Calvarial diploic venous channels: an anatomic study using high-resolution magnetic resonance imaging

Acute epidural hemorrhage following burr-hole irrigation for chronic subdural hematoma: A possible association with the diploic veins

A 50-year-old man presented with headache and left hemiparesis. No noticeable preceding head trauma was observed. Computed tomography (CT) scans revealed a compressive chronic subdural hematoma (CSDH). The patient underwent burr-hole irrigation, during which he was considerably restless. In addition, extensive avulsion was found in the parietal dura mater posterior to the burr hole. CT performed immediately after the surgery revealed the emergence of a thick epidural hematoma (EDH) located posterior to the burr-hole. During emergency craniotomy for the EDH, there was no identifiable injury to the dura mater or the meningeal vessels. However, a review of the CT scans confirmed well-developed diploic spaces just above the center of the EDH, with connecting channels between the diploic spaces and extracranial sites. Based on these observations, we assumed that the diploic vein might have caused the EDH. Diploic veins can cause AEDH after burr hole irrigation for CSDH. Appropriate intraoperative sedation and protective irrigation maneuvers can reduce the risk of such AEDH.

Investigating the relationship between cranial bone thickness and diploic channels: A first comparison between fossil Homo sapiens and Homo neanderthalensis

Diploic veins are part of the circulatory system of the head. They transport venous blood and cerebrospinal fluid and are housed in diploic channels (DCs). DCs are highly variable in terms of their position, extension, and size. These parameters were hypothesized to be related to the variations in cranial vault thickness (CVT). For the first time, we analyzed the spatial relationship between CVT and DCs in a sample of eight H. neanderthalensis and H. sapiens cranial fossils. Using micro-CT scanning data, we constructed color maps of the CVT and visually inspected whether the regional thickness variation was associated with the morphology and distribution of the DC branches. The results showed that when regional bone thickness was below a certain threshold, no DCs or scattered small DC branches were present. Larger DC branches appeared only when the thickness exceeded the threshold. However, once the threshold was reached, further increases in thickness no longer resulted in more or larger DCs. This study also found that our sample of H. neanderthalensis and H. sapiens have different distribution patterns in thin areas, which may affect how their DCs connect with different branches of the middle meningeal vessels. This preliminary study provides evidence for the discussion on the interaction between the cranium, brain, and blood vessels. Future research should include more hominin fossils to better document the variation within each species and possible evolutionary trends among hominin lineages.

Vascular microforamina and endocranial surface: Normal variation and distribution in adult humans: Vascular biology

The term craniovascular traits refers to the imprints left by arteries and veins on the skull bones. These features can be used in biological anthropology and archaeology to investigate the morphology of the vascular network in extinct species and past populations. Generally, the term refers to macrovascular features of the endocranial cavity, like those associated with the middle meningeal artery, venous sinuses, emissary foramina, and diploic channels. However, small vascular passages (here called microforamina or microchannels) have been occasionally described on the endocranial surface. The larger ones (generally with a diameter between 0.5 and 2.0 mm) can be detected through medical scanners on osteological collections. In this study, we describe and quantify the number and distribution of these microforamina in adult humans (N = 45) and, preliminarily, in a small sample of children (N = 7). Adults display more microchannels than juvenile skulls. A higher frequency in females is also observed, although this result is not statistically significant and might be associated with allometric cranial variations. The distribution of the microforamina is particularly concentrated on the top of the vault, in particular along the sagittal, metopic, and coronal sutures, matching the course of major venous sinuses and parasagittal bridging veins. Nonetheless, the density is lower in the region posterior to bregma. Beyond oxygenation, these vessels are likely involved in endocranial thermal regulation, infection, inflammation, and immune responses, and their distribution and prevalence can hence be of interest in human biology, evolutionary anthropology, and medicine.

The diploic venous system in Homo neanderthalensis and fossil Homo sapiens: A study using high-resolution computed tomography

OBJECTIVES

The diploic venous system has been hypothesized to be related to human brain evolution, though its evolutionary trajectory and physiological functions remain largely unclear. This study examines the characteristics of the diploic venous channels (DCs) in a selection of well-preserved Homo neanderthalensis and Upper Paleolithic Homo sapiens crania, searching for the differences between the two taxa and exploring the associations between brain anatomy and DCs.

