MR imaging of syringobulbia

The magnetic resonance (MR) examinations of 65 patients with syringomyelia were evaluated to determine the incidence and MR characteristics of syringobulbia. Syringobulbia was identified in 11 patients (17%), 10 of whom had communicating syringomyelia (associated with the Chiari I malformation) and one idiopathic syringomyelia. The cavities extended from 5 to 20 mm above the plane of the foramen magnum. Two types of syringobulbia were identified. The 10 patients with Chiari I malformation had thin clefts or slits extending into the medulla. These cavities were much smaller than the cervical cavities. The other patient had saccular syringobulbia in which the medullary cavity was similar to the cervical syrinx cavity. The T1-weighted images were most useful in detection of syringobulbic cavities. The theory of syringobulbia development and a brief review of the literature are included.     

Increased pulsatile movement of the hindbrain in syringomyelia associated with the Chiari malformation: cine-MRI with presaturation bolus tracking

Cine-MRI with presaturation bolus tracking was used in patients with syringomyelia associated with a Chiari malformation to study pulsatile movement of the hindbrain, cervical spinal cord, cerebrospinal fluid and the fluid within the syrinx. Nine patients had 13 examinations, 6 preoperative, 3 after syringosubarachnoid shunting and 4 after posterior fossa decompression. Five controls were also examined. Dynamic display of the acquired images demonstrated downward displacement of the presaturation bolus on the cerebellar tonsils and medulla oblongata (or upper cervical cord) at the C1 level in all preoperative examinations and in two patients after syringo-subarachnoid shunting but with residual foramen magnum obstruction. Downward displacement of the bolus on the cervical spinal cord was also demonstrated in 7 examintions, but not observed in the controls. Thus, the hind-brain-spinal cord axis showed larger pulsatile movements in patients with foramen magnum obstruction. Based on these observations and a review of the literature, a new theory on the mode of extension of syringomyelia, emphasising the role of increased pulsatile movement of the hind-brain-spinal cord axis is proposed: that the pulsatile movements, together with a one-way valve mechanism in the syrinx cavity act as a vacuum-pump to enlarge the syrinx.     

CSF pulsations within nonneoplastic spinal cord cysts

Because of its sensitivity to fluid motion, MR imaging was used to investigate fluid dynamics in syringomyelia. Three major findings characterized syringomyelia: pulsatile fluid in cysts, nonpulsatile fluid in cysts, and damaged cord tissue. The fluid in preoperative syrinx cavities pulsated in a fashion similar to subarachnoid CSF. Pulsation was more prominent in large cysts but was also seen in small cysts. Nonpulsatile cysts were generally of smaller diameter, were shorter in length, and often were single; they could, however, coexist with pulsatile cysts. Nonpulsatile cysts had etiologies similar to those of pulsatile cysts: Chiari malformation, trauma, and unknown. Damaged cord, characterized by abnormal high signal on T2-weighted sequences, was seen in 15 of 16 patients and could be either focal or diffuse but was always adjacent to syrinx cavities. Postsurgical MR scans had a lower incidence of pulsatile cysts. In five patients with both pre- and postoperative MR scans, shunting of the cyst reduced the size of the pulsating cyst (two patients) or reduced the size of the cyst and eliminated pulsation altogether (three patients). Axial, T2-weighted images are recommended in the investigation of spinal cord cysts to determine the presence or absence of pulsatile fluid. The presence of pulsation indicates a nonneoplastic cyst. The absence or reduction of CSF pulsation may prove to be a valuable indicator of the success of a shunting procedure.     

Intracranial MR imaging of achondroplasia]

Intracranial MR imaging was performed in five patients with achondroplasia. All patients had narrowing of the subarachnoid space at the level of the foramen magnum that was mainly due to protrusion of the posterior aspect. Three patients had compressive deformities of the brainstem and/or upper cervical spine. Among them, two patients had deformities of the pons. Relative upward displacement of the brainstem was seen in all patients. Hydrocephalus was seen in three patients.     

