Utility of Photon-Counting Detector CT Myelography for the Detection of CSF-Venous Fistulas.

CSF-venous fistulas are an increasingly recognized type of CSF leak that can be particularly challenging to detect, even with recently improved imaging techniques. Currently, most institutions use decubitus digital subtraction myelography or dynamic CT myelography to localize CSF-venous fistulas. Photon-counting detector CT is a relatively recent advancement that has many theoretical benefits, including excellent spatial resolution, high temporal resolution, and spectral imaging capabilities. We describe 6 cases of CSF-venous fistulas detected on decubitus photon-counting detector CT myelography. In 5 of these cases, the CSF-venous fistula was previously occult on decubitus digital subtraction myelography or decubitus dynamic CT myelography using an energy-integrating detector system. All 6 cases exemplify the potential benefits of photon-counting detector CT myelography in identifying CSF-venous fistulas. We suggest that further implementation of this imaging technique will likely be valuable to improve the detection of fistulas that might otherwise be missed with currently used techniques.

Temporal Characteristics of CSF-Venous Fistulas on Digital Subtraction Myelography.

BACKGROUND AND PURPOSE: CSF-venous fistula can be diagnosed with multiple myelographic techniques; however, no prior work has characterized the time to contrast opacification and the duration of visualization. The purpose of our study was to evaluate the temporal characteristics of CSF-venous fistula on digital subtraction myelography. MATERIALS AND METHODS: We reviewed the digital subtraction myelography images of 26 patients with CSF-venous fistulas. We evaluated how long the CSF-venous fistula took to opacify after contrast reached the spinal level of interest and how long it remained opacified. Patient demographics, CSF-venous fistula treatment, brain MR imaging findings, CSF-venous fistula spinal level, and CSF-venous fistula laterality were recorded. RESULTS: Eight of the 26 CSF-venous fistulas were seen on both the upper- and lower-FOV digital subtraction myelography, for a total of 34 CSF-venous fistula views evaluated on digital subtraction myelography. The mean time to appearance was 9.1 seconds (range, 0-30 seconds). Twenty-two (84.6%) of the CSF-venous fistulas were on the right. The highest fistula level was C7, while the lowest was T13 (13 rib-bearing vertebral bodies). The most common CSF-venous fistula levels were T6 (4 patients) followed by T8, T10, and T11 (3 patients each). The mean age was 58.3 years (range, 31.7-87.6 years). Sixteen patients were women (61.5%). CONCLUSIONS: This is the first study to report the temporal characteristics of CSF-venous fistulas using digital subtraction myelography. We found that on average, the CSF-venous fistula appeared 9.1 seconds (range, 0-30 seconds) after intrathecal contrast reached the spinal level.

Conebeam CT as an Adjunct to Digital Subtraction Myelography for Detection of CSF-Venous Fistulas.

Lateral decubitus digital subtraction myelography is an effective technique for precisely localizing CSF-venous fistulas, a common cause of spontaneous intracranial hypotension. However, despite an optimal imaging technique, digital subtraction myelography fails to identify some CSF-venous fistulas for a variety of reasons. Here, we describe a technique involving conebeam CT performed during intrathecal contrast injection as an adjunct to digital subtraction myelography, allowing identification of some otherwise-missed CSF-venous fistulas.

The Monro-Kellie Doctrine: A Review and Call for Revision.

The Monro-Kellie doctrine is a well-accepted principle of intracranial hemodynamics. It has undergone few consequential revisions since it was established. Its principle is straightforward: The combined volume of neuronal tissue, blood, and CSF is constant. To maintain homeostatic intracranial pressure, any increase or decrease in one of these elements leads to a reciprocal and opposite change in the others. The Monro-Kellie doctrine assumes a rigid, unadaptable calvaria. Recent studies have disproven this assumption. The skull expands and grows in response to pathologic changes in intracranial pressure. In this review, we outline what is known about calvarial changes in the setting of pressure dysregulation and suggest a revision to the Monro-Kellie doctrine that includes an adaptable skull as a fourth component.

Sacral CSF-Venous Fistulas and Potential Imaging Techniques.

This is the first study to describe CSF-venous fistulas involving the sacrum, a location that may be underrecognized on the basis of current imaging techniques. We describe a delayed decubitus flat CT myelogram technique that may be useful to identify sacral CSF-venous fistulas.

Diffuse Calvarial Hyperostosis and Spontaneous Intracranial Hypotension: A Case-Control Study.