MATERIALS AND METHODS

Five H. neanderthalensis and four H. sapiens fossil specimens from Western Europe were analyzed. Based on Micro-CT scanning and 3D reconstruction, the distribution pattern and draining orifices of the DCs were inspected qualitatively. The size of the DCs was quantified by volume calculation, and the degree of complexity was quantified by fractal analyses.

RESULTS

High-resolution data show the details of the DC structures not documented in previous studies. H. neanderthalensis and H. sapiens specimens share substantial similarities in the DCs. The noticeable differences between the two samples manifest in the connecting points surrounding the frontal sinuses, parietal foramina, and asterional area.

DISCUSSION

This study provides a better understanding of the anatomy of the DCs in H. neanderthalensis and H. sapiens. The connection patterns of the DCs have potential utility in distinguishing between the two taxa and in the phylogenetic and taxonomic discussion of the Neandertal-like specimens with controversial taxonomic status.

Evaluating diploic vein blood flow using time-resolved whole-head computed tomography angiography and determining the positional relationship between typical craniotomy approaches and diploic veins in patients with meningioma

BACKGROUND

Diploic veins may act as collateral venous pathways in cases of meningioma with venous sinus invasion. Diploic vein blood flow should be preoperatively evaluated to consider preserving the veins. In this study, we evaluated the use of time-resolved whole-head computed tomography angiography (4D-CTA)-which is less patient-intensive than digital subtraction angiography (DSA)-for assessing diploic vein blood flow and the positional relationship between typical craniotomy approaches and diploic veins.

METHODS

We retrospectively examined 231 patients who underwent surgery for intracranial meningioma. We performed contrast-enhanced magnetic resonance imaging (MRI) to evaluate diploic vein pathways and compared the visualization rates of diploic vein blood flow assessed using 4D-CTA and DSA. Subsequently, we evaluated the rates of the diploic veins transected during craniotomy by comparing the pre- and postoperative contrast-enhanced MRI.

RESULTS

The diagnostic performance of 4D-CTA was assessed in 45 patients. Of the 320 diploic veins identified in these patients, blood flow in 70 (21.9%) diploic veins was identified by 4D-CTA and DSA, and both results were consistent. To assess the transection rates of the diploic veins, 150 patients were included. A trend towards a high transection rate of the diploic vein in the basal interhemispheric, frontotemporal, orbitozygomatic, combined transpetrosal, and convexity craniotomy approaches was observed.

CONCLUSIONS

In patients with meningiomas, both 4D-CTA and DSA are useful in evaluating diploic vein blood flow. In meningiomas with venous sinus invasion, determining the extent of craniotomy after understanding the pathways and blood flow of diploic veins is recommended.

Does diploic venous flow drain extracranially in the pterional area? A magnetic resonance imaging study

Background:

To the best of our knowledge, no study using neuroimaging modalities has documented calvarial diploic veins (DVs) connected to the extracranial sites. This study aimed to characterize them using magnetic resonance imaging (MRI).

Methods:

A total of 88 patients underwent thin-sliced contrast MRI. In addition, the DVs coursing through the pterional area were observed on three injected cadaver heads.

Results:

On postcontrast MRI, the DVs of the pterional area directly drained into the temporalis muscle or supplied branches coursing into the muscle in 43% on the right side and 40% on the left. The DVs and their branches were highly variable in diameter and number. In 9% of cases, the DV of the pterional area was found to drain into an extracranial site and connected to large venous channels distributed in the temporalis muscle. Furthermore, in 17% of cases, the DVs drained into the extracranial sites in the frontal skull region, followed by 9% in the parietal, 2% in the occipital, and 1% in the temporal regions. The DVs coursed superficially in the pterional area on both sides of all three cadaver heads. On one side, the DV in the area was open to an extracranial site.

Conclusion:

Part of the diploic venous flow drains extracranially in the pterional area. This area may provide an important interface between the calvarial DVs and the extracranial venous system.

