Dorsal thoracic arachnoid web refers to a thickened band of arachnoid over the dorsal aspect of the cord. It usually causes a focal thoracic cord distortion with consequent neurological dysfunction.On imaging, it is characterised by a focal dorsal indentation and anterior displacement of the thoracic spinal cord leading to widening of the dorsal CSF space.
Magnetic Resonance Imaging (MRI) of the dorsal spine is a non invasive process used to scan the dorsal section of your spinal cord. It uses radio waves and high intensity magnetic fields to learn about the internal tissue structures of the dorsal spine. This scanning technique is used for various diagnostic as well as treatment purposes.
Clinical presentation
Due to the limited number of reported cases the incidence of this condition may well be under-recognised. The cases reported have a variety of signs and symptoms attributed to the band, including:
Radiographic features
Although direct visualisation of the web is beyond routine imaging able to visualise the thoracic cord (CT, CT myelography and MRI, the key feature which implies the diagnosis is a focal dorsal indentation and anterior displacement of the thoracic cord. This is best routinely imaged on MRI, with CT myelogram as an alternative.
MRI
The thoracic cord appears focally displaced anteriorly, with the widening of the dorsal CSF space. The outline of this enlarged CSF space on sagittal imaging has been likened to the silhouette of a surgical scalpel and has been termed the scalpel sign .
The thoracic cord above or below the band often demonstrates high T2 signal sometimes with a defined syrinx.