivity (24 patients, 63%), phonophobia (24 patients, 63%) nausea/vomiting (23 patients 61%), photophobia (23 patients, 61%), difficulties concentrating (13 patients, 34%), audiovestibular disturbances (aural fullness and/or muffled hearing, 11 patients, 29%), osmophobia (9 patients, 24%) and tinnitus (9 patients, 24%).

Fig. 1

Headache intensity Verbal Reporting Scale (VRS) in supine and upright posture

Before consideration of ICP monitoring, all patients were investigated with imaging. All patients had brain MRI with contrast that did not demonstrate any sign of low CSF pressure/volume state. Thirty-three patients underwent spinal MRI with contrast and 18 patients had CT myelograms; none of these investigations showed evidence of a CSF leak. Fourteen patients had a lumbar puncture performed elsewhere and the results were normal. Five patients underwent lumbar infusion studies externally; the results were negative in all (Table 1). Twenty-six patients received non-targeted lumbar epidural blood patches (median 3 patches per patient, range 1–6) while intravenous caffeine infusion was received by sixteen patients; these treatments were either ineffective or provided only a partial or temporary improvement of the symptoms. Table 1 provides a summary of the investigations and treatments for each patient, as well as the rationale for performing ICP monitoring.

Table 1 Summary of patients’ investigation findings, treatment outcomes and intracranial pressure monitoring results

The median 24-hour ICP monitoring results ranged from − 4.1 mmHg to + 12.5 mmHg. According to the prespecified criteria for low and high ICP monitoring results (see methods), 3 patients had low ICP (8%) and 6 patients had high ICP (16%). The remaining 29 patients did not meet the prespecified criteria for low or high pressure (76%). Figure 2 displays the 24-hour, daytime and nighttime median ICP results of the patients stratified by ICP monitoring results (low, high and normal/borderline ICP groups).

Fig. 2

24-hour, daytime and nighttime median Intracranial Pressure (ICP) results of the patients stratified by ICP monitoring results (low, high and normal/borderline ICP groups)

The clinical presentation and headache phenotype did not differ across the three groups, except for the presence of audiovestibular disturbances, namely aural fullness and/or muffled hearing, that were more common in patients with abnormal ICP results compared to normal/borderline ICP results (67% and 17% respectively, Fisher’s exact test p = 0.015, Table 2). Consistent with the study methodology and patient stratification, 24-hour, daytime and nighttime mean ICPs were significantly higher in patients with high ICP and significantly lower in patients with low ICP (Kruskal-Wallis H Test p < 0.01 in all analyses, Table 2). In addition, the proportion of time spent in negative ICP territories was significantly lower for patients with high ICP and significantly higher in patients with low ICP (Kruskal-Wallis H Test p < 0.01 in all analyses, Table 2). The mean pulse amplitude of the patients in the three groups did not significantly differ (Table 3).

Table 2 Clinical presentation and investigation findings of patients with orthostatic headache stratified by intracranial pressure monitoring results

Table 3 Outcomes of six patients with high intracranial pressure state

The six patients with high ICP did not have any ophthalmic sign of intracranial hypertension on clinical examination and did not complain of visual blurring, reduced visual acuity or transient visual obscuration. Only one of the patients mentioned intermittent diplopia, which was not associated with cranial nerve palsy, and one patient reported longstanding diplopia since childhood, which was treated with prism. Four of these patients were obese (BMI above 30) and two had normal weight. Brain MRI of these patients revealed some non-specific signs that can be observed in high ICP states, namely 3 patients had concave sella and 2 patients had prominence of the optic nerve sheaths. Five out of these six patients were treated with insertion of a CSF diversion shunt and one was managed medically with acetazolamide. Of the five patients treated with a CSF diversion shunt, two had resolution of their orthostatic headaches and were left with milder non-orthostatic headaches; one had complete resolution of headaches for seven months and a partial improvement for a further 17 months before headaches returned to baseline; and two patients derived no benefit. One patient developed abdominal discomfort following VPS insertion and eventually required surgical revision of the abdominal segment of the VPS. The sole patient treated with acetazolamide did not tolerate a dose greater than 750 mg per day due to its side-effects, and derived no benefit at this dosage. Of the three patients with low ICP results, one died of unrelated causes, while two have an ongoing orthostatic headache and are waiting for further specialist investigations. There were no complications from the ICP monitoring procedure for any of the patients.