Diploic vein morphology in normal and craniosynostotic adult human skulls

Diploic veins (DV) run within the cranial diploe, where they leave channels that can be studied in osteological samples. This study investigates overall DV variability in human adults and the effects of sex, age, cranial dimensions, and dysmorphogenesis associated with craniosynostosis (CS). The morphology of macroscopic diploic channels was analyzed in a set of the qualitative and quantitative variables in computed tomography-images of crania of anatomically normal and craniosynostotic adult individuals. Macroscopic diploic channels occur most frequently in the frontal and parietal bones, often with a bilaterally symmetrical pattern. DV-features (especially DV-pattern) are characterized by high individual diversity. On average, there are 5.4 ± 3.5 large macroscopic channels (with diameters >1 mm) per individual, with a mean diameter of 1.7 ± 0.4 mm. Age and sex have minor effects on DV, and cranial proportions significantly influence DV only in CS skulls. CS is associated with changes in the DV numbers, distributions, and diameters. Craniosynostotic skulls, especially brachycephalic skulls, generally present smaller DV diameters, and dolichocephalic skulls display increased number of frontal DV. CS, associated with altered cranial dimensions, suture imbalance, increased intracranial pressure, and with changes of the endocranial craniovascular system, significantly also affects the macroscopic morphology of DV in adults, in terms of both structural (topological redistribution) and functional factors. The research on craniovascular morphology and CS may be of interest in biological anthropology, paleopathology, medicine (e.g., surgical planning), but also in zoology and paleontology.

Anatomy of the Calvaria and Skull Base

A thorough understanding of the skull anatomy is of key importance to radiologists as well as specialist physicians and surgeons. We describe the anatomy of the neurocranium comprising calvaria (the skull vault) and the skull base and discuss the most common and clinically relevant anatomic variants.

The gut-meningeal immune axis: Priming brain defense against the most likely invaders

The gastrointestinal tract contains trillions of microorganisms that exist symbiotically with the host due to a tolerant, regulatory cell–rich intestinal immune system. However, this intimate relationship with the microbiome inevitably comes with risks, with intestinal organisms being the most common cause of bacteremia. The vasculature of the brain-lining meninges contains fenestrated endothelium, conferring vulnerability to invasion by circulating microbes. We propose that this has evolutionarily led to close links between gut and meningeal immunity, to prime the central nervous system defense against the most likely invaders. This paradigm is exemplified by the dural venous sinus IgA defense system, where the antibody repertoire mirrors that of the gut.

Diploic veins as collateral venous pathways in patients with dural venous sinus invasion by meningiomas

BACKGROUND

Although it is known that diploic veins frequently communicate with the dural venous sinuses, the role of diploic veins in patients with venous sinus invasion from meningiomas remains unknown.

METHODS

We retrospectively examined the medical records of 159 patients who underwent their first craniotomies for intracranial meningiomas. Contrast-enhanced magnetic resonance imaging was used to evaluate diploic vein routes, and digital subtraction angiography (DSA) was used to evaluate diploic vein blood flow. When high blood flow was visualized concurrently with the venous sinuses, the veins were classified as of the "early type." Diploic vein routes were classified into five routes.

RESULTS

DSA was performed in 110 patients, with 14 showing superior sagittal sinus (SSS) invasion (SSS group) and 23 showing non-SSS venous sinus invasion (non-SSS group). The proportion of early type diploic veins was significantly higher in the SSS group (27.1%) than in other patients (patients without venous sinus invasion, 2.1%; non-SSS, 4.3%) (p < 0.01). In patients not in the SSS group, diploic veins were sacrificed during craniotomy in 76 patients, including four patients with veins of the early type. No patients demonstrated new neurological deficits postoperatively. In the SSS group, diploic veins were sacrificed in all patients, and early type diploic veins were cut in five patients. Two of these five patients showed postoperative neurological deficits.

CONCLUSIONS

In the SSS group, diploic veins may function as collateral venous pathways, and attention is recommended for their interruption. In patients without SSS invasion, diploic veins, even of the early type, can be sacrificed.

