Tentorial Venous Anatomy: Cadaveric and Radiographic Study with Discussion of Origin and Surgical Significance

Combined cone-beam CT imaging and microsurgical dissection of cadaver specimens to study cerebral venous anatomy: a technical note

PURPOSE

Cadaver dissections and X-ray based 3D angiography are considered gold standards for studying neurovascular anatomy. We sought to develop a model that utilize the combination of both these techniques to improve current tools for anatomical research, teaching and preoperative surgical planning, particularly addressing the venous system of the brain.

MATERIALS AND METHODS

Seven ethanol-fixed human cadaveric heads and one arm were injected with a latex-barium mixture into the internal jugular veins and the brachial artery. After the ethanol-based fixation, specimens were scanned by high-resolution cone-beam CT and images were post-processed on a 3D-workstation. Subsequent, microsurgical dissections were performed by an experienced neurosurgeon and venous anatomy was compared with relevant 3D venograms.

RESULTS

Latex-barium mixtures resulted in a homogenous cast with filling of the cerebral venous structures down to 150 μm in diameter. The ethanol-based preparation of the cadaveric brains allowed for near-realistic microsurgical maneuverability during dissection. The model improves assessment of the venous system for anatomical education and hands-on surgical training.

CONCLUSION

To our knowledge we describe the first preparation method which combines near-realistic microsurgical dissection of human heads with high-resolution 3D imaging of the cerebral venous system in the same specimens.

Tentorial venous anatomy of mice and humans

We recently described a transtentorial venous system (TTVS), which to our knowledge was previously unknown, connecting venous drainage throughout the brain in humans. Prior to this finding, it was believed that the embryologic tentorial plexus regresses, resulting in a largely avascular tentorium. Our finding contradicted this understanding and necessitated further investigation into the development of the TTVS. Herein, we sought to investigate mice as a model to study the development of this system. First, using vascular casting and ex vivo micro-CT, we demonstrated that this TTVS is conserved in adult mice. Next, using high-resolution MRI, we identified the primitive tentorial venous plexus in the murine embryo at day 14.5. We also found that, at this embryologic stage, the tentorial plexus drains the choroid plexus. Finally, using vascular casting and micro-CT, we found that the TTVS is the dominant venous drainage in the early postnatal period (P8). Herein, we demonstrated that the TTVS is conserved between mice and humans, and we present a longitudinal study of its development. In addition, our findings establish mice as a translational model for further study of this system and its relationship to intracranial physiology.

Dural venous system: angiographic technique and correlation with ex vivo investigations

BACKGROUND

The dural vasculature plays a key role in several important conditions, including dural fistulas and subdural collections. While in vivo investigations of intrinsic dural arterial angioarchitecture are rare, no angiographic studies of dural venous drainage exist to our knowledge.

OBJECTIVE

To describe methods by which dural venous drainage might be visualized with current angiographic equipment and technique, and to correlate our results with existing ex vivo literature.

METHODS

Digital subtraction angiography and 3D angiography (rotational and Dyna CT) of dural neurovasculature were acquired in the context of subdural hematoma embolization and normal dura. Protocols for visualization of dural venous drainage were established, and findings correlated with ex vivo studies.

RESULTS

Meningeal arteries supply both the skull and dura. Normal dural enhancement is accentuated by the presence of hypervascular membranes. Intrinsic meningeal veins/sinuses parallel outer layer arteries with well-known tram-tracking appearance. Dura adjacent to main arterial trunks drains via skull base foramina into the pterygopalatine venous plexus, or via emissary veins into the temporalis venous plexus. Dura near the sinuses drains into venous pouches adjacent to the sinus, before emptying into the sinus proper-possibly the same pouches implicated in the angioarchitecture of dural fistulas. Finally, posterior temporoparietal convexity dura, situated in a watershed-like region between middle and posterior meningeal territories, frequently empties into diploic and emissary veins of the skull. Wide variation in balance is expected between these three routes. Drainage patterns appear to correlate with venous embryologic investigations of Padget and ex vivo studies in adults.

CONCLUSIONS

Continued attention to dural venous drainage may prove useful in the diagnosis and management of dural-based vascular diseases.

Bridging veins of the cerebellum: a magnetic resonance imaging study

PURPOSE

To date, no study has yet explored the bridging veins (BVs) of the cerebellum using neuroimaging modalities. Therefore, this study aimed to characterize them using magnetic resonance imaging (MRI).

METHODS

A total of 90 patients with intact cerebellar hemispheres and intracranial dural sinuses underwent thin-sliced, contrast-enhanced MRI.

