Evaluation of dural venous sinuses and confluence of sinuses via MRI venography: anatomy, anatomic variations, and the classification of variations

Falx cerebelli and its associated occipital venous sinus: an anatomical study

PURPOSE

This study presents the morphological variation of falx cerebelli, which helps to identify the possible variations in the presence of the occipital sinus in the posterior margin of the fold whose damage during midline incision of posterior cranial fossa surgeries may lead to internal hemorrhage.

METHOD

The study was conducted on 48 cranial cavities exploring the falx cerebelli. Variations in the number of folds, its proximal and distal attachments, and the drainage pattern of the occipital sinus were evaluated by histological processing of the upper 1/3rd section of the falx fold.

RESULTS

The variation in the number of folds recorded are single folds in 87.5%, double folded in 8.3%, and multiple folds (five and seven folded) in 4.2% of the cases. The variation in the proximal and distal attachments in single falx folds showed three combinations: Ramified triangular in 66.7%, both ramified type in 12.5%, and both triangular type in 8.3% of the cases. Double and multiple folds showed ramified and triangular types of variation in their attachments. Histological findings showed the presence of occipital venous sinuses in most of the single falx fold. Two aberrant venous sinuses were seen in a double and five-folded falx cerebelli.

CONCLUSIONS

This study records the variations in the morphology of falx cerebelli. The histological data of this study sheds light on the drainage pattern of venous sinuses in the area whose negligence during midline incisions of brain surgeries may increase the possibility of hemorrhage.

The effect of the occipital sinus on the torcular Herophili and neighboring structures

Objective

The occipital sinus (OS) has many variations. It is unknown whether OS can change the angioarchitecture of torcular Herophili. Therefore, we performed magnetic resonance venography (MRV) in a cohort of Han Chinese individuals to determine whether OS can change the angioarchitecture of torcular Herophili.

Methods

Participants were divided into a normal OS group and a hyperplastic OS group. Parameters of the OS and torcular Herophili and its neighboring structures were recorded. Statistical analysis was used to determine the effects of OS on torcular Herophili and neighboring structures.

Results

One hundred forty-five healthy participants were enrolled. One hundred patients were in the normal OS group, and 45 were in the hyperplastic OS group. In the normal OS group, the diameters at the transverse sinus (TS) origin were 5.8 ± 2.3 mm on the left side and 7.5 ± 2.2 mm on the right side. In the hyperplastic OS group, the diameters at the TS origin were 6.0 ± 2.1 mm on the left side and 7.0 ± 2.7 mm on the right side. Fenestration was observed in 33% of the torculars in the normal OS group and 6.7% of the torculars in the hyperplastic group. An unpaired t-test revealed a significant difference between bilateral TSs in the normal OS group (P < 0.05) but no difference in the hyperplastic OS group. The chi-square test revealed a significant difference in torcular Herophili fenestration between the normal and hyperplastic OS groups (P < 0.05).

Conclusions

Hyperplastic OS makes bilateral TSs equal in diameter and weakens the predominance of the right TS. A hyperplastic OS reduces the occurrence of torcular Herophili fenestration.

Variations in the morphology of lagomorph confluence sinuum on contrast enhanced CT

Knowledge of lagomorph confluence sinuum anatomy on contrast-enhanced CT may prevent the misdiagnoses of intracranial, extra-axial masses. The purpose of this retrospective, observational, descriptive study was to describe the characteristics of the confluence sinuum in rabbits on contrast-enhanced CT. Images of 24 rabbits who had pre- and postcontrast CT sequences of the skull were reviewed by an American College of Veterinary Radiology-certified veterinary radiologist and third-year radiology resident. Degree of contrast enhancement within the region of the confluence sinuum was graded based on consensus as no (0), mild (1), moderate (2), or marked (3) contrast enhancement. Hounsfield units (HU) of the confluence sinuum was measured in three different regions of interest, averaged for each patient, and divided into each group for comparison using one-way ANOVA analysis. Contrast enhancement was mild in 45.8% (11/24) rabbits, moderate in 33.3% (8/24), marked in 20.8% (5/24), and none in 0.0% (0/24). There were significant differences (P < 0.05) between the average HU of the mild and marked group (P-value = 0.0001) and moderate and marked groups (P-value = 0.0010). Two rabbits with marked contrast enhancement were initially misdiagnosed with an intracranial, extra-axial mass along the parietal lobe based on contrast-enhanced CT. On necropsy, no gross or histopathological abnormalities were identified in the brain for these rabbits. In summary, contrast enhancement was identified in all rabbits (24/24) on contrast-enhanced CT imaging . This normal structure can be variable in size should not be mistaken for a pathological lesion in the absence of mass effect, secondary calvarial lysis, or hyperostosis.

