Discussion
Epidural metastasis affects 5-10% of patients with systemic cancers11. Breast cancer accounts for 15-20% of all metastatic epidural spinal cord compressions 12. There are three routes for a metastatic tumor to reach the epidural space: indirectly through vertebral column (85%), local invasion from paravertebral tissues (15%), and direct metastasis to epidural space (rare) 11,13. The first is the most common route for most tumors including breast cancer, in which the tumor grows in the highly vascular vertebral bone and then invades the epidural space. The second route is mostly seen with tumors like lymphoma and neuroblastoma. However, the third route, which is the case in our patient, is extremely rare. To the best of our knowledge, it is the first report of a direct epidural metastasis of breast cancer. Although due to the higher vasculature of thoracic spine, it is the most common site of epidural metastasis (60%), our case was in the lumbosacral region (10%)14.
DS can be a diagnostic challenge based on its shape, size, and place within the spinal canal 8,10. Our review of literature showed such challenge can exist in either of patterns: a DS mimicking a tumor, and a tumor simulating a DS. In both patterns, the clinical manifestations of disc herniation and the morphologic similarity between DS and tumor coexist. The former has been reported much more frequently in the literature, as we found 31 reports of DS resembling tumoral lesions in the extradural 6,8,10,15-27, intradural19,28-32, intramedullary 33, foraminal 34-39, and extraforaminal40-42 sites. Almost all the cases were in lower lumbar region with few cases in cervical and thoracic spine.
However, the second scenario, which is the case in our report, has been rarely reported 43,44. One was a 65-year-old male with chordoma presenting as DS in the epidural space posterior to L4 and extending into L4-L5 foramina 43. The other was a 41-year-old patients with a solitary fibrous tumor in the extradural space along L4 mimicking a DS 44. Both patients had worsening lumbar pain and radiculopathy and underwent laminectomy, discectomy, and lesion resection, which was proved to be a tumor after pathologic study. To our knowledge, no case of metastatic breast cancer mimicking a DS has been reported so far. In our case, the extradural lesion seemed to originate from L4-L5 disc and moved caudally along the posterior surface of L5 to cause stenosis at the level of L5 and L5-S1 foramina. Our case was a metastatic tumor, while the two former studies reported primary tumors. It should be kept in mind that in such settings, the history of a previous malignancy, although remote, can help the diagnosis tremendously.
MRI is the gold standard for assessing spinal intracanal lesions, as it is unparalleled in visualization of bone marrow, disco-ligamentous structures, and tumors 45,46. Generally, DS shows low intensity in T1- and high intensity (80%) in T2-weighted MRI. Although, in 20% of cases, it is isointense relative to the parent disc47. In our case, the lesion was isointense, peripherally extended around the disc, and occupied both foramina in axial T2 cuts highly mimicking a DS. The intracanal part was teardrop-shaped in the sagittal and polygonal in the axial cuts with clear distinction from the dural sac, not in favor of malignancy. Another misleading finding was the seemingly disrupted posterior annulus fibrosus of L4-L5 disc and the apparent origin of teardrop from it in sagittal T2 cuts (Figure 1a). However, what makes us suspect the nature of lesion as a DS was the unchanged disc height. As it should have been decreased, had such a large sequestrum have originated from it. In addition, gadolinium-enhanced MRI can help in differentiating the spinal tumors 45. However, we did not have time to do it, as the patient had a full blown CES.