Numbers
- Prevalence: 5% and 9% of the population
- Most are incidental
- These perineural cysts are common incidental findings on MR scans, usually but not exclusively located in the sacral canal, and often multiple.
Location
- Most located in S2 and S3 nerve roots.
- There is often remodelling of the sacrum.
Aetiology is unknown
- Is likely due to incomplete obliteration of the perineural space and CSF pulsatility.
Pathology
- Arise between the endo- and perineurium
- There are neural elements in the walls
- At the junction of the nerve root and the dorsal root ganglion (DRG)
- Encompassing or invading the nerve root with compressed nerve fibres forming part of the cyst wall.
- Potential communication with the subarachnoid space
- In comparison to meningeal diverticulae which occur proximal to the DRG and communicate freely with the subarachnoid space.
Radiology
- CT myelography
- Reveals late or no filling whereas other meningeal cysts fill early.
Clinical presentation
- Normally asymptomatic
- If symptomatic
- Rarely cysts can exert mass effect and present with pain which is exacerbated by Valsalva manoeuvres.
- Progressive sacral radicular pain, numbness, and paraesthesia, poorly localized sacral, perineal, or rectal pain,
- Bowel, bladder, and sexual dysfunction.
- Sacral insufficiency fractures have been described secondary to scalloping of the sacrum.
Management
Conservatively
- Pain management
- Most
Surgical treatment
- Indicated
- Clear problems with sphincter control or sexual function, caused by hydraulic pressure on the lower sacral rootlets.
- Rarely, surgery is considered in patients with progressive symptoms despite optimal pain management.
- Dissection is difficult as the cyst walls are extremely thin and adherent to these vital structures.
- Various techniques are described
- Fenestration
- Definitive management
- Sacral laminectomy, cyst fenestration/ resection and closure with a sacrospinalis myocutaneous flap.
- Intraoperative electrophysiology is recommended.
- Plication of the wall
- Placement of shunts
- Lumbo-peritoneal shunting
- Cysto-subarachnoid shunting
- Glue injection
- Trial aspiration may be carried out, prior to open surgery being planned.
- Anecdotal reports suggest CSF drainage provides temporary relief of symptoms.