MRI of mannosidosis

MR findings in three patients with mannosidosis are reported. They all had diploic space widening with underdevelopment of the sinuses, prominent periventricular Virchow-Robin spaces and perioptic CSF spaces. Two had tight foramen magnum, one of which was associated with a cervical syrinx and markedly widened perioptic CSF spaces with papilledema. Received: 1 August 2000/Accepted: 1 February 2001     

Significance of cerebellar tonsillar position on MR

It has been noted that a low degree of ectopia of the cerebellar tonsils on MR is of questionable significance. We measured the position of the cerebellar tonsils with respect to the inferior aspect of the foramen magnum in 200 normal patients and in 25 patients with a firm diagnosis of Chiari I malformation. In the normal group, the mean position of the tonsils was 1 mm above the foramen magnum with a range from 8 mm above the foramen magnum to 5 mm below. In the patients with Chiari I malformations, the mean position was 13 mm below the foramen magnum with a range from 3 mm below the foramen magnum to 29 mm below. Fourteen percent of normal patients had tonsils extending slightly below the foramen magnum. If 2 mm below the foramen magnum is taken as the lowest extent for tonsils in a normal patient, our sensitivity in predicting symptomatic patients is 100% and our specificity is 98.5% (three false positives). If 3 mm below the foramen magnum is taken as the lowest normal tonsillar position, our sensitivity is 96% and our specificity is 99.5%. MR demonstration of less than 2 mm of tonsillar ectopia is probably of no clinical significance in the absence of syringomyelia.     

MR imaging with gadolinium-DTPA in the differentiation of tumor, syrinx, and cyst of the spinal cord

Intravenous Gd-diethylenetriamine pentaacetic acid was used in 16 patients to differentiate between syringomyelia, syringomyelia in association with tumor, and cystic tumor in the spinal cord. Contrast enhancement occurred in all 12 histologically proven cases of tumor and enabled clear demarcation of neoplastic tissue from syrinx or cyst. Eleven of the twelve tumors seen in association with spinal cord cavitation were malignant; all tumors apart from one (a schwannoma) were intramedullary in location. Enhanced scans were more helpful than unenhanced scans in diagnosing and defining the extent of tumors associated with a syrinx or cyst.     

The hypoglossal canal: normal MR enhancement pattern.

PURPOSETo review the anatomy of the hypoglossal canal and present the normal precontrast and postcontrast MR appearance of axial posterior fossa images.METHODSThirty-one axial MR examinations of the normal posterior fossa were retrospectively reviewed.RESULTSThe hypoglossal canals are well seen on 3-mm-thick axial MR images of the posterior fossa (28 [90%] of 31 patients). Symmetric intense intracanalicular enhancement after intravenous administration of gadopentetate dimeglumine is routine, typically with minor anterior extension into the nasopharyngeal region (28 [100%] of 28). A linear filling defect traversing the enhanced canal often is seen (21 [75%] of 28) and may represent hypoglossal nerve rootlets. Circumferential enhancement of the meninges at the level of the foramen magnum was a common finding (19 [64%] of 28).CONCLUSIONEnhancement within the hypoglossal canal with anterior extension beneath the skull base is a normal finding. This pattern is characteristic enough on MR imaging to aid interpretation of skull base lesions and to exclude the possibility of a mass within the hypoglossal canal.     

Chiari I malformations: clinical and radiologic reappraisal.

