Multi-modality imaging evaluation of the dorsal arachnoid web

A case of neurosurgical treatment of thoracic dorsal arachnoid web

Background

Dorsal arachnoid webs constitute abnormal formations of arachnoid that tend to occur in the upper thoracic spine and can lead to spinal cord displacement. Patients typically present with back pain, sensory disturbances, and weakness. It may also obstruct the cerebrospinal fluid (CSF) flow, leading to syringomyelia. In magnetic resonance (MR) studies, the "scalpel sign" is a classical finding, and it may also be accompanied by syringomyelia attributed to CSF flow. Definitive surgical resection is the mainstay of treatment.

Case Description

A 31-year-old male presented with mild weakness in the right leg and diffuse lower extremity sensory changes. The MR showed the typical "scalpel sign" at the T7 level consistent with diagnosing a spinal arachnoid web. He underwent a T6-T8 laminotomy for lysis of the web and decompression of the thoracic cord. Postoperatively, his symptoms improved markedly.

Conclusion

Surgical resection is the treatment of choice when an arachnoid web is documented on an MR and correlates with the patient's clinical symptoms/signs.

Dorsal arachnoid web: A rare cause of syringomyelia and myelopathy

Dorsal arachnoidal webs are condensations of arachnoidal tissue densely adherent to the pial surface of the posterior aspect of the dorsal spinal cord. Infrequently described in literature they disrupt the flow of CSF in the spinal subarachnoid space leading to syringomyelia and myelopathy. While there are several theories on their origin, the "scalpel sign" on magnetic resonance imaging is considered to be pathognomonic of this condition. An illustrative case of a 58 year old man with syringomyelia and dorsal cord indentation who presented with spastic paraparesis, gait instability, parasthesias and bilateral non radicular upper limb pain that resolved following excision of the web is described to highlight the importance of considering this diagnosis when cases of so called "idiopathic" syringomyelia are encountered.

Imaging of intraspinal cystic lesions: A review

Several distinct conditions present as cystic or pseudocystic lesions within the spinal canal. Some of the most common spinal cystic lesions include spinal meningeal cysts, juxtafacet cysts, dermoid/epidermoid cysts, nerve sheath tumors, and syringohydromyelia. Clinical presentation is usually nonspecific and imaging characteristics are frequently overlapping, which may pose a challenging presurgical diagnosis. We provide a pictorial review of cystic intraspinal lesions and discuss the main imaging features that can aid the neuroradiologist in the differential diagnosis. First, we propose a categorization of the lesions according to their location as extradural, intradural extramedullary, and intramedullary. This is a crucial initial step in the diagnostic workup and surgical planning. Second, for each of these locations, we organize the lesions according to their etiology: congenital and developmental disorders, degenerative disorders, traumatic or postsurgical collections, infectious conditions, neoplastic lesions, and other miscellaneous disorders. Finally, we summarize the clinical highlights and MR features that provide important insights for the differential diagnosis. MR is the technique of choice in presurgical evaluation and postsurgery follow-up. It provides accurate lesion localization and characterization and, most of the times, it will allow a confident differential diagnosis. High-resolution three-dimensional T2-weighted sequences and diffusion-weighted imaging can provide important hints in specific cases. Signal correlation with T1-weighted and fat-saturated sequences allows to differentiate true cystic lesions from hemorrhage or fat tissue.