What is the significance of thecal sac flattening?

From the Guidelines

Flattening of the thecal sac is a medical emergency that requires urgent MRI assessment to accurately depict soft-tissue pathology and assess spinal canal patency, as recommended by a prospective cohort study by Bell et al 1. When evaluating suspected cauda equina syndrome, multifocal deficit, or progressive neurologic deficit, MRI lumbar spine without IV contrast is the preferred initial study due to its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency 1. Some key points to consider in the evaluation of flattening of the thecal sac include:

• The most common cause of cauda equina syndrome is lumbar disc herniation at the L4-L5 and L5-S1 levels 1
• Multifocal deficits and progressive neurologic deficits can be caused by a number of other noncompressive etiologies with some overlapping clinical features 1
• CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, but MRI is superior in soft-tissue contrast and characterizing the etiology of CES 1
• A recent retrospective review of 151 patients with clinically suspected CES showed that 50% thecal sac effacement on CT predicted significant spinal stenosis, and <50% thecal sac effacement reliably excluded cauda equina impingement, using MRI as the reference standard 1 Treatment options for flattening of the thecal sac vary based on the underlying cause and symptom severity, ranging from conservative approaches to surgical intervention, with early diagnosis and appropriate treatment being important to prevent permanent nerve damage and maintain spinal function.

From the Research

Flattening of the Thecal Sac

• The flattening of the thecal sac can be caused by various factors, including metastatic epidural spinal cord compression 2, lumbar spinal stenosis 3, and spinal cord herniation 4.
• Metastatic epidural spinal cord compression can cause compression of the thecal sac and the spinal cord by extradural metastatic mass, leading to pain and potentially irreversible loss of neurologic function 2.
• Lumbar spinal stenosis can result in impingement on the nerves of the cauda equina or on the thecal sac itself, leading to debilitating symptoms such as severe leg pain or restriction in the perimeter of ambulation 3.
• Spinal cord herniation is a relatively rare pathologic condition that is frequently misdiagnosed, characterized by the spontaneous herniation and tethering of the spinal cord through a ventral dural defect, which can cause flattening of the thecal sac 4.
• The diagnosis of thecal sac flattening can be difficult and involves a combination of radiological and clinical findings, including MRI and CT scans 5, 6.
• MRI is generally the preferred imaging modality for evaluating the thecal sac and spinal cord, while CT scans can be used to evaluate osseous integrity and detect significant spinal stenosis and cauda equina impingement 5.
• The treatment of thecal sac flattening depends on the underlying cause and can range from conservative measures such as physical therapy and core strengthening, to surgical decompression and repair of the dural defect 3, 4.