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Surgical Management of Sacral
Arachnoid (Perineural) Cysts
with Autogenous Fat Grafts




This is the book cover of the classic 1971 publication by neurosurgeon Isadore Tarlov  on the subject of sacral nerve root cysts.  Most of these sacral (or lumbar) nerve root cysts were appreciated as being benign but, it became evident to clinicians that when these cysts involved the sacrum, they were capable of  becoming another important cause of the "Sciatic or Cauda Equina Syndrome."
When sacral or lumbar nerve root cysts increase in size and internal tension increases to the point where they actually erode adjacent bone they may require surgical intervention.  Present options for treatment vary.  Some advocate shunting these cysts to the abdomen or injecting them.  With respect to William of Occam's Razor the Editor is pleased to present a series of  examples of sacral nerve root (Tarlov)  cysts treated effectively by other means.
In order to fully appreciate the series of cases being presented one needs to recognize the fact that a typical "Tarlov Nerve Root Cyst"  is only an interesting finding on an MRI scan, and of no clinical significance .  An example of this is shown (incidental finding) on a routine MRI scan.  The red dot identifies the cyst.

Since Tarlov's pioneering work it has been recognized that the sometimes tenuous communication of these congenital cysts to the subarachnoid space (and the cerebrospinal fluid) can become partially or completely occluded. 
When partially occluded (usually due to the obstruction produced by proteinaceous material) a "ball valve" phenomenon can occur where fluid can enter and not leave the cyst.  In such a circumstance the tension within the cysts gradually increases producing erosion of surrounding bone and compression of local nerves.
These images show the case of a 48 year old female who was progressively incapacitated by leg pain and numbness.  In addition to a large sacral cyst eroding the sacrum the nerve roots (shown with a green dot) were clumped together from a focal and local adhesive arachnoiditis. 
The surgical view shows the opened cyst.  Autogenous, soft, fat grafts, were used to fill the defect.  Following decompression the patient experienced immediate, and continued relief of all symptoms.  The image to the left shows a post-operative CT scan with a label over the fat graft.
    
Immediately above is another case of a large sacral cyst (red dot) extending from the Lumbar 5 to Sacral 3 levels and eroding the surrounding bone.  The surgical view of the opened cyst reveals nerve roots adherent to the dura demonstrating a local adhesive arachnoiditis.  This patient was also successfully treated with an autogenous fat graft.
In the case shown above the sacral cyst was eroding the sacrum anteriorally as well as the vertebral lamina posteriorally.  The nerve compression was producing sciatica and radiculopathy.  The autogenous fat graft graft used to fill the void is shown.
  Other Patterns of Sacral Arachnoid Cysts   
           
 
              
            
        

The Editor's Experience, in treating clinically significant large sacral nerve root cysts over the years, has indicated that appropriate fat grafting techniques are a most effective surgical means of dealing with these unusual entities.  There do exist other treatment modalities but these sometimes create more problems than they solve. 
Shown here is this an example where a fibrin glue was injected into the cyst (red dot).  This glue did not alleviate the clinical problem.  The material is now adherent to the surrounding impaired nerves.  Further attempted surgical dissection runs a significant risk of producing associated permanent nerve injury.
Donlin Long at Johns Hopkins Hospital in Baltimore has begun an investigation on managing large sacral cysts with more advanced tissue adhesives.  Clearly, an effective percutaneous treatment would be preferable to any surgical approach.