= abnormal dilatation of meninges within sacral canal / foramina ± presacral component
Prevalence: 5%
Cause: diverticulum of spinal meningeal sac / nerve root sheath / arachnoid
- unilocular / multilocular cyst
- remodeling erosion of sacral canal / foramen ← CSF pulsations
- thinned cortical margins
DDx of presacral cyst: cystic sacrococcygeal teratoma; anal duct cyst; degenerative neurogenic tumor; adnexal cyst
Perineural Sacral Cyst / Tarlov Cyst
[Isadore Max Tarlov (1905–1977), professor of neurology and neurosurgery at New York Medical College]
= dilated nerve-root sleeve as normal variant
Cause: ? congenital, traumatic
Location: posterior rootlets (S2 + S3 most common)
- neurologic symptoms if large (in 22%)
- cyst communicates freely with subarachnoid space
- cyst wall continuous with arachnoid + dura
- cyst cavity occupies space between peri- and endoneurium
- bone remodeling + enlargement of neural foramen
Rx: surgical decompression, sacral laminectomy, percutaneous drainage
Sacral Meningeal / Arachnoid Cyst (less common)
= OCCULT intrasacral MENINGOCELE
- usually asymptomatic
- cyst does not communicate with subarachnoid space