British Journal of Radiology (2006) 79, e67-e70
© 2006 British Institute of Radiology
doi: 10.1259/bjr/15381140
Unusual CT/MR features of putative ligamentum flavum ossification in a North African woman
I Jaffan, MD
1
B Abu-Serieh, MD
1
T Duprez, MD
2
G Cosnard, MD
2 and
C Raftopoulos, MD, PhD
1
Departments of 1Neurosurgery and 2Radiology, Saint-Luc Hospital, Université Catholique de Louvain, Brussels, Belgium
Correspondence: Christian Raftopoulos, Department of Neurosurgery, Saint Luc University Hospital, Université Catholique de Louvain, Avenue Hippocrate 10, 1200 Brussels, Belgium
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Abstract
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To display the unusual spinal CT and MR findings in a 48-year-old North African woman presenting with two adjacent intracanalar mineralized epidural outgrowths exhibiting mature bone organization with "cortical" and "trabecular" areas and pseudoarthritic changes at their interface. An unusual form of ligamentum flavum ossification (LFO) was speculated, of which features are discussed under the light of the available literature.
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Introduction
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Ligamentum flavum ossification (LFO) is an acquired degenerative disease mainly affecting 20% of Asian individuals older than 65 years [1–4]. To our knowledge, there are around 31 reported cases in the non-Asian population [3, 4]. The pathogenesis of this form of ectopic ossification remains under debate. Some authors have correlated it to systemic diseases such as diabetes mellitus and hypoparathyroidism [5, 6]. Others have correlated LFO to the elevated plasma concentration of fibronectin (a proactive protein in endochondral ossification), independently of the patients' endocrinological profiles [6]. On the other hand, some reports highlighted the importance of the mechanical factors in LFO development [7].
Classically, up to now, the radiological reports have shown LFO as intracanalar bone efflorescences made of cortical bone without spongy trabeculae [1–4]. No pseudoarthritic changes have been reported in this peculiar degenerative condition.
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Case report
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A white North African 48-year-old woman with type II (non insulin-dependant) diabetes mellitus presented with a 2-year history of recurrent episodes of low back pain and sciatica resolving with oral analgesic treatment. She now complained of sensory disturbances and motor weakness in both lower limbs, predominantly on the right side. Neurological examination revealed spastic paraparesis with brisk but symmetric osteotendinous reflexes. Impairment of light touch and pain perception was observed at and below the T10 dermatome. Strength testing was graded III/V in the right leg, and III+/V in the left one.
Spiral CT and MR images disclosed the presence of two epidural abnormal beak-like excrescences at the dorsal aspect of T9–T10, which dramatically impinged on the spinal cord (
Figures 1a and 2). Both abnormal outgrowths had remarkable mature bone organization with a peripheral margin of cortical bone, and a central area of trabecular bone, just as though they were supernumerary ossicles (Figure 1a,b).
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Figure 1. Spiral CT work-up. (a) Mid-sagittal reformatted image at the T9–T10 level showing intracanalar protrusion of two supernumerary bone outgrowths originating from the posterior elements. Observe cortical/spongy differentiation of the abnormal "bones", and pseudoarthritic changes at their interface, with focal cortical thickening and "degenerative" geode filled with air at the caudal aspect of the "pseudoarthrosis" (arrow). (b) Axial transverse reformatted image through the T9 level showing perfect cortical/spongy differentiation of abnormal ossicles together with calcifications of the ligamenta flava from which they are originating. (c) Axial transverse reformatted image through the T10 level showing pseudoarthritic thickening of the inferior border of the "pseudoarthosis", and the same air-filled geode as in Figure 1a (arrow). (d) Frontal reformatted image, well disclosing the pseudoarthritic interface between the two supernumerary ossicles. Their origin from posterior elements is obvious.
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Figure 2. MR work-up. (a) Mid-sagittal T2 weighted image showing spinal cord compression at the T9–T10 level, with abnormal hyperintensity within cord parenchyma. (b) Mid-sagittal T1 weighted image showing hypointensity on the margins of the "pseudoarthrosis" due to reactive hyperostosis (arrowheads), and fatty bone marrow within central areas of the protruded ossicles (arrows). Normal epidural fat is present up and below the level of the intracanalar abnormalities (double ball-arrowheads). Compare similar slice location on CT image (Figure 1a).
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Moreover, pseudoarthritic changes were present at their interface with irregular thickening of the cortical margin (Figure 1a,d) and with the unexpected presence of a "degenerative" air-filled geode (Figure 1c). MR examination demonstrated similar textural organization with the additional relevant feature of the presence of fatty bone marrow within the trabeculae of the spongy component (Figure 2).
The patient underwent selective posterior decompressive laminectomy at T9 and complete removal of the two bony outgrowths. The resected material was intimately adherent to the dura-mater. Histopathological examination of the specimens confirmed the presence of bone tissue, fibrocartilagineous tissue and fragments of ligamentum flavum without any tumorous component. The patient completely recovered within a few months after surgery.
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Discussion
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LFO is a well-featured entity in the radiological literature, appearing as bilateral bulging-mass made of ectopic compact bone [1–4]. The most frequently reported location of LFO is the lower third of the thoracic spine [2, 8]. A few reports have described anatomical variants involving either unilateral ossification, or unusual locations [9–12]. The observation reported herein highlighted two additional unreported features in the entity.
The first was the perfect cortical/spongy differentiation, leading to a pattern of mature but supernumerary bone-like outgrowths showing thin cortical margin and central spongy bone trabeculae containing fatty marrow. This was well seen on both CT and MR images in a synergistic way. The former showed an intracanalar well-differentiated "bone" with cortical and trabecular areas (Figure 1a,b) and the latter showed the presence of hyperintense material corresponding to fatty marrow within trabeculae on the unenhanced T1 weighted images (Figure 2).
The second peculiarity was the presence of pseudodegenerative changes at the interface between the two separated bony outgrowths, leading to a pseudoarthritic pattern of so-called neo-joint or neoarticulation. Changes included irregular thickening of the cortical margins at each side of contact areas and the presence of an air-filled pseudo-geode at the inferior border of the neo-joint (Figure 1a,d). The synergy between CT and MR information was also demonstrated for the degenerative changes since a thick hyperostotic/fibrotic border was seen as a hypointense marginal band-like area on T1 weighted MR images which extended far beyond the hyperdense thickening seen on CT reformats (Figure 2b). We consider that hyperdensity on CT images featured true reactive hyperostosis and that wider hypointensity on MR images represented the combination of hyperostosis together with fibrotic changes within the bone marrow adjacent to the pseudoarthritic interface.
The described features strongly suggest a very unusual appearance of LFO rather than alternative hypotheses such as calcified meningioma, developmental abnormality or ossified haematoma. Calcified meningioma may exceptionally mimic the LFO [13]. However, it seemed highly unlikely in the presence of well-differentiated bone outgrowth. Besides, the histopathological examination did not reveal any meningeal tissue. A developmental abnormality such as this has never been described, and the absence of corresponding defect within adjacent vertebrae lowers the probability of such hypothesis. Ossified haematomas are poorly probable in the absence of acute episode of traumatic cord compression and in the presence of such homogeneous and symmetrical ossification.
In conclusion, the herein reported case revealed two undescribed features in a putative case of LFO, i.e. the mature bone organization and the pseudoarthritic changes at the interface of two contiguous outgrowths.
Received for publication June 9, 2005.
Revision received August 17, 2005.
Accepted for publication September 5, 2005.
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References
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Abstract
Introduction
