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subarachnoid space of spinal cord

The subarachnoid space (SAS) is the fluid-filled interval between the arachnoid mater and pia mater surrounding the spinal cord. It contains cerebrospinal fluid (CSF), which cushions and protects the spinal cord, provides a medium for nutrient exchange, and facilitates waste removal. The SAS also contains spinal nerve roots, arteries, and veins, and extends from the foramen magnum down to the level of the second sacral vertebra, gradually narrowing in the lumbar cistern.

The SAS communicates freely with the cranial subarachnoid space, allowing CSF flow between brain and spinal cord. It plays a vital role in spinal cord protection, shock absorption, and pressure regulation. Enlargement, compression, or obstruction of the SAS may result from arachnoid cysts, hemorrhage, tumors, or spinal stenosis, making accurate imaging crucial.

Function

  • Cushions and protects the spinal cord and nerve roots

  • Circulates cerebrospinal fluid for nutrient delivery and waste removal

  • Facilitates pressure regulation and shock absorption along the spinal cord

  • Provides space for spinal nerve roots, blood vessels, and CSF sampling (e.g., lumbar puncture)

  • Important in the pathophysiology of arachnoid cysts, hemorrhage, infection, and tumors

Synonyms

  • Spinal subarachnoid space

  • SAS

  • Cerebrospinal fluid space

MRI Appearance

T1-weighted images:

  • SAS appears as a low signal intensity space surrounding the intermediate signal spinal cord

  • CSF is dark to intermediate signal depending on flow and sequence

  • Pathological contents (e.g., blood, pus, or proteinaceous material) may increase signal intensity

T2-weighted images:

  • CSF in the SAS is hyperintense (bright), sharply outlining the spinal cord and nerve roots

  • Flow artifacts may create signal voids in areas of rapid CSF motion

  • Useful for identifying arachnoid cysts, syrinxes, spinal cord compression, or hemorrhage

STIR (Short Tau Inversion Recovery):

  • Normal SAS is hyperintense (bright) signal in fat-suppressed sequences

  • Detects pathological fluid collections, edema, or inflammatory changes

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal SAS does not enhance

  • Enhancement occurs with arachnoiditis, tumors, or infectious processes, highlighting abnormal leptomeningeal involvement

CT Appearance:

  • SAS is indirectly visualized as the CSF-filled space surrounding the spinal cord

  • Appears hypodense relative to the spinal cord and vertebrae

  • Contrast-enhanced CT myelography delineates the SAS, showing nerve root sleeves, blockages, or CSF leaks

  • Excellent for evaluating arachnoid cysts, subarachnoid hemorrhage, or CSF flow obstructions

MRI images

subarachnoid space of spinal cord axial c spine mri

MRI images

subarachnoid space of spinal cord sag c spine mri

MRI images

subarachnoid space of spinal cord sag l spine mri