BACKGROUND AND PURPOSE: Diagnosing spontaneous intracranial hypotension and associated CSF leaks can be challenging, and additional supportive imaging findings would be useful to direct further evaluation. This retrospective study evaluated whether there was a difference in the prevalence of calvarial hyperostosis in a cohort of patients with spontaneous intracranial hypotension compared with an age- and sex-matched control population. MATERIALS AND METHODS: Cross-sectional imaging (CT of the head or brain MR imaging examinations) for 166 patients with spontaneous intracranial hypotension and 321 matched controls was assessed by neuroradiologists blinded to the patient's clinical status. The readers qualitatively evaluated the presence of diffuse or layered calvarial hyperostosis and measured calvarial thickness in the axial and coronal planes. RESULTS: A significant difference in the frequency of layered hyperostosis (31.9%, 53/166 subjects versus 5.0%, 16/321 controls, P < .001, OR = 11.58) as well as the frequency of overall (layered and diffuse) hyperostosis (38.6%, 64/166 subjects versus 13.2%, 42/321 controls, P < .001, OR = 4.66) was observed between groups. There was no significant difference in the frequency of diffuse hyperostosis between groups (6.6%, 11/166 subjects versus 8.2%, 26/321 controls, P = .465). A significant difference was also found between groups for calvarial thickness measured in the axial (P < .001) and coronal (P < .001) planes. CONCLUSIONS: Layered calvarial hyperostosis is more prevalent in spontaneous intracranial hypotension compared with the general population and can be used as an additional noninvasive brain imaging marker of spontaneous intracranial hypotension and an underlying spinal CSF leak.

Anatomy of Spinal Venous Drainage for the Neurointerventionalist: From Puncture Site to Intervertebral Foramen.

CSF-venous fistula is a relatively novel entity that is increasingly being recognized as a cause for spontaneous intracranial hypotension. Recently, our group published the first series of transvenous embolization of CSF-venous fistulas in this journal. Having now performed the procedure in 60 patients, we have garnered increasing familiarity with the anatomy and how to navigate our way through the venous system to any intervertebral foramen in the cervical, thoracic, and lumbar spine. The first part of this review summarizes the organization of spinal venous drainage as described in classic anatomy and interventional radiology texts, the same works that we studied when attempting our first cases. In the second part, we draw mostly on our own experience to provide a practical roadmap from the puncture site to the foramen. On the basis of these 2 parts, we hope this article will serve to collate the relevant anatomic knowledge and give confidence to colleagues who wish to embark on transvenous spinal procedures.

Idiopathic Intracranial Hypertension is Associated with a Higher Burden of Visible Cerebral Perivascular Spaces: The Glymphatic Connection.

BACKGROUND AND PURPOSE: Research suggests a connection between idiopathic intracranial hypertension and the cerebral glymphatic system. We hypothesized that visible dilated perivascular spaces, possible glymphatic pathways, would be more prevalent in patients with idiopathic intracranial hypertension. This prevalence could provide a biomarker and add evidence to the glymphatic connection in the pathogenesis of idiopathic intracranial hypertension. MATERIALS AND METHODS: We evaluated 36 adult (older than 21 years of age) patients with idiopathic intracranial hypertension and 19 controls, 21-69 years of age, who underwent a standardized MR imaging protocol that included high-resolution precontrast T2- and T1-weighted images. All patients had complete neuro-ophthalmic examinations for papilledema. The number of visible perivascular spaces was evaluated using a comprehensive 4-point qualitative rating scale, which graded the number of visible perivascular spaces in the centrum semiovale and basal ganglia; a 2-point scale was used for the midbrain. Readers were blinded to patient diagnoses. Continuous variables were compared using a Student t test. RESULTS: The mean number of visible perivascular spaces overall was greater in the idiopathic intracranial hypertension group than in controls (4.5 [SD, 1.9] versus 2.9 [SD, 1.9], respectively; P = .004). This finding was significant for centrum semiovale idiopathic intracranial hypertension (2.3 [SD, 1.4] versus controls, 1.3 [SD, 1.1], P = .003) and basal ganglia idiopathic intracranial hypertension (1.7 [SD, 0.6] versus controls, 1.2 [SD, 0.7], P = .009). There was no significant difference in midbrain idiopathic intracranial hypertension (0.5 [SD, 0.5] versus controls, 0.4 [SD, 0.5], P = .47). CONCLUSIONS: Idiopathic intracranial hypertension is associated with an increased number of visible intracranial perivascular spaces. This finding provides insight into the pathophysiology of idiopathic intracranial hypertension, suggesting a possible relationship between idiopathic intracranial hypertension and glymphatic dysfunction and providing another useful biomarker for the disease.

