Normal Lateral Recess Height Size on CT and MRI
The lateral recess is a bony channel in the lumbar spine, bounded anteriorly by the vertebral body, posteriorly by the superior articular facet, and laterally by the pedicle, through which exiting nerve roots travel. Accurate measurement of lateral recess height is essential for identifying lateral recess stenosis, a common cause of radiculopathy in patients with low back pain. CT and MRI both provide reliable assessment and guide surgical planning when stenosis is suspected.
Normal Reference Values
| Measurement |
|---|
| >2 mm |
Clinical Significance
A lateral recess height greater than 2 mm is considered normal. Values of 3–4 mm are regarded as borderline, while measurements at or below 2 mm are consistent with stenosis and may correlate with nerve root compression and radicular symptoms. Lateral recess stenosis most commonly affects the L4–L5 and L5–S1 levels, where degenerative changes are most prevalent.
Clinicians should correlate imaging findings with dermatomal pain patterns, neurological deficits, and response to conservative therapy. It is important to note that symptom severity does not always correlate linearly with measured recess height — symptomatic stenosis may occur at borderline dimensions in some patients.
- Degenerative facet hypertrophy
- Ligamentum flavum hypertrophy
- Osteophyte formation / spondylosis
- Synovial cyst from facet joint
- Disc herniation encroaching on lateral recess
Reference: Chapman MW, Madison M. Operative orthopaedics. Lippincott Williams & Wilkins. (1993).
Imaging Notes
On CT, lateral recess height is measured in the axial plane at the level of the superior endplate, from the posterior surface of the vertebral body to the anterior margin of the superior articular facet. Bone windows optimize visualization of the bony boundaries. MRI assessment is performed on axial T1- or T2-weighted sequences; T2 imaging highlights nerve root compression within the recess by demonstrating effacement of the surrounding high-signal CSF and epidural fat.
Consistent slice angulation parallel to the endplate is critical to avoid oblique measurements that may artificially alter the apparent recess height. MRI has the advantage of directly visualizing soft-tissue contributors such as ligamentum flavum and disc material, whereas CT better delineates osteophytic bony narrowing.