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.

Spine Anatomy

🧩 Key Structures

🎞️ Imaging Planes & Modalities

📏 Landmarks & Normal Values

🔀 Anatomical Variants

🧠 Pathology Correlation

💡 Pitfalls & Mimics