Adhesive Arachnoiditis 
and the
Foix-Alajouanine Syndrome
 

Modern understanding of the non-infectious neuropathologic entity "adhesive arachnoiditis" began in 1926 with the publication "La Myélite nécrotique subaiguë (Myélite central angiohypertrophique évolution progressive). Paraplégie amyotrophique lentement ascendan d'abord spasmodique, puis flasque"  by authors C. Foix and T. Alajounanine in the French Revue Neurologique (Paris), 2: 1-42).  What these authors described were cases which, in all probability, represented primary spinal cord arteriovenous malformations ("A-V Mals") producing recurrent subarachnoid hemorrhage.  The blood, and breakdown products, acting as a foreign body substance in the subarachnoid space produced local adhesive arachnoiditis.  The progression of this inflammation acted to not only infarct the spinal cord producing myelomalacia (and sometimes also creating cystic degeneration) but also the clinical symptoms of transverse myelitis and associated progressive loss of function in the lower body (i.e. paraplegia).  

Initially the Foix-Alajouanine pathologic entity was only an autopsy phenomenon.  This remained the case for many decades until the advent of high resolution MRI and associated modern spinal angiography.  This entity was mainly a medical curiosity until the midpart of the 20th century when some clinicians took a special interest in this entity.  David B. Clark, neurologist at the Johns Hopkins Hospital was one of these pioneers.  With better neuropathologic definition combined with more astute clinical observation the Foix-Alajouanine Syndrome (FAS) became part of a patient's differential diagnosis.

Even today the true incidence of the FAS is unknown and often under appreciated.  But, similar to many patients with post-oil myelography or ill-advised epidural steroid administration producing adhesive arachnoiditis, the neurologic insult is typically slowly progressive thus allowing acclimization by the nervous system.  This means that most individuals afflicted with this neuropathologic entity may be completely asymptomatic despite living with a "sword" hanging over their heads.  This balance is, however, often a tenuous one and can be upset by something as simple as a routine epidural anesthetic administered during childbirth.

FAS usually occurs in the thoracic spinal cord.  In the case shown above the pathology is in "watershed" zone of the thoracic spinal cord.  Because this spinal area has the most tenuous arterial blood supply it is most prone to injury when its vascular nourishment becomes impaired.  The remittent leakage of blood from the A-V malformation promotes slowly progressive local arachnoid fibrosis (adhesive arachnoiditis) which physically and physiologically "chokes" the spinal cord.  Normal arterial supply, venous return and the nutrient role of cerebrospinal fluid is slowly impaired.  As degeneration progresses in the spinal cord (myelomalacia) some of the neural tissue may liquefy producing a cavity  (also referred to as a cyst or syrinx) .  This is shown in the illustration by the color green.
This is a typical FAS shown on MRI.  Myelomalacia and local adhesive arachnoiditis are well demonstrated.  The red dot is over the area of secondary spinal cord degeneration. There is no cyst or syrinx seen in this case.  Because the changes are slow the patient may not experience any neurologic symptoms until some event produces a situation akin to "the straw that broke the camel's back."  This patient had only minor symptoms which were brought on by an event which, under normal circumstances, would not have been thought to be remarkable. 
A-V malformations represent congenital abnormalities of blood vessel development.  They are collections of abnormal and flimsy blood vessels which shunt blood directly from arteries (red dot) to veins (blue dot).  An actual A-V Mal is shown to the right. side below.  Because these blood vessels are so fragile they are likely to spontaneously bleed on an intermittent basis.
         
The subarachnoid space represents the "salum sanctorum" of the human body.  It abhors all foreign body substances.  Even the presence of injected air is considered to be a "foreign body."  Blood is definitely considered a foreign body (particularly the breakdown products of blood ).  Repeat exposure to foreign body substances in the subarachnoid space can initiate auto-immune amnestic reactions which may potentiate and magnify the ongoing inflammatory process.  In the case of FAS repeated insult secondary to reoccurring subarachnoid hemorrhage typically produces severe local arachnoid fibrosis, associated thrombosis of local blood vessels and progressive destruction of the spinal cord (as indicated above). 

Few clinicians appreciate that significant pathologic change can occur unaccompanied by clinical symptoms because of the body's remarkable ability to adjust to, and compensate for, slowly occurring insult .  This is particularly true of nervous system which does not respond well to acute change or acute insult  (i.e. sudden trauma, acute intracranial hemorrhage or acute rupture of an aneurysm).  The ability of the body to compensate is an important reason why most individual afflicted with adhesive arachnoiditis have few in the way of clinical symptoms.  This state is, however, a tenuous one, which can change dramatically with only minimal additional insult.

Because of the factors noted above the presentation and the nature of FAS, may, not unexpectedly, vary in individual cases. This  is due, in large part, to each individual's unique immnunologic response to the progression of acute and chronic inflammation.

We live in a medical era still characterized by lumbar puncture routinely utilized for the following purposes:

Initiation of spinal anesthesia.
Diagnostic taps to obtain spinal fluid samples, i.e. to rule out meningitis.

We also live in a medical era where frequent (inadvertent) lumbar punctures are performed by ill-advised blind-technique in cases of attempted epidural steroid administration or epidural anesthesia..
  
It is not unusual for patients to experience, as a complication of spinal tap, continued leakage of cerebro-spinal fluid producing postural headache, lightheadedness and inability to function due to these complaints.  The commonly employed treatment for this is a "blood patch."  Blood drawn from a vein is purposely injected into the supposed epidural space as a means of "patching" the leaking fluid.

Appropriate blood patches routinely introduce some blood into the subarachnoid space and inappropriate ones may introduce as much as 10-12cc of blood directly into the subarachnoid space.  How much blood, introduced how often, is necessary to create adhesive arachnoiditis?  This question has not yet been answered.  We only know at this point in time, that blood, and its breakdown products, can serve to create adhesive arachnoiditis and  the introduction of any foreign body substance (for any purpose) into the subarachnoid space is not a wonderful idea.
  Summary  
The diagnosis of the syndrome of Foix and Alajounanine (FAS) can occur only when the clinicians involved in the case know that this entity exists and also understand adhesive arachnoiditis as a pathologic entity.  Even at the start of the new millennium few radiologists (other than neuroradiologists) or clinicians possess this awareness.