What is Syringomyelia?
Syringomyelia is a neurological condition where fluid filled cysts form within the spinal cord. The fluid filled cyst (or syrinx) can occur anywhere along the spinal cord, however most are located between C2 and T9. These can expand, damaging to the spinal cord. The true prevalence is unknown, but studies estimate prevalence ranges from 1.9-8.2 per 100,000.1, 2
Causes can be idiopathic or due to other conditions such as infection and malignancy but is most often associated with the Chiari-I malformation. Anatomical classification is based on whether they communicate with the fourth ventricle and whether the central spinal canal is dilated.3
Communicating syringomyelia are thought to develop due to obstruction of cerebrospinal fluid distal to the fourth ventricle. The syrinx is within the central canal and is connected to the fourth ventricle, therefore the spinal central canal and all four ventricles are dilated. Causes include Chiari II malformations and Dandy-Walker cysts.
There are two types of non-communicating syringomyelia, neither of which connect with the fourth ventricle. Causes of the first type include Chiari I malformations or extramedullary compression from tumours or cysts. They are associated with obstruction of the path of CSF flow at or below the foramen magnum, causing dilation of the central spinal canal. The second less common type do not cause dilatation of the central canal and are parenchymal cavitations, caused by trauma, ischaemia or haemorrhage to the spinal cord.
Atrophic cavitations are not connected to the fourth ventricle and may, or may not, involve the spinal central canal, being either dilatations here or microcysts. These are associated with degenerative changes within the spinal cord.
Neoplastic cavitation occurs from degeneration of intramedullary tumours or other neoplasms. As they are not connected to the fourth ventricle and do not involve dilation of the central canal, as such they do not contain cerebrospinal fluid.
How does Syringomyelia Present?
Many patients do not present with symptoms and the syringomyelia are incidental findings on routine MRI scanning for other causes2. Patients may present with isolated or a combination of motor, sensory and autonomic symptoms which can be unilateral or bilateral. These are determined by the location and extent of the syrinx within the spinal cord.
Initially weakness and wasting of intrinsic hand muscles
Progress as the lesion expands to weak and atrophied arms and shoulders, with decreased reflexes due to anterior horn cell compression.
Exaggerated lower limb reflexes due to extension of syrinx into corticospinal tracts
Can present with a mixed picture of upper and lower motor neuron signs if extend to the lower limbs
Occasionally impacts on bladder and bowel function.
Occur in up to 90% patients4
Preferentially affects decussating fibres in dorsal roots spinothalamic tracts (pain and temperature) with preservation of other dorsal column sensory modalities (soft touch, vibration, proprioception)
Initially loss of temperature sensation in hands
Rarely affects trigeminal nerve and nucleus if syrinx extends cranially
Over 50% have moderate pain, with 2/5 showing neuropathic features, dysesthesias and numbness however intensity is not necessarily related to the syrinx size.5
Pain is radicular often in a cape-like distribution over thorax and upper limbs, rarely lower limbs are affected.
Autonomic symptoms can include
How is Syringomyelia Investigated?
Diagnostic imaging is MRI which demonstrate syrinxes filled with CSF (except for neoplastic cavities which have higher protein content). This should include anatomical areas which may highlight the cause of the syrinx, such as intracranial masses or spinal cord tumours.
Electromyography and nerve conduction studies may show conduction abnormalities and quantitative sensory testing may indicate sensory gain and losses.
Syringomyelia management and prognosis
Often management is conservative unless there is increasing size, spinal cord compression or progression of symptoms. Surgery is based on the underlying aetiology of the syringomyelia. For example with a Chiari I malformation causing obvious obstruction to CSF flow, surgery is performed to correct CSF flow and prevent the syrinx increasing in size. Surgery may stabilise neurological symptoms and, in some cases, these improve, however pain often remains.
Pain management involves multimodal, multidisciplinary pathways. These can include pharmacotherapy for neuropathic pain following NICE guidance, such as anticonvulsant or antidepressant medications6, pain management programs and input from teams such as occupational therapy/hand therapy. Other analgesic medications including opioids are unlikely to be helpful.
As symptoms, presentation and disease progression vary widely dependent on cause, for some individual’s symptoms will stabilise or improve on their own, however so will progress and require follow-up, often within a neurosurgical umbrella of care.