= SYRINGOMYELIA = SYRINX (used in a general manner reflecting difficulty in classification)
= longitudinally oriented CSF-filled cavities + gliosis within spinal cord frequently involving both parenchyma + central canal
Age: primarily childhood / early adult life
Cause: Chiari I malformation (41%), trauma (28%), neoplasm (15%), idiopathic (15%)
- loss of sensation to pain + temperature ← interruption of spinothalamic tracts
- trophic changes = (skin lesions; Charcot joints in 25% affecting shoulder, elbow, wrist)
- muscle weakness ← anterior horn cell involvement
- spasticity, hyperreflexia ← upper motor neuron involvement
- abnormal plantar reflexes ← pyramidal tract involvement
Location: predominantly lower end of cervical cord; extension into brainstem (= syringobulbia)
CT:
- distinct area of decreased attenuation in spinal cord (100%)
- swollen / normal-sized / atrophic cord
- NO contrast enhancement
- change in shape + size of cord with change in position (rare)
- flattened vertebral border (rare) with increased transverse diameter of cord
- filling of syringohydromyelia with intrathecal contrast
- early filling ← direct communication with subarachnoid space
- late filling after 4–8 hours (80–90%) ← permeation of contrast material
Myelography:
- enlarged cord (DDx: intramedullary tumor)
- “collapsing cord” sign = collapsing of cord with gas myelography as fluid content moves caudad in the erect position (rare)
MR:
- cord enlargement
- cystic area → low SI on T1WI + increased SI on T2WI
- presence of CSF flow-void (= low SI on T2WI) within cavity ← pulsations
- beaded cavity ← multiple incomplete septations
DDx:pseudosyrinx = truncation artifact consisting of linear abnormal signal within cord on sagittal images in phase-encoding direction ← limited number of frequencies for fast Fourier transform
= PRIMARY / CONGENITAL SYRINGOHYDROMYELIA
= dilatation of persistent central canal of spinal cord (normally obliterated in 70–80%) which communicates with 4th ventricle (= communicating syringomyelia)
Histo: lined by ependymal tissue
Associated with:
- Chiari malformation in 20–70%
- metameric haustrations within syrinx on sagittal T1WI
- Spinal dysraphism
- Myelocele
- Dandy-Walker syndrome
- Diastematomyelia
- Scoliosis in 48–87%
- Klippel-Feil syndrome
- Spinal segmentation defects
- Tethered cord (in up to 25%)
DDx: transient dilatation of the central canal (transient finding in newborns during the first weeks in life)
= ACQUIRED / SECONDARY SYRINGOHYDROMYELIA
= any cavity within substance of spinal cord that may communicate with the central canal, usually extending over several vertebral segments
Histo: not lined by ependymal tissue
Pathophysiology: interrupted flow of CSF through the perivascular spaces of cord between subarachnoid space + central canal
Cause:
- Posttraumatic syringomyelia
Prevalence: in 3.2% after spinal cord injury
Location: 68% in thoracic cord
Average length: 6.0 (range, 0.5–40.0) cm- syrinx may be septated (parallel areas of cavitation) on transverse T1WI
- loss of sharp cord-CSF interface (obliteration of arachnoid space by adhesions)
- in 44% associated with arachnoid loculations (extra-medullary arachnoid cysts) at upper aspect of syrinx
- Postinflammatory syringomyelia
subarachnoid hemorrhage, arachnoid adhesions, S/P surgery, infection (tuberculosis, syphilis) - Tumor-associated syringomyelia = peritumoral cyst of spinal cord tumor / herniated disk ← circulatory disturbance + thoracic spinal cord atrophy
Prevalence: in 60% of all intramedullary tumors- polar / satellite cysts = rostral / caudal cysts ← reactive dilatation of central canal
- A higher location within spinal canal raises the likelihood of syrinx development
- Vascular insufficiency
= POSTTRAUMATIC SPINAL CORD CYST
= CSF-filled cyst adjacent to level of trauma; usually single (75%)
- late deterioration in patients with spinal cord injury (NOT related to severity of original injury)
Rx: shunting leads to clinical improvement