Intracranial Hypotension Symposium 2020

SIH is more common than we were initially inclined to believe and the increase in awareness is improving our ability to recognise it.

Prof. Schievink and his team (Cedars-Sinai hospital, Los Angeles) are world experts on SIH and have diagnosed more than one thousand patients so far. They noticed a very interesting trend, which is that more patients are referred and investigated for suspected SIH compared to the past. This is very positive as it suggests that we are becoming more vigilant.

Unfortunately, misdiagnosis of SIH is still a serious problem. During the symposium various cases of SIH patients who were initially misdiagnosed were discussed. For example, SIH often gives the appearance of a ‘sinking brain’ on brain MRIs. This characteristic can very commonly be misinterpreted and lead to a wrong diagnosis of Chiari malformation. Another finding that can be misinterpreted is the SIH enlargement of the pituitary gland, as this can occasionally be mistaken for a pituitary gland disease. This is concerning, especially if we consider that some of the patients who are misdiagnosed receive invasive and unnecessary treatments. Additionally, Dr Gray (Duke University Medical Center, Durham) also shared her concerns regarding the numerous misdiagnosis of SIH as dementia or Alzheimer’s disease. Cognitive impairment is not uncommon in SIH, and can improve with EBPs, therefore by labelling these patients with the diagnosis of dementia we would preclude them the possibility to be treated for SIH and to improve.

Another important issue raised at the symposium is the significant overlap between the symptoms of SIH and Postural Orthostatic Tachycardia Syndrome (also know as POTS). POTS should be considered as a possible alternative diagnosis in patients with orthostatic headache, especially when other imaging findings do not clearly fit with a diagnosis of SIH. Whilst the distinction between Chiari Malformation (or pituitary gland disease) and SIH can be achieved by an attentive analysis of the brain MRI scan and the patient’s clinical presentation, the differentiation between POTS and SIH is more challenging. Appropriate autonomic tests are important for a diagnosis of POTS, but they are not always conclusive. A new study suggested that ultrasound of the optic nerve sheath can help differentiate between POTS and SIH in complex cases. This test looks at the diameter of the CSF that normally surrounds the optic nerve. According to this recent study, and in contrast to POTS, SIH patients have a significant reduction of the CSF that surrounds the optic nerve when moving from flat to upright position. This study was based on a very small group of patients and the results will need to be confirmed with further research, however it is very promising and shows that non-invasive strategies to help distinguish between POTS and SIH are being explored.

Events like the Intracranial Hypotension Symposium and the activities of the CSF Leak Association are essential to further improve our ability to correctly diagnose SIH and CSF leaks. Further efforts should aim at improving the knowledge of junior doctors on this disease.

Imaging is essential for both the diagnosis and treatment of SIH. Brain MRI should be considered our best ally for the identification of SIH patients, in fact it detects signs of SIH in about 80% of the patients. On the other side, spinal imaging is not as sensitive and despite the use of different spinal imaging techniques, many faculty members shared their struggle in finding a CSF leak in a significant proportion of patients (20-30%). Not being able to identify a CSF leak precludes patients from the possibility of being treated with targeted epidural blood patches or surgery. Two particularly interesting advances in the imaging of SIH were discussed: the cranial hyperostosis sign and the role of Digital Subtraction Myelography (DSM) for the recognition of CSF-venous fistulas.

Prof. Cutsforth-Gregory, neurologist at the Rochester Mayo Clinic, in a recent unpublished study found that some patients with SIH present skull thickening on brain imaging defined as the “cranial hyperostosis sign”. According to his theory, the reduction in CSF volume (or pressure) could facilitate further growing of the bone of the skull. Out of 310 patients included in the study, the cranial hyperostosis sign appeared in 40 (13%). I am looking forward to reading the full publication of this research, because if this sign is present in patients who do not have the other typical SIH brain imaging findings, it could significantly improve the overall sensitivity of brain imaging.

With regards to the spinal imaging techniques, Digital Subtraction Myelography (DSM) has been demonstrated to help the identification of the exact site of CSF leaks. This technique requires the injection of intrathecal contrast and imaging before and after the contrast is injected. It can be performed under sedation or general anaesthesia; this choice is made based on the radiologist’s preference and patient’s characteristic. Many of the faculty members agreed in saying that DSM is extremely useful especially for the detection of CSF-venous fistulas (type 3 CSF leaks). Moreover, according to Dr Kranz’s experience, a DSM performed in lateral decubitus (patient lying on the side) with a coordinated respiratory hold (Valsalva manoeuvre) increases the chances of identifying the CSF-venous fistula. DSM seems extremely promising, but further information will be needed on the role that these CSF-venous fistulas have in patients’ symptoms and the long-term outcomes of patients who had CSF-venous fistulas treated.

The ability to diagnose SIH and identify CSF leaks has clearly improved over the last few years. While we remain uncertain of which spinal imaging strategy is perfect, I am hopeful that new advances in artificial intelligence and upright MRI scanners will help to develop more sensitive spinal imaging techniques that will be less invasive and will expose SIH patients to lower radiation doses.

SIH can be diagnosed based on the clinical presentation and imaging findings, even when the exact site of the leak is unknown. Moreover, several scientific papers demonstrate that blind epidural blood patches (EBP) work in a large number (but unfortunately not all) of SIH patients. This raises the question as to what the best treatment approach would be. Do we necessarily have to find the exact leak site before any EBP? Or shall we attempt treatment with a blind EBP first? This second option is preferred by Dr Dillon (from University of California San Francisco) and has the clear advantage of reducing the exposure of SIH patients to radiations as well as invasive spinal investigations. A similar strategy is employed by Dr Schievink’s team: only a baseline brain and spinal MRI are performed before attempting the first EBP.