Discussion

In this single-centre observational study, ICP monitoring of patients with clinically suspected SIH identified a low ICP in 8%, while pathologically high ICP was observed in 16% of patients. These results demonstrate that a significant proportion of patients with orthostatic headache who have a negative diagnostic work-up and are non-responsive to epidural blood patches, have a CSF dynamics disorder that can be identified through ICP monitoring. As suggested in previously published case reports, this study provides evidence on the potential utility of ICP monitoring in patients with suspected SIH but a negative diagnostic work-up [10, 15].

Interestingly, these results also demonstrate that orthostatic headache can be misleading and may represent the paradoxical presentation for a high ICP state. It could be speculated that some of these patients were affected by idiopathic intracranial hypertension (IIH) without papilloedema and that they paradoxically presented with an orthostatic headache. Another possibility is that some of these patients were originally affected by IIH and then developed a CSF leak that could not be identified with the spinal imaging available at the time. This hypothesis is in part supported by the findings of Craven et al. who noted that a high ICP state can drive a persistent CSF leak in patients with previous spinal surgery [20]. A third possible explanation is that some of these patients were originally affected by a CSF leak but developed rebound intracranial hypertension after treatment with epidural blood patches, with persistence of the orthostatic headache due to central sensitisation. Alternatively, as highlighted in previous studies, some of these cases may in fact represent chronic CSF leaks with elevated CSF pressures as part of the physiological compensatory mechanisms.

The study by Kranz et al. investigated the lumbar puncture opening pressures of 106 patients with a diagnosis of SIH and reported that 5% of them had a CSF opening pressure above 20 cm H₂O [8]. In addition, Hani et al. noted normalisation of lumbar baseline CSF pressure with increasing duration of symptoms, and all of the patients in this study had longstanding symptoms at the time of ICP monitoring [14].

The presence of audiovestibular disturbances such as aural fullness and/or muffled hearing was significantly more common in patients with abnormal CSF dynamics (high or low ICP) than patients with normal/borderline ICP results (Fisher’s exact test p = 0.015, Table 2), and may represent potential clinical markers for CSF pressure dysregulation as the cause of orthostatic headaches in imaging-negative patients with suspected SIH However, no reliable clinical predictors of low ICP results were identified in this study, although the study is not sufficiently powered to be able to draw definitive conclusion (Table 2).

There are limited and conflicting reports on the utility of ICP monitoring in patients with low CSF pressure/volume syndromes. Case reports by Jensen et al. and Zada et al. described the helpfulness of ICP monitoring in the diagnosis of SIH and for assessment of treatment response, whereas Fichtner et al. could not detect any ICP increase after epidural blood patch using a subdural ICP monitor and hypothesised that a rise in ICP may not be the therapeutic mechanism of epidural blood patches [10, 12, 15].

Eide et al. performed ICP monitoring in patients with low CSF pressure/volume syndrome (only four were SIH patients) and found that morphological changes of the ICP pulse waveform only occurred when ICP fell below − 15 mmHg [11]. The patients with low ICP in our study had median ICPs above this threshold and this may be the reason why we did not identify significant differences in pulse amplitude among the three ICP groups (Table 2). Furthermore, lumbar infusion studies have provided useful insights in the CSF dynamics of patients with confirmed CSF leaks and it is interesting to note how the abnormalities in CSF dynamics tend to become less evident in the chronic stages of the disease and may be relevant in our study given the chronicity of symptoms prior to ICP monitoring [13, 14].

Lumbar puncture opening pressure is often tested when SIH is suspected, but this investigation can be misleading. Whilst low CSF opening pressures are suggestive of SIH, normal or high CSF opening pressures do not allow exclusion of this diagnosis [2, 8]. As noted above, both Kranz and Hani have shown normal or high CSF opening pressure in patients with SIH [8, 14]. Mokri et al. also described the cases of patients with confirmed CSF leaks and consistently normal lumbar puncture opening pressures [21]. These studies emphasise the fact that a diagnosis of SIH cannot be based solely on the results of a lumbar puncture [21, 22]. This is also supported by the results of our study in which three of the patients who had normal CSF opening pressures, had abnormal ICP monitoring results (two low and one high ICP readings) as noted in Table 1. Lumbar punctures should be undertaken with caution bearing in mind that the sensitivity of this investigation is modest and there is a risk of worsening symptoms of CSF leak. The exception to this recommendation would be when performing a lateral decubitus myelographic study; low CSF opening pressure measurement would be highly suggestive of SIH and would help negate the potential need for ICP monitoring in the future.

