Both CT and MRI are good imaging procedures that allow the detection of extradural spinal masses such as<unk> s. Magnetic resonance neurography is an emerging imaging technology based on MRI that highlights neurologic tissue. Often cysts are under reported and under diagnosed as radiologists and neurosurgeons have been traditionally taught to ignore these cysts. Patients frequently experience difficulty in diagnosis, however this is changing as<unk> s have now been recognized by NORD as a rare disease. MRI MRI sagittal image of sacral and dorso-lumbar perineural cysts. MRI, or Magnetic Resonance Imaging, is considered the imaging study of choice in identifying<unk> s. MRI provides better resolution of tissue density, absence of bone interference, multiplanar capabilities, and is noninvasive. Plain films may show bony erosion of the spinal canal or of the sacral foramina. On MRI pictures, the signal is the same as the CSF one. If MRI made with a contrast medium: * The signal in the cyst is the same as in the dural bag. * The signal for cysts due to traumas is a little stronger at the periphery or nerve root location. * The signal is more important for other causes: synovial cysts, dermoïdes or épidermoïdes cysts, teratomes. CT A computed tomography (CT) scan is another examination method often used for the diagnosis of<unk> . Unenhanced CT scans may show sacral erosion, asymmetric epidural fat distribution, and cystic masses that have the same density with CSF. CT Myelogram is minimally invasive, and could be employed when MRI cannot be performed on patient. Misdiagnosis The terms<unk> " or "sacral perineural cyst" refer to cystic lesions of the spinal meninges with innervation as well as nerve sheath dilatations with subarchnoid communication. While they were once thought to be a histopathological finding, they can be radiologically confirmed by specialized time lapsed MRI and CT imaging techniques showing subarchnoid communication from the nerve fibers in the cysts. They can also be surgically verified when the nerve fibers are visualized in the cystic sac. Often the cysts cause erosion from enlargement, damaging vertebrae and discs and can be misdiagnosed as primary stenosis or disc herniation. Classification<unk> s are considered Type II lesions, being defined as extradural meningeal cysts with nerve fibers. Nabors et al. classify Arachnoïd cysts into three types: * Type I : Extra-dural; no nerve roots or rootlets such as intra-sacral meningoceles; probably of congenital origin developing from the dural sac to which they are connected by a little collar. They are found at the point of exit of a dorsal nerve root from the dural sac. They are sometimes difficult to identify and can be "seen" as a type II cyst on imaging. These cysts are often associated with foramina enlargement and scalloping of the vertebrae. It is very important to distinguish them from sacral meningoceles going to the pelvic area; they are often associated with other congenital abnormalities (teratomes, dermoïdes, lipomes, and other abnormalities(uro-genital and ano-rectal)) * Type II: Extra-dural; nerve root present (such as<unk>  or perineural cysts). There are often not only one but multiple cysts, mostly found in the sacrum area. There are two types:<unk>  (perineural) cysts are located posteriorly to the root ganglion, with nerve fibres inside or nerve tissue in the walls; they are not communicating with the perineural arachnoid space. Type-II cysts are very small in the upper sacral area, but can be bigger (up to ) if found located in the lower part of the sacrum. The second variant of type-II cysts are called "meningeal diverticuli". They are located anteriorly to the nerve root ganglion, with nerves fibres inside and communicating with the subarachnoid space. * Type III: intra-dural; these are either congenital or caused by trauma; they are rarely associated with other abnormalities and rare in occurrence. About 75% can be found in the dorsal area. Most of the congenital type-III cysts can be found posteriorly to the spinal cord, as opposed to those caused by trauma which can be found anteriorly to the spinal cord.Post traumatic inflammation induces cavitation and cystic formation and leads to greater secondary CNS injury. Cellular migration causing these cyst cavities was observed both in vitro and in vivo and cavitation was observed to be prevented with the use of an anti-inflammatory. Further more migration inflammatory cells into traumatized tissue has been observed with inflammation.
Tarlov cyst
Tornwaldt cyst
Dentigerous cyst
Colloid cyst
Epidermoid cyst
Choristoma
Ganglion cyst
Gartner's duct cyst