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Arachnoiditis and Syringomyelia


Summary of Key Points

  • Syringomyelia is the formation of a fluid cavity within the spinal cord thought to result from a pathophysiological disruption of cerebrospinal fluid flow.

  • Arachnoiditis is the scaring of the arachnoid and pia resulting from multiple etiologies, most commonly infection, subarachnoid hemorrhage, or prior lumbar surgery.

  • Arachnoiditis is a well-known predisposing condition to syringomyelia.

  • Radicular and myelopathic symptoms of arachnoiditis typically progress despite nonsurgical treatments, including oral steroids or intrathecal steroid or hyaluronidase administration.

  • Surgical treatments of arachnoiditis, including repeat surgery, arachnoid lysis, and spinal cord stimulation, have also shown limited efficacy.

  • Syringomyelia associated with arachnoiditis typically progresses, and surgical intervention should be considered.

  • Operative treatments of syringomyelia include syringocavitary shunting, especially in the setting of excessive adhesions. In addition, adhesion lysis or duraplasty are other surgical options available to address this progressive and difficult-to-treat condition.

Syringomyelia can develop secondary to many pathological processes, such as Chiari malformations, spinal tumors, cysts, traumatic events, spinal deformities, and arachnoiditis. All of these conditions likely share a common pathophysiological disruption of cerebrospinal fluid (CSF) flow regulation. , This chapter focuses solely on syringomyelia derived from spinal arachnoiditis, excluding all other etiologies. Spinal adhesive arachnoiditis (SAA) has been associated most commonly with postsurgical inflammation, myelography, and infection. However, rare cases of idiopathic arachnoiditis, arachnoiditis after spinal subarachnoid hemorrhage, and familial arachnoiditis have also been reported. The first clinical presentation of syringomyelia was described by Portal in 1804. However, the first case of cervical spinal cord cavitation secondary to arachnoiditis was probably described in 1861 by Vulpian during necropsy. The first treatment was performed by Abbe and Coley in 1892 as drainage of a postmeningitic syrinx. Subsequently, more clinical cases attributed to postsyphilitic inflammation were published. The first association between degenerative disc disease and arachnoiditis is largely attributed to French in 1946. Although theories about the pathological process and causative agents have evolved, treatment of arachnoiditis has improved little over the years.

Epidemiology and Definition

SAA describes the scarring of pia and arachnoid membranes within the thecal sac. Although the pathophysiology remains elusive, thickening and adhesion of pia and arachnoid membranes are thought to arise secondarily from chronic inflammation. SAA can range from mild focal adhesions to severe scarring, as is seen with arachnoid ossificans. SAA has a predilection for the lumbar spine (up to 86% in some series), although this may simply reflect a bias in the literature due to the predominance of postmyelographic arachnoiditis. The diagnosis of arachnoiditis is confirmed radiographically by using magnetic resonance imaging (MRI) or, classically, myelography. The disease spectrum varies considerably from focal scarring or slight nerve root sheath changes to dense scarring throughout the spinal axis. Variations in defining the severity of arachnoiditis likely influence the reported incidence.

Risk factors are largely inherent in the varying underlying pathological processes that cause inflammation ( Box 94.1 ). Infection, subarachnoid hemorrhage, degenerative lumbar disease, history of myelography, prior lumbar anesthesia (i.e., intrathecal injection), prior spine surgery, transverse myelitis, prior baclofen pump insertion, and even intrathecal steroid injection have all been postulated as causative triggers leading to the development of SAA. Infectious etiologies include tuberculous meningitis, pyogenic infections, cysticercosis, candida tropicalis, chromoblastomycosis, cryptococcosis, listeriosis, and syphilis. , Some studies have suggested that the addition of blood products to contrast agents in myelography contributed to an increased risk of arachnoiditis. A familial form of arachnoiditis causing syringomyelia has been reported. The first report was of a Japanese family in 1974, and in 2000, Nagai et al. confirmed this by demonstrating vertical transmission of the disease over three generations. In addition, a Belgian family has been reported to have several cases of adhesive arachnoiditis with associated syringomyelia. No study has evaluated whether durotomies or synthetic sealants used to reinforce durotomy closures influence the risk of developing arachnoiditis.

Box 94.1
Etiologies of Arachnoiditis

  • Infection (bacteria, tuberculosis, cysticercosis, candidiasis, chromoblastomycosis, cryptococcosis, listeriosis, syphilis)

  • Subarachnoid hemorrhage

  • Myelography

  • Degenerative disc disease

  • Prior spine surgery/prior lumbar anesthesia

  • Transverse myelitis

  • Intrathecal steroid injection

  • Baclofen pump implantation

Several series have estimated the incidence of lumbar postmyelography arachnoiditis and symptomatic fibrosis to be near 1%. , However, published data on postmyelography arachnoiditis are limited by the use of varying contrast agents and a variable time to presentation. For example, one study reported the development of syringomyelia 44 years after myelography. Some series have found asymptomatic but radiographic signs of arachnoiditis in 16.5% to 35% of patients after myelography. However, other studies suggest a lower incidence in the absence of surgical intervention with myelography alone. Laitt and coworkers reported that 62.4% (68 of 109) of their patients had some degree of arachnoiditis after Myodil myelography, but 50 of their patients had prior lumbar surgery. The incidence was only 3% in patients with myelography alone, whereas arachnoiditis was present in 88% of people who had prior lumbar surgery and myelography. Ultimately, the use of oil-based contrast dyes, including Myodil and iophendylate, was discontinued in 1988, and these dyes have since been replaced with water-soluble contrast media, from which there have been no reported cases of arachnoiditis.

Failed back syndrome is an entity that is familiar to most spine surgeons. Some series have estimated that 6% to 16% of patients who have had prior spine surgery develop some degree of arachnoiditis contributing to persistent pain. Fitt and Stevens found 20% (26 of 129) of patients with a history of lumbar surgery to have some degree of arachnoiditis. Many studies have grouped epidural scarring and intradural pathology such as arachnoiditis together in their evaluations; therefore, the incidence of arachnoiditis alone is likely overreported in the literature. Burton reported that 11% of their failed back surgeries were attributed to arachnoiditis. Several studies have clearly associated an increased risk of arachnoiditis in patients who have undergone prior spine surgeries. , Certainly, it should be considered in postoperative patients with persistent or recurrent symptoms.

Pathophysiology of Arachnoiditis-Associated Syringomyelia

Arachnoiditis

Although no definitive pathological mechanism of arachnoiditis-associated syringomyelia has been elucidated thus far, several different theories have been postulated. One of these theories speculates that the blood products from myelography act as a catalyst, coating oil droplets in fibrin, thus emulsifying them and contributing to the development of severe arachnoiditis. Several other authors have proposed that an initial minor trauma or a local irritant such as contrast-myelography could serve as a causative agent that triggers an inflammatory response. , McLean and colleagues hypothesized that tethering of the spinal cord from arachnoiditis causes repeated compression along the spinal cord, with normal physiological movements leading to pathological injury. ,

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