Transmantle and transvenous pressure gradients in cerebrospinal fluid disorders

Transmantle pressure under the influence of free breathing: non-invasive quantification of the aqueduct pressure gradient in healthy adults

BACKGROUND

The pressure gradient between the ventricles and the subarachnoid space (transmantle pressure) is crucial for understanding CSF circulation and the pathogenesis of certain neurodegenerative diseases. This pressure can be approximated by the pressure difference across the aqueduct (ΔP). Currently, no dedicated platform exists for quantifying ΔP, and no research has been conducted on the impact of breathing on ΔP. This study aims to develop a post-processing platform that balances accuracy and ease of use to quantify aqueduct resistance and, in combination with real-time phase contrast MRI, quantify ΔP driven by free breathing and cardiac activities.

METHODS

Thirty-four healthy participants underwent 3D balanced fast field echo (BFFE) sequence and real-time phase contrast (RT-PC) imaging on a 3T scanner. We used the developed post-processing platform to analyse the BFFE images to quantify the aqueduct morphological parameters such as resistance. RT-PC data were then processed to quantify peak flow rates driven by cardiac and free breathing activity (Qc and Qb) in both directions. By multiplying these Q by resistance, ΔP driven by cardiac and breathing activity was obtained (ΔPc and ΔPb). The relationships between aqueduct resistance and flow rates and ΔP driven by cardiac and breathing activity were analysed, including a sex difference analysis.

RESULTS

The aqueduct resistance was 78 ± 51 mPa·s/mm³. The peak-to-peak cardiac-driven ΔP (Sum of ΔPc+ and ΔPc-) was 24.2 ± 11.4 Pa, i.e., 0.18 ± 0.09 mmHg. The peak-to-peak breath-driven ΔP was 19 ± 14.4 Pa, i.e., 0.14 ± 0.11 mmHg. Males had a longer aqueduct than females (17.9 ± 3.1 mm vs. 15 ± 2.5 mm, p < 0.01) and a larger average diameter (2.0 ± 0.2 mm vs. 1.8 ± 0.3 mm, p = 0.024), but there was no gender difference in resistance values (p = 0.25). Aqueduct resistance was negatively correlated with stroke volume and the peak cardiac-driven flow (p < 0.05); however, there was no correlation between aqueduct resistance and breath-driven peak flow rate.

CONCLUSIONS

The highly automated post-processing software developed in this study effectively balances ease of use and accuracy for quantifying aqueduct resistance, providing technical support for future research on cerebral circulation physiology and the exploration of new clinical diagnostic methods. By integrating real-time phase contrast MRI, this study is the first to quantify the aqueduct pressure difference under the influence of free breathing. This provides an important physiological reference for further studies on the impact of breathing on transmantle pressure and cerebral circulation mechanisms.

Quantifying CSF Dynamics disruption in idiopathic normal pressure hydrocephalus using phase lag between transmantle pressure and volumetric flow rate

Background and purpose

Idiopathic normal pressure hydrocephalus (iNPH) is a cerebrospinal fluid (CSF) dynamics disorder as evidenced by the delayed ascent of radiotracers over the cerebral convexity on radionuclide cisternography. However, the exact mechanism causing this disruption remains unclear. Elucidating the pathophysiology of iNPH is crucial, as it is a treatable cause of dementia. Improving the diagnosis and treatment prognosis rely on the better understanding of this disease. In this study, we calculated the pulsatile transmantle pressure and investigated the phase lag between this pressure and the volumetric CSF flow rate as a novel biomarker of CSF dynamics disruption in iNPH.

Methods

44 iNPH patients and 44 age- and sex-matched cognitively unimpaired (CU) control participants underwent MRI scans on a 3T Siemens scanner. Pulsatile transmantle pressure was calculated analytically and computationally using volumetric CSF flow rate, cardiac frequency, and aqueduct dimensions as inputs. CSF flow rate through the aqueduct was acquired using phase-contrast MRI. The aqueduct length and radius were measured using 3D T1-weighted anatomical images.

Results

Peak pressure amplitudes and the pressure load (integrated pressure exerted over a cardiac cycle) were similar between the groups, but the non-dimensionalized pressure load (adjusted for anatomical factors) was significantly lower in the iNPH group ( p < 0.001 , Welch's t-test). The phase lag between the pressure and the flow rate, arising due to viscous drag, was significantly higher in the iNPH group ( p < 0.001 ).

Conclusion

The increased phase lag is a promising new biomarker for quantifying CSF dynamics dysfunction in iNPH.

