Extradural Lesion, T1 Hypointense

Bryson Borg, MD

DIFFERENTIAL DIAGNOSIS

Common

Disc Herniation
Osteophyte
Degenerated, Hypertrophic Ligamentum Flavum
Post-Operative Change, Normal
- Epidural Gas
- Metal Artifact
- Peridural Fibrosis
Facet Joint Synovial Cyst
Epidural Fluid Collections
- Pseudomeningocele
- Hematoma (Acute)
- Epidural Abscess
Epidural Metastatic Disease

Less Common

Neurofibroma
Arachnoid Cyst
Ossification of the Posterior Longitudinal Ligament (OPLL)

Rare but Important

Extramedullary Hematopoiesis
Extraosseous Component of a Hemangioma
Primary Bone Tumor
- Plasmacytoma
- Osteoblastoma
- Aneurysmal Bone Cyst
- Lymphoma/Leukemia
- Giant Cell Tumor
- Chordoma
- Osteosarcoma
- Chondrosarcoma
- Ewing Sarcoma
Tumoral Calcinosis
Extradural Arteriovenous Fistula

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Vast majority of “extradural lesions” relate to degeneration of intervertebral disc and dorsal elements
Impact of epidural mass lesion on spinal cord and nerve roots is best evaluated with MR
CT myelography alternative in patients who cannot undergo MR (e.g., pacemaker, spinal stimulator, etc.)
Contrast-enhanced sequences recommended for evaluation of infection, tumor, and post-operative spine

Helpful Clues for Common Diagnoses

Disc Herniation
- Most common ventral epidural lesion at level of disc space
- Extrusions extend away from disc space; sequestered fragments will be separated from disc level
- “Vacuum disc phenomenon” (nitrogen gas) in disc herniation can manifest as epidural signal void
Peridural Fibrosis
- Post-operative epidural scar/fibrosis in the surgical bed following discectomy, laminectomy
- Peridural scar/fibrosis enhances, recurrent disc herniation won’t enhance (distinction important as it influences decision to re-operate in cases of failed back surgery)
Facet Joint Synovial Cyst
- Circumscribed cystic lesion contiguous with facet joint
- Invariably associated with degenerative facet disease
- If marked enhancement or severe T2 hyperintensity in adjacent marrow, consider infected facet joint
Pseudomeningocele
- Epidural CSF collection at site of dural defect (post-surgical or post-traumatic)
Hematoma (Acute)
- Lobulated collection, typically extending over multiple vertebral segments
- Oxyhemoglobin and deoxyhemoglobin both isointense or hypointense on T1WI, becoming hyperintense in the subacute phase with the conversion to methemoglobin
- No or relatively mild peripheral enhancement
- May be spontaneous, due to coagulopathy, instrumentation, or trauma
Epidural Abscess
- Lobulated collection, typically extending over 1-2 vertebral segments
- Marked peripheral enhancement (abscess); epidural phlegmon may enhance more homogeneously
- Associated findings: Discitis/osteomyelitis, psoas abscess; patient typically has clinical signs of infection
Epidural Metastatic Disease
- Epidural extension from bony vertebral metastasis (renal cell, lung, lymphoma) or transforaminal extension from paraspinal tumor (neuroblastoma)

Helpful Clues for Less Common Diagnoses

Neurofibroma
- Can be completely extradural, can also be intradural or transdural
- Circumscribed margins, foraminal remodeling/enlargement
- Rapid enlargement or pain: Consider malignant degeneration
Arachnoid Cyst
- Typically dorsal to thecal sac, may extend laterally into neural foramina
- Follows CSF on all pulse sequences
- Chronic CSF pressure leads to remodeling and thinning of neural arch
Ossification of the Posterior Longitudinal Ligament (OPLL)
- Longitudinal structure in ventral epidural space: When large, often develops central T1 hyperintensity (marrow space)
- Cervical spine involvement more frequent than thoracic
- Can cause significant canal compromise