Syringomyelia: current concepts in pathogenesis, diagnosis, and treatment.

Syringomyelia is a condition that results in fluid-containing cavities within the parenchyma of the spinal cord as a consequence of altered cerebrospinal fluid dynamics. This review discusses the history and the classification of the disorder, the current theories of pathogenesis, and the advanced imaging modalities used in the diagnosis. The intramedullary pulse pressure theory (a new pathophysiologic concept of syringomyelia) also is presented. In addition, the current understanding of the painful nature of this condition is discussed and the current trends in medical and surgical management are reviewed.

Subarcuate venous malformation causing audio-vestibular symptoms similar to those in superior canal dehiscence syndrome.

OBJECTIVE: To present a patient with symptoms similar to those of superior canal dehiscence syndrome due to another cause. STUDY DESIGN: Case report. SETTING: University hospital, tertiary referral center. PATIENT: The 65-year-old woman had suffered for 4 years from hearing loss, tinnitus, and pressure-induced vertigo. INTERVENTION: Audio-vestibular testing, high-resolution computed tomography, and magnetic resonance angiography. MAIN OUTCOME MEASURE: The superior canal dehiscence syndrome is caused by failure of normal postnatal bone development in the middle cranial fossa leading to absence of bone at the most superior part of the superior semicircular canal. The typical features for this syndrome are sound and pressure-induced vertigo with torsional eye movements, pulse synchronous tinnitus and apparent conductive hearing loss in spite of normal middle ear function. We present a patient with very similar symptoms and findings, who instead had a superior canal dehiscence close to the common crus. Neuroradiologic findings suggested that the dehiscence was related to a venous malformation. CONCLUSIONS: Symptoms and findings suggesting superior canal dehiscence syndrome can have a different cause.

On the active vascular absorption of plasma proteins from tissue: rethinking the role of the lymphatic system.

According to Starling's hypothesis, the osmotic pressure of plasma proteins in the capillary is the principal force for fluid absorption. The leakage of plasma proteins from capillaries to tissue during 24 h accounts for the total amount of plasma proteins in the vascular system. The same amount must therefore be reabsorbed by the lymphatic system, which is considered to be the sole absorber of proteins from tissue. However, it is a well-established routine in all kinds of organ transplantation to not restore the lymphatic system of the transplant. Experience has shown that this reconstruction is unnecessary, which consequently implies that the lymphatics are not of crucial importance for the survival of the organ. Inevitably, we must therefore question the vital role that the lymphatic system has been attributed in maintaining homeostasis as the sole absorber of proteins. Instead, it is proposed that the major part of plasma proteins in tissue is actively absorbed by the capillaries.

Orbital phlebography in idiopathic intracranial hypertension and chronic tension-type headache.

BACKGROUND: Pathologic signs in orbital phlebographies have been reported in various neurological diseases. PURPOSE: To study if pathologic signs in orbital phlebography may be markers of inflammation primarily affecting intracranial capillaries, which would cause intracranial hypertension. MATERIAL AND METHODS: Two groups with different intracranial cerebrospinal fluid pressures (Pcsf) were compared as to inflammatory markers in serum and pathologic signs in orbital phlebographies. Nine consecutive patients with idiopathic intracranial hypertension (IIH) with bilateral papilledema and eight consecutive patients with chronic tension-type headache (CTTH) were investigated prospectively with fibrinogen, orosomucoid, haptoglobin in serum, and invasive orbital phlebograms. The angiograms were evaluated by two skilled neuroradiologists, independent of each other and without knowledge of the diagnoses or aim of the study, as to the following pathologic signs: (i) narrowing of superior ophthalmic veins; (ii) caliber changes of intraorbital veins; (iii) collaterals of intraorbital veins; (iv) flow to cavernous sinus; and (v) asymmetric drainage of cavernous sinus. RESULTS: Mean body mass index was >30 kg/m(2) in both groups. Pcsf was >200 < 250 mm H2O in 50% of the CTTH and >350 mm H2O in all IIH patients. No difference in inflammatory markers in blood was found. The phlebographies of the IIH patients had more pathologic signs and were considered pathologic significantly more often than the ones of the CTTH patients (P < 0.001). CONCLUSION: The difference as to phlebographic pathologic signs between the IIH and the CTTH patients with different Pcsf supports the hypothesis that such phlebographic signs are markers of inflammation primarily affecting intracranial capillaries, which would disturb cerebrospinal fluid regulation causing intracranial hypertension.