Statement of Significance

The exact mechanism causing the disruption of CSF circulation in idiopathic normal pressure hydrocephalus (iNPH) remains unclear. Elucidating the pathophysiology of iNPH is crucial, as it is a treatable cause of dementia. In this study, we provided an analytical and a computational method to calculate the pulsatile transmantle pressure and the phase lag between the pressure and the volumetric CSF flow rate across the cerebral aqueduct. The phase lag was significantly higher in iNPH patients than in controls and may serve as a novel biomarker of CSF dynamics disruption in iNPH.

Venous congestive encephalopathy secondary to arteriovenous fistula aggravated by cerebrospinal fluid shunt

We present a unique clinical case of venous congestive encephalopathy in the context of a cerebral arteriovenous fistula with clinical worsening secondary to valvular overdrainage. ICP monitoring, the different pressure settings of the programable CSF shunt and the detailed clinical description that is carried out offer us enough data to understand that this case provides important pathophysiological knowledge to a little-known disease.

Paediatric hydrocephalus

Hydrocephalus is classically considered as a failure of cerebrospinal fluid (CSF) homeostasis that results in the active expansion of the cerebral ventricles. Infants with hydrocephalus can present with progressive increases in head circumference whereas older children often present with signs and symptoms of elevated intracranial pressure. Congenital hydrocephalus is present at or near birth and some cases have been linked to gene mutations that disrupt brain morphogenesis and alter the biomechanics of the CSF-brain interface. Acquired hydrocephalus can develop at any time after birth, is often caused by central nervous system infection or haemorrhage and has been associated with blockage of CSF pathways and inflammation-dependent dysregulation of CSF secretion and clearance. Treatments for hydrocephalus mainly include surgical CSF shunting or endoscopic third ventriculostomy with or without choroid plexus cauterization. In utero treatment of fetal hydrocephalus is possible via surgical closure of associated neural tube defects. Long-term outcomes for children with hydrocephalus vary widely and depend on intrinsic (genetic) and extrinsic factors. Advances in genomics, brain imaging and other technologies are beginning to refine the definition of hydrocephalus, increase precision of prognostication and identify nonsurgical treatment strategies.

Predictors of visual and endocrine outcomes after endoscopic transsphenoidal surgery for pituitary adenomas

Surgery for pituitary adenoma is indicated for relief of mass effect and control of endocrinopathy. Setting benchmarks for visual and hormonal outcomes is important for monitoring performance of surgical centres, while understanding the preoperative factors that predict endocrine cure and visual improvement facilitates tailored counselling for patients prior to surgery. A prospective, consecutive cohort of surgically managed (endoscopic transsphenoidal) pituitary adenoma (n = 304) were analysed. Preoperative and postoperative endocrine and visual field assessments were performed and compared to demographic, imaging and pathological data. Larger adenomas tended to have preoperative endocrine deficiency (p < 0.001) and visual field defects (p < 0.001). The largest tumours did not experience normalisation of their endocrinopathy or visual fields with surgery. Of the adenomas with normal preoperative endocrine function, 92.0% (126/137) maintained this postoperatively; only 2 of the 11 patients with new hypopituitarism required long-term hormone replacement. Functional tumour cure was achieved in 65.2% (86/116) after surgery; 74.4% (32/43) of acromegalics and 70.0 (35/50) of Cushing's disease patients achieved hormonal control. All patients with isolated hyperprolactinaemia from stalk effect normalised with surgery, while only 15.9% (7/44) with hypopituitarism recovered normal endocrine function. New hypopituitarism was predicted by younger age and functional adenoma, particularly Cushing's disease. Resolution of endocrinopathy was less likely with reoperative cases and those with cavernous sinus invasion (Knosp grade > 2) or preoperative ophthalmoplegia. One-third of the cohort (102/304, 33.6%) had a preoperative field cut, most commonly an incomplete (51.0%) or complete (31.4%) bitemporal hemianopsia. Only two patients (2/304, 0.7%) had visual field worsening after surgery, while 71.6% (73/102) experienced partial or complete resolution of their field cut after surgery. Complete resolution of visual field defect was predicted by younger age and incomplete bitemporal hemianopsia. Surgery is a safe and effective therapy for pituitary adenomas. Nearly all patients experience improvement in visual fields, especially the young and those with incomplete bitemporal defects. Reoperative cases and those with cavernous sinus involvement (high Knosp grade/ophthalmoplegia) are less likely to have resolution of endocrinopathy. Visual worsening, new ophthalmoplegia or endocrinopathy were rare complications of surgery.