Clinical findings and magnetic resonance (MR) images in 68 patients with Chiari I malformations were retrospectively analyzed to identify those radiologic features that correlated best with clinical symptoms. A statistically significant (P = .03) female predominance of the malformation was observed, with a female: male ratio of approximately 3:2. Associated skeletal anomalies were seen in 24% of patients. Syringomyelia was detected in 40% of patients, most commonly between the C-4 and C-6 levels. Of the 25 patients who presented with spinal symptoms, 23 (92%) proved to have a syrinx at MR imaging. When the syrinx extended into the medulla (n = 3), however, brain stem symptoms predominated. Patients with objective brain stem or cerebellar signs had the largest mean tonsillar herniations. Patients with tonsillar herniations greater than 12 mm were invariably symptomatic, but approximately 30% of patients with tonsils herniating 5-10 mm below the foramen magnum were asymptomatic at MR imaging. "Incidental" Chiari I malformations are thus much more common than previously recognized, and careful clinical assessment remains the cornerstone for proper diagnosis and management.     

The MR appearance of syringomyelia: new observations

Fifty-eight patients with spinal cord cavities were studied with MR imaging. Patients were separated into four groups, and the appearance of the cavities were compared. There were 24 patients (41.4%) with communicating syringomyelia (associated with the Chiari I malformation). Sixteen patients (27.6%) had posttraumatic syringomyelia, nine patients (15.5%) had associated tumors, and nine patients (15.5%) had idiopathic syringomyelia. The characteristics of each syrinx, the spinal cord, and the appearance of the cerebellar tonsils were analyzed on T2- and T1-weighted images. There is a striking similarity in the appearance of many syrinx cavities regardless of the cause. Characteristics that were found in some patients in every group included areas of increased intensity on T2-weighted images, the presence of the CSF flow-void sign (CFVS) in the syrinx cavity, eccentric cavities, "beaded" cavities, and cord enlargement. Tonsillar ectopia alone does not indicate that a syrinx is of the "communicating" type, since it was present in two of 16 patients (13%) with trauma and in two of five patients (40%) with tumors. T1-weighted images were most useful in evaluating the anatomic characteristics of the syrinx and the cerebellar tonsils. Most syrinx cavities involved the cervicothoracic junction. The average length was between five and nine vertebral segments (depending on category) but varied between one and 20 vertebral segments. T2-weighted images revealed areas of increased intensity in the spinal cord in 13 patients without tumors. Two of these cases were shown to represent gliosis on histopathologic review. The CFVS was present in the syrinx cavities of 23 patients (40%), probably reflecting pulsatile movements of the syrinx fluid. It has been proposed that such movements are a cause of syrinx propagation, and the observation of the CFVS may have prognostic significance. The development and progression of the CFVS was documented in serial MR examinations in one patient over an 18-month period. The theories of syrinx development and propagation are reviewed.     

MR imaging of syringomyelia and hydromyelia

The relative effectiveness of plain computed tomography (CT), metrizamide CT, conventional myelography, and magnetic resonance (MR) imaging was compared for the examination of cystic spinal cord lesions. Intramedullary cavities in 18 patients were demonstrated by MR imaging: cavities were uncomplicated in 13 patients, associated with spinal tumors in two, and studied after occipital craniectomy for treatment of Chiari malformation and syringomyelia in two. Cavities were shown by MR imaging in all enlarged spinal cords, but a cavity was shown in only one of four small cords. The rostral limits of the cavities were demonstrated better than were the caudal extensions. Ventricular communication was not demonstrated. Chiari malformation was shown only in cavities that did not involve the medulla. Syringes associated with tumor were indistinguishable from uncomplicated cavities, but the tumor had abnormal signal on long spin-echo sequences in two cases. Cystic cord tumor (one case) had an inhomogeneous appearance. Caudal displacement of the cerebellar hemisphere through the surgical defect associated with compression of the fourth ventricle was shown in two cases after posterior fossa craniectomy. Thirteen patients were studied with metrizamide CT also. MR imaging proved to be as accurate as metrizamide CT in the diagnosis of intramedullary cavities that result in spinal cord enlargement, but it was less sensitive in detecting cavities within normal-sized or diminished spinal cords. It had the advantage that tumor tissue could be distinguished from associated syrinx cavities by differences in signal characteristics; and cerebellar ectopia was evaluated easily on sagittal MR views.     

