Investigation of the human bridging veins structure using optical microscopy

Macroscopic and histological examination of human bridging veins

In infantile abusive head injury (AHT), subdural haemorrhage (SDH) is commonly held to result from traumatic damage to bridging veins traversing from the surface of the brain to the dura and dural venous sinuses. However, there are limited published radiological or autopsy demonstrations of ruptured bridging veins and several authors also assert that bridging veins are too large to rupture due to the forces associated with AHT. There have been several studies on the size, locations and numbers of adult bridging veins and there is one small study of infant bridging veins. However, there are no microscopic studies of infant bridging veins and only a select few ultrastructural investigations of adult bridging veins. Hitherto, it has been assumed that bridging veins from infants and younger children will display the same anatomical characteristics as those in adulthood. At 19 neonatal, infant and young child post-mortem examinations, we macroscopically examined and sampled bridging veins for microscopy. We compared the histology of those samples with bridging veins from an older child and two adults. We demonstrate that adult bridging veins are usually surrounded by supportive meningeal tissue that appears to be lacking or minimally present around the bridging veins of younger children. Neonatal, infant and young children's veins had a free 'bridging' section. Neonatal and infant bridging veins had smaller diameter ranges and thinner walls (some only 5-7 µm) than those seen in older children and adults. Bridging vein walls contained both fine strands of elastic fibers and a more pronounced elastic lamina. The presence of an elastic lamina occurred more frequently in the older age groups These anatomical differences between the veins of adults and young children may help to explain apparent increased vulnerability of neonatal/infant bridging veins to the forces associated with a shaking-type traumatic event.

Thrombosis is not a marker of bridging vein rupture in infants with alleged abusive head trauma

Aim

Thrombosis of bridging veins has been suggested to be a marker of bridging vein rupture, and thus AHT, in infants with subdural haematoma.

Methods

This is a non‐systematic review based on Pubmed search, secondary reference tracking and authors’ own article collections.

Results

Radiological studies asserting that imaging signs of cortical vein thrombosis were indicative of traumatic bridging vein rupture were unreliable as they lacked pathological verification of either thrombosis or rupture, and paid little regard to medical conditions other than trauma. Autopsy attempts at confirmation of ruptured bridging veins as the origin of SDH were fraught with difficulty. Moreover, microscopic anatomy demonstrated alternative non‐traumatic sources of a clot in or around bridging veins. Objective pathological observations did not support the hypothesis that a radiological finding of bridging vein thrombosis was the result of traumatic rupture by AHT. No biomechanical models have produced reliable and reproducible data to demonstrate that shaking alone can be a cause of bridging vein rupture.

Conclusion

There is no conclusive evidence supporting the hypothesis that diagnostic imaging showing thrombosed bridging veins in infants correlates with bridging vein rupture. Hence, there is no literature support for the use of thrombosis as a marker for AHT.

Venous injury in pediatric abusive head trauma: a pictorial review

Abusive head trauma (AHT) is the leading cause of fatal head injuries in children younger than 2 years. An intracranial pathology can exist even in the setting of a normal physical exam. A delay in the diagnosis of AHT can have serious life-threatening consequences for the child and increases the potential the child will be abused again. In this article, we review the traumatic subdural hematoma as well as various morpho-structural patterns of shearing injuries and thrombosis of intracranial bridging veins. This work serves as a summary of patterns of imaging features of intracranial venous injury in AHT, as described in the literature, to facilitate familiarity and early detection of abusive head trauma in the pediatric population. Essentially, in AHT there is a traumatic injury to the bridging vein with either partial or complete tear. This can secondarily result in thrombosis at the terminal end of the bridging vein with blood clots adjacent to the bridging vein.

Venous injury in pediatric abusive head trauma: a pictorial review

Abusive head trauma (AHT) is the leading cause of fatal head injuries in children younger than 2 years. An intracranial pathology can exist even in the setting of a normal physical exam. A delay in the diagnosis of AHT can have serious life-threatening consequences for the child and increases the potential the child will be abused again. In this article, we review the traumatic subdural hematoma as well as various morpho-structural patterns of shearing injuries and thrombosis of intracranial bridging veins. This work serves as a summary of patterns of imaging features of intracranial venous injury in AHT, as described in the literature, to facilitate familiarity and early detection of abusive head trauma in the pediatric population. Essentially, in AHT there is a traumatic injury to the bridging vein with either partial or complete tear. This can secondarily result in thrombosis at the terminal end of the bridging vein with blood clots adjacent to the bridging vein.