Paradigm shift in hydrocephalus research in legacy of Dandy's pioneering work: rationale for third ventriculostomy in communicating hydrocephalus.

OBJECTIVE: This study aims to question the generally accepted cerebrospinal fluid (CSF) bulk flow theory suggesting that the CSF is exclusively absorbed by the arachnoid villi and that the cause of hydrocephalus is a CSF absorption deficit. In addition, this study aims to briefly describe the new hydrodynamic concept of hydrocephalus and the rationale for endoscopic third ventriculostomy (ETV) in communicating hydrocephalus. CRITIQUE: The bulk flow theory has proven incapable of explaining the pivotal mechanisms behind communicating hydrocephalus. Thus, the theory is unable to explain why the ventricles enlarge, why the CSF pressure remains normal and why some patients improve after ETV. HYDRODYNAMIC CONCEPT OF HYDROCEPHALUS: Communicating hydrocephalus is caused by decreased intracranial compliance increasing the systolic pressure transmission into the brain parenchyma. The increased systolic pressure in the brain distends the brain towards the skull and simultaneously compresses the periventricular region of the brain against the ventricles. The final result is the predominant enlargement of the ventricles and narrowing of the subarachnoid space. The ETV reduces the increased systolic pressure in the brain simply by venting ventricular CSF through the stoma. The patent aqueduct in communicating hydrocephalus is too narrow to vent the CSF sufficiently.

Unraveling the riddle of syringomyelia.

The pathophysiology of syringomyelia development is not fully understood. Current prevailing theories suggest that increased pulse pressure in the subarachnoid space forces cerebrospinal fluid (CSF) through the spinal cord into the syrinx. It is generally accepted that the syrinx consists of CSF. The here-proposed intramedullary pulse pressure theory instead suggests that syringomyelia is caused by increased pulse pressure in the spinal cord and that the syrinx consists of extracellular fluid. A new principle is introduced implying that the distending force in the production of syringomyelia is a relative increase in pulse pressure in the spinal cord compared to that in the nearby subarachnoid space. The formation of a syrinx then occurs by the accumulation of extracellular fluid in the distended cord. A previously unrecognized mechanism for syrinx formation, the Bernoulli theorem, is also described. The Bernoulli theorem or the Venturi effect states that the regional increase in fluid velocity in a narrowed flow channel decreases fluid pressure. In Chiari I malformations, the systolic CSF pulse pressure and downward motion of the cerebellar tonsils are significantly increased. This leads to increased spinal CSF velocities and, as a consequence of the Bernoulli theorem, decreased fluid pressure in narrow regions of the spinal CSF pathways. The resulting relatively low CSF pressure in the narrowed CSF pathway causes a suction effect on the spinal cord that distends the cord during each systole. Syringomyelia develops by the accumulation of extracellular fluid in the distended cord. In posttraumatic syringomyelia, the downwards directed systolic CSF pulse pressure is transmitted and reflected into the spinal cord below and above the traumatic subarachnoid blockage, respectively. The ensuing increase in intramedullary pulse pressure distends the spinal cord and causes syringomyelia on both sides of the blockage. The here-proposed concept has the potential to unravel the riddle of syringomyelia and affords explanations to previously unanswered clinical and theoretical problems with syringomyelia. It also explains why syringomyelia associated with Chiari I malformations may develop in any part of the spinal cord including the medullary conus. Syringomyelia thus preferentially develops where the systolic CSF flow causes a suction effect on the spinal cord, i.e., at or immediately caudal to physiological or pathological encroachments of the spinal subarachnoid space.

Reprint of: Radiological assessment of hydrocephalus: new theories and implications for therapy.