Magnetic resonance imaging analysis of human skull diploic venous anatomy

Background:

The skull diploic venous space (DVS) represents a potential route for cerebrospinal fluid (CSF) diversion and absorption in the treatment of hydrocephalus. The goal of this study was to carry out a detailed characterization of the drainage pattern of the DVS of the skull using high-resolution MRI, especially the diploic veins draining to the lacunae laterales (LLs) since the LLs constitute an important channel for the CSF to access the superior sagittal sinus and subsequently the systemic circulation. The objective was to identify those skull regions optimally suited for an intraosseous CSF diversion system.

Methods:

High-resolution, T1-weighted MRI scans from 20 adult and 16 pediatric subjects were selected for analysis. Skulls were divided into four regions, that is, frontal, parietal, temporal, and occipital. On each scan, a trained observer counted all diploic veins in every skull region. Each diploic vein was also followed to determine its final drainage pathway (i.e., dural venous sinus, dural vein, LL, or indeterminate).

Results:

In the adult age group, the frontal and occipital skull regions showed the highest number of diploic veins. However, the highest number of draining diploic veins connecting to the lacunae lateralis was found in the frontal and parietal skull region, just anterior and just posterior to the coronal suture. In the pediatric age group, the parietal skull region, just posterior to the coronal suture, showed the highest overall number of diploic veins and also the highest number of draining diploic veins connecting to the LL.

Conclusion:

This study suggested that diploic venous density across the skull varies with age, with more parietal diploic veins in the pediatric age range, and more occipital and frontal diploic veins in adults. If the DVS is ultimately used for CSF diversion, our anatomical data point to optimal sites for the insertion of specially designed intraosseous infusion devices for the treatment of hydrocephalus. Likely the optimal sites for CSF diversion would be the parietal region just posterior to the coronal suture in children, and in adults, frontal and/or parietal just anterior or just posterior to the coronal suture.

Calvarial diploic venous channels: delineation with maximal intensity projection technique

PURPOSE

To date, very few studies have explored the three-dimensional architecture of calvarial diploic venous channels (CDVCs). This study aimed to characterize the three-dimensional architecture of CDVCs using maximum intensity projection (MIP) images based on contrast-enhanced magnetic resonance imaging (MRI).

METHODS

A total of 77 patients with intact calvarial hemispheres and underlying dura mater and dural sinuses underwent contrast-enhanced MRI. Among them, we extracted the data of 49 with at least a part of the major CDVC pathways identified on the MIP images for analysis.

RESULTS

On serial contrast-enhanced MRI images, the CDVCs were commonly detected as curvilinear structures with inhomogeneous diameters and tributaries, while the MIP images delineated the three-dimensional architecture of the developed CDVC pathways. More than such CDVC pathway was entirely delineated on the right in 67.3% and on the left in 71.4%, most frequently in the frontal and temporal regions, with their connecting sites to the sphenoparietal and superior sagittal sinuses. The morphology, distribution, and course of the identified CDVCs were highly variable. In 55.1%, the CDVCs formed fenestrations that were variable in size, shape, and number.

CONCLUSIONS

The developed CDVC pathways may be characterized by morphological variability and fenestrations. Thin-sliced, contrast-enhanced MRI is useful to depict diploic veins, while MIP images allow for better appreciation of the entire course of the developed CDVC pathways. Traumatic and intraoperative disconnection between the dura mater overlying the dural sinuses and the adjacent inner table of the skull can cause epidural venous bleeding.

Traumatic acute epidural hematoma caused by injury of the diploic channels

Background

Traumatic acute epidural hematomas (EDHs) commonly develop by rupture of the meningeal arteries. EDH caused by an injury of the diploic channel (DC) has not been reported.

Case Description

A 21-year-old man suffered a head injury while falling off the skateboard. At presentation, the patient was drowsy but did not exhibit any focal neurological deficits. Cranial computed tomography (CT) revealed a biconvex intracranial hematoma with 18-mm thickness in the high parietal region and a linear fracture that involved both the outer and inner tables and passed above the hematoma. A well-developed and large DC was observed near the hematoma. Patient's consciousness level decreased at 12 h after admission with considerable growth of the hematoma. A frontoparietal craniotomy revealed an EDH. The dura mater and the meningeal arteries underneath the hematoma were intact. The medial bone cut caused brisk bleeds from the large DC. Postoperative CT revealed the cut of the DC and other finer DCs exhibiting air density and lying near the fracture. Based on these findings, we assumed that the EDH was developed by an injury of the DCs.