Delayed metrizamide CT enhancement of syringomyelia: postoperative observations

Delayed metrizamide computed tomography (CT) was performed both preoperatively and postoperatively in 11 syringomyelia patients. Change of syrinx size between the studies was easily assessed on CT. The morphologic change of the syrinx gave useful information about its continuity. One of our cases had reoperation as a result of this CT information. All cases with Chiari I malformation still showed filling of the syrinx cavity by metrizamide after posterior fossa decompression and obex plugging. This supports the idea that the abnormal fluid circulation maintaining syringomyelic cavities is more than just the flow through the obex to the central canal but may also be from fluid passage through the cord substance.     

Chiari-Ⅰ型畸型的影像学检查

Objective:To discuss the relationship between the Chiari- Ⅰ deformity and the perioccipital foramen magnum region defor mity in imaging, clinical and pathological manifestation. Methods: Forty one cases of Chiair- Ⅰ deformity in which 28 cases had undergone MRI, 29 cases for CT, and 9 cases for both these two examinations were studied. Results: There was the tonsilla cerebelli herniation in all CT cases which had extent downward from foramen magnum, 25 to C1 bottom level, 4 down to C2 level and below. The tonsilla cerebelli as a soft mass is posterior to cervical spinal cord in magnum foramen level in all axial imaging. In 8 of 9 cases of CTM show the cervical spinal cord deformation due to tonsilla cerebelli compression. Sagittal reconstruction images show that the tonsilla cerebelli extended downward to the spinal canal from the posterior fossa. All 28 cases of MRIgroup showed wedge-shaped tonsilla herniation extending 5 ～ 8 mm down ward magnum foremen; non indicate pathologic characteristics of Chian- Ⅰ deformity. Conclusion: The cervical and medullary curvature was due to the posterior fossa invagination but not to the Chiari- Ⅰ deformity itself.     

Posterior fossa epithelial cyst: case report and review of the literature.

A 49-year old woman with progressive cranial nerve signs and hemiparesis was found at MR imaging and at surgery to have a cyst at the foramen magnum. Immunohistochemistry and electron microscopy showed an epithelial cyst of endodermal origin. MR findings were of an extraaxial mass, with short T1 and T2 times. Unless immunohistochemistry and electron microscopy are used in the final diagnosis of such cysts, all posterior fossa cysts lined by a single layer of epithelium should be described simply as epithelial cysts.     

Posterior fossa hemangioblastomas: MR imaging

The magnetic resonance (MR) imaging findings of 18 surgically proved posterior fossa hemangioblastomas (15 patients) were retrospectively analyzed and correlated with computed tomographic (ten patients) and angiographic (eight patients) findings. Thirteen tumors were located in the cerebellar hemisphere, three in the vermis, and two in the medulla with associated syrinxes. Three patients had von Hippel-Lindau disease, two of whom had multiple cerebellar hemangioblastomas. Seven hemangioblastomas appeared as solid tumors, six as solid masses with central cysts, and five as cysts with mural nodules. Abnormal tumor vessels, with characteristic signal void, were demonstrated in 13 tumors. Associated hemorrhage was present in four tumors. Although angiography is usually required for the diagnosis and preoperative assessment of this tumor, MR imaging demonstration of a posterior fossa mass with abnormal vessels should suggest the diagnosis of hemangioblastoma. Moreover, the combination of a peripheral posterior fossa cyst with a mural nodule supplied by enlarged vessels may be pathognomonic.     

Radiographic studies of the ventricles in syringomyelia

Summary Radiographic investigations of 171 patients with communicating syringomyelia have been reviewed. Hydrocephalus was found in onethird of the cases and has occasionally progressed after operation on the posterior fossa, sometimes with accompanying clinical deterioration. The outlets of the fourth ventricle were usually abnormal; tonsillar descent, arachnoiditis and both together were seen. Arachnoiditis correlated strongly with a history of difficult birth. The foramen of Magendie was sometimes patent and sometimes blocked. There was no consistent level of occlusion corresponding to a persistent roof of the fourth ventricle. The cisterna magna was usually small or obliterated but some examples of large cisterns or subarachnoid pouches were found. Radiological demonstration of a communication from the fourth ventricle to the syrinx occurred in only seven patients by positive contrast material and not by air. It is suggested that a sizable communication is rare at the time when patients seek treatment.     