It is almost a century since Dandy made the first experimental studies on hydrocephalus, but its underlying mechanism has been unknown up to now. The conventional view is that cerebrospinal fluid (CSF) malabsorption due to hindrance of the CSF circulation causes either obstructive or communicating hydrocephalus. Analyses of the intracranial hydrodynamics related to the pulse pressure show that this is an over-simplification. The new hydrodynamic concept presented here divides hydrocephalus into two main groups, acute hydrocephalus and chronic hydrocephalus. It is still accepted that acute hydrocephalus is caused by an intraventricular CSF obstruction, in accordance with the conventional view. Chronic hydrocephalus consists of two subtypes, communicating hydrocephalus and chronic obstructive hydrocephalus. The associated malabsorption of CSF is not involved as a causative factor in chronic hydrocephalus. Instead, it is suggested that increased pulse pressure in the brain capillaries maintains the ventricular enlargement in chronic hydrocephalus. Chronic hydrocephalus is due to decreased intracranial compliance, causing restricted arterial pulsations and increased capillary pulsations. The terms "restricted arterial pulsation hydrocephalus" or "increased capillary pulsation hydrocephalus" can be used to stress the hydrodynamic origin of both types of chronic hydrocephalus. The new hydrodynamic theories explain why third ventriculostomy may cure patients with communicating hydrocephalus, a treatment incompatible with the conventional view.

Delayed contrast agent kinetics in ischemic skeletal muscle.

PURPOSE: To detect skeletal muscle ischemia with first-pass gadolinium (Gd) kinetics after exercise. MATERIALS AND METHODS: Eleven subjects with intermittent claudication performed a symptom-limited bilateral plantar flexion exercise in the magnet. Regional ROIs were placed bilaterally in the gastrocnemius and soleus muscles, and a signal intensity (SI) time-curve analysis was performed. Induced ischemia was validated prior to the MRI with the systolic ankle-arm blood pressure index (AAI) measured after a symptom-limited treadmill exercise. RESULTS: Exercise induced ischemic pain in 16 of 22 legs with a significantly reduced AAI (0.31 +/- 0.15). The time to contrast arrival (TCA) was delayed in symptomatic ischemic legs vs. asymptomatic legs (16.3 +/- 6.9 seconds vs. 11.1 +/- 2.7 seconds, P < 0.05). The maximum SI during recovery was higher in the soleus muscle than in the gastrocnemius muscle in ischemic legs (1.55 +/- 0.1 vs. 1.44 +/- 0.1, P < 0.05). Symptomatic regions had a less steep upslope than asymptomatic regions (43 +/- 15 vs. 63 +/- 14, P < 0.001), with a graded upslope response to ischemia. However, a normal upslope was found in 10 of 29 ischemic regions, and some of the regions showed delayed contrast arrival, suggesting a pseudonormal upslope in ischemic regions. CONCLUSION: Exercise-induced ischemia was detected with the use of an SI time-curve analysis. However, disregarding the arterial input function and distribution volume of the tracer may lead to misinterpretation of some ischemic regions.

Radiological assessment of hydrocephalus: new theories and implications for therapy.

It is almost a century since Dandy made the first experimental studies on hydrocephalus, but its underlying mechanism has been unknown up to now. The conventional view is that cerebrospinal fluid (CSF) malabsorption due to hindrance of the CSF circulation causes either obstructive or communicating hydrocephalus. Analyses of the intracranial hydrodynamics related to the pulse pressure show that this is an over-simplification. The new hydrodynamic concept presented here divides hydrocephalus into two main groups, acute hydrocephalus and chronic hydrocephalus. It is still accepted that acute hydrocephalus is caused by an intraventricular CSF obstruction, in accordance with the conventional view. Chronic hydrocephalus consists of two subtypes, communicating hydrocephalus and chronic obstructive hydrocephalus. The associated malabsorption of CSF is not involved as a causative factor in chronic hydrocephalus. Instead, it is suggested that increased pulse pressure in the brain capillaries maintains the ventricular enlargement in chronic hydrocephalus. Chronic hydrocephalus is due to decreased intracranial compliance, causing restricted arterial pulsations and increased capillary pulsations. The terms "restricted arterial pulsation hydrocephalus" or "increased capillary pulsation hydrocephalus" can be used to stress the hydrodynamic origin of both types of chronic hydrocephalus. The new hydrodynamic theories explain why third ventriculostomy may cure patients with communicating hydrocephalus, a treatment incompatible with the conventional view.