← Back to BrowseHome
Musculoskeletal

Spine Anatomy

The spine is a segmented column of vertebrae, discs, ligaments, and facet joints enclosing the cord and nerve roots. MRI is the primary modality for the cord, discs, and marrow, while CT excels at cortical/bony detail and radiographs assess alignment. Systematic evaluation of alignment, bone, disc, canal, foramina, and cord is essential.

Key Structures

  • Vertebrae: 7 cervical, 12 thoracic, 5 lumbar, sacrum, coccyx; each with body, pedicles, laminae, transverse and spinous processes, and paired facets
  • Intervertebral discs: central nucleus pulposus (high T2) and peripheral annulus fibrosus (low T2); provide load distribution
  • Spinal canal and cord: cord ends at the conus medullaris (~L1-2) continuing as the cauda equina and filum terminale
  • Neural foramina: exit points bounded by pedicles, disc, and facet; contain the exiting nerve root and dorsal root ganglion
  • Facet (zygapophyseal) joints: paired synovial joints guiding motion and resisting shear
  • Ligaments: anterior and posterior longitudinal ligaments, ligamentum flavum, interspinous and supraspinous ligaments
  • Paraspinal muscles: erector spinae, multifidus, psoas, and quadratus lumborum supporting posture

Imaging Planes & Modalities

  • MRI sagittal and axial T1 and T2 are the core; STIR/fat-suppressed for marrow edema, infection, and trauma; post-contrast for tumor/infection/postoperative
  • Sagittal shows alignment, disc height, marrow, and cord; axial shows canal, foramina, discs, and facets at each level
  • CT for fractures, bony canal/foraminal stenosis, and postoperative hardware; excellent cortical detail
  • Radiographs (including flexion/extension) for alignment, instability, and spondylolisthesis
  • CT myelography when MRI is contraindicated or hardware degrades images
  • DWI and chemical-shift imaging help characterize marrow lesions and differentiate benign from malignant collapse

Landmarks & Normal Values

  • Conus medullaris typically terminates at the L1-L2 level; a lower termination suggests tethering
  • Normal lumbar canal AP diameter ~15 mm; <10-12 mm suggests stenosis
  • Sagittal disc signal (Pfirrmann grading) tracks degeneration; disc height loss and vacuum phenomenon indicate degeneration
  • Cervical cord AP diameter ~7-8 mm; thecal sac and cord effacement mark canal compromise
  • Vertebral body marrow normally brighter than the disc on T1 in adults (reversal suggests marrow infiltration)
  • Standard counting from the sacrum/C2 to assign levels; identify transitional anatomy carefully

Anatomical Variants

  • Transitional lumbosacral vertebrae (sacralization/lumbarization, Castellvi types) causing level-numbering errors
  • Limbus vertebra and Schmorl nodes as developmental/degenerative endplate variants
  • Conjoined/anomalous nerve roots that mimic a herniated disc
  • Spina bifida occulta and variant posterior element fusion
  • Cervical ribs and variant rib articulations at the thoracolumbar junction
  • Prominent epidural venous plexus and asymmetric ligamentum flavum

Pathology Correlation

  • Disc anatomy underlies protrusion versus extrusion and their relation to the traversing versus exiting nerve root
  • Facet arthropathy and ligamentum flavum hypertrophy are principal contributors to acquired central and lateral recess stenosis
  • Pars defects (spondylolysis) lead to spondylolisthesis and foraminal narrowing
  • Marrow signal patterns distinguish osteoporotic from malignant compression fractures and detect infiltration
  • Endplate/disc involvement with paraspinal collections characterizes discitis-osteomyelitis (contrasted with degenerative Modic changes)
  • Cord signal change on T2 correlates with myelopathy from compression, ischemia, or demyelination

Pitfalls & Mimics

  • Miscounting levels, especially with transitional anatomy; always correlate with a full sagittal localizer
  • Truncation/Gibbs artifact simulating a syrinx within the cord
  • CSF flow artifact in the canal mimicking intradural lesions or cord signal change
  • Hemangioma and focal fatty marrow mistaken for aggressive lesions (chemical shift helps)
  • Conjoined nerve roots misdiagnosed as disc herniation
  • Postoperative epidural fibrosis versus recurrent disc (contrast enhancement distinguishes them)

References

  • Ross, Moore. Diagnostic Imaging: Spine
  • Modic, Masaryk. Magnetic Resonance Imaging of the Spine
  • Fardon et al. Lumbar Disc Nomenclature (2.0), ASSR/ASNR/NASS
  • Netter. Atlas of Human Anatomy

⚕️ Educational reference — correlate with clinical context and confirm with a qualified radiologist.