OPLL (Ossification of the Posterior Longitudinal Ligament) is heterotopic ossification of the posterior longitudinal ligament (PLL). The cervical region is most commonly affected (70%), with predilection for C2-C6 levels. It is significantly more common in Asian populations (2-4% Japan vs <0.5% Western populations). It can cause progressive myelopathy by narrowing the spinal canal. Four types have been described: segmental (isolated behind vertebral body), continuous (multilevel uninterrupted), mixed (segmental + continuous), and circumscribed (isolated behind disc level). CT is the gold standard for diagnosis — linear ossification along the PLL on the posterior vertebral surface is clearly demonstrated. MRI evaluates spinal cord compression and myelopathic signal changes. Surgical decompression is required when canal compromise exceeds 60%.
Age Range
40-75
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
In OPLL, fibroblasts within the posterior longitudinal ligament transform into osteoblast-like cells (metaplasia) under the influence of genetic and mechanical factors, initiating heterotopic bone formation. BMP-2 (Bone Morphogenetic Protein-2), TGF-beta, and COL6A1 genes have been implicated in this process. Ossification progresses through endochondral ossification within the ligament — a cartilage intermediate phase followed by bone formation. The resulting bony structure grows as a linear plaque along the PLL, narrowing the anterior wall of the spinal canal. On CT, this ossified plaque appears as a high-density (~500-1000 HU) linear structure on the posterior vertebral surface — creating marked contrast with surrounding low-density epidural fat and CSF. On MRI, the ossified ligament is hypointense on T1 and T2 because cortical bone has very low proton density. When spinal cord compression develops, T2 hyperintense myelopathic signal changes are seen within the cord — reflecting axonal damage and gliosis. Cervical predilection results from this region's dynamic loading (flexion-extension) applying the greatest mechanical stress to the PLL. High prevalence in Asian populations is explained by the frequency of COL6A1 and other genetic variants in these communities.
The signature finding of OPLL is a linear high-density ossification plaque on the posterior surface of the vertebral body protruding into the spinal canal on axial CT. This plaque represents heterotopic ossification of the PLL and is markedly thickened compared to normal PLL (thin linear structure on MRI). The distance between the ossified plaque and the spinal cord determines myelopathy risk.
Linear high-density ossification along the PLL on the posterior surface of the vertebral body. Appears as a thickened ossified plaque on the anterior wall of the spinal canal on axial images. Ossification thickness can range from a few mm to >10 mm. Sagittal reformat evaluates the craniocaudal extent and type (segmental/continuous/mixed/circumscribed) of ossification.
Report Sentence
Linear ossification ___ mm thick along the posterior longitudinal ligament between C___-C___ levels in the cervical spine is identified, consistent with OPLL (___ type); spinal canal anteroposterior diameter measures ___ mm.
Spinal cord compression and myelopathic signal changes: T2 hyperintense signal within the cord at the level of OPLL compression (myelomalacia/gliosis). T1 hypointense signal (in severe cases). Degree of cord compression and extent of myelopathic changes determine surgical decision and prognosis.
Report Sentence
Spinal cord compression secondary to OPLL at C___-C___ level and T2 hyperintense myelopathic signal change within the cord is identified; neurosurgery consultation is recommended.
Four types of OPLL classified on CT sagittal reformat: (1) Segmental — isolated behind one or few vertebral bodies, disc levels spared; (2) Continuous — uninterrupted ossification across multiple consecutive levels including disc levels; (3) Mixed — combination of segmental and continuous types; (4) Circumscribed — isolated behind disc level. Continuous type has the most severe canal narrowing and worst prognosis.
Report Sentence
OPLL is classified as ___ type, extending from C___ to C___; the most significant canal narrowing is at the C___ level.
The ossified PLL plaque shows hypointense signal on T1 and T2 on MRI (cortical bone — signal void). Creates contrast with surrounding hyperintense epidural fat (bright on T1). The size of ossification may appear smaller on MRI than actual — therefore comparison with CT is recommended.
Report Sentence
A hypointense ossified plaque on the anterior wall of the cervical spinal canal on MRI is identified, consistent with OPLL; CT correlation is recommended for precise size and type evaluation.
Spinal canal compromise ratio measurement: ratio of ossification thickness to spinal canal anteroposterior diameter. Below 40% usually asymptomatic, 40-60% increased myelopathy risk, above 60% very high myelopathy risk with strong surgical indication. Measured at the narrowest level on CT axial images.
Report Sentence
Spinal canal anteroposterior diameter narrowed to ___ mm due to OPLL at C___ level with canal compromise ratio calculated at ___%; this ratio supports the indication for surgical decompression.
Criteria
Ossification limited behind isolated one or few vertebral bodies, disc levels spared.
Distinct Features
Mildest form, usually asymptomatic. Minimal canal narrowing. Conservative follow-up may suffice.
Criteria
Uninterrupted ossification across multiple consecutive levels including disc levels.
Distinct Features
Most severe form. Long-segment canal narrowing. Highest myelopathy risk. Surgical planning more complex (long-segment decompression).
Criteria
Combination of segmental and continuous types.
Distinct Features
Prognosis and treatment determined by dominant component and degree of canal narrowing.
Criteria
Isolated ossification behind disc level.
Distinct Features
May be confused with disc herniation but ossified structure clearly separated on CT. Focal treatment possible.
Distinguishing Feature
DISH is anterior (ALL), OPLL is posterior (PLL); DISH thoracic dominant, OPLL cervical dominant; DISH rarely causes canal stenosis
Distinguishing Feature
AS has sacroiliitis + syndesmophytes + facet ankylosis, inflammatory process; OPLL has isolated PLL ossification, no sacroiliitis, non-inflammatory
Distinguishing Feature
Sacral insufficiency fracture has sacral ala edema, OPLL has cervical PLL ossification; completely different location and pathology
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
6-monthOPLL can lead to progressive spinal canal stenosis and cervical myelopathy. Surgical decompression (anterior corpectomy + fusion or posterior laminoplasty) is indicated when canal compromise >60% or symptomatic myelopathy is present. In the anterior approach, removal of the ossified PLL increases the risk of dural tear. In asymptomatic cases, progression is evaluated with 6-12 month MRI + CT follow-up. Cervical collar and trauma precautions are recommended for OPLL-diagnosed patients due to the risk of acute myelopathy after cervical trauma.
OPLL can lead to progressive spinal canal stenosis and cervical myelopathy. Surgical decompression (anterior corpectomy or posterior laminoplasty) is required when canal narrowing exceeds 60%. Risk of acute deterioration after cervical trauma exists. Regular neurological and radiological follow-up is recommended.