[Bridging vein injuries in shaken baby syndrome : Forensic-radiological meta-analysis with special focus on the tadpole sign]

Shaken baby syndrome is a common variant of the abusive head trauma in infants and toddlers and is still subject of intensive research. In recent years, a number of radiological studies on the diagnostic and forensic relevance of injured bridging veins were conducted using different imaging modalities. The present article will give an overview on the current state of research in this field and will discuss the forensic implications. The meta-analysis of the seven currently existing studies revealed that injuries of the bridging veins and bridging vein thromboses, respectively, frequently appear as rounded, enlarged, and/or tubular structures. The "tadpole sign" may serve as a valuable tool for the identification of these formations. Especially, T2*/SWI (susceptibility-weighted imaging) sequences allow for good detectability of these lesions and should always be generated when abusive head trauma is suspected. In conclusion, it can be recommended that the presence of radiologically detectable bridging vein injuries should give reason to search for other manifestations of physical child abuse.

Cortical and bridging veins of the upper cerebral convexity: a magnetic resonance imaging study

PURPOSE

There is no study exploring the cortical veins (CVs) and connecting bridging veins (BVs) with neuroimaging modalities. The present study aimed to characterize these veins of the upper cerebral convexity.

METHODS

A total of 89 patients with intact cerebral hemispheres and covering meninges underwent thin-sliced, contrast magnetic resonance imaging (MRI). In addition, three injected specimens were dissected in this study.

RESULTS

In cadaver dissection, the BVs were observed to course in the arachnoid sheaths, suspended from the dura mater. The medial parts of the BVs, located near the superior sagittal sinus (SSS)-BV junction site, were occasionally exposed subdurally. The CVs were formed by venous channels arising from the cerebral gyri and those emerging from the sulci. On MRI, the CVs and connecting BVs were identified in the medial and latera convexity areas and medial surface of the cerebrum. These veins were highly variable in number, thickness, length, course, and distribution. In the medial convexity area, the CVs arising from the gyri were identified in 58% of patients, while they were found only in 11% of patients in the lateral convexity area.

CONCLUSION

In the medial convexity area, involving the parasagittal region, the CVs connect more densely with the BVs that may predispose to injury during neurosurgical procedures. Mechanical impact exerted the area, diameter of the veins in the craniocaudal direction, and number of venous afferences may affect the SSS-BV junctional region in an indirect manner and lead to the development of acute subdural hematoma.

Effects of Possible Osteoporotic Conditions on the Recurrence of Chronic Subdural Hematoma

The recurrence rate of chronic subdural hematoma (CSDH) has been reported to range from 2.3 to 33%. As bridging veins are composed of abundant collagen bundles and bone matrix, we aimed to investigate the possible associations between skull Hounsfield unit (HU) values and the recurrence of CSDH. We retrospectively enrolled patients with CSDH who underwent burr hole surgery. The HU values of the frontal skull were measured on brain CT scans. The cumulative hazard for recurrence was estimated according to predictive factors. To identify the independent predictors associated with the recurrence of CSDH, hazard ratios (HRs) were estimated using multivariate Cox regression analysis. A total of 208 consecutive patients who underwent burr hole trephination for CSDH over a 7-years period at a single institution were enrolled in this study. We found that age, greater midline shift (≥10.5 mm), lower skull HU (<769.5), and diabetes were independent predictors for the recurrence of CSDH (HR 1.06, 95% confidence interval [CI] 1.00–1.12, p = 0.042; HR 5.37, 95% CI 1.48–19.46, p = 0.010; HR 6.71, 95% CI 1.84–24.45, p = 0.004; and HR 3.30, 95% CI 1.05–10.43, p = 0.042, respectively). A relationship between possible low bone mineral density (BMD) and CSDH recurrence was observed. In addition, age, greater preoperative midline shift, and diabetes were also identified as predictive factors for recurrence. We expect that our findings may facilitate our understanding of the possible association between CSDH and BMD.

Understanding Subdural Collections in Pediatric Abusive Head Trauma

Life-threatening physical abuse of infants and toddlers is frequently correlated with head injuries. A common variant of the abusive head trauma is the shaken baby syndrome. The present review article sheds light on subdural collections in children with abusive head trauma and aims at providing a recent knowledge base for various medical disciplines involved in diagnostic procedures and legal proceedings. To this end, the different subdural collection entities are presented and illustrated. The pathophysiologic background is explained. Differential and age-diagnostic aspects are discussed and summarized by tabular and graphic overviews. Two problematic constellations frequently occurring during initial CT investigations are evaluated: A mixed-density subdural collection does not prove repeated trauma, and hypodense subdural collections are not synonymous with chronicity. The neuroradiologic analysis and assessment of subdural collections may decisively contribute to answering differential diagnostic and forensic questions. In addition to more reference data, a harmonization of terminology and methodology is urgently needed, especially with respect to age-diagnostic aspects.

