Clinicopathological correlations in syringomyelia using axial magnetic resonance imaging

Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients

OBJECTIVE

Chiari malformations are regarded as a pathological continuum of hindbrain maldevelopments characterized by downward herniation of the cerebellar tonsils. The Chiari I malformation (CMI) is defined as tonsillar herniation of at least 3 to 5 mm below the foramen magnum. Increased detection of CMI has emphasized the need for more information regarding the clinical features of the disorder.

METHODS

We examined a prospective cohort of 364 symptomatic patients. All patients underwent magnetic resonance imaging of the head and spine, and some were evaluated using CINE-magnetic resonance imaging and other neurodiagnostic tests. For 50 patients and 50 age- and gender-matched control subjects, the volume of the posterior cranial fossa was calculated by the Cavalieri method. The families of 21 patients participated in a study of familial aggregation.

RESULTS

There were 275 female and 89 male patients. The age of onset was 24.9+/-15.8 years (mean +/- standard deviation), and 89 patients (24%) cited trauma as the precipitating event. Common associated problems included syringomyelia (65%), scoliosis (42%), and basilar invagination (12%). Forty-three patients (12%) reported positive family histories of CMI or syringomyelia. Pedigrees for 21 families showed patterns consistent with autosomal dominant or recessive inheritance. The clinical syndrome of CMI was found to consist of the following: 1) headaches, 2) pseudotumor-like episodes, 3) a Meniere's disease-like syndrome, 4) lower cranial nerve signs, and 5) spinal cord disturbances in the absence of syringomyelia. The most consistent magnetic resonance imaging findings were obliteration of the retrocerebellar cerebrospinal fluid spaces (364 patients), tonsillar herniation of at least 5 mm (332 patients), and varying degrees of cranial base dysplasia. Volumetric calculations for the posterior cranial fossa revealed a significant reduction of total volume (mean, 13.4 ml) and a 40% reduction of cerebrospinal fluid volume (mean, 10.8 ml), with normal brain volume.

CONCLUSION

These data support accumulating evidence that CMI is a disorder of the para-axial mesoderm that is characterized by underdevelopment of the posterior cranial fossa and overcrowding of the normally developed hindbrain. Tonsillar herniation of less than 5 mm does not exclude the diagnosis. Clinical manifestations of CMI seem to be related to cerebrospinal fluid disturbances (which are responsible for headaches, pseudotumor-like episodes, endolymphatic hydrops, syringomyelia, and hydrocephalus) and direct compression of nervous tissue. The demonstration of familial aggregation suggests a genetic component of transmission.

Cerebrospinal fluid flow in an animal model of noncommunicating syringomyelia

OBJECTIVE

The source of fluid and the mechanism of cyst enlargement in syringomyelia are unknown. It has been demonstrated that cerebrospinal fluid (CSF) normally flows from the subarachnoid space through perivascular spaces and into the spinal cord central canal. The aim of this study was to investigate whether this flow continues during cyst formation in an animal model of syringomyelia and to determine the role of subarachnoid CSF flow in this model.

METHODS

The intraparenchymal kaolin model of noncommunicating syringomyelia was established in 78 Sprague-Dawley rats. Horseradish peroxidase was used as a tracer to study CSF flow at 1 day, 3 days, 1 week, and 6 weeks after kaolin injection. CSF flow was studied at 0, 10, and 30 minutes after horseradish peroxidase injection into the cisterna magna or thoracic subarachnoid space.

RESULTS

The central canal became occluded at the level of the kaolin injection and at one or more rostral levels. Segments of the central canal isolated between occlusions gradually dilated, and axonal retraction balls were detected in the surrounding white matter. There was a partial blockage of subarachnoid CSF flow at the site of the kaolin injection, both in a rostral-caudal direction and in a caudal-rostral direction. Horseradish peroxidase was detected at all time points, in a distinctive pattern, in perivascular spaces and the central canal. This pattern was seen even where segments of the central canal were isolated and dilated.

CONCLUSION

In this animal model, noncommunicating syringes continue to enlarge even when there is evidence that they are under high pressure. There may be an increase in pulse pressure rostral to the block of subarachnoid CSF flow, causing an increase in perivascular flow and contributing to syrinx formation. The source of fluid in noncommunicating syringomyelia may be arterial pulsation-dependent CSF flow from perivascular spaces into the central canal.

