Ligamentum flavum pathology (Ligamentum flavum)
Symmetrical thickening (hypertrophy) of the ligament frequently accompanies facet joint arthropathy. The process is driven by effusion, fibrous tissue proliferation, and calcification. The most vulnerable levels are L4–L5 and L3–L4, which inevitably leads to spinal canal stenosis.
Calcification of the periarticular zone is considered a typical sign of degeneration. The process is closely associated with a number of metabolic and systemic diseases:
- Rheumatologic disorders: ankylosing spondylitis, Forestier's disease (DISH).
- Metabolic disorders: hyperparathyroidism, renal failure, hemochromatosis.
- Calcium pyrophosphate dihydrate crystal deposition disease (pseudogout), which rarely affects the spine, but can cause pronounced inflammation and compression of structures in the cervical and lumbar regions.
To differentiate hypertrophy with calcifications from true ossification, sagittal CT reconstructions are used, while MRI is indispensable for assessing spinal cord involvement.
Ligament ossification (“Japanese disease”)
Progressive replacement of fibrous tissue with mature lamellar bone is known as “Japanese disease.”
For the ligamentum flavum, the process is most characteristic in the thoracic region in men younger than 50 years. The pathology starts from the facet joint capsule: cartilage proliferation triggers endochondral ossification. CT reveals bilateral radiopaque V-shaped lines along the vertebral arches growing medially into the epidural space. Clinically, this manifests as spastic paraparesis due to stenosis.
Involvement of the posterior longitudinal ligament (Ligamentum longitudinale posterius) is more common in the cervical region (at the C2–C5 level), also leading to severe stenosis, often requiring surgical decompression.
Cystic lesions
Cysts in the spinal canal area cause compression of nerve roots and the dural sac. They are differentiated by location and imaging findings:
- Ligamentum flavum cysts: extradural lesions. On CT, they show decreased density without marginal calcification. On MRI (T2-weighted images), they appear as hyperintense structures with a dark rim that enhances with contrast.
- Juxtafacet (ganglion) cysts: originate from the facet joint and obliterate the lateral recess. Unlike ligamentum flavum cysts, they may exhibit marginal calcification.
- Discogenic cysts: form directly from the intervertebral disc. On T1-weighted images with gadolinium, they demonstrate ring-like contrast enhancement.
Changes in arches and spinous processes
Excessive lumbar lordosis leads to abnormal contact between adjacent vertebrae. An intervertebral neoarthrosis of the arches forms, accompanied by sclerosis of the pedicles and laminae.
A specific condition is Baastrup's phenomenon (“kissing spinous processes”). Approximation, friction, and flattening of adjacent spinous processes occur. Constant periosteal irritation causes intense low back pain.
Complications of Baastrup's syndrome:
- Interspinous bursitis, which may communicate with the facet joints (responds well to steroid therapy).
- Formation of cysts penetrating into the epidural space through a cleft in the ligamentum flavum.
- Fatty degeneration of paraspinal muscles.
Briefly: answers to topical questions
What clinical symptoms does ossification of the ligamentum flavum cause besides spastic paraparesis?
Ossification of the thoracic ligamentum flavum causes spinal canal stenosis with or without myelopathy and/or radiculopathy. The clinical presentation may include progressive myelopathy leading to spastic paraparesis. This condition is described as “Japanese disease.” The lower third of the thoracic spine is most frequently affected; the risk group is predominantly men under 50 years of age.
What MRI sequences are necessary for a comprehensive differential diagnosis of spinal canal cysts?
For the differential diagnosis of the described spinal canal cysts, T1- and T2-weighted images, as well as T1-weighted images with gadolinium, are used.
- T2-weighted images: allow assessment of the hyperintense or moderately hyperintense signal of the cyst contents and a low-signal peripheral rim.
- T1-weighted images without contrast: allow assessment of the lesion signal; for juxtafacet and discogenic cysts, it is described as intermediate.
- T1-weighted images with gadolinium: may reveal peripheral contrast enhancement: peripheral enhancement is described for discogenic cysts, and the rim of the ligamentum flavum cyst enhances with contrast.
To differentiate cysts on MRI, remember: all are bright on T2, but their nature lies in their source. Juxtafacet cysts grow from the joint (and often calcify at the periphery), discogenic cysts from the disc, and ligamentum flavum cysts are tightly adjacent to the ligament itself.
Class and exam questions
What is the main CT difference between a ligamentum flavum cyst and a juxtafacet cyst?
Marginal calcification is not characteristic of ligamentum flavum cysts, whereas juxtafacet cysts frequently show peripheral calcification.
Which method is best to use for assessing ligament ossification?
CT is the gold standard: it clearly visualizes high-density lines of ossifications, their shape, and growth direction.
What is Baastrup's phenomenon?
This is the pathological approximation and friction of adjacent vertebral spinous processes, leading to their sclerosis, interspinous bursitis, and chronic low back pain.
What else to study on this topic
- Association of ligament degeneration with calcium pyrophosphate dihydrate crystal deposition disease (CPPD)
- Radiological criteria for Forestier's disease (DISH)
- MRI appearance of compressive myelopathy in spinal stenosis
- Simple laminectomy technique for ligamentum flavum cysts
- Formation of intervertebral neoarthrosis of the arches in the setting of hyperlordosis
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