Conclusion

Traumatic EDH can develop by an injury of the DCs. Careful observation of patient's neurological status and precise interpretation of neuroimages is important to identify venous EDHs.

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.

Diploic veins of the cranial base: an anatomical study using magnetic resonance imaging

PURPOSE

The anatomy and distribution of the diploic veins (DVs) of the cranial base have not been fully documented. The aim of this study was to characterize these veins using contrast magnetic resonance imaging (MRI).

METHODS

In total, 95 patients underwent thin-sliced, contrast MRI. Coronal and sagittal images were used for the analysis. The cranial base was divided into the anterior, middle, and posterior bases. Then, each base was further subdivided into three equal parts in the anteroposterior and lateromedial directions. The anteroposterior parts were evaluated on coronal images, while the lateromedial parts were evaluated on sagittal images.

RESULTS

The DVs were identified over the entire cranial base. However, they were more frequent in the posterior-third of the lateral-third region of the anterior, middle-third of the lateral and middle-third regions of the middle, and middle-third region of the posterior cranial base, and sparse in the posterior and medial-third regions of the middle cranial base. The DVs showed marked morphological variability. For instance, the DVs of the pterional area were generally well defined, as pivotal channels connecting the lateral parts of the anterior and middle cranial base, but were highly varied in appearance.

CONCLUSIONS

The DVs of the cranial base are distinct structures characterized by morphological variability and topographical predilection. Contrast MRI is useful for delineating these veins.

The Diploic Veins: A Comprehensive Review with Clinical Applications

The diploic veins serve as an important connection between the extracranial and intracranial venous systems. They change in size during growth from adolescence to adulthood. The diploic space has been identified as an additional site of reabsorption of cerebrospinal fluid (CSF). Herein, the anatomy and physiology of the diploic veins are reviewed.

The Bone Does Not Predict the Brain in Sturge-Weber Syndrome

BACKGROUND AND PURPOSE

It has been hypothesized that skull marrow signal alteration may represent an early disease manifestation of Sturge-Weber syndrome before development of its intracranial manifestations. We alternatively hypothesized that intraosseous changes are associated with the overlying port-wine stain rather than the intracranial stigmata of Sturge-Weber syndrome and hence are not a predictor of brain involvement.

MATERIALS AND METHODS

MR imaging of children presenting with port-wine stain and/or Sturge-Weber syndrome between 1998 and 2017 was evaluated by 2 pediatric neuroradiologists for marrow signal abnormality and pial angioma and other Sturge-Weber syndrome features: ocular hemangioma, atrophy, and white matter changes (advanced myelination). Groups were divided into port-wine stain-only (without intracranial Sturge-Weber syndrome features) and Sturge-Weber syndrome (the presence of cerebral pial angioma). The χ² test was performed to evaluate the association between port-wine stain and bone marrow changes and between osseous change and pial angioma.

RESULTS

We reviewed 139 cases: 40 with port-wine stain-only and 99 with Sturge-Weber syndrome with pial angioma. Fifteen of 99 cases of Sturge-Weber syndrome had no port-wine stain. In the port-wine stain-only cohort, 78% had ipsilateral bony changes and 17% had no intraosseous changes. In the Sturge-Weber syndrome cohort, 84/99 had associated port-wine stain, 91% (P < .01) had bony changes ipsilateral to the port-wine stain or had no bone changes in the absence of port-wine stain, and 77% (P = .27) had bony changes ipsilateral to a cerebral pial angioma. Eighty percent of patients with Sturge-Weber syndrome who lacked a port-wine stain also lacked marrow changes. Five patients with bilateral port-wine stain and bilateral marrow changes had only a unilateral pial angioma.

CONCLUSIONS

Intraosseous marrow changes are strongly associated with facial port-wine stain; no significant association was found between pial angioma and bone marrow changes.

Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.

Chronic orbital and calvarial fungal infection with Apophysomyces variabilis in an immunocompetent patient

Apophysomyces is a rare fungal organism causing rhino-orbito-cerebral mycotic infections with high morbidity and mortality, typically in immunocompetent individuals. Several cases of Apophysomyces elegans orbital disease have been reported. Herein, we report a case of Apophysomyces variabilis infection involving the orbit, sinuses, and calvarium in an immunocompetent 74-year-old woman, with a review of the literature. Unlike prior cases of A. elegans classic rhino-orbito-cerebral infection, our case included diffuse calvarial lytic lesions and overlying soft tissue nodules, but without parenchymal intracranial involvement. There was radiographic and clinical evidence of infarction of the orbital contents and cavernous sinus thrombosis. Anastomoses between the superior orbital (ophthalmic) vein and diploic veins of the calvarium are believed to be primarily responsible for the unusual mode of spread on the extradural surface of the brain. Although the patient stabilized without definitive surgical intervention, her disease slowly and intermittently progressed for over a year after presentation, requiring multiple courses of antifungal treatment.

Cerebrospinal fluid drainage through the diploic and spinal epidural veins

The aim of this study was to quantitatively evaluate the function of the cranial diploic and spinal epidural veins as cerebrospinal fluid (CSF) drainage pathways by measuring lipocalin-type prostaglandin D synthase (PGDS) and cystatin C (CysC) dissolved in the blood of these veins. This was a prospective study involving 51 consecutive patients, 31 males and 20 females, who underwent 41 cranial and 10 spinal surgeries. Intraoperatively, peripheral venous blood and diploic venous blood, or peripheral venous blood and spinal epidural venous blood samples were simultaneously collected and immediately centrifuged. For all samples, dissolved albumin (for reference), PGDS and CysC were measured using an enzyme-linked immunosorbent assay. The diploic vein/peripheral vein ratios in five cranial locations and epidural vein/peripheral vein ratios were calculated and statistically evaluated for the three biomarkers. For PGDS, the diploic vein/peripheral vein ratio was significantly increased in the frontal (P = 0.011), temporal (P = 0.028), parietal (P = 0.046) and skull base (P = 0.039), while it did not reach statistical significance for CysC. For patients older than 45 years, the diploic vein/peripheral vein ratio for PGDS was significantly decreased in the frontal region (P = 0.028), and the epidural vein/peripheral vein ratio for CysC was significantly decreased (P = 0.014). These results show that the diploic veins constitute CSF drainage pathways with heterogeneous functional intensity at different cranial locations. Compared with the diploic veins, spinal epidural veins seem to drain less CSF. The cranial diploic and spinal epidural veins may jointly function as an alternative, age-related trans-dural CSF drainage system.

Cranial arachnoid protrusions and contiguous diploic veins in CSF drainage

BACKGROUND AND PURPOSE

Studies have suggested that arachnoid villi or granulations found in the walls of the cranial dural sinuses, olfactory mucosa, and cranial nerve sheaths function as outlets for intracranial CSF. However, their role as CSF outlets has not yet been verified. Here we show that arachnoid protrusions and contiguous diploic veins provide an alternative drainage route for intracranial CSF.

MATERIALS AND METHODS

Four hundred patients with intact skull, dura mater, and dural sinuses underwent MR imaging to explore arachnoids protruding into the skull and diploic veins. Patients with symptoms of increased intracranial pressure or intracranial hypotension were excluded. For 15 patients undergoing craniotomy, both peripheral and diploic venous blood was collected. Albumin and the CSF-specific biomarkers were measured by enzyme-linked immunosorbent assay.

RESULTS

With MR imaging, arachnoid protrusions into the skull and contiguous diploic veins were consistently identified throughout the cranium with their characteristic appearance depending on the cranial region. In addition, elevated amounts of prostaglandin D synthase and cystatin C were confirmed in diploic veins compared with peripheral venous blood.

CONCLUSIONS

Diploic veins are distributed ubiquitously throughout the cranium. A portion of the intracranial CSF may be drained through arachnoid protrusions and contiguous diploic veins.