Far Lateral Disc Herniation¶
Definition¶
A far lateral disc herniation (also called extraforaminal or extreme lateral herniation) is a disc herniation that occurs lateral to the neural foramen, beyond the lateral margin of the pedicle. It compresses the exiting nerve root (one level higher than a typical paracentral herniation at the same level) and accounts for approximately 5–10% of lumbar disc herniations.
Nerve Root Affected¶
The critical distinction from paracentral herniations:
| Level | Paracentral (Traversing Root) | Far Lateral (Exiting Root) |
|---|---|---|
| L3–L4 | L4 | L3 |
| L4–L5 | L5 | L4 |
| L5–S1 | S1 | L5 |
Imaging Findings¶
MRI¶
- Sagittal T1: the most important sequence — loss of the normal bright epidural fat around the exiting nerve root in the foramen
- Axial T2: disc material lateral to the pedicle margin; the traversing root in the central canal is typically unaffected
- Easy to miss if the radiologist only reviews axial images at the disc level — the far lateral fragment may be at or below the pedicle level
- Must scroll through sagittal images lateral to the thecal sac
CT¶
- Soft tissue mass lateral to the foramen, isodense to disc
- Best seen on axial images; may require sagittal reformats for correlation
Clinical Pearl
Far lateral herniations are the most commonly missed lumbar disc herniations on MRI because they lie outside the area of typical focus (the central canal and lateral recess). If a patient has clinical symptoms localizing to the exiting root (e.g., L4 radiculopathy with a normal-appearing L3–L4 and L4–L5 central canal), always look lateral to the foramen at the symptomatic level. The sagittal T1 sequence scrolled laterally is the key to diagnosis.
Key Points¶
- Far lateral herniations occur lateral to the foramen and compress the exiting root (one level higher)
- Account for 5–10% of lumbar herniations — commonly missed
- Sagittal T1 through the foramen is the key diagnostic sequence
- Must scroll axial images lateral to the pedicle to detect them
- Clinical presentation may be confusing if only the central canal is assessed
References¶
- Berra LV, Di Rita A, Longhitano F, Mailland E, Reganati P, Frati A, Santoro A. Far lateral lumbar disc herniation part 1: Imaging, neurophysiology and clinical features. World J Orthop. 2021;12(12):961-969. doi:10.5312/wjo.v12.i12.961. PMC8696601
- Lee IS, Kim HJ, Lee JS, Moon TY, Jeon UB. Extraforaminal with or without foraminal disk herniation: reliable MRI findings. AJR Am J Roentgenol. 2009;192(5):1392-1396. PubMed 19380567
- Moon KP, Suh KT, Lee JS. Reliability of MRI findings for symptomatic extraforaminal disc herniation in lumbar spine. Asian Spine J. 2009;3(1):16-20. PMC2852038
- Grenier N, Gréselle JF, Douws C, Vital JM, Sénégas J, Broussin J, Caillé JM. MR imaging of foraminal and extraforaminal lumbar disk herniations. J Comput Assist Tomogr. 1990;14(2):243-249. PubMed 2312853
- Smithuis R. Lumbar Disc Herniation and other causes of nerve compression. The Radiology Assistant. 2014. radiologyassistant.nl
- Foraminal lumbar disc herniation. Radiopaedia.org. radiopaedia.org/cases/foraminal-lumbar-disc-herniation