Schmorl Node

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Definition. A Schmorl node is a focal herniation of nucleus pulposus through a defect in the cartilaginous endplate and subchondral bone plate, into the cancellous bone of the vertebral body. It is an intravertebral disc herniation. The defect arises where the endplate is congenitally weak — the notochordal remnant, a vascular channel scar, or an area thinned by degeneration, osteoporosis, Paget disease or tumour.

Where it occurs. Lower thoracic and thoracolumbar spine predominantly (T8 to L2). Within the endplate it favours the posterior two-thirds, near the midline, and the inferior endplate slightly more than the superior. In Scheuermann disease the nodes cluster in the mid-to-lower thoracic spine with anterior wedging.

Confirming it is genuinely present.

1. There must be a defect in the endplate cortex — a break in the thin white line, continuous with the disc.
2. The lucency must be based on the endplate, not floating in the middle of the vertebral body.
3. There should be a corticated or sclerotic rim around the intraosseous portion in chronic lesions.
4. Disc height is preserved or only mildly reduced — the disc has moved up or down, not disappeared.
5. On sagittal MRI, the herniated material follows disc signal (T2 bright if hydrated, dark if degenerate) and is contiguous with the parent disc.

Saying it out loud in a viva. "There is a rounded, corticated indentation of the inferior endplate of L1 in the posterior third, with an interruption of the endplate cortex and preserved disc height at T12–L1. There is no vertebral body collapse, no paravertebral soft tissue and no involvement of the opposing endplate. The appearances are those of a Schmorl node — an intravertebral disc herniation. I would look for further nodes and for anterior wedging to determine whether this is isolated or part of Scheuermann disease."

Mimics — the false positives.

• Cupid's bow deformity — bilateral, symmetric parasagittal concavities of the inferior endplates of L3–L5; on axial imaging two paramedian depressions, not a single midline defect. Normal variant.
• Coronal cleft vertebra — infantile, vertical lucency splitting the body, resolves with growth.
• Limbus vertebra — anterosuperior corner ossicle from herniation beneath the ring apophysis; corticated cleft, sharp triangular fragment. Not acute trauma.
• Endplate erosion of discitis — irregular, ill-defined, both sides of the disc, disc height lost.
• Osteoporotic endplate impaction — diffuse endplate concavity ("fish vertebra"), not a focal corticated defect.
• Focal fat deposition / Modic type 2 — signal follows fat on all sequences, no cortical break.
• Intraosseous haemangioma abutting the endplate — polka-dot on axial CT, T1 bright with fat, no endplate defect.

Related pages. The disease that is multiple Schmorl nodes plus wedging: Scheuermann Kyphosis — and Paediatric Back Pain, where the adolescent with thoracic pain is assessed. The endplate and disc it comes from: Degenerative Disc Disease, Discogenic Back Pain, Lumbar Disc Herniation and Thoracic Disc Herniation — a Schmorl node is the same herniation taking a vertical route. The mimic that must not be missed: Pyogenic Discitis and Osteomyelitis — paired endplate destruction across ONE disc with height loss — plus Spinal Epidural Abscess and Tuberculosis of the Spine (Pott's). The other mimic, and the one situation where this diagnosis genuinely matters: Metastatic Bone Disease, Multiple Myeloma and Primary Bone Tumours of the Spine — a NEW endplate lesion in a patient with cancer — with Biopsy Principles and Techniques, Predicting Bone Tumour by Age and Periosteal Reaction Patterns. When multiple nodes are a systemic sign: Osteoporosis and Thoracolumbar Fractures for biconcave bodies, Sickle Cell Disease (Orthopaedic) for the H-shaped vertebra, Renal Osteodystrophy for the rugger-jersey spine, and Regional (Local) Osteopenia. The lesion it is confused with in the young: Limbus Vertebra and Apophyseal Fracture — anterior, beneath the ring apophysis, corticated, and not acute trauma. Assessing the patient rather than the film: Low Back Pain Assessment, Spondylolisthesis, Adult Spinal Deformity and Spinopelvic Parameters.

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The differential is twofold: (a) causes of a genuine Schmorl node — that is, what weakened the endplate; and (b) lesions that mimic an endplate-based lucency. Both are listed because in a viva you must exclude the sinister before attributing to degeneration.