Absence of the torcular, review of venous sinus anatomy, and the simplified dural sinus classification

BACKGROUND

Classically, the torcular Herophili is described as the symmetric junction between the superior sagittal sinus (SSS), transverse sinuses (TSs), and straight sinus (SS). However, finding this pattern in practice is not standard. Anatomical variations are common, and different drainage patterns should be expected. Existing literature proposes highly detailed descriptions and classifications of this region. Still, a simplified and practical categorization is not available.

METHODS

We present an anatomical finding of the torcular Herophili discovered on a cadaveric dissection. Then, we conducted a retrospective study examining the 100 most recent cranial magnetic resonance venographies (MRVs) from the Mayo Clinic, labeling them with a new proposed dural sinus classification system. Images were initially classified by two authors and further validated by a board-certified neurosurgeon and a board-certified neuroradiologist from our institution. To measure consistency in image identification, two additional international neurosurgeons were asked to classify a subset of the same MRV images, and their answers were compared.

RESULTS

Of the MRV cohort, 33 patients were male and 67 were female. Their ages ranged from 18 to 86 years, with a mean of 47.35 years and a median of 49 years. Upon examination, 53 patients presented as confluent (53%), 9 as SSS divergent (9%), 25 as SS divergent (25%), 11 as circular (11%), and 2 as trifurcated (2%). The inter-rater reliability ranked very good; agreement between the two neurosurgeons was 83% (κ = 0.830, p < 0.0005).

CONCLUSION

The confluence of the venous sinuses is a highly variable anatomical area that is rarely evaluated with neuroimaging before surgery. The classic textbook configuration is not the rule. Using a simplified classification system may increase awareness and hopefully patient safety by preparing the physician for anatomical variations that they will encounter in a surgical or clinical scenario.

Craniovascular variation in four late Holocene human samples from southern South America

Craniovascular traits in the endocranium (traces of middle meningeal vessels and dural venous sinuses, emissary foramina) provide evidence of vascular anatomy in osteological samples. We investigate the craniovascular variation in four South American samples and the effect of artificial cranial modifications (ACM). CT scans of human adult crania from four archeological samples from southern South America (including skulls with ACM) are used for the analyses. The craniovascular features in the four samples are described, skulls with and without ACM are compared, and additionally, South Americans are compared to a previously analyzed sample of Europeans. Of the four South American samples, the Southern Patagonian differs the most, showing the most distinct cranial dimensions, no ACM, and larger diameters of the emissary foramina. Unlike previous studies, we did not find any major differences in craniovascular features between modified and non-modified skulls, except that the skulls with ACM present somewhat smaller foramina. South Americans significantly differed from Europeans, especially in the anteroposterior dominance of the middle meningeal artery, in the pattern of sinus confluence, in the occurrence of enlarged occipito-marginal sinuses, and in foramina frequencies and diameters. Craniovascular morphology is not affected by the cranial size, even in skulls with ACM, indicating a minor or null influence of structural topological factors. Concerning the samples from distinct geographic and climatic environments, it must be evaluated whether the craniovascular morphogenesis might be partially influenced by specific functions possibly associated with thermoregulation, intracranial pressure, and the maintenance of intracranial homeostasis.

