The arrow-tipped loop is a marker of radiculomedullary vein thrombosis linked to the anti-reflux mechanism--angiographic anatomy and clinical implications

Spinal cord motor disorders

Spinal cord diseases are frequently devastating due to the precipitous and often permanently debilitating nature of the deficits. Spastic or flaccid paraparesis accompanied by dermatomal and myotomal signatures complementary to the incurred deficits facilitates localization of the insult within the cord. However, laboratory studies often employing disease-specific serology, neuroradiology, neurophysiology, and cerebrospinal fluid analysis aid in the etiologic diagnosis. While many spinal cord diseases are reversible and treatable, especially when recognized early, more than ever, neuroscientists are being called to investigate endogenous mechanisms of neural plasticity. This chapter is a review of the embryology, neuroanatomy, clinical localization, evaluation, and management of adult and childhood spinal cord motor disorders.

Spinal vascular malformations: Angiographic evaluation and endovascular management

Spinal vascular malformations (SVM) are classified based on their location (intramedullary, perimedullary, radicular, extradural) and flow pattern (high-flow, low-flow, no arteriovenous shunt). High-flow SVMs are generally congenital lesions diagnosed in children and young patients without gender predominance. They present with hemodynamic disturbances, mass effect, or hemorrhages, but may also be discovered incidentally. Low-flow SVMs tend to be acquired lesions presenting in older men with progressive myelopathy caused by spinal venous hypertension. They are rarely associated with vascular syndromes but may accompany prothrombotic conditions. The sensitivity and specificity of conventional MRI are excellent for high-flow SVMs but poor for low-flow lesions, which are frequently diagnosed with extensive delays reducing the potential for favorable outcomes. The sensitivity of advanced MRI techniques remains unclear, notably for the detection of low-flow shunts without flow voids on conventional MRI. Catheter angiography remains the gold standard modality for the evaluation of the spinal vasculature and its disorders. SVMs can be treated by surgical or endovascular means. Initially plagued by high recurrence rates due to inadequate embolization material, endovascular techniques represent nowadays a valid alternative to surgery, thanks notably to the introduction of liquid embolic agents.

Neurovascular anatomy: Spine

The arterial supply of the spinal cord is provided by the spinal branch of the cervical, thoracic, and lumbar intersegmental arteries. While supply is initially provided at each embryonic segment, only a few prominent anterior radiculomedullary arteries remain at the adult stage, including the arteries of the cervical and lumbosacral enlargements as well as a constant upper thoracic contributor. The spinal cord is surrounded by the vasocorona, an arterial network that includes several longitudinal anastomotic chains, notably the anterior and posterior spinal arteries, which respectively supply the central and peripheral components of the intrinsic vascularization. The intrinsic venous circulation is also divided into central and peripheral components. The perimedullary venous system includes several longitudinal anastomotic chains interconnected by the coronary plexus. The radiculomedullary veins loosely follow the spinal nerve roots on their way to the epidural plexus. Their point of passage through the thecal sac forms an important valve-like structure, the antireflux mechanism.

The antireflux mechanism - Angiographic anatomy and clinical implications

BACKGROUND

Early anatomists suspected that the radiculomedullary veins draining the spinal cord had valves preventing their retrograde filling with anatomical casting material. Modern investigations have discarded the presence of true valves and introduced instead the notion of a pseudo-valvular configuration for which the term antireflux mechanism was coined in the 1970s. The angiographic anatomy of the antireflux mechanism has not been well documented so far.

METHODS

This article discusses anatomical and clinical features of the antireflux mechanism with a series of 12 angiographic observations documenting the antireflux mechanism under normal and pathological circumstances.

RESULTS

The antireflux mechanism divides radiculomedullary veins into intradural and extradural segments. While the structure of the antireflux mechanism is not yet fully clarified, it includes at least a tight narrowing of the radiculomedullary vein at its point of passage through the thecal sac, which is angiographically detectable and likely protects the intradural venous system from transient or persistent surges in venous pressure (e.g. sneezing, pregnancy). This tight narrowing of the antireflux mechanism likely also represents an obstacle to normal anterograde flow, potentially leading to venous stagnation and thrombosis.

CONCLUSIONS

The antireflux mechanism includes at least a tight narrowing of the radiculomedullary vein, which likely influences the development and clinical expression of low-flow spinal arteriovenous fistulas and might impact the spinal venous drainage even in the absence of arteriovenous shunts.

Spinal Vascular Anatomy

This article reviews the arterial and venous anatomy of the spine and spinal cord. Special emphasis is placed on vessels critical to the conduct and interpretation of spinal angiography, notably the intersegmental artery and its cranial and caudal derivatives: the vertebral, supreme intercostal, and sacral arteries.