The main limitations of this study include the relatively small cohort, its retrospective design, and its heterogeneity (e.g., variable and inconsistent management profiles prior to ICP monitoring). Despite these limitations, this case series remains the largest study to date describing ICP monitoring results in patients with suspected SIH. Given that ICP monitoring is an invasive procedure, it is reserved for highly disabled patients with a clinical phenotype suggestive of SIH, where less invasive work-up has been inconclusive. Therefore, the relatively small size of the cohort is reflective of the judicious use of invasive options at our centre.

Despite the retrospective design, the standardised screening process and the systematic structure of both clinical letters and ICP monitoring protocol, reduced the risk of selection, detection and reporting biases. As for the heterogeneity in patient characteristics, this was expected given the absence in evidence- or consensus-based guidelines for the management of SIH at the time of the study.

Another important limitation is the scarce knowledge on normal ICP ranges. Performing ICP monitoring on healthy volunteers to obtain normative data would be unethical. In this context, the systematic review and meta-analysis by Norager et al. currently provide the best evidence on normal ICP ranges [19]. The results of this review align with our clinical experience and partly rely on data published by our centre [17]. We have used this evidence to classify the ICP monitoring results in our study in an objective and repeatable manner, while being open to the possibility that some patients classified as having a normal ICP in our study may be better classified as having borderline high or low ICP results.

In more recent years, a better understanding of SIH has led to the discovery of CSF-venous fistulas (CVF) as the cause of some cases of SIH [23, 24]. They were first described in 2014 and are not typically associated with a SLEC and their identification with traditional spinal imaging techniques can be challenging [23]. Dynamic CT myelography or digital subtraction myelography (DSM) with lateral decubitus views can be useful in the identification of CSF-venous fistulas, though these techniques were not previously widely available. Many of the patients included in this study had been investigated for SIH prior to the recognition of the CVF as an entity, and/or the availability of specialised spinal imaging techniques required to make the diagnosis. Schievink et al. (2020) reported that 10% of patients with orthostatic headaches who had normal brain and spinal imaging, including CT myelography, were found to have a CVF on digital subtraction myelography [25]. Future studies should investigate for the presence of CVFs with dedicated spinal imaging before ICP monitoring is employed.

Based on this study, ICP monitoring can be valuable for the investigation of a subset of patients with orthostatic headache. However, its use requires careful patient selection rather than being seen as part of the routine work-up for SIH. In all cases, the potential benefits of ICP monitoring must outweigh the possible risks. The procedure should be conducted at a specialist centre with expertise in managing SIH and performing ICP monitoring. In addition, the following criteria for the employment of ICP monitoring are suggested:

i. strong clinical suspicion for SIH,

ii. normal brain imaging (brain MRI with contrast),

iii. normal spinal imaging dedicated to the identification of possible epidural fluid collections (e.g., whole spine MRI with contrast, and dynamic CTM or DSM),

iv. normal spinal imaging dedicated to the identification of CSF-venous fistulas (e.g., dynamic CTM or DSM with lateral decubitus views),

v. normal lumbar puncture opening pressures, if this investigation is performed in the context of myelography (or for other diagnostic reasons),

vi. exclusion of other potential causes of orthostatic headaches including PoTS (unless already optimally treated), cervicogenic headaches, primary new daily persistent headaches and craniocervical instability,

vii. failure to respond to large volume epidural blood patch.

Conclusions

Carefully selected patients with a clinical picture strongly suggestive of SIH but negative investigation findings can benefit from invasive ICP monitoring. This study provides evidence that ICP monitoring can confirm a low CSF pressure state in 8% of such patients, and thus providing clinical grounds for a more aggressive search of an underlying spinal CSF leak or CVF. The study also demonstrates that 16% of patients with a clinical syndrome compatible with SIH, but negative work-up, had an underlying high CSF pressure state that may respond to pressure-lowering treatment. Lastly, ICP monitoring was observed to be a safe procedure with no reported complications in our cohort.