Residency · Residency · Diagnostic Radiology

Spine Emergencies: Cord Compression and Cauda Equina Syndrome

Overview

Clinical Urgency

Spinal cord compression and cauda equina syndrome are time-critical diagnoses where delayed recognition leads to irreversible neurologic deficits. MRI is the modality of choice and should be performed urgently, within hours of clinical suspicion. When these findings are identified, the radiologist must communicate them immediately as critical results.

Anatomy Review

The spinal cord terminates at the conus medullaris, which typically sits at the L1-L2 level in adults. Compression above the conus produces upper motor neuron signs such as spasticity, hyperreflexia, and a positive Babinski sign. Compression below the conus, affecting the cauda equina nerve roots, produces lower motor neuron signs including flaccidity, areflexia, and bowel or bladder dysfunction.

Metastatic Epidural Spinal Cord Compression (MESCC)

Epidemiology and Pathogenesis

MESCC is the most common cause of malignant cord compression. The most frequent primary tumors responsible are lung, breast, prostate, and renal cell carcinoma, along with lymphoma and myeloma. Metastases reach the spine most commonly via hematogenous spread to the vertebral body, though direct extension from a paravertebral mass and drop metastases through the leptomeninges also occur. The thoracic spine is the most commonly affected region, accounting for roughly 60% of cases, followed by the lumbar spine at 25% and the cervical spine at 15%.

MRI Findings

On MRI, the hallmarks of MESCC include vertebral body signal abnormality with T1 hypointense marrow replacement (signal lower than adjacent normal marrow or muscle), variable T2 signal, and enhancement with contrast. An epidural soft tissue mass extending from the vertebral body into the epidural space is typically present, causing narrowing of the thecal sac, effacement of CSF around the cord, and cord deformity. When T2 hyperintensity is seen within the cord at or below the level of compression, it indicates myelopathy and may represent irreversible injury.

Bilsky Epidural Spinal Cord Compression Scale

The Bilsky scale grades the severity of epidural compression. Grade 0 indicates bone disease only without epidural involvement. Grade 1a shows epidural disease without thecal sac deformation, grade 1b shows thecal sac deformation without cord contact, and grade 1c shows thecal sac deformation with cord contact but no compression. Grade 2 indicates cord compression with visible CSF still present around the cord. Grade 3 represents cord compression without any visible surrounding CSF, indicating circumferential epidural disease.

Differentiating Pathologic from Benign Compression Fracture

Distinguishing pathologic from osteoporotic compression fractures on MRI is critical. Features favoring a pathologic fracture include a convex posterior cortex, an enhancing epidural soft tissue mass, involvement of the pedicles or posterior elements, diffuse T1 hypointense marrow replacement throughout the vertebral body, and signal abnormality in other vertebral bodies. Features favoring a benign osteoporotic fracture include a retropulsed fragment, a linear T1 low-signal fracture line, spared posterior elements, the fluid sign (a T2-bright cleft within the body), normal marrow signal in other vertebral bodies, and band-like enhancement.

Epidural Abscess

Clinical Context

Epidural abscess typically occurs in patients with risk factors such as intravenous drug use, diabetes, immunosuppression, prior spinal surgery or intervention, and bacteremia. Staphylococcus aureus is the most common causative organism. The abscess is often associated with discitis-osteomyelitis and most commonly occupies the posterior epidural space, arriving via hematogenous spread or direct extension.

MRI Findings

On MRI, the epidural collection appears T2 hyperintense and T1 iso-to-hypointense. Post-contrast images reveal peripheral rim enhancement representing the abscess wall. Restricted diffusion on DWI, appearing as bright signal within the abscess cavity, is a key distinguishing feature from other fluid collections. Associated discitis-osteomyelitis manifests as a T2 hyperintense disc, T1 hypointense endplates, endplate erosion, and a paraspinal phlegmon. Cord compression may be the presenting emergency.

Phlegmon vs. Abscess

A phlegmon demonstrates diffuse enhancement without a drainable fluid collection and may respond to antibiotics alone. An abscess, by contrast, shows a rim-enhancing fluid collection and may require surgical drainage, especially when causing cord compression.

Cauda Equina Syndrome (CES)

Clinical Presentation

CES presents with bilateral leg pain and weakness, saddle anesthesia, and bowel or bladder dysfunction, particularly urinary retention. Progressive bilateral lower extremity deficits are characteristic. CES is a surgical emergency, and decompression within 24-48 hours provides the best outcomes.

Causes

The most frequent cause is a large central disc herniation, most commonly at L4-5 or L5-S1. Other causes include intradural or epidural tumor, epidural abscess or hematoma, severe multilevel spinal stenosis, and post-surgical complications such as epidural hematoma or a retained disc fragment.

MRI Findings

MRI typically reveals a large central disc extrusion or sequestration compressing the cauda equina nerve roots. Clumping or displacement of the cauda equina is visible, and nerve root enhancement may be present, indicating inflammation or ischemia. The report should specify the level, the size of the herniation, the degree of thecal sac compression, and which nerve roots are involved.

