Correlation of histopathological findings and magnetic resonance imaging in the spine of patients with ankylosing spondylitis

Abstract

Ankylosing spondylitis (AS) is a chronic inflammatory disease which affects primarily the sacroiliac joints and the spine. In patients with active disease, magnetic resonance imaging (MRI) of the spine shows areas of bone marrow edema, the histopathological equivalent of which is unknown. In this study we correlate inflammation in the spine of patients with AS as revealed by histological examination with bone marrow edema as detected by MRI. We have compared the histopathological findings of zygapophyseal joints from 8 patients with AS (age: 30 to 64, disease duration 7 to 33 years) undergoing spinal surgery with findings in MRI. For histopathological analysis, we quantified infiltrates of CD3+, CD4+ and CD8+ T cells as well as CD20+ B cells immunohistochemically. Bone marrow edema was evaluated in hematoxylin and eosin stained sections and quantified as the percentage of the bone marrow area involved. All patients with AS showed interstitial mononuclear cell infiltrates and various degrees of bone marrow edema (range from 10% to 60%) in histopathological analysis. However, in only three of eight patients histopathological inflammation and edema in the zygapophyseal joints correlated with bone marrow edema in zygapophyseal joints of the lumbar spine as detected by MRI. Interestingly, two of these patients showed the highest histological score for bone marrow edema (60%). This first study correlating histopathological changes in the spine of patients with AS with findings in MRI scans suggests that a substantial degree of bone marrow inflammation and edema is necessary to be detected by MRI.

Figure 1

Macroscopic and microscopic assessment of zygapophyseal joints. (a) Macroscopic picture of a zygapophyseal joint from a patient with ankylosing spondylitis (AS). (b) Hematoxylin and eosin staining of a zygapophyseal joint from an AS patient: weakly eosinophilic fluid accumulation in the bone marrow interstitium (red arrows) neighboring dense interstitial infiltrates of mononuclear cells (yellow arrows). The black arrow indicates fat vacuoles. (c) Immunohistochemical analysis of CD3⁺ T cells in the zygapophyseal joint of an AS patient: dense formations of CD3⁺ T cells (red stain, yellow arrow) neighboring bone marrow edema (red arrow). (d) Immunohistochemical analysis of CD3⁺ T cells in a zygapophyseal joint of a non-AS control with only few loosely distributed CD3⁺ T cells in the bone marrow without edema.

Figure 2

Positive correlation of bone marrow edema in histopathological assessment and magnetic resonance imaging. (a) Magnetic resonance imaging (T2 sequence) of a zygapophyseal joint with bone marrow edema (cyan arrow) (asterisk, vertebral body; open square, epidural space; plus signs, superior and inferior articular processes of the zygapophyseal joint; hash sign, processus spinosus). (b) Hematoxylin and eosin staining, revealing dense infiltrations of mononuclear cells (yellow arrow) and interstitial bone marrow edema (red arrow). (c) Immunohistochemical analysis of CD3⁺ T cells, revealing mononuclear cell aggregates in the same zygapophyseal joint (yellow arrow).

Figure 3

Negative correlation of bone marrow edema in histopathological assessment and magnetic resonance imaging. (a) Magnetic resonance imaging of zygapophyseal joints (cyan arrows) without detectable bone marrow edema (asterisk, vertebral body; open square, epidural space; plus signs, superior and inferior articular processes of the zygapophyseal joint; hash sign, processus spinosus). (b) Hematoxylin and eosin staining of the zygapophyseal joint, revealing numerous mononuclear cells in the bone marrow (yellow arrow) and a relatively small amount of edema (20%) in the bone marrow (red arrow). (c) Immunohistochemical analysis of CD3⁺ T cells (red arrow), showing dense infiltrates of CD3⁺ T cells (yellow arrow).