Craniovascular traits and braincase morphology in craniosynostotic human skulls

Middle meningeal vessels, dural venous sinuses, and emissary veins leave imprints and canals in the endocranium, and thus provide evidence of vascular patterns in osteological samples. This paper investigates whether craniovascular morphology undergoes changes in craniosynostotic human skulls, and if specific alterations may reflect structural and functional relationships in the cranium. The analyzed osteological sample consists of adult individuals with craniosynostoses generally associated with dolichocephalic or brachycephalic proportions, and a control sample of anatomically normal adult skulls. The pattern and dominance of the middle meningeal artery, the morphology of the confluence of the sinuses, and the size and number of the emissary foramina were evaluated. Craniovascular morphology was more diverse in craniosynostotic skulls than in anatomically normal skulls. The craniosynostotic skulls often displayed enlarged occipito-marginal sinuses and more numerous emissary foramina. The craniosynostotic skulls associated with more brachycephalic morphology often presented enlarged emissary foramina, while the craniosynostotic skulls associated with dolichocephalic effects frequently displayed more developed posterior branches of the middle meningeal artery. The course and morphology of the middle meningeal vessels, dural venous sinuses, and emissary veins in craniosynostotic skulls can be related to the redistribution of growth forces, higher intracranial pressure, venous hypertension, or thermal constraints. These functional and structural changes are of interest in both anthropology and medicine, involving epigenetic traits that concern the functional and ontogenetic balance between soft and hard tissues.

Angiographic classification of the inferior sagittal sinus based on the venous drainage patterns

PURPOSE

The inferior sagittal sinus (ISS) and its tributaries have received little attention because of its inconspicuous appearance, and its anatomical variations are also unknown. This study aimed to evaluate the morphological variations of the ISS.

MATERIALS AND METHODS

We retrospectively reviewed 518 patients in whom cerebral angiography was clinically indicated. The detailed angioarchitecture of the cerebral venous system, including the ISS and their tributaries, and the morphological variations of the ISS were evaluated. Abnormalities of the rostral third superior sagittal sinus (SSS) were also evaluated.

RESULTS

The ISS was visualized in 270 (52.1%) patients. We proposed an angiographic ISS classification according to the venous drainage patterns: Type 0, not visualized; Type 1, small ISS with faint tributaries; Type 2, moderate ISS with developed tributaries; and Type 3: large ISS with well-developed tributaries, which are responsible for the venous drainage of the anterior frontal lobe. The frequency of each ISS type was as follows: Type 0, 248 (47.9%); Type 1, 211 (40.7%); Type 2, 44 (8.5%); and Type 3, 15 (2.9%). The mean ISS size was significantly larger with an increase in the type of ISS (p < 0.0001). The rostral third SSS hypoplasia was observed in all cases of Type 3. The hypoplasia of the rostral third SSS and development of the ISS were strongly correlated and complementary to each other.

CONCLUSION

This study provided the angiographic ISS classification, and our proposed angiographic ISS classification could be helpful in better understanding of the ISS anatomy and its venous drainage pattern.

Effectiveness of Transvenous Aspiration Thrombectomy for Cerebral Venous Sinus Thrombosis: A Report of Three Cases

Objective

We report three patients successfully treated by emergent transvenous thrombectomy for cerebral venous sinus thrombosis (CVST).

Case Presentation

(Case 1) A 77-year-old man presented with vomiting, dizziness, and headache. CT revealed local subarachnoid hemorrhage (l-SAH), and angiography confirmed occlusion of the right transverse sigmoid sinus and superior sagittal sinus (SSS). Emergent transvenous aspiration thrombectomy using a Penumbra catheter (PC) resulted in effective reperfusion. (Case 2) A 60-year-old man developed disorientation, sensory aphasia, and right hemiparesis. MRI demonstrated extensive cerebral edema caused by venous congestion in both thalami, and angiography revealed poor opacification of the SSS, straight sinus, and bilateral transverse sinuses. Venous sinus flow was restored by catheter aspiration using a PC and topical infusion of urokinase (UK). (Case 3) A 19-year-old man developed a headache, numbness of the right upper limb, motor paralysis, and convulsions. CT revealed l-SAH and dense clot sign in the SSS. The SSS was poorly delineated on angiography. Thrombus aspiration using a PC and topical UK administration achieved partial recanalization.

