1. Differential Diagnosis - Adult extramedullary intradural tumor
- Schwannoma (30%)
- Meningioma (25%)
- Neurofibroma
- Ependymoma
- Paraganglioma
- Lipoma
- Hemangioblastoma
- Lymphoma
- Plasmacytoma
- Chloroma (solid leukemia)
- Meningeal Melanocytoma
- Spine PNET
- Metastases (Drop- AA, GBM, ependymoma : more common in kids)
- Metastases (hematogenous – breast, lung: more common in adults)
2. Differential Diagnosis - Adult extramedullary intradural non-tumor lesion
- Cysts: Dermoid, Epidermoid, Arachnoid
- Infection:  Abscess, TB, Neurocysticercosis
- Vascular: AVF, AVM, Cavernoma
- Other: Sarcoidosis
3. Differential (extramedullary intradural): Schwannoma 

Most common extradural intramedullary tumor - 30% overall, 2/3 of all nerve sheath tumors.
- Originate from schwann cells, particularly in dorsal root ganglion
- Generally occur in C and L spine, rarely T-spine (vs meningomas)
- Can be radiographically indistinguishable from neurofibromas - but more prone to fatty degeneration, vascular changes (thrombosis, dilatation), hemorrhage than neurofibromas are
- Can be associated with NF2 (MISME: multiple inherited schwannomas, meningiomas, ependymomas)
4. Differential (extramedullary intradural): Neurofibroma 

- Less common than schwannomas, comprise 1/3 of peripheral nerve sheath tumors
- Usually occur in c-spine
- May carry "target sign" - representing Antoni A (fibrous core) and Antoni B (myxoid periphery) which can also occur in schwannomas
- Often associated with NF1
5. Schwannomas vs Neurofibromas: surgical approach 

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- Schwannomas tend to displace the nerves/nerve roots to one side, which renders GTR more feasible 

- Neurofibromas tend to grow within the nerves, which makes complete surgical resection more difficult and sometimes impossible 

6. Differential (extramedullary intradural): Spinal Meningomas: 

About spinal meningiomas: 

- Occur primarily in thoracic spine (~80%), after that next most common in c-spine (~15%). Almost never occur in L-spine. 

- Believed to originate from dentate ligaments 

- 10x more common in women than in men. Vs intracranial meningiomas which are female-predominant, but not to quite an extent. 

- Often have dural tail 

- Usually posterolateral (vs nerve sheath tumors which are more likely to be anterior) 

7. Differential (extramedullary intradural): Paraganglioma

- Originate from chromaffin-negative paraganglial cells. Neuroendocrine tumors. Like a non-secreting version of a pheochromocytoma. 

- Secrete very low levels of some hormones (somatostatin, 5-OH tryptamine) but no physiologic effects 

- Almost always located below conus, but generally rare so only represent ~3% of all tumors below conus

- Highly vascular tumors that often have flow voids on imaging

- Rarely associated with superficial siderosis-- syndrome of myelopathy, CN deficits, sensory impairment) 

8. Differential (extramedullary intradural): Myxopapillary ependymomas 

- Typically occur in the cauda/filum

- 90% of tumors that occur in the cauda/filum are myxopapillary ependymomas. 

- Believed to originate from ependymal glial cells: histologically appear as papillary structures in myxoid background, with ependymoma cells. 

- WHO grade I, however 14-43% CSF dissemination or multiple lesions. 

- Can appear homogenously enhancing, however very prone to intratumoral hemorrhage or cystic degeneration, so can appear very heterogenous. 

- Present with pain primarily; 25% will present with weakness 

9. Differential (extramedullary intradural): Epidermoid cyst 

- May be congenital or acquired (rarely occur after LPs-- from progenitor cells in epidermal space being pushed into thecal sac. The use of the stylet in the LP needle is designed to prevent this. 

- Same consistency as CSF (T1 hypo, T2 hyper) except slightly sludgier 

- Restrict on DWI-- this is how you differentiate from arachnoid cyst, which appears identical to CSF and does NOT restrict with DWI. 

10. Differential (extramedullary intradural): Lipoma