Changes in Ventricular and Cortical Volumes following Shunt Placement in Patients with Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND AND PURPOSE: While changes in ventricular and extraventricular CSF spaces have been studied following shunt placement in patients with idiopathic normal pressure hydrocephalus, regional changes in cortical volumes have not. These changes are important to better inform disease pathophysiology and evaluation for copathology. The purpose of this work is to investigate changes in ventricular and cortical volumes in patients with idiopathic normal pressure hydrocephalus following ventriculoperitoneal shunt placement. MATERIALS AND METHODS: This is a retrospective cohort study of patients with idiopathic normal pressure hydrocephalus who underwent 3D T1-weighted MR imaging before and after ventriculoperitoneal shunt placement. Images were analyzed using tensor-based morphometry with symmetric normalization to determine the percentage change in ventricular and regional cortical volumes. Ventricular volume changes were assessed using the Wilcoxon signed rank test, and cortical volume changes, using a linear mixed-effects model (P < .05). RESULTS: The study included 22 patients (5 women/17 men; mean age, 73 [SD, 6] years). Ventricular volume decreased after shunt placement with a mean change of -15.4% (P < .001). Measured cortical volume across all participants and cortical ROIs showed a mean percentage increase of 1.4% (P < .001). ROIs near the vertex showed the greatest percentage increase in volume after shunt placement, with smaller decreases in volume in the medial temporal lobes. CONCLUSIONS: Overall, cortical volumes mildly increased after shunt placement in patients with idiopathic normal pressure hydrocephalus with the greatest increases in regions near the vertex, indicating postshunt decompression of the cortex and sulci. Ventricular volumes showed an expected decrease after shunt placement.

A Novel Endovascular Therapy for CSF Hypotension Secondary to CSF-Venous Fistulas.

We report a consecutive case series of patients who underwent transvenous embolization of the paraspinal vein, which was draining the CSF-venous fistula, for treatment of spontaneous intracranial hypotension. These are the first-ever reported cases of this treatment for CSF-venous fistulas. All patients underwent spinal venography following catheterization of the azygous vein and then selective catheterization of the paraspinal vein followed by embolization of the vein with Onyx. All patients had improvement of clinical and radiologic findings with 4 patients having complete resolution of headaches and 1 patient having 50% reduction in headache symptoms. Pachymeningeal enhancement resolved in 4 patients and improved but did not resolve in 1 patient. Brain sag resolved in 4 patients and improved but did not resolve in 1 patient. There were no cases of permanent neurologic complications. All patients were discharged home on the day of the procedure.

Spontaneous Intracranial Hypotension: Atypical Radiologic Appearances, Imaging Mimickers, and Clinical Look-Alikes.

Spontaneous intracranial hypotension is a condition characterized by low CSF volume secondary to leakage through a dural defect with no identifiable cause. Patients classically present with orthostatic headaches, but this symptom is not specific to spontaneous intracranial hypotension, and initial misdiagnosis is common. The most prominent features of spontaneous intracranial hypotension on intracranial MR imaging include "brain sag" and diffuse pachymeningeal enhancement, but these characteristics can be seen in several other conditions. Understanding the clinical and imaging features of spontaneous intracranial hypotension and its mimickers will lead to more prompt and accurate diagnoses. Here we discuss conditions that mimic the radiologic and clinical presentation of spontaneous intracranial hypotension as well as other disorders that CSF leaks can imitate.

Lateral Decubitus Digital Subtraction Myelography: Tips, Tricks, and Pitfalls.

Digital subtraction myelography is a valuable diagnostic technique to detect the exact location of CSF leaks in the spine to facilitate appropriate diagnosis and treatment of spontaneous spinal CSF leaks. Digital subtraction myelography is an excellent diagnostic tool for assessment of various types of CSF leaks, and lateral decubitus digital subtraction myelography is increasingly being used to diagnose CSF-venous fistulas. Lateral decubitus digital subtraction myelography differs from typical CT and fluoroscopy-guided myelograms in many ways, including equipment, supplies, and injection and image-acquisition techniques. Operators should be familiar with techniques, common pitfalls, and artifacts to improve diagnostic yield and prevent nondiagnostic examinations.