Cervical Spine MRI Anatomy & Positioning

Cervical Spine MRI Anatomy & Positioning

Cervical Spine Anatomy & Biomechanics

The cervical spine forms the superior column of the axial skeleton, comprising seven vertebrae (C1–C7) that display distinct anatomical characteristics:

Atypical Cervical Vertebrae (C1 & C2)

• C1 (Atlas): Lacks a vertebral body and spinous process. Consists of anterior and posterior arches and paired lateral masses that articulate superiorly with the occipital condyles (atlanto-occipital joint, permitting nodding/flexion-extension) and inferiorly with C2.
• C2 (Axis): Features the prominent vertical dens (odontoid process) projecting superiorly from its vertebral body to articulate with the anterior arch of the atlas (atlanto-axial joint, permitting rotational "no" head motion). Trauma or rheumatoid pannus can cause atlanto-axial subluxation, posing an acute threat to the adjacent cervicomedullary junction.

Typical Cervical Vertebrae (C3–C7)

• Vertebral Bodies: Small, transversely elongated bodies with raised lateral uncinate processes (forming the joints of Luschka or uncovertebral joints, a frequent site of osteophytic spurring causing nerve root impingement).
• Bifid Spinous Processes: Vertebrae C2 through C6 typically possess notched or bifid spinous processes.
• C7 (Vertebra Prominens): Characterized by a long, non-bifid, prominent spinous process easily palpable at the base of the neck posteriorly.
• Transverse Foramina: A hallmark feature present in all cervical transverse processes. The vertebral arteries traverse the transverse foramina of C6 through C1 before entering the skull through the foramen magnum to form the basilar artery.

Neural & Soft-Tissue Structures

• Cervical Spinal Cord: The cord is widest in the cervical region due to the cervical enlargement (giving rise to the brachial plexus supplying the upper limbs).
• Thecal Sac & Subarachnoid Space: Surrounds the cord, filled with bright T2 cerebrospinal fluid (CSF), providing an intrinsic "myelographic effect" on T2-weighted fast spin-echo (FSE) images.
• Exiting Nerve Roots (C1–C8): Note an essential neuroanatomical rule: There are 8 pairs of cervical spinal nerves for 7 cervical vertebrae. Nerve roots C1 through C7 exit above their numerically corresponding vertebrae (e.g., C5 nerve root exits through the C4–C5 neural foramen). The C8 nerve root exits below the C7 vertebra (between C7 and T1).
• Normal Curvature (Cervical Lordosis): The cervical spine exhibits an anteriorly convex curvature (cervical lordosis). Muscle spasm, trauma, or degenerative disc disease frequently causes straightening or reversal (kyphosis) of this curvature.

Patient Positioning & Coil Selection

Coil Architecture & Setup

• Cervical Spine Coils: Specialized phased-array cervical spine coils consist of a contoured posterior base embedded in or attached to the table, paired with a contoured anterior neck array that locks securely over the throat.
• Integrated Spine Matrix: Modern scanners utilize posterior spine matrix elements integrated directly beneath the table couch pad, combined with an anterior multi-channel neck or neurovascular coil overlay.
• Patient Orientation: The patient is positioned head-first supine (HFS) along the midline of the scanner couch.

Preserving Normal Cervical Lordosis

• Contoured Foam Support: A specially designed, radiolucent foam wedge or contoured cervical roll must be placed beneath the nape of the neck. This provides comfortable structural support that maintains the patient's natural lordosis without creating air gaps between the neck and the posterior coil elements.
• Avoiding Position Extremes:
  • Hyper-extension: Tipping the chin too far backward stretches the anterior neck tissues, narrows the neural foramina, and increases patient swallowing discomfort.
  • Hyper-flexion: Tucking the chin tightly toward the chest flattens the lordosis, displaces anterior neck coil elements away from the skin, and can compress the anterior subarachnoid space.
  • Target Alignment: The patient's face should be parallel to the ceiling, with the neck in a neutral, relaxed position.

Shoulders, Pain and Trauma Precautions

Support the shoulders comfortably and keep the neck in a tolerated neutral position unless the clinical protocol specifies otherwise. Do not use forceful shoulder traction to imitate an x-ray positioning maneuver. MRI does not require depressing the shoulders to eliminate radiographic bony superimposition. Coil coverage, patient size and motion still matter. For suspected instability, preserve prescribed immobilization and obtain clinical direction before moving the neck or removing a collar.

Anatomical Landmarking & Laser Crosshair Centering

Precise laser crosshair alignment ensures the cervical canal resides at the scanner magnetic isocenter:

Cervical Spine Landmarking:
Supine Head-First ➔ Position Lordosis Pad ➔ Drop Shoulders ➔ Anterior Neck Coil Latched
➔ Sagittal Laser to Midline Trachea ➔ Transverse Laser to Thyroid Cartilage (C4-C5)
➔ Zero Table ➔ Advance to Magnetic Isocenter

• Primary Landmark: The thyroid cartilage (Adam's apple). This prominent laryngeal cartilaginous structure corresponds internally to the C4–C5 intervertebral disc space, placing the mid-cervical spine directly at the isocenter.
• Alternative Landmarks:
  • Cricoid Cartilage: Located approximately 1.5–2.0 cm inferior to the thyroid cartilage, corresponding to the C6 level.
  • Angle of the Mandible (Gonion): Corresponds internally to the C2–C3 level.
  • Sternal Notch: Used as an inferior reference mark for lower cervical / upper thoracic studies.
• Laser Alignment:
  • Sagittal Laser: Aligned strictly along the anterior midline of the neck (trachea, chin tip).
  • Transverse Laser: Centered over the prominence of the thyroid cartilage.
  • Coronal / Vertical Laser: Aligned to the mid-coronal plane of the neck (passing through the external auditory meatus and mid-vertebral bodies).

Artifact Mitigation: Swallowing & Vascular Pulsation

• Swallowing Motion: The esophagus and larynx sit immediately anterior to the cervical spine. Swallowing or coughing causes abrupt anterior-to-posterior and craniocaudal tissue displacement, propagating severe phase-encoding ghosting across the spinal cord.
  • Mitigation: Apply an anterior saturation band (spatial presaturation band) across the pharynx, larynx, and esophagus anterior to the vertebral bodies. Instruct the patient to swallow between sequences rather than during active scanning noise.
• CSF Flow Pulsatility: Pulsatile systolic CSF motion within the thecal sac creates flow voids and ghosting on T2-weighted images.
  • Mitigation: Utilize flow compensation (gradient moment nulling / GMN) and specialized flip-angle sequences.

Positioning Scenario

A trauma patient arrives wearing a cervical collar. Do not remove it or pull the shoulders to improve the appearance of the setup. Check the collar's MR labeling with the technologist, maintain prescribed spinal precautions and obtain an authorized positioning plan. Report new weakness, pain or breathing difficulty immediately.