From the Guidelines
Orthopedic referral and MRI are indicated for suspected thecal sac compression when patients present with red flag symptoms suggesting cauda equina syndrome or severe neurological compromise, as recommended by the most recent guidelines 1. These red flags include new onset bowel or bladder dysfunction (particularly urinary retention or incontinence), saddle anesthesia (numbness in the perineal region), bilateral leg weakness or numbness, and severe or rapidly progressing neurological deficits.
- Emergency referral should be made when these symptoms are present, as they represent a potential surgical emergency requiring immediate decompression.
- MRI is the imaging modality of choice because it provides detailed visualization of soft tissues including the spinal cord, nerve roots, and surrounding structures, as stated in the ACR Appropriateness Criteria 1. Other indications for orthopedic referral and MRI include:
- Persistent radicular symptoms despite 4-6 weeks of conservative management
- Significant trauma with suspected spinal injury
- Suspected infection (discitis or epidural abscess)
- Concern for malignancy (especially in patients with a history of cancer, unexplained weight loss, or pain that worsens at night) The urgency of referral depends on symptom severity, with cauda equina syndrome requiring same-day evaluation, while less severe presentations may be managed with urgent rather than emergency referral, as suggested by the American College of Physicians and the American Pain Society 1. Early identification and treatment of thecal sac compression is critical to prevent permanent neurological damage, which can occur if decompression is delayed. In terms of imaging, MRI lumbar spine without IV contrast is the preferred initial study for evaluating suspected thecal sac compression, as it can accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency 1.
From the Research
Indications for Orthopedic Referral
- Patients with suspected malignant spinal cord compression (MSCC) should be referred for orthopedic evaluation, as early diagnosis and treatment can significantly impact outcomes 2
- Referral is also indicated for patients with symptoms of nerve root compression, such as severe back pain and radiating pain, especially if there is a history of malignancy 3
- Patients with low back pain and sciatica may also benefit from orthopedic referral, as they are more likely to have spinal canal stenosis, disc extrusion, and nerve root compression 4
Indications for MRI
- MRI is essential in the diagnosis and treatment of suspected MSCC, as it can confirm the presence and level of compression, and guide radiotherapy planning 2
- MRI is also indicated for patients with suspected lumbar epidural lipomatosis, as it can demonstrate the characteristic "Y" sign of thecal sac compression 5
- In patients with low back pain and sciatica, MRI can help identify the underlying cause of symptoms, such as spinal canal stenosis, disc herniation, and nerve root compression 4
- MRI may also be useful in guiding percutaneous procedures, such as aspiration of lumbar zygapophyseal joint synovial cysts, which can cause thecal sac compression 6
Thecal Sac Compression
- Thecal sac compression can occur due to various causes, including malignant spinal cord compression, lumbar epidural lipomatosis, and disc herniation 2, 5, 4
- The presence of thecal sac compression can be confirmed by MRI, which can also guide treatment planning 2, 5
- Patients with thecal sac compression may present with symptoms such as back pain, radiating pain, and neurological deficits, and should be referred for orthopedic evaluation and MRI 3, 4