Arachnoid Web of the Spine: Optimal Detection and Management

Peer Reviewed

Surgery for arachnoid web of the spine (AWS) has a high success rate in symptomatic cases, according to findings from the largest systematic literature review reported online ahead of print in the Journal of Neurosurgery: Spine.

Arachnoid web of the spine is a relatively rare lesion of the spinal cord that is difficult to diagnose owing to subtle findings typically found on advanced imaging studies.

Sagittal and axial T2 MRI of spinal arachnoid webPreoperative sagittal and axial T2 MRIs demonstrate arachnoid web of the spine. In the sagittal view of the thoracic spine, the "scalpel sign" is seen. Imaging provided courtesy of Peyton L. Nisson, BS, Ibrahim Hussain, MD, Ali A. Baaj, MD, and SpineUniverse.com.

“We are seeing more patients with unexplained leg weakness and other neurological deficits, and thoracic lesions—such as arachnoid webs—are increasingly diagnosed,” said senior author Ali A. Baaj, MD, Associate Professor of Neurological Surgery, Co-Director, Spinal Deformity and Scoliosis Program, Weill Cornell Medical College, Cornell University, New York, NY.

Dr. Baaj and colleagues conducted this systematic review of 43 surgically treated patients with AWS “to provide a comprehensive review of the published literature on this topic to help other physicians who see these patients.”

Etiology of Spinal Arachnoid Web

The etiology of AWS is unknown. While previous studies have suggested that traumatic injury or history of spine surgery may be associated with an increased risk for AWS, these variables were found in only 16% of the patient population.

Syrinx was found in 67% of cases in this review. The most frequently reported symptoms included weakness (67%) and numbness and/or sensory loss (65%), both of which were primarily found in the lower extremities (81%). Incontinence was found in 19% of cases.

Signs and Symptoms of Arachnoid Web of the Spine

“Symptoms and signs of spinal cord compression should raise the suspicion of a lesion in the cervical or thoracic spine, like an AWS, Dr. Baaj said. “Any unexplained lower extremity symptoms (pain, numbness/tingling, or weakness) should alert the provider to obtain advanced imaging of the spine. This is especially true if the lumbar spine MRI, for example, does not account for these symptoms.”

“Many of these patients present with vague neuropathic symptoms and subtle radiological findings, often delaying or preventing definitive surgical management,” the researchers noted. In fact, nearly half of patients (47%) experienced symptoms for one year or longer before surgery was performed, with symptoms progressively worsening in over 35% of cases.

“Careful history taking and examination of the patient are paramount to avoid missing these findings,” Dr. Baaj added.

CT myelgraphy, thoracic sagittal and axial, spinal arachnoid webPreoperative sagittal and axial CT myelograms demonstrate arachnoid web of the spine. In the sagittal view of the thoracic spine, the "scalpel sign" is seen. Imaging provided courtesy of Peyton L. Nisson, BS, Ibrahim Hussain, MD, Ali A. Baaj, MD, and SpineUniverse.com.

Optimal Treatment of Arachnoid Web of the Spine

Patients most commonly underwent laminectomy with intradural excision of the arachnoid web (n=36; 86%). The remaining patients underwent shunt placement (n=3; 7%) and stent placement (n=3; 7%), which help bypass the cerebral spinal fluid (CSF) flow at the level of the AWS.

Nearly all patients (n=39; 91%) reported improvement in neurological symptoms following surgery. Two patients reported no change, and two patients developed new neurological deficits (leg numbness in one and paraplegia in one) after placement of a syringopleural shunt.

When Is Surgery Appropriate?

“In patients with no symptoms, in which AWS is incidentally discovered, surgery can be deferred and ‘watchful waiting’ is appropriate,” Dr. Baaj concluded. “If patients are demonstrating neurological deficits, even if mild, surgery should be considered to decompress the spinal cord.”

“Symptoms and signs of spinal cord compression should raise the suspicion of a lesion in the cervical or thoracic spine, like an AWS,” Dr. Baaj added. “Careful history taking and examination of the patient are paramount to avoid missing these findings.”

intraoperative pictures, surgery for arachnoid web of the spineIntraoperative photographs provided courtesy of Peyton L. Nisson, BS, Ibrahim Hussain, MD, Ali A. Baaj, MD, and SpineUniverse.com.

Commentary

Amer Khalil, MD
Director of Spine Surgery
Department of Neurological Surgery
University of California at Irvine
Irvine, CA

Arachnoid web of the spine is a very rare condition and often misdiagnosed. Patients usually present with progressive bilateral lower extremity weakness and numbness with gait difficulties that persist for a long duration without an accurate diagnosis. Physicians need to have a high level of suspicion if more common etiologies of these symptoms—such as degenerative diseases or tumors—are excluded. 

Thoracic spine MRI and CT myelogram are the tests of choice to identify AWS. Treatment usually involves laminectomy with excision of the arachnoid web. The success rate with surgery is very high with close to 90% of improvement in symptoms, as shown in this review.

This review demonstrates that AWS is a benign lesion that is similar to spinal arachnoid cysts and has similar symptoms. In the future, I hope to see research on cerebral spinal fluid flow dynamics to assess the CSF flow and pressure within the spinal cord and to determine how syrinx form in the spinal cord.

Disclosures
Dr. Baaj has no relevant disclosures.
Dr. Khalil has no relevant disclosures.

Updated on: 09/17/19
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