General prevalence: The prevalence of syringomyelia in the general population is unknown. In a search of the literature before 2009, Dr. Marcy Speer found estimates for how frequently syringomyelia is associated with various primary conditions (Chiari I malformation, spinal cord tumor, trauma, etc.) and how frequently these conditions appear to occur in the population. Based on these data, she estimated that the prevalence of syringomyelia is between 1 to 1,300 and 1 to 1,900, which is about 10 times higher than previous estimates (70). Since then, the original estimates for disorders such as Chiari I malformation have changed dramatically, which impacts the syringomyelia estimates.
Chiari-associated syringomyelia: The incidence of syringomyelia associated with Chiari malformations has traditionally been known to range between 30 and 70% with Chiari I malformation and between 40 and 95% with Chiari II malformation (8). However, according to the largest MRI study to date, syringomyelia is found in 23% of children with Chiari I malformation and is much less frequent in the first 5 years of life (41).
Trauma-associated syringomyelia: The exact incidence of symptomatic syringomyelia from trauma is estimated to be 3 – 5% (42, 43) and approximately 3% for posttraumatic arachnoiditis (44).
Tumor-associated syringomyelia: A syrinx is found in 25 – 60% of patients with intrinsic spinal cord tumors (45, 46).
Mean onset of symptoms 30 years: Although symptom onset is common in children, the mean age of onset is approximately 30 years.
Male > female: No large population-based studies have been done, but syringomyelia appears to occur more frequently in men than in women.
None: There is no particular ethnic or geographic distribution.
Family history: A family history of syringomyelia or Chiari malformation may be considered a risk factor since these disorders are often familial (60, 61).
Presence of potential etiology: The presence of a predisposing condition such as a Chiari I malformation, spina bifida (myelomeningocele), or history of spinal trauma may predispose to the development of syringomyelia.
Relationships to Other Disease States and Syndromes
Chiari most common: Syringomyelia is believed to occur as a result of a primary cranial or spinal abnormality. It is most frequently associated with Chiari malformation types I and II.
Other causes: Other known disorders that can give rise to a syrinx include spinal cord tumor, trauma, tethered spinal cord, vascular malformations, and traumatic and infectious adhesive arachnoiditis.
Idiopathic common: Idiopathic syringomyelia is common. However, it is likely that as diagnostic technology improves, previously unknown causes will become evident.