Conclusion

Transvenous aspiration thrombectomy using large lumen catheters for patients with CVST is effective and safe. In particular, this method may be a better option than anti-coagulation therapy alone for patients presenting with a severe neurological condition or intracranial hemorrhage.

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.

Mechanical and structural characterisation of the dural venous sinuses

The dural venous sinuses play an integral role in draining venous blood from the cranial cavity. As a result of the sinuses anatomical location, they are of significant importance when evaluating the mechanopathology of traumatic brain injury (TBI). Despite the importance of the dural venous sinuses in normal neurophysiology, no mechanical analyses have been conducted on the tissues. In this study, we conduct mechanical and structural analysis on porcine dural venous sinus tissue to help elucidate the tissues’ function in healthy and diseased conditions. With longitudinal elastic moduli values ranging from 33 to 58 MPa, we demonstrate that the sinuses exhibit higher mechanical stiffness than that of native dural tissue, which may be of interest to the field of TBI modelling. Furthermore, by employing histological staining and a colour deconvolution protocol, we show that the sinuses have a collagen-dominant extracellular matrix, with collagen area fractions ranging from 84 to 94%, which likely explains the tissue’s large mechanical stiffness. In summary, we provide the first investigation of the dural venous sinus mechanical behaviour with accompanying structural analysis, which may aid in understanding TBI mechanopathology.

Normal craniovascular variation in two modern European adult populations

The vascular networks running into the meningeal layers, between the brain and braincase, leave imprints on the endocranial surface. These traces are visible in osteological specimens and skeletal collections, providing indirect evidence of vascular patterns in those cases in which bone remains are the only source of anatomical information, such as in forensic science, bioarchaeology and paleontology. The main vascular elements are associated with the middle meningeal artery, the venous sinuses of the dura mater, and the emissary veins. Most of these vascular systems have been hypothesized to be involved in endocranial thermal regulation. Although these traits deal with macroanatomical features, much information on their variation is still lacking. In this survey, we analyze a set of craniovascular imprints in two European dry skull samples with different neurocranial proportions: a brachycephalic Czech sample (n = 103) and a mesocephalic Italian sample (n = 152). We analyzed variation and distribution, correlation with cranial metrics, and sex differences in the dominance of the branches of the middle meningeal artery, the patterns of confluence of the sinuses, and the size of the emissary foramina. The descriptive statistics provide a reference to compare specimens and samples from different case studies. When compared with the Italian skulls, the Czech skulls display a greater dominance of the anterior branch of the middle meningeal artery and more asymmetric right-dominance of the confluence of the venous sinuses. There is no sex difference in the middle meningeal vessels, but males show a greater prevalence of the occipito-marginal draining system. Differences in the middle meningeal vessels or venous sinuses are apparently not influenced by cranial dimensions or proportions. The mastoid foramina are larger in larger and more brachycephalic skulls, which increases the emissary potential flow in the Czech sample and males, when compared with the Italian samples and females, respectively. The number of mastoid foramina increases in wider skulls. This anatomic information is necessary to develop further morphological and functional inferences on the relationships between neurocranial bones and vessels at the genetic, ontogenetic, and phylogenetic levels.

Variations of the Transverse Sinus: Review with an Unusual Case Report

The dural venous sinuses are venous channels in the cranium that drain blood and cerebrospinal fluid circulating from the brain into the vascular system via the internal jugular veins. The transverse sinus is a dural venous sinus present in the posterior aspect of the cranium. We report an unusual variant of this sinus with the presence of a fenestration at its proximal segment. We will review and discuss the background and the potential clinical relevance of this anatomical variation.