Evaluation of intrasyrinx fluid motion by spatial modulation of magnetization-magnetic resonance imaging in syringomyelia with long-term follow-up: a predictor of postoperative prognosis?

OBJECTIVE: To evaluate the use of measuring intrasyrinx fluid motion in syringomyelia by spatial modulation of magnetization (SPAMM)-magnetic resonance imaging (MRI) for predicting postoperative results. MATERIALS AND METHODS: Fourteen patients with syringomyelia, who underwent surgery between 1995 and 2004 and took both preoperative SPAMM-MRI and postoperative MRI, were reviewed retrospectively. The SPAMM-MRI was obtained on a 1.5-T system using the electrocardiogram-triggered multiphase image technique with repetition time/time to echo/diffusion time/flip angle = 42 milliseconds/7.2 milliseconds/0 to 600 milliseconds/20 degrees. Three radiologists analyzed the tagging band shifting of the intrasyrinx fluid motions on the preoperative SPAMM-MRI. If the tagging band shifting during the systolic phase was more than half of the band space, it was regarded as good fluid motion. The correlation between the preoperative intrasyrinx fluid motion and the postoperative shrinkage of the syrinx was statistically analyzed. RESULTS: The underlying causes of the syringomyelia were Arnold-Chiari malformation (7 patients), trauma (4 patients), and infectious disease (3 patients). Eight of 9 patients who had good fluid motion in the syrinx showed postoperative shrinkage of the syrinx. However, the 5 patients who had poor fluid motion showed no shrinkage of the syrinx. The fluid motion of the syrinx was highly correlated with the postoperative shrinkage of the syrinx (P < 0.01). CONCLUSIONS: Evaluation of the intrasyrinx fluid motion in syringomyelia using the SPAMM-MRI can be a useful predictor of postoperative results and may indicate how well the pulse wave is transmitted from the heart to the syrinx.     

The Cervical Spinal Canal Tapers Differently in Patients with Chiari I with and without Syringomyelia

BACKGROUND AND PURPOSE:The cause of syringomyelia in patients with Chiari I remains uncertain. Cervical spine anatomy modifies CSF velocities, flow patterns, and pressure gradients, which may affect the spinal cord. We tested the hypothesis that cervical spinal anatomy differs between Chiari I patients with and without syringomyelia.MATERIALS AND METHODS:We identified consecutive patients with Chiari I at 3 institutions and divided them into groups with and without syringomyelia. Five readers measured anteroposterior cervical spinal diameters, tonsillar herniation, and syrinx dimensions on cervical MR images. Taper ratios for C1–C7, C1–C4, and C4–C7 spinal segments were calculated by linear least squares fitting to the appropriate spinal canal diameters. Mean taper ratios and tonsillar herniation for groups were compared and tested for statistical significance with a Kruskal-Wallis test. Inter- and intrareader agreement and correlations in the data were measured.RESULTS:One hundred fifty patients were included, of which 49 had syringomyelia. C1–C7 taper ratios were smaller and C4–C7 taper ratios greater for patients with syringomyelia than for those without it. C1–C4 taper ratios did not differ significantly between groups. Patients with syringomyelia had, on average, greater tonsillar herniation than those without a syrinx. However, C4–C7 taper ratios were steeper, for all degrees of tonsil herniation, in patients with syringomyelia. Differences among readers did not exceed differences among patient groups.CONCLUSIONS:The tapering of the lower cervical spine may contribute to the development of syringomyelia in patients with Chiari I.