During the symposium, Prof. Louy (Cedars-Sinai hospital, Los Angeles) gave a comprehensive overview of the evidence on EBP in SIH patients. Several studies demonstrated that large EBPs (>20 ml) give better outcomes than small EBPs. Evidence also suggests that injecting the EBP at multiple levels is more effective than single level EBPs. While we still do not know why EBPs work in SIH, we could speculate that large and multi-level EBPs have higher probability of spreading over more spinal levels and therefore reach the CSF leak site.

One of the shortcomings of performing multi-level blood patches concerns the patients’ experience. There are patients who find a lumbar EBP quite painful, I imagine that they would find it even more uncomfortable to undergo two EBP at different levels in the same occasion. A solution to this problem could be represented by the new single-catheter multi-level EBP technique proposed by Prof. Gemmete (University of Michigan Hospitals). This new technique is based on the insertion of a long catheter at a single spinal level. The catheter is then directed to all spinal levels and few ml of EBP distributed at each level. This technique achieves what we really want from an EBP: it allows the administration of large quantities of solution and ensures a good distribution to all spinal levels. I found this technique quite interesting and, if performed by expert hands, it could represent a valid strategy to obtain good outcomes with a single EBP.

Surgical repair of CSF leaks has a role in the treatment of patients who do not respond to EBPs. Dr Schievink has exceptional experience in the surgical treatment of CSF leaks and has developed techniques that allow him to reach and repair CSF leaks of different types in different locations. A very important message he shared during the symposium is that the exact location of the CSF leak needs to be known with certainty before performing any surgical treatment. This strategy reduces the need for invasive procedures that expose and explore large areas of the spine. Another important message is that while 98% of the patients operated have their leak successfully repaired (radiological outcome), this does not necessarily correspond to a clinical resolution of the symptoms. In fact, according to Prof. Schievink’s experience, there are patients that achieve complete radiological resolution of the CSF leak after surgical treatment, but continue being symptomatic. Large databases collecting information on the long-term outcomes of patients treated with surgery could provide further guidance on the best treatment strategy to adopt

SIH has traditionally been considered as a syndrome caused by a spontaneous CSF leak in the spine, however, despite all the imaging advances, we are still unable to identify a CSF leak in 20-30% of patients with a clear SIH syndrome. A possibility that we should consider, is that maybe some of the patients with SIH do not have an active spinal leak.

Our understanding of the exact mechanism that leads to SIH is very limited, and this is not surprising considering that our knowledge on normal CSF dynamics is still very poor. During the symposium, Dr Moghekar (Johns Hopkins Hospital, Baltimore) went through several physiology concepts on CSF production, circulation and absorption. This talk clearly highlighted how most of the knowledge taught in medical schools on CSF physiology is incorrect. If we don’t know how things work normally, how can we understand what happens in SIH? I think it is crucial that, while we work towards better imaging and treatment techniques for SIH, we simultaneously conduct research that can improve our knowledge of the mechanisms causing SIH. Dr Moghekar suggested that since CSF is 99% water, we should focus on monitoring the movement of labelled water in the brain through special imaging techniques.

A very interesting theory on the mechanism causing orthostatic headache in SIH was provided by Dr Silberstein (Thomas Jefferson University Hospital, Philadelphia). According to Dr Silberstein, SIH patients may have a problem of spinal dura compliance, consisting in the excessive ability of the spinal dura to relax and accommodate CSF. When SIH patients are upright, their spinal dura expands and accommodates an excessive amount of CSF causing low brain pressure and headache. The validity of this theory would be supported by the known association between SIH and connective tissue disorders and could be tested through the use of dynamic imaging techniques that observe the behaviour of the spinal dura in different body positions.

SIH is a moving target.

The symposium demonstrated that research on SIH and CSF leaks is ongoing with great enthusiasm and that many new advances for the management of these conditions are achieved year by year. This is extremely encouraging, but it also demands that doctors caring for SIH and CSF leak patients should continue to keep up to date with the new findings in this field.

Knowledge is power.

This symposium was a great opportunity for me to consolidate my knowledge on SIH and learn about the newest findings and advances. It also offered a simultaneous track of presentations especially dedicated to patients and caregivers. The activities of the CSF Leak Association (including this bursary) have been essential to raise awareness in the UK. Improving our knowledge on SIH and CSF leaks will allow us to improve our ability to recognise this condition and avoid misdiagnosis. I hope that in the future we will see more events raising awareness on SIH and that training and teaching activities for junior doctors will be implemented.

Research can help answer the fundamental questions on SIH.

Something I particularly liked at the symposium was seeing how many doctors around the world share similar fundamental questions about SIH and CSF leaks. Why do people get SIH? Can we prevent it in some way? Is there always a CSF leak in SIH? Can we find a definitive cure for this disease? The symposium demonstrated that we are not simply focusing on the treatment and investigations for SIH, but we are also thinking about strategies to approach these important questions that will help SIH patients in the long run.

Most importantly, I would like to thank the CSF Leak Association for this amazing opportunity. The symposium gave me the chance to learn more from world experts about SIH and my research will greatly benefit from this experience. I think the ‘Intracranial Hypotension Symposium Attendance Bursary’ is a very important initiative, and I hope that regular training events on SIH, similar to the Intracranial Hypotension Symposium, will start to take place also in the UK soon.