Disc degeneration itself is a normal process in the elderly, beginning
as early in the twenties. There are 3 complications of degenerative disease of
the spinal column, making the normal process to a pathologic condition for
the individual : disc hemiation, spinal stenosis, and erosive osteochondritis.
MRI of erosive osteochondritis is characterized by disc vascularization and
bone marrow edema, both imaging features also found in infectious
spondylitis. Schmorl’s nodes can become vascularized like disc tissue in
erosive osteochondritis. There exist two types of Schmorl’s nodes: intraosseous
hemiation of nucleus pulposus tissue through the cartilaginous
endplate and hyaline cartilage proliferation originating in the trabecular bone
in erosive osteochondritis.
In disc degeneration, erosions of the adjacent vertebral endplates can be
present. However, the peripheral cortical bone of the vertebra is intact in disc
degeneration and frequently sclerosis can be found. Disc infections, on the
other hand, are frequently associated with destruction of the cortical borders
of the vertebra, the distinct dark rim of the endplate is then often focally not
visible on T1-weighted images. A gas density on CT is helpful to
distinguish degenerative disc vascularization in erosive osteochondritis from
spinal infection.
There is a high prevalence of degeneratively affected lumbar discs in MRI
examinations of people without back pain, and all degrees of disc
degeneration can be generally found in asymptomatic populations. However,
band-like vascularity in the disc space at the disco-vertebral junction is
associated with severe painful back syndromes . As bony changes and spurs at the endplates
are absent or only moderately developed segmental instability may play a causative role in
the development of disc vascularity. Secondary disc vascularization represents a clinical condition
which can be diagnosed easily only by means of contrast enhanced MRI.
Therefore, MRI protocols in the work-up of patients with painful back
syndromes should include the application of paramagnetic contrast medium
and sagittal imaging planes after contrast medium injection, when previous
CT studies do not show disc herniation or other significant findings to explain
the patients symptoms. Degenerative disc vascularization is an important
differential diagnosis to bacterial spondylitis. It can be causative for pain in
patients with post-discectomy syndrome.
Gadopentetate dimeglumine enhanced MR imaging examinations of the
lumbar and thoracic spine is indicated for Schmorl’s nodes,
vascularization of Schmorl’s nodes, and associated bone marrow edema.
Sagittal T2-weighted SE and T1-weighted enhanced and non-enhanced SE
images with and without fat suppression may be employed.
As the prevalence of Schmorl’s nodes decreases with age from youth to
adulthood, healing may be possible. Therefore, proliferative processes must
take place in the area of intraosseous herniation. At postmortem microscopic
examination, abnormal cartilage proliferation was noted in a 16 years old boy
with juvenile kyphosis in abnormal vertebrae and growth plates. In the
peripheral regions of the Schmorl’s nodes, where the vertebral bodies are in
contact with the node, growth of cartilaginous cells can occur. After
intraosseous herniation, ingrowth of vessels takes place from the adjacent
bone marrow into the periphery of the node and will progress to the center of
the node. It can be hypothesized that vascularization is requisite for cartilage
formation. Subsequent ossification contributes to sclerosis. By this
mechanism, sclerotic healing may be possible after ossification of the
cartilage.
Only very few Schmorl’s nodes become symptomatic. Vascularity may be a
normal attempt to heal intraosseous cartilaginous hernias and is not
necessarily accompanied by back pain. However, enhancing Schmorl’s nodes
were bigger and more often accompanied by bone marrow edema in patients
with back pain than in those without. Enhancing Schmorl’s nodes should not
be confused with tumor or infection.
Suggested reading:
1.
Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR Degenerative disc disease: asessment of changes in vertebral bony marrow with MR imaging.Radiology 1988; 166:193-199
2.Ross JS, Modic MT, Massaryk TJTears of the annulus fibrosus: assessment with Gd-DTPA-enhanced MR imaging.AJR 1990; 154:159-162
3.Hamanishi C, Kawabata T, Yosii T, Tanaka SSchmorl’s nodes on magnetic resonance imaging. Their incidence andclinical relevance. Spine 1994; 19:450-453
4.Resnick D, Niwayama GIntravertebral disk herniations: Cartilaginous (Schmorl’s) nodes.Radiology 1978; 126:57-65
5.Martel W, Seeger JF, Wicks JD, Washbum RLTraumatic lesions of the discovertebral junction in the lumbar spine.Am J Roentgenol 1976; 127:457-464 6. Dr Axel Staebler, M.D. MR in D/D of disc space pathology : Disc vascularization in acute degeneration , spondylitis,enhancing schmorls nodes
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