Patients with a Chiari I malformation frequently develop syringomyelia, in theory the result of CSF flow obstructed by ectopic cerebellar tonsils. Phase-contrast MR imaging studies of CSF flow in the foramen magnum support this theory. Oscillatory CSF fluid flow has greater velocities and greater complexity in patients with Chiari I than in healthy subjects.¹ Why some patients with Chiari I develop syringomyelia and other do not has not yet been explained. How hyperdynamic CSF flow at the craniovertebral junction causes syringomyelia lower in the cervical spine has also not been elucidated.Abnormal tonsil position is not a necessary or a sufficient cause for syringomyelia because not all patients with Chiari I have syringomyelia and not all patients with syringomyelia have tonsillar herniation. The extent of tonsillar herniation does not predict the presence of syringomyelia. Therefore, factors other than tonsil herniation may have a role in the pathogenesis of syringomyelia. For example, one factor may be the size of the posterior cranial fossa; another pathogenetic factor may be the patency of the central canal within the cervical or thoracic spinal cord.^2,3The possibility that cervical spinal canal anatomy has a role in the pathogenesis of syringomyelia has not been extensively studied. The spinal canal narrows between C1 and C4 in healthy subjects⁴ and in patients with Chiari I.⁵ The tapering of the upper cervical spinal canal causes peak CSF velocities to increase from C1 to C4.^6,7 Taper ratios, the slope of a line fit to spinal canal diameters at multiple spinal levels, differ between patients with Chiari I and controls.^5,8 We designed this study to test the hypothesis that Chiari I patients with syringomyelia have different cervical spinal canal taper ratios than Chiari I patients without syringomyelia.     

Effect of craniocervical decompression on peak CSF velocities in symptomatic patients with Chiari I malformation

BACKGROUND AND PURPOSE: Peak CSF velocities detected in individual voxels in the subarachnoid space in patients with Chiari I malformations exceed those in similar locations in the subarachnoid space in healthy subjects. The purpose of this study was to test the hypothesis that the peak voxel velocities are decreased by craniocervical decompression. METHODS: A consecutive series of patients with symptomatic Chiari I malformations was studied before and after craniocervical decompression with cardiac-gated, phase contrast MR imaging. Velocities were calculated for each voxel within the foramen magnum at 14 time points throughout the cardiac cycle. The greatest velocities measured in a voxel during the cephalad and caudad phases of CSF flow through the foramen magnum were tabulated for each patient before and after surgery. The differences in these velocities between the preoperative and postoperative studies were tested for statistical significance by using a single-tailed Student's t test of paired samples. RESULTS: Eight patients with a Chiari I malformation, including four with a syrinx, were studied. Peak caudad velocity diminished after craniocervical decompression in six of the eight patients, and the average diminished significantly from 3.4 cm/s preoperatively to 2.4 cm/s postoperatively (P =.01). Peak cephalad velocity diminished in six of the eight cases. The average diminished from 6.9 cm/s preoperatively to 3.9 cm/s postoperatively, a change that nearly reached the significance level of.05 (P =.055). CONCLUSION: Craniocervical decompression in patients with Chiari I malformations decreases peak CSF velocities in the foramen magnum. The study supports the hypothesis that successful treatment of the Chiari I malformation is associated with improvement in CSF flow patterns.     

Osteogenesis imperfecta associated with basilar impression and cerebral atrophy: a case report

Osteogenesis imperfecta is a disease of bone formation subdivided into two types, congenita and tarda. It is associated with bony fragility, blue sclerae and abnormality of tooth dentin. Rarely the tarda form is associated with basilar invagination or infolding of the foramen magnum and upper cervical segments into the posterior fossa. This results in hydrocephalus and a spectrum of neurologic dysfunction known as the foramen magnum compression syndrome. Many radiologic methods have been used to evaluate basilar invagination including plain film and CT. We describe a patient with osteogenesis imperfecta tarda examined with CT, with a unique finding of diffuse cerebral atrophy associated with basilar invagination.