Figure 3. Schematic diagram of the spinal MRI (created using Microsoft PowerPoint drawing function) illustrated the various spinal lesions distributed in different compartments within the spine. Intramedullary lesions are often associated with spinal cord expansion, while extramedullary lesions narrow the calibre of the spinal cord. Extramedullary lesions are further divided into those commonly found in the intradural extramedullary and extradural compartments by virtue of the state of the surrounding CSF and the angle between the lesions and cord/CSF space. Intradural extramedullary lesion compresses the spinal cord and forms an acute angle with the cord and gives the appearance of a “marble above the carpet”; the marble represents the tumor/lesion and the carpet resembles the dura mater. Besides, the CSF space is relatively preserved and there is a smooth interface between the cord and the tumor. Extradural lesions often efface the surrounding CSF space and form an obtuse angle with the CSF on sagittal T2w image. It gives the appearance of a “marble under the carpet”. AVM – arteriovenous malformation; AVF – arteriovenous fistula; CSF – cerebrospinal fluid; mets – metastases