Extradural vs Intradural Classification¶
Overview¶
Spinal tumors are classified by their anatomical compartment relative to the dura mater and spinal cord. This three-compartment system is the most clinically useful framework because the location of a tumor strongly predicts its histological diagnosis, and MRI can reliably determine the compartment of origin in most cases.
The Three Compartments¶
Extradural (Epidural)¶
Tumors arising outside the dura, typically from the vertebral body, posterior elements, or epidural soft tissues.
Most common tumors:
- Metastases (most common overall)
- Multiple myeloma / plasmacytoma
- Lymphoma
- Vertebral hemangioma
- Chordoma
- Primary bone tumors (giant cell tumor, osteosarcoma, chondrosarcoma, osteoid osteoma/osteoblastoma)
- Aneurysmal bone cyst
MRI features: The tumor is centered in bone or epidural space. The dura is displaced inward, compressing the thecal sac. An epidural fat plane may be obliterated. The spinal cord is compressed from outside.
Intradural Extramedullary¶
Tumors arising within the dura but outside the spinal cord, typically from the meninges, nerve roots, or leptomeninges.
Most common tumors:
- Schwannoma (most common)
- Meningioma
- Neurofibroma
- Drop metastases (leptomeningeal carcinomatosis)
MRI features: The tumor is within the thecal sac but separate from the cord. The cord is displaced to one side. A CSF "cap" sign is present — a crescent of CSF is visible between the tumor and the cord, and between the tumor and the dura. The dural margin may show a "dural tail" (meningioma). The tumor may widen the neural foramen (dumbbell lesion).
Intramedullary¶
Tumors arising within the substance of the spinal cord itself.
Most common tumors:
- Ependymoma (most common in adults)
- Astrocytoma (most common in children)
- Hemangioblastoma
- Spinal cord metastases (rare)
- Lipoma
MRI features: The spinal cord is expanded. The tumor is centered within the cord. No CSF cap between the tumor and the cord surface. Surrounding edema and/or syrinx may be present. Enhancement pattern varies by tumor type.
MRI Differentiation¶
| Feature | Extradural | Intradural Extramedullary | Intramedullary |
|---|---|---|---|
| Cord | Compressed from outside | Displaced to one side | Expanded |
| CSF cap | Absent | Present (between tumor and cord) | Absent |
| Dura | Displaced inward | Tumor within dura | Intact, cord expanded |
| Bone involvement | Common | Rare | Absent |
| Enhancement | Variable | Usually homogeneous | Variable |
Clinical Pearl
The CSF cap sign is the single most useful MRI feature for distinguishing intradural extramedullary from intramedullary tumors. If you can see a rim of bright CSF on T2 between the tumor and the cord surface, the tumor is extramedullary. If the cord is expanded and no CSF separates tumor from cord, it is intramedullary.
Key Points¶
- Three compartments: extradural, intradural extramedullary, and intramedullary
- Metastases are the most common extradural tumor
- Schwannoma is the most common intradural extramedullary tumor
- Ependymoma is the most common intramedullary tumor in adults
- The CSF cap sign distinguishes extramedullary from intramedullary lesions
- MRI with contrast is the definitive imaging study for compartment localization
References¶
- Koeller KK, Shih RY. Intradural extramedullary spinal neoplasms: radiologic-pathologic correlation. RadioGraphics. 2019;39(2):468-490. Available from: https://pubmed.ncbi.nlm.nih.gov/30844353/
- Shih RY, Koeller KK. Intramedullary masses of the spinal cord: radiologic-pathologic correlation. RadioGraphics. 2020;40(4):1125-1145. Available from: https://pubmed.ncbi.nlm.nih.gov/32530746/
- Abul-Kasim K, Thurnher MM, McKeever P, Sundgren PC. Intradural spinal tumors: current classification and MRI features. Neuroradiology. 2008;50(4):301-314. Available from: https://pubmed.ncbi.nlm.nih.gov/18084751/
- Arnautovic K, Arnautovic A. Extramedullary intradural spinal tumors: a review of modern diagnostic and treatment options and a report of a series. Bosn J Basic Med Sci. 2009;9(Suppl 1):S40-S45. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC5655171/
- Khanna AJ, Shindle MK, Wasserman BA, Gokaslan ZL, Gonzales RA, Buchowski JM, et al. Use of magnetic resonance imaging in differentiating compartmental location of spinal tumors. Am J Orthop (Belle Mead NJ). 2005;34(10):472-476. Available from: https://pubmed.ncbi.nlm.nih.gov/16304794/
- Sąsiadek M, Romanowski C, Jacków-Nowicka J. Imaging of intramedullary tumours of the spinal cord. Pol J Radiol. 2024;89:e531-e540. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11705043/
- Gaillard F, et al. Intradural extramedullary spinal tumours. Radiopaedia.org. Available from: https://radiopaedia.org/articles/intradural-extramedullary-spinal-tumours-1