Imaging Studies

Plain radiographs are noncontributory in these patients. CT is frequently interpreted as negative as the syrinx may be small or isodense to the cord and thus may remain invisible. Occasionally, a large-diameter syrinx may be seen on CT studies. Frequently the only clue to the presence of a syrinx may be spinal cord expansion. Postcontrast CT, especially when films are obtained an hour or more after contrast administration, may demonstrate the cyst as it fills with contrast.

MRI is the study of choice. T1-weighted images (T1WI) will show a hypointense space, similar to that of the CSF, within the cord. Sagittal views help determine the extent of the syrinx. On T2-weighted images (T2WI), the signal within the cavity should correspond to that of the CSF: hyperintense (Figures 14-1A and 14-1B). Occasionally the cranial and caudal ends of the syrinx may enhance on T2WI, representing reactive gliosis. Axial cuts determine whether the syrinx is symmetrical, centrally located (relatively asymptomatic lesions), centrally located with paracentral expansion (usually associated with segmental signs), or eccentrically located (following trauma, producing combination of segmental signs and long tract signs). Contrast administration is necessary in order to rule out intramedullary tumors. The syrinx itself does not enhance (Figures 14-2 and 14-3).

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