Spinal meningeal cysts are diverticulae of the arachnoid or dura mater or of the nerve root sheath. They are uncommon, usually asymptomatic and invariably found incidentally at MRI (that has been performed for another reason).
The cysts contain CSF and have thin walls. They may be intradural or extradural and may contain neural tissue. The spinal meningeal cyst classification uses these features to separate the different type of cysts.
They cysts are usually asymptomatic, but if they are large, they may cause mass effect and symptoms relating to compression of local structures, e.g. nerve roots.
CSF pulsation can also remodel the surrounding bone, e.g. sacral canal.
Spinal meningeal cysts can be classified according to a system
- type I : extradural meningeal cyst without neural tissue
- type Ia : extradural spinal arachnoid cyst
- type Ib : sacral meningocoele
- type II : extradural meningeal cyst containing neural tissue, e.g. Tarlov cyst
- type III : intradural spinal arachnoid cyst
Classification of spinal meningeal cysts
Spinal arachnoid cysts are relatively uncommon and may be either intra-dural (type III meningeal cyst) or extra-dural (type IA meningeal cyst). This article specifically relates to spinal arachnoid cysts.
Spinal arachnoid cysts may present at any age. There is no gender predilection. Clinical presentation Most spinal arachnoid cysts are asymptomatic and are discovered incidentally. If present, clinical symptoms may include pain, weakness, numbness or bladder/bowel incontinence. Symptoms may be exacerbated with postural changes and the Valsalva maneuver. Pathology As with any arachnoid cyst, spinal arachnoid cysts are CSF filled sacs contained by arachnoid mater. The degree of communication with the surrounding CSF space is variable with some cyst freely communicating and other not at all 9. They may be congenital or acquired. Secondary arachnoid cysts are usually due to trauma, haemorrhage, inflammation, surgery or lumbar puncture 3,4.
Most primary intradural spinal arachnoid cysts are dorsal to the cord. They occur at the following locations: • thoracic : 80% • cervical : 15% • lumbar : 5% Secondary spinal arachnoid cysts can be located anywhere. A Tarlov cyst (also called a perineural cyst) is a CSF filled dilatation of the nerve root sheath at the dorsal root ganglion. These are type II spinal meningeal cysts that are, by definition, extra dural, but contain neural tissue. Like other spinal meningeal cysts, these are largely asymptomatic and found incidentally. Large cysts may cause local pressure effect, but they need to be large. Symptoms however don't appear to correlate with size 2. Epidemiology They occur in approximately 5% of the population, more commonly in women. Radiographic features If large may be seen as a posterior extra-ovarian cystic mass. The sacral foramina may be widened. Morphology can vary from a simple rounded cyst to a complex loculated cystic mass. There may be bone scalloping of the exit foramen.
Initially described by I.M Tarlov in 1938