The use of the general term 'syrinx' has grown out of the difficulty in distinguishing between hydromyelia and syringomyelia using current imaging modalities. Strictly speaking, in hydromyelia, there is dilatation of the central canal of the spinal cord, and thus the lesion is lined by ependyma. While in syringomyelia and more proximal variants, there is cystic dissection through the ependymal lining of the central canal and a CSF collection within the cord itself, and thus this lesion is not lined by ependyma. Clinically, there is no difference between the two and severity of symptoms is related to the location and size of the syrinx, and thus 'syrinx' may be used as a general descriptor.
See syrinx terminology for further clarifications.
Neurological symptoms vary considerably depending on where the syrinx is located in the neuraxis. Classically there is a mix of motor and sensory features, with both acute and chronic effects.
As mentioned, a syrinx refers to refers to any cavity within the spinal cord which may or may not communicate with the central canal. When a syrinx is present rostrally into the neuraxis, syringomyelia is generally also present and the resultant syrinx is generally appreciated as an 'extension' from this.
They may be congenital (90%) or acquired in aetiology.
Congenital causes include:
- Chiari I malformation
- Chiari II malformation
- Dandy-Walker malformation
- Klippel-Feil syndrome
Acquired (secondary) causes include:
- post-traumatic: occurs in ~5% of patients with spinal cord injury usually from a whiplash type injury; symptoms may start many months or years after injury
- cervical canal stenosis
- secondary to a spinal cord tumour
- secondary to a haemorrhage
- due to vascular insufficiency
Radiographic investigations may reveal many anomalies depending on the cause of the syrinx. This section will solely describe imaging characteristics of the syrinx itself.
Plain films of the spine may show subtle widening of the spinal canal in both the sagittal and coronal planes.
The syrinx may be appreciated as an area of decreased attenuation, similar to that of CSF, within the spinal cord.
The syrinx follows CSF signal characteristics on all sequences:
- T1: hypointense
- T2: hyperintense, although there may be hypointense regions representing flow or pulsation artefact
Treatment and prognosis
When symptomatic, neurosurgical intervention may be required.
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