Questionable Adequacy of Magnetic Resonance for the Detection of Ossification of the Posterior Longitudinal Ligament of the Cervical Spine

JJ Wong, OC Leung, MK Yuen

Hong Kong J Radiol 2011;14:78-83

Objective: To investigate the sensitivity of magnetic resonance for detecting cervical ossification of the posterior longitudinal ligament.

Methods: A retrospective review of 427 patients in whom cervical ossification of the posterior longitudinal ligament was reported on either magnetic resonance or computed tomography at a regional hospital between 2004 and 2010. Computed tomography was the gold standard for confirming the presence of such ossification. Those patients in whom computed tomography was performed before magnetic resonance were excluded to eliminate bias. Thickness, length, and type of ossification of the posterior longitudinal ligament were investigated to evaluate their influence on sensitivity.

Results: In all, 45 eligible patients were identified, of which 20 were correctly identified by magnetic resonance and 21 were incorrectly identified, yielding a sensitivity of 49%. In four patients, the ossification was incorrectly identified as positive (positive predictive value, 83%). The mean (± standard deviation) maximum ossification thickness in patients correctly identified was thicker than in those whose ossification was not noted (4.5 ± 2.1 mm vs. 3.2 ± 1.2 mm, p = 0.0189). On average more vertebrae were affected by ossification in those that were correctly identified compared to those that were not (3.0 ± 1.4 vs. 2.4 ± 1.0 vertebrae), but the difference was not statistically significant.

Conclusion: In our series, the sensitivity of magnetic resonance in detecting ossification of the posterior longitudinal ligament was only moderate; ossification cannot be excluded by such imaging. In our study, magnetic resonance yielded a sensitivity of 49%, which compared unfavourably with the two largest Japanese studies, but differences in disease morphology and frequency could account for such diversity. Although magnetic resonance is not the first-choice imaging modality to study ossification of the posterior longitudinal ligament, familiarisation with its subtle suggestive features is recommended, as it is increasingly used as the initial imaging modality to investigate myelopathy. In the event of unexplained spinal canal narrowing, a search for ossification of the posterior longitudinal ligament should be made first by plain X-ray, and then by computed tomography.

中文摘要

磁共振造影作為評估頸椎後縱韌帶骨化的影像學工具是否適當？

王佳、梁安祥、袁銘強

目的：探討使用磁共振造影評估頸椎後縱韌帶骨化的敏感度。

方法：回顧2004年至2010年間於一所分區醫院內，曾接受磁共振或電腦斷層造影（CT）發現頸椎後縱韌帶骨化的427名患者。CT是確診此症的黃金標準。為避免影響結果，本研究並不包括在磁共振 造影之先已接受CT的患者。我們亦探討了頸椎後縱韌帶骨化的厚度、長度及種類會否影響磁共振造 影的敏感度。

結果：共45位患者被納入研究範圍，其中20人的磁共振正確診斷頸椎後縱韌帶骨化的情況，另21人 的磁共振未能診斷骨化的情況，得出的敏感度為49%。其餘4人被誤診為頸椎後縱韌帶骨化（陽性預 測值為83%）。被正確診斷病情的患者中，骨化的最大平均（±標準差）厚度比那些未被診斷者大 （4.5 ± 2.1毫米比3.2 ± 1.2毫米，p = 0.0189），另外，他們受影響的椎骨數目亦相對較多（3.0 ± 1.4比 2.4 ± 1.0），但未達統計顯著性。

結論：本研究結果顯示磁共振造影對於評估頸椎後縱韌帶骨化的敏感度只有49%，屬中等，顯示此 技術未必可以排除病人骨化的可能性。本研究結果與另外兩個日本大型研究的結果不相乎，可能是 因為各研究對於頸椎後縱韌帶骨化的嚴重程度及種類，以至發病率並不相同。雖然磁共振並不是診 斷頸椎後縱韌帶骨化的第一線篩檢工具，醫生應熟習這症在磁共振影像上的細微表現，因為這技術 漸漸被廣泛應用在脊髓病的影像學上。如果遇上不能解釋的椎管狹窄病例，應先利用X射線檢查是 否有頸椎後縱韌帶骨化，繼而使用CT為病人確診。