A New Study Explores Thecal Sac Volume in Spontaneous Intracranial Hypotension
A recent study published in Headache: The Journal of Head and Face Pain, Quantitative Analysis of Thecal Sac Volume and Morphology as a Diagnostic Tool in Intracranial Hypotension, by Dr. Kerry Knievel and colleagues, takes a closer look at imaging-based markers that may aid in the diagnosis of spontaneous intracranial hypotension (SIH).
This work addresses a critical gap in headache medicine: patients with high clinical suspicion for SIH often go undiagnosed when imaging does not reveal a clear cerebrospinal fluid (CSF) leak. By investigating thecal sac volume through MRI analysis, the study highlights potential new diagnostic pathways for this difficult-to-manage condition.
As Dr. Knievel explained in a recent interview, “Just because we don't have abnormal imaging or just because we don't have a clearly identified leak, there's probably something else going on. We've improved our imaging techniques and imaging modalities, but there's still a large population that we can't help here. And so there's something else going on. So we just need to keep the interest, keep the curiosity, and keep looking into this.”
Watch the full discussion with Dr. Knievel:
Headache is the official journal of the American Headache Society and serves as a leading platform for clinical and basic research on head and face pain. This study contributes to a growing body of research aimed at understanding SIH, a condition that can cause debilitating symptoms but remains underdiagnosed and undertreated.
Researchers compared spine MRIs of patients who met the ICHD-3 diagnostic criteria for headache attributed to low CSF pressure with age-, height-, and sex-matched controls. Using volumetric software, they analyzed thecal sac volume across both groups. The analysis revealed a statistically significant difference: patients with spinal CSF leak and SIH showed a larger thecal sac volume compared with matched controls. While the team did not know what to expect going into the study, this finding points to the possibility of new diagnostic markers that may help identify patients who do not present with a clearly visible leak.
The results also raise important questions about the underlying mechanisms of SIH. Dr. Knievel noted that not every patient with symptoms has an identifiable dural defect or CSF venous fistula. Instead, the findings suggest that issues related to dura compliance, connective tissue associations, or other structural factors may contribute to the condition. This broadens the conversation about SIH beyond the presence or absence of a leak and underscores the need to keep an open mind in clinical practice.
For clinicians, this work reinforces the importance of not dismissing patients who exhibit strong signs of SIH but lack traditional imaging confirmation. As Dr. Knievel emphasized, these individuals represent one of the most debilitated and refractory patient populations. Continued attention, research, and clinical curiosity are essential to improving outcomes for this group.
Looking ahead, the study lays the groundwork for additional research into diagnostic imaging and pathophysiology. Future studies may further examine dura compliance and other structural contributors, helping to refine both diagnostic and treatment strategies. The authors also acknowledged the support of the Spinal CSF Leak Foundation and their colleagues at the Lewis Headache Center at Barrow, highlighting the collaborative effort required to advance this complex field.
This research offers an important step toward broadening the diagnostic framework for SIH. By pointing to measurable differences in thecal sac volume, the study provides both clinicians and researchers with new avenues to explore in the pursuit of better care for patients with intracranial hypotension.
Read the Interview Transcript:
Dr. Rashmi Halker Singh:
I am Dr. Rashmi Halker Singh. I'm the Deputy Editor of Headache, and it's my pleasure to be joined today by Dr. Kerry Knievel, who's one of the authors of a recent publication entitled Quantitative Analysis of Fecal Sac Volume and Morphology as a Diagnostic Tool in Intracranial Hypotension. Welcome, Dr. Knievel. I'm so happy to talk to you about this manuscript.
Dr. Kerry Knievel:
Thank you so much. Thank you for having me, Dr. Halker Singh.
Dr. Rashmi Halker Singh:
So first of all, this is a really exciting piece of work. There's a lot of interest in intracranial hypotension, but I'm curious what inspired you and your colleagues to do this research?
