Movement Disorders in Brain Sagging Syndrome Due To Spontaneous Intracranial Hypotension: A Review, 2024, Abhishek Lenka et al

[Mij]

Abstract
Background: Spontaneous intracranial hypotension (SIH), a treatable condition that stems from spinal leakage of cerebrospinal fluid, usually presents with orthostatic headache, nausea, vomiting, dizziness, and tinnitus. A subset of patients, especially those with sagging of brain structures (“brain sagging syndrome”), develop several movement abnormalities. As SIH is treatable with epidural blood patch (EBP), movement disorders neurologists should be familiar with this syndrome.

Method: The authors performed a literature search in PubMed in July 2024 using the Boolean phrase- ((“Brain sagging”)OR(“Intracranial hypotension”))AND((((((((((“Movement disorders”)OR(“Involuntary movements”))OR(“Tremor”))OR(“Dystonia”))OR(“Chorea”))OR(“Ballismus”))OR(“Myorhythmia”))OR (“Tic”))OR(“Ataxia”))OR(“Parkinsonism”)).

Result: We tabulated 21 case reports/series that highlighted the presence of movement disorders. The most reported phenomenology is gait unsteadiness. While it usually emerges in the background of the classic SIH symptoms, rarely, patients may present with isolated gait dysfunction. Tremor is the second most reported phenomenology with postural and kinetic tremor being the common subtypes. Holmes tremor has also been reported in SIH. Other reported phenomenologies are parkinsonism, chorea, and dystonia. One study reported a unique phenomenology i.e. compulsive repetitive flexion and breath holding in 35.3% of the patients. In majority of the patients, EBP resulted in substantial clinical and radiological improvement.

Discussion: Brain sagging syndrome due to SIH may present with a wide range of movement disorders. Mechanical distortion of the posterior fossa and subcortical structures result in the emergence of such movement abnormality. SIH adds to the list of conditions that result in “treatable movement disorders.” Therefore, movement disorders neurologists should be versed with the diagnosis and clinical features of this condition.

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[Jonathan Edwards]

Why would intracranial hypotension lead to brain sagging? Unless there are actually bubbles of nitrogen collecting above the brain I cannot see any reason why it should sag. If anything it should be sucked upwards I think.

I also think it pretty unlikely that brain sagging should give rise to movement disorders, other than perhaps stiff spastic gait.

 

[SNT Gatchaman]

Hypotension is probably a misnomer as normal opening pressures on LP, or with intracranial pressure monitors are common, so doesn't exclude the diagnosis. Perhaps a better term would be something like CSF hypovolaemia to reflect the reduced intracranial CSF volume.

The Monro-Kellie* doctrine is over 200 years old, though there are recent moves to refine it further. It assumes (for an intact adult skull) that the cranium represents a rigid, closed box, so the sum of contents — brain tissue, blood, CSF — is invariable. This allows some compensation, eg if there is brain swelling or ventricular obstruction, the vascular spaces can reduce, though there are limits to the physiological compensation. Unless there is brain inflammation or tumour, the brain itself is relatively static, so if CSF volume is reduced the vascular volume will increase, eg you see eg enlarged dural venous sinuses. Other things can remodel, so you may get pachymeningeal (dural) thickening and apparent expansion of the pituitary.

Over a longer time frame the skull can also remodel, with inward expansion of its inner table with low CSF, or alternatively calvarial thinning with increased CSF. This is where the Monro-Kellie doctrine might be refined to allow that the skull is not permanently rigid as initially postulated.

The idea behind brain sag is that the brain "floats" within/upon extra-axial CSF and brain shape is also dictated by its ventricles. Loss of CSF volume within and around the brain leads to "settling" / low grade compartment shift. It's a recently recognised mimic of frontotemporal dementia (without the atrophy), important because the clinical course is relentless and devastating, yet even severe symptoms can be completely reversed if the spinal CSF leak is corrected. Interestingly CSF leaks in the supratentorial compartment don't seem to cause "SIH", so "spinal dementia" has been proposed as a term in this context. However, it may also occur uncommonly with infratentorial, not just spinal CSF leaks/fistulae. The reasons are not yet understood.

Prior studies have suggested that skull base CSF leaks, as opposed to spinal CSF leaks, do not present with SIH. This idea was largely based on observations of spinal CSF leaks only. We approached the question from the perspective of skull base CSF leaks and found further evidence for the same conclusion. Skull base leaks and spinal CSF leaks may indeed represent distinct disorders of CSF dynamics.

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* Alexander Monro secundus who described the foramina of Monro (a little incorrectly).

Spoiler: References

The Monro–Kellie hypothesis (2001, Neurology)

How common is normal cerebrospinal fluid pressure in spontaneous intracranial hypotension? (2015, Cephalalgia)

Brain Sagging Dementia—Diagnosis, Treatment, and Outcome (2022, Neurology)

Brain Sagging Dementia (2023, Current Neurology and Neuroscience Reports)

The Monro-Kellie Doctrine: A Review and Call for Revision (2023, American Journal of Neuroradiology)

Skull Base CSF Leaks: Potential Underlying Pathophysiology and Evaluation of Brain MR Imaging Findings Associated with Spontaneous Intracranial Hypotension (2024, American Journal of Neuroradiology)

 

[Jonathan Edwards]

The idea behind brain sag is that the brain "floats" within/upon extra-axial CSF and brain shape is also dictated by its ventricles. Loss of CSF volume within and around the brain leads to "settling" / low grade compartment shift.

Are we sure this is real physiology rather than a misconception. It doesn't seem right to me. If there is no gas present how or why does the brain 'settle'? If the space normally taken by CSF is taken by venous blood why doesn't the brain float just the same?


I guess the answer must be that venous capacity is mostly on the upper surface the brain, so if CSF volume is low the brain is actually pushed down by swelling sinuses. And that wouldn't necessarily relate to low CSF pressure, just volume.

I worry with papers like this that we are seeing stories like the CCI fatigue story and the 'hEDS' story, not to mention the tethered cord story, emerging. Patients with margin radiological features, or even significant radiological features, get put into a clinical syndrome simply because of referral to centres that believe in that syndrome. The text of the posted paper is not particularly reassuring on critical rigour.

 

[SNT Gatchaman]

I think principally because the blood is in a different spatially less extensive compartment. Ie confined to compensatory expansion of venous structures, such as dural venous sinuses, rather than a more global "bath" that the extra-axial CSF would represent.

Some of the figures from the above refs show the effect. Presumably it's an open question what would happen if the patient were permanently supine (or head-down for that matter). The first image is before treatment, reversing the brain sagging. (Panel D looks a little horizontally compressed in the article but the effect is still evident.) The second image is normal and after developing brain sag, where they're noting the skull thickening over many years.

 

[Creachur]

Why would intracranial hypotension lead to brain sagging? Unless there are actually bubbles of nitrogen collecting above the brain I cannot see any reason why it should sag. If anything it should be sucked upwards I think.

I also think it pretty unlikely that brain sagging should give rise to movement disorders, other than perhaps stiff spastic gait.

Couldn't gait ataxia arise from a compromised (compressed) cerebellum?

 

[Jonathan Edwards]

Couldn't gait ataxia arise from a compromised (compressed) cerebellum?

I am not sure the whole cerebellum would be squashed rather than the tonsils and they would need to be abnormal already to go through the foramen I would think.

And ataxia isn't usually thought of as a movement disorder, I guess.