Asymptomatic spinal dural arteriovenous fistula: case series and systematic review

OBJECTIVE

Spinal dural arteriovenous fistulas (SDAVFs) commonly present with symptoms of myelopathy due to venous congestion in the spinal cord; asymptomatic SDAVFs are rarely encountered. To elucidate the clinical characteristics of asymptomatic SDAVFs, the authors present 5 new cases of asymptomatic SDAVF and report the results of their systematical review of the associated literature.

METHODS

Five databases were systematically searched for all relevant English-language articles on SDAVFs published from 1990 to 2018. The clinical features and imaging findings of asymptomatic SDAVFs were collected and compared with those of symptomatic SDAVFs.

RESULTS

Twenty cases, including the 5 cases from the authors' experience, were found. Asymptomatic SDAVFs were more prevalent in the cervical region (35.0%); cervical lesions account for only 2% of all symptomatic SDAVFs. The affected perimedullary veins tended to drain more cranially (50.0%) than caudally (10.0%). Four cases of asymptomatic SDAVF became symptomatic, 1 case spontaneously disappeared, and the remaining 15 cases were unchanged or surgically treated.

CONCLUSIONS

The higher prevalence of asymptomatic SDAVFs in the cervical spine might be a distinct feature of asymptomatic SDAVFs. Given that venous congestion is the pathophysiology of a symptomatic SDAVF, abundant collateral venous pathways and unique flow dynamics of the CSF in the cervical spine might prevent asymptomatic cervical SDAVFs from becoming symptomatic. In cases in which venous congestion is avoidable, not all asymptomatic SDAVFs will become symptomatic.

Spinal dural arteriovenous fistula (SDAVF) variant with dual perimedullary and epidural drainage

PURPOSE

A spinal dural arteriovenous fistula (SDAVF) is an abnormal connection between a radiculomeningeal artery and a radiculomedullary vein (RMV) characteristically draining into the perimedullary venous system. We present an observation of SDAVF draining simultaneously into the perimedullary and epidural venous systems.

METHODS

A 67-year-old man presented with lower extremity weakness and sphincter dysfunction. MRI documented a longitudinally extensive myelopathy with parenchymal enhancement and flow-voids on T2-weighted images. Spinal angiography revealed the presence of two SDAVFs, at left T9 and right L1.

RESULTS

The right L1 SDAVF was treated endovascularly. Superselective angiography of the main feeder, a right T12 radiculomeningeal branch, documented an unusual drainage pattern, with contrast flowing both retrogradely towards the perimedullary venous system and antegradely into the epidural plexus. The meningeal branch was embolized using a liquid embolic agent with adequate penetration of the embolic material into the proximal segment of the draining vein. The left T9 SDAVF was surgically resected, as the radicular artery supplying the fistula also provided the artery of Adamkiewicz.

CONCLUSIONS

Dual drainage of the right L1 SDAVF into the perimedullary and epidural venous systems allowed to locate the site of the arteriovenous shunt at the point of transdural passage of the RMV, a narrowed segment also known to represent an anti-reflux mechanism. The potential role played by the topographical relationship between the shunt and the anti-reflux mechanism of the RMV in the formation and clinical expression of SDAVFs is discussed.

The Transdural Course of Radicular Spinal Cord Veins--A Microangiographical and Microscopical Study

PURPOSE

This study focuses on the following questions: What are the morphological features at the transdural course of radiculomedullary veins? How are these short transdural segments that may harbour pathological arteriovenous shunts connected to the internal vertebral venous plexus? Is the conception of a reflux-impeding mechanism at the transdural segment indispensable and convincing?

METHODS

A total of 102 radiculospinal veins were studied microscopically at various levels of the spinal canal using serial paraffin and semi-thin sections. In addition, 26 vessels were investigated microangiographically following orthograde (12) or attempted retrograde (14) opacification of the intradural venous segment with barium sulphate. After paraplast-embedding, contact-microradiographs were taken using high-resolution spectroscopic plates.

RESULTS

At their transdural course, the veins showed narrowing of their lumen accompanied by changes in the vessel wall composition and a tortuous course. Two structurally distinct arrangements of the transdural segment could be identified: A slit type was seen in 60% of the veins studied and a bulge- or nodular type was seen in 35% of the veins. In total, 5% of cases could not be assigned to either one of these types. Reflux to radicular veins from the outside of the dura mater could be produced in 2 out of 14 specimens. The extradural venous plexus, which primarily receives the radicular vein, was composed more frequently of lacunar spaces rather than plexiform blood vessel convolutions. Rare observations were fibrotic, blind ending radiculomedullary veins and continuation of a distinct venous blood vessel after crossing the dura.

CONCLUSIONS

Reflux from the epidural plexus to radicular veins is not reliably stopped at the dural level and possibly physiological. Different arrangements of the transdural course of the veins appear to be at least appropriate to modulate flow. The purpose for two different types of radicular vein exit is unclear. The clinical impact of disturbed reflux-control is uncertain, which is in stark contrast to the severe consequences resulting from dural arteriovenous shunts. The functional role of the probably predominant epidural venous plexus for the spinal cord blood circulation remains poorly understood.