Dr. Kerry Knievel:
I think really first and foremost, it's our patients, specifically patients with CSF pressure and volume disorders. I think this is really a big evolving field in headache, but it's still one of the fields where there's a lot of unmet need for our patients. Often we have difficulty finding the site of leak, but we have a very high suspicion, a high clinical suspicion, and even sometimes a high imaging suspicion that patients have spontaneous intracranial hypotension. So we wanted to look for potentially some other causes or imaging biomarkers.
Dr. Rashmi Halker Singh:
Oh yeah, I mean, what you said resonates with me so much with all these patients. I think that I have in my clinical practice some, which I actually share with you that we consider the diagnosis of intra hypotension, but that source of leak can be so challenging to find. So tell me about your study. What did you all do
Dr. Kerry Knievel:
For the standard of care, for the majority of our patients with spinal CSF leak, spontaneous intracranial hypotension, we obtain an MRI of the spine heavily T2-weighted to look for epidural fluid. So we used patients who met the diagnostic criteria, the ICHD-3 diagnostic criteria for headache attributed to low CSF pressure. So they either needed to have a low opening pressure, less than six, or brain or spine imaging findings consistent with CSF leak. So we compared those patients', MRI spines, to age, height, and sex matched controls, and evaluated the volume of the thecal sac using a volumetric analysis software for MRI.
Dr. Rashmi Halker Singh:
And so what did you find? What were the key takeaways and did anything surprise you all?
Dr. Kerry Knievel:
Yeah, well, we didn't really know what to expect, but we did find a statistically significant difference, a larger CSF volume at larger thecal SAC volume in patients who met the diagnostic criteria for headache attributed to spinal CSF leak.
Dr. Rashmi Halker Singh:
So what does this mean for clinical practice as a clinician? What should I take from your work?
Dr. Kerry Knievel:
Yeah, I think the main thing that I think is an open mind, and I think we need this anyway with regards to this diagnosis, to think that we know everything about spontaneous intracranial hypotension and spinal CSF leak. It does not make sense. We have a lot of patients who were either unable to find a leak due to a dural defect or a leak due to CSF venous fistula, and certainly we've improved our imaging modalities and techniques with our given imaging modalities. But still, there's a lot of patients who we have a very high clinical suspicion whether they have abnormal brain or spine imaging findings or not. We have a high clinical suspicion that they have a spontaneous intracranial hypotension without an identifiable leak. So perhaps there's something else. Perhaps not all patients have a dural defect or a CSF venous fistula.
Maybe there's something related to compliance of the dura. We certainly know that there's a component or association with connective tissue disease, so perhaps there's just something else going on and the findings in this study do kind of support that. There could be a stretching of the dura and the thecal sac or some sort of compliance change for some patients with spontaneous intracranial hypotension symptoms.
Dr. Rashmi Halker Singh:
I think this really adds to that conversation and hopefully there's more research coming
Dr. Kerry Knievel:
For sure.
Dr. Rashmi Halker Singh:
So any final thoughts that you want to share with our audience?
Dr. Kerry Knievel:
Yeah, I think in general, this is one of our more debilitated patient populations and certainly one of our more refractory patient populations that we see in practice. And I think just not giving up on the patients for sure, but not giving up on this as a potential diagnosis or underlying etiology for their symptomatology. Just because we don't have abnormal imaging or just because we don't have a clearly identified leak, there's probably something else going on. We've improved our imaging techniques and imaging modalities, but there's still a large population that we can't help here. And so there's something else going on. So we just need to keep the interest, keep the curiosity, and keep looking into this.
Dr. Rashmi Halker Singh:
Well, thank you so much for your work. Your passion is very clear and we really appreciate everything you do.
Dr. Kerry Knievel:
Thank you so much. And I just also want to thank the Spinal CSF Leak Foundation for the grant that supported this work and also their research program and the other physicians and providers at the Lewis Headache Center at Barrow for participating in this research.
Dr. Rashmi Halker Singh:
Fantastic.