Assessing the three-dimensional collagen network in soft tissues using contrast agents and high resolution micro-CT: Application to porcine iliac veins

The assessment of the three-dimensional architecture of collagen fibers inside vessel walls constitutes one of the bases for building structural models for the description of the mechanical behavior of these tissues. Multiphoton microscopy allows for such observations, but is limited to volumes of around a thousand of microns. In the present work, we propose to observe the collagenous network of vascular tissues using micro-CT. To get a contrast, three staining solutions (phosphotungstic acid, phosphomolybdic acid and iodine potassium iodide) were tested. Two of these stains were showed to lead to similar results and to a satisfactory contrast within the tissue. A detailed observation of a small porcine iliac vein sample allowed assessing the collagen fibers orientations within the medial and adventitial layers of the vein. The vasa vasorum network, which is present inside the adventitia of the vein, was also observed. Finally, the demonstrated micro-CT staining technique for the three-dimensional observation of thin soft tissues samples, like vein walls, contributes to the assessment of their structure at different scales while keeping a global overview of the tissue.

Imaging of bridging vein thrombosis in infants with abusive head trauma: the "Tadpole Sign"

OBJECTIVES

Abusive head trauma (AHT) in infants is usually diagnosed using a multi-disciplinary approach by investigating the circumstances and identifying morphological indicators, for example, subdural hematomas (SDHs), subdural hygromas (SDHys), retinal haemorrhages and encephalopathy. The present morphological study investigates the incidence, radiological characteristics and non-radiological co-factors of bridging vein thrombosis (BVT) in infants with AHT.

METHODS

From 2002 to 2013, computed tomography (CT) and magnetic resonance imaging (MRI) material of 628 infants aged 0-2 years were analysed retrospectively. If available, medicolegal expert opinions were additionally considered. Cases with SDHs and/or SDHys were identified and systematically evaluated as to the presence and characteristics of BVT.

RESULTS

SDHs and/or SDHys were present in 29 of the 81 cases exhibiting morphological abnormalities in the initial CT. Among these, 11 cases (40%) had BVT (mean age = 5.0 months). BVT could be best depicted in the T1-weighted spin echo and T2*/susceptibility-weighted MRI. In one case, BVT could be depicted indirectly using time-of-flight MR venography. The predominant (73%) BVT shape was found to be tadpole-like ("Tadpole Sign").

CONCLUSIONS

In the absence of appropriate accidental trauma, BVT appears to be a strong indicator of AHT. Therefore, the BVT/Tadpole Sign represents compelling cause to search for other signs of AHT.

KEY POINTS

• BVT is an excellent indicator of AHT in SDH/SDHy cases. • Accidental trauma must be ruled out before diagnosing AHT. • The Tadpole Sign appears to be the most characteristic shape of BVT. • BVT can be depicted using CT, MRI and MR venography. • The Tadpole Sign suggests searching for other signs of AHT.

Structural and mechanical characterisation of bridging veins: A review

Bridging veins drain the venous blood from the cerebral cortex into the superior sagittal sinus (SSS) and doing so they bridge the subdural space. Despite their importance in head impact biomechanics, little is known about their properties with respect to histology, morphology and mechanical behaviour. Knowledge of these characteristics is essential for creating a biofidelic finite element model to study the biomechanics of head impact, ultimately leading to the improved design of protective devices by setting up tolerance criteria. This paper presents a comprehensive review of the state-of-the-art knowledge on bridging veins. Tolerance criteria to prevent head injury through impact have been set by a number of research groups, either directly through impact experiments or by means of finite element (FE) simulations. Current state-of-the-art FE head models still lack a biofidelic representation of the bridging veins. To achieve this, a thorough insight into their nature and behaviour is required. Therefore, an overview of the general morphology and histology is provided here, showing the clearly heterogeneous nature of the bridging vein complex, with its three different layers and distinct morphological and histological changes at the region of outflow into the superior sagittal sinus. Apart from a complex morphology, bridging veins also exhibit complex mechanical behaviour, being nonlinear, viscoelastic and prone to damage. Existing material models capable of capturing these properties, as well as methods for experimental characterisation, are discussed. Future work required in bridging vein research is firstly to achieve consensus on aspects regarding morphology and histology, especially in the outflow cuff segment. Secondly, the advised material models need to be populated with realistic parameters through biaxial mechanical experiments adapted to the dimensions of the bridging vein samples. Finally, updating the existing finite element head models with these parameters will render them truly biofidelic, allowing the establishment of accurate tolerance criteria and, ultimately, better head protection devices.

A new multiscale model for the mechanical behavior of vein walls

The purpose of the present work is to propose a new multiscale model for the prediction of the mechanical behavior of vein walls. This model is based on one of our previous works which considered scale transitions applied to undulated collagen fibers. In the present work, the scale below was added to take the anisotropy of collagen fibrils into account. One scale above was also added, modeling the global reorientation of collagen fibers inside the vessel wall. The model was verified on experimental data from the literature, leading to a satisfactory agreement. The proposed multiscale approach also allows the extraction of local stresses and strains at each scale. This approach is presented here in the case of vein walls, but can easily be extended to other tissues which contain similar constituents.