Imaging signs for preoperative diagnosis of dural ossification in patients with thoracic ossification of the ligamentum flavum: a blind, randomized diagnostic accuracy study

Background

Dural ossification (DO) is the leading cause of surgery-related dural tear in patients with ossification of the ligamentum flavum (OLF). An accurate preoperative diagnosis of DO is conducive to the selection of appropriate surgical methods. Although several imaging signs, such as Banner cloud sign (BCs), tram-track sign (TTs), and comma sign (Cs) have been proposed for the preoperative diagnosis of DO, their diagnostic value has not been well studied. The aim of this study was to explore the diagnostic value of BCs, TTs, and Cs, and provide evidence-based data for their clinical application.

Methods

This is a blind, randomized diagnostic study using retrospectively collected data from 102 consecutive patients who were diagnosed with OLF and underwent decompression surgery between January 2018 and June 2019. A total of 8 surgeons with different qualifications were recruited to read these imaging signs to identify the presence of DO. Surgical records were used as the reference standard. Sensitivity, specificity, and the area under the receiver operating characteristic (ROC) curve (AUC) were used to evaluate the diagnostic accuracy of each imaging sign and their different combinations.

Results

Of the 102 patients, 21 were diagnosed with DO. BCs had a significantly higher diagnostic accuracy than TTs and Cs, with the AUC of 0.704, 0.607, and 0.593, respectively. The specificity of BCs, Cs, TTs, and their combination in diagnosing DO was 91.5%, 92.1%, 68.3%, and 62.2%, respectively. In the combined diagnostic test, the results showed that the combined diagnosis accuracy of BCs and Cs was the highest, and the AUC was 0.738. The combination of BCs, Cs, and TTs increased the sensitivity of diagnosing DO (77.5%), but did not improve the diagnostic accuracy, and the AUC was 0.699.

Conclusions

BCs had higher diagnostic accuracy than TTs and Cs. BCs and Cs were highly specific for DO, whereas TTs could be confusing due to their non-specific presentations. The combination of BCs, TTs, and Cs improved the sensitivity of DO diagnosis, but not the specificity and accuracy.

Navigation-Assisted Micro-Window Excision of Thoracic Ossification of Ligamentum Flavum (Mishima Surgery) in Professional Baseball Pitchers: A Case Report and Technical Note

Background and Objectives: Thoracic ossification of the ligamentum flavum (OLF) often causes myelopathy and/or radiculopathy. The disease is frequently observed in East Asian populations. Although thoracic OLF in young athletes who have underwent decompression surgery has been reported, the removal of posterior spinal bony elements and ligamentous complex may often cause postoperative thoracolumbar instability. We established a novel surgical technique that preserves the posterior spinal elements, including the spinous processes, facet joints, and supraspinous and interspinous ligaments for thoracic OLF. This is the first case report to describe a navigation-assisted micro-window excision of thoracic OLF. Case: A 32-year-old male right-handed professional baseball pitcher with significant weakness and numbness in the left leg was referred to our hospital. The patient was diagnosed with thoracic OLF at T10-11 based on radiographic and magnetic resonance images in August 2022. After exposure of the left T10-11 laminae via a small unilateral incision, the location of T10-11 OLF was detected over the lamina by O-arm navigation. Then, the micro-window was made directly above the OLF using a navigated air drill, and the OLF was removed on the ipsilateral side. The contralateral side of OLF was also resected through the same micro-window, achieving complete spinal cord decompression. Results: The next day of the surgery, his leg weakness and numbness were significantly improved. Six weeks after the surgery, he started pitching. Three months after surgery, his symptoms had gone completely, and he pitched from the mound. Approximately 6 months after surgery, he successfully pitched in a professional baseball game. Conclusions: A navigation-assisted micro-window excision of thoracic OLF effectively preserved the spinal posterior bony elements and ligamentous complex. However, long-term clinical outcomes should be evaluated in future studies.

Ossification of the ligamentum flavum

Ossification of the ligamentum flavum (OLF or OYL: ossification of the yellow ligament) usually occurs at the lower thoracic level and causes various types of neurological symptoms in accordance with the compression level of the spinal cord, the nerve roots, the conus medullaris, and the cauda equina. Although the greatest compression level to the nerve tissues is thought to be the most pathognomonic one, it is difficult to diagnose it in some cases. The effectiveness of conservative treatment such as applying a corset is small. Early surgical treatment is strongly recommended for the patients with spastic gait, severe decrease of muscle power in the lower extremities, bladder-bowel disturbance, combined ossification of the posterior longitudinal ligament at the same level, and severe compression to the spinal cord due to thickly hypertrophied ossification. However, numbness of the lower extremities and spastic gait tend to remain even after surgery.