Arterial pulsation-dependent perivascular cerebrospinal fluid flow into the central canal in the sheep spinal cord

The impetus for the enlargement of syringes is unknown. The authors hypothesize that there is a flow of cerebrospinal fluid (CSF) from perivascular spaces into the central canal and that the flow is driven by arterial pulsations. Using horseradish peroxidase as a tracer, the CSF flow was studied in normal sheep, in sheep with damped arterial pulsations, and in sheep with lowered spinal subarachnoid pressure. The CSF flow from perivascular spaces into the central canal was demonstrated in the normal sheep, and two patterns of flow were identified: 1) from perivascular spaces in the central gray matter; and 2) from perivascular spaces in the ventral white commissure. Flow into the central canal was also observed in the sheep with lowered spinal subarachnoid pressure, but not in those with reduced arterial pulse pressure. This study provides evidence that CSF flow from perivascular spaces into the central canal is dependent on arterial pulsations. Arterial pulsation-driven CSF flow may be the impetus for the expansion of syringes.

Morphological study of experimental syringomyelia with kaolin-induced hydrocephalus in a canine model

In this morphological study the authors investigated whether spinal cord cavitation, produced in young mongrel dogs that had been rendered hydrocephalic by cisternal injection of kaolin, consists of a dilated central canal or intramedullary cavities. Hydrocephalus was noted in 50 of 56 dogs treated with kaolin. Of the 50 hydrocephalic young dogs, 29 were shown to have central canal dilation that was prominent at the thoracic level and 21 to have cervical intramedullary cavities in the posterior column and/or the posterior horn. In 11 dogs from the latter group these cavities were demonstrated to have no communication with the central canal. This finding could not be explained by the hydrodynamic theory. On histopathological examination, myelomalacia and hemorrhagic infarction following ventricular shunting were noted adjacent to the cervical cavities, which suggested vascular impairment. A perfusion study revealed insufficient blood flow within the cervical cord at the level of the intramedullary cavities. A close correlation between the vascular insufficiency of the cervical cord and the pressure cone resulting from significant hydrocephalus was observed. The latter may cause cervicomedullary compression at the foramen magnum, affecting the venous drainage of the cervical cord below that level, resulting in intramedullary cavitation. Accordingly, vascular impairment was thought to play a significant role in the development of cervical syrinx formation in our kaolin model. The current results may provide a reasonable explanation for the formation of noncommunicating cervical syringomyelia in Chiari I malformation.

Distribution of substance P in the spinal cord of patients with syringomyelia

The distribution of substance P, a putative neurotransmitter and pain-related peptide, was studied using the peroxidase-antiperoxidase immunohistochemical method in the spinal cords obtained from autopsy of 10 patients with syringo-myelia and 10 age- and sex-matched, neurologically normal individuals. Substance P immunoreactivity was present in axons and in terminal-like processes in close apposition to neurons in the first, second, and third laminae of the dorsal horn. Smaller amounts of peroxidase-positive staining were found in the fifth lamina of the dorsal horn, the intermediolateral nucleus, the intermediomedial nucleus, and the ventral horn. In nine of 10 patients with syringomyelia, there was a substantial increase in substance P immunoreactivity in the first, second, third, and fifth laminae below the level of the lesion. A marked reduction or absence of staining was present in segments of the spinal cord occupied by the syrinx. Central cavities produced bilateral abnormalities, whereas eccentric cavities produced changes that were ipsilateral to the lesion. No alterations in staining were found in the spinal cord of an asymptomatic patient with a small central syrinx. The authors conclude that syringomyelia can be associated with abnormalities in spinal cord levels of substance P, which may affect the modulation and perception of pain.

Dysesthetic pain in patients with syringomyelia

Dysesthethic pain is a common complaint of patients with syringomyelia, traumatic paraplegia, and various myelopathic conditions. Because cavitary lesions of the spinal cord can be defined with good resolution by magnetic resonance imaging, syringomyelia provides a potential model for examining anatomic correlates of central pain. In this study, a syndrome of segmental dysesthesias, characterized by burning pain, hyperesthesia, and a variable incidence of trophic changes, was described by 51 of 137 patients (37%) with syringomyelia at the time of clinical presentation. Complete magnetic resonance scans, including axial images, demonstrated extension of the syrinx into the dorsolateral quadrant of the spinal cord on the same side and at the level of pain in 43 of 51 patients (84%). Surgical treatment of syringomyelia resulted in the relief or improvement of dysesthetic pain in 22 of 37 patients (59%), but 15 patients (41%) reported no improvement or an intensification of pain despite collapse of the syrinx. Postoperative dysesthetic pain was often a disabling complaint that responded poorly to medical therapy, including analgesics, sedatives, antiepileptics, antispasmodics, and anti-inflammatory agents. In most cases, there was a gradual improvement of symptoms, although six patients continued to complain of pain 24 to 74 months postoperatively. Prompt but transient relief was achieved in two of two patients with regional sympathetic blocks, and prolonged relief was achieved in one patient by stellate ganglionectomy. We conclude that painful dysesthesias can be caused by a disturbance of pain-modulating centers in the dorsolateral quadrant of the spinal cord and have certain causalgia-like features that respond in an unpredictable way to surgical collapse of the syrinx.