RESULTS

The BVs were classified into six routes based on the draining pattern into the dural sinuses. The superior vermian vein emptying into the straight sinus was delineated in 100% of the patients. The inferior vermian vein emptying into the confluence of the sinuses was identified in 66.7% of the patients. The inferior hemispheric and cerebellar cortical veins emptying into the transverse sinus were identified in 54.4% and 26.7% of the patients, respectively. The inferior vermian and cerebellar cortical veins emptying into the straight sinus were identified in 77.8% and 12.2% of the patients, respectively. The cerebellar cortical vein emptying into the tentorial sinus was identified in 83.3% of the patients; it was delineated on 54 sides with an average number per right hemisphere of 1.9 and 63 sides with an average number per left hemisphere of 2. The pontine-trigeminal and anterior hemispheric veins emptying into the superior petrosal sinus were identified in 42.2% of the patients.

CONCLUSIONS

The BVs of the cerebellum can be classified into six distinct routes. Radiological classification may be useful for understanding the drainage pattern of the cerebellum.

Related Structures in the Straight Sinus: An Endoscopic Anatomy and Histological Study

Some structure might be encountered with endovascular procedures within the straight sinus and is not now readily seen on digital subtraction angiography (DSA). We investigated the morphological and histological characteristics of the straight sinus, chordae willisii (CW), and junction between the great cerebral vein (GCV) and straight sinus. A total of 22 cadaveric heads and 135 patients were analyzed with either anatomic dissection or neuroimaging. The morphological features of the CW and the junction between the GCV and straight sinus were analyzed by endoscope. The histology of the junction between the GCV and straight sinus was evaluated under the microscope with staining for elastic fiber, Masson’s, and immunohistochemistry. We found that fold, elevation, small bugle, or nodule and CW were detected by endoscope in the straight sinus. The most common type of CW was valve-like lamellae, which comprised 40.46% of all CW. Three different types of junctions between the GCV and straight sinus were identified: type 1 has folds in the GCV and elevation on the floor of the straight sinus; type 2 has folds and a small bugle; and type 3 presents with an intraluminal nodule located at the opening of the GCV. Compared with arachnoid granulation, the nodule consists of smooth muscle fibers and higher rate of elastic fibers. Understanding the detailed anatomy of the straight sinus may help surgeons to avoid procedural difficulties and to achieve higher success rate.

Tentorial Venous Anatomy: Variation in the Healthy Population

BACKGROUND AND PURPOSE

A new transtentorial venous system consisting of medial, intermediate, and lateral tentorial veins, connecting infra- and supratentorial compartments, was recently shown in 2 cadaver dissections and 2 patient scans. We sought to characterize the venous patterns within the tentorium and their relation to measures of skull development in a cohort of healthy adults.

MATERIALS AND METHODS

We retrospectively reviewed tentorial venous anatomy of the head using CTA/CTV performed for routine care or research purposes in 238 patients. Included studies had adequate contrast opacification of venous structures and a section thickness of ≤2 mm; we excluded cases with space-occupying lesions and vascular pathologies. Tentorial angle, dural sinus configurations, and measures of skull base development were assessed as predictors of tentorial venous anatomy variation via Cramér V association, the binary encoded Pearson correlation, and nearest-point algorithm with the Euclidean distance metric for clustering.

RESULTS

Tentorial vein development was related to the ringed configuration of the tentorial sinuses (P < .005). There were 3 configurations. Groups 1A and 1B (n = 50/238) had ringed configuration, while group 2 did not (n = 188/238). Group 1A (n = 38/50) had a medialized ringed configuration, and group 1B had a lateralized ringed configuration (n = 12/50). Measurements of skull base development were predictive of these groups. The ringed configuration of group 1 was related to the presence of a split confluens, which correlated with a decreased internal auditory canal-petroclival fissure angle. Configuration 1A was related to the degree of petrous apex pneumatization (P value = .010).

CONCLUSIONS

Variations in the transtentorial venous system directly correlate with cranial development.

Topographical anatomy of the tentorium cerebelli and venous confluences in human midterm fetuses

Early development of veins and sinuses at and around the posterior cranial fossa seemed not to be shown by photographs except for our recent study (Ann Anat, 2020). Examination of histological sections of 38 fetuses at 10-16 weeks gestational age (GA) demonstrated that: (1) the superior petrosal sinus passed posterosuperiorly through the tentorium cerebelli and, distant and lateral to both the cerebellum and internal ear, drained into the transverse sinus; (2) the superior sagittal sinus was underdeveloped, and the inferior sagittal sinus was not yet evident; (3) the straight sinus (STS) originated from a joining of the bilateral pial veins from the lateral ventricular choroid plexus, passed through the inferoposterior part of the falx cerebri, reached the initial confluens sinuum, and then divided into the bilateral transverse sinuses. The STS origin was immediately behind the pineal body, and near the inferoposterior end of the third ventricle. The falx had a thick attachment to the tentorium below the entire course of the STS and was behind other parts of the brain. Therefore, the development and growth of the posterior dural system seemed to be independent from brain growth, and occurred well before the cerebellum grew to fill the posterior cranial fossa. A basic configuration of intracranial veins and sinuses, including embryonic transient veins (such as the vena capitis prima) seemed to be established by venous return from the choroid plexus and cranial wall, without greatly increasing the abundance of neuronal or glial cells in the brain.