Other Spine Emergencies

Epidural Hematoma

Epidural hematomas arise from a variety of causes, including post-procedural bleeding after spinal surgery, lumbar puncture, or epidural anesthesia, as well as anticoagulation, coagulopathy, vascular malformations, or spontaneous hemorrhage. MRI signal characteristics reflect the age of the blood: acute hematoma appears T1 isointense and T2 hypointense due to deoxyhemoglobin, while subacute hematoma shows T1 hyperintensity from methemoglobin. The posterior epidural space is the most common location, reflecting the venous plexus origin. Cord compression from an epidural hematoma may require emergent surgical evacuation.

Acute Transverse Myelitis

Acute transverse myelitis is an inflammatory myelopathy that is often post-infectious or associated with MS, NMOSD, or sarcoidosis. MRI shows a T2 hyperintense intramedullary lesion with variable enhancement and cord expansion. In MS, the lesion is short-segment (less than 2 vertebral segments), while in NMOSD it is long-segment (3 or more vertebral segments). It may present as acute paralysis mimicking cord compression.

Spinal Cord Infarction

Anterior spinal artery syndrome is the most common pattern of spinal cord infarction. Causes include aortic surgery or dissection, hypotension, atherosclerosis, and vertebral artery dissection. MRI demonstrates T2 hyperintensity in the anterior two-thirds of the cord with restricted diffusion on DWI. On axial images, bilateral ventral horn involvement produces the characteristic "owl's eye" or "snake eye" appearance. The dorsal columns are spared because they are supplied by the posterior spinal arteries.

Unstable Cervical Spine Fracture

Unstable cervical spine fractures are discussed in detail in Topic 70. The primary concern is the potential for cord injury if an unstable fracture is not immobilized. MRI evaluates ligamentous injury, cord compression or contusion, and disc herniation.

<image>A sagittal MRI panel showing metastatic epidural spinal cord compression. T1-weighted image showing a T1 hypointense vertebral body (marrow replacement) at T8 with an epidural soft tissue mass causing severe cord compression (Bilsky Grade 3). T2-weighted image showing the epidural mass and T2 hyperintensity within the compressed spinal cord (myelopathy signal). Post-contrast T1 fat-saturated image showing enhancement of the vertebral metastasis and epidural mass. An axial T2 image at the level of compression shows circumferential epidural disease with absent surrounding CSF and cord deformity. Arrows label the metastasis, epidural mass, cord compression, and cord signal change.</image>

<image>A sagittal and axial MRI panel showing an epidural abscess with associated discitis-osteomyelitis. Sagittal T2 image showing a T2 hyperintense disc at L3-4 with adjacent endplate edema and a posterior epidural collection extending over multiple levels. Sagittal post-contrast T1 fat-saturated image showing peripheral rim enhancement of the epidural abscess and enhancement of the infected disc and endplates. An axial DWI image at the level of the abscess shows restricted diffusion within the collection (bright signal). Arrows label the infected disc, eroded endplates, and rim-enhancing epidural abscess.</image>

<image>A sagittal T2-weighted MRI of the lumbar spine showing cauda equina syndrome caused by a large central disc extrusion at L4-5. The extruded disc material fills the central spinal canal and compresses the cauda equina nerve roots. An axial T2 image at L4-5 shows the disc fragment occupying greater than 75% of the spinal canal cross-section with displacement and compression of the nerve roots. The normal appearance of the cauda equina above and below the herniation is shown for comparison. Arrows indicate the disc fragment, compressed nerve roots, and a second axial image at a normal level showing freely floating nerve roots in CSF.</image>

Clinical Pearls

T2 hyperintensity within the spinal cord at the level of compression (myelopathy signal) indicates cord injury and may be irreversible, increasing the urgency for decompression. The distinction between pathologic and benign compression fracture on MRI is critical, with convex posterior cortex, epidural soft tissue mass, and pedicle involvement favoring malignancy. Epidural abscess shows peripheral rim enhancement and restricted diffusion on DWI, a combination that distinguishes it from epidural tumor or hematoma. Cauda equina syndrome from disc herniation is a surgical emergency requiring decompression within 24-48 hours, as delayed surgery is associated with permanent bowel and bladder dysfunction. Always image the entire spine when evaluating for metastatic cord compression, since multiple levels of disease are common and change surgical planning. Spinal cord infarction produces the characteristic "owl's eye" pattern on axial T2 images due to bilateral ventral horn involvement, and aortic pathology should always be considered as the underlying cause.

References

• Bilsky MH, et al. "Reliability Analysis of the Epidural Spinal Cord Compression Scale." Journal of Neurosurgery: Spine, 2010
• Patchell RA, et al. "Direct Decompressive Surgical Resection in the Treatment of Spinal Cord Compression." Lancet, 2005
• ACR Appropriateness Criteria: Myelopathy, 2018
• ACR Appropriateness Criteria: Back Pain with Red Flags, 2021

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