intradural extramedullary metastases

Intradural extramedullary metastases are rare and only account for approximately 5% of spinal metastases.

Please review leptomeningeal metastases (brain) for a general discussion focused on the brain's subarachnoid space involvement.

Epidemiology

The age at presentation depends on tumor type. Metastases from central nervous system malignancies generally occur at a younger age.

Clinical presentation

Presentation is highly variable. As the most commonly affected site is the lumbosacral spine, symptoms and signs include back or radicular pain, weakness, paresthesias, gait disturbance, cauda equina syndrome and symptoms/signs of meningeal irritation.

Pathology

In the pediatric population, the most common intradural extramedullary neoplasms are leptomeningeal metastases resulting from primary brain tumors whereas in adults non-CNS tumors are most commonly encountered. Multiple lesions are common.

Primary tumors include:

CNS (drop metastases)
- cerebral glioblastoma
- anaplastic astrocytoma
- ependymoma and myxopapillary ependymoma
- posterior fossa medulloblastoma (PNET-MB)
- pineal tumors (e.g. germinoma, pineoblastoma)
- choroid plexus neoplasms
non-CNS
- solid tumors
  - lung cancer
  - breast cancer
- melanoma
- haemopoietic neoplasms
  - lymphoma
  - leukemia
- papillary carcinoma of thyroid

Radiographic features

Plain films and CT are inadequate for the assessment of possible leptomeningeal metastatic disease, and in these cases, MRI is required.

MRI

MRI without contrast may be normal, and thus when suspected contrast should be administered. Typical signal characteristics include:

T1: thickened nerve roots or nodular lesions that are isointense with the spinal cord may be seen
T2: cord edema may be seen with more extensive disease, especially if there is an intramedullary component
T1 C+ (Gd)
- enhancing tumor nodules on the spinal cord, nerve roots or cauda equina.
- “sugar coating” of the spinal cord and nerve roots

Treatment and prognosis

Prognosis is poor, and depends on the primary tumor. No surgical cure is possible, and treatment revolves around systemic chemotherapy and radiotherapy to the neuraxis (again, this depends on the primary tumor).

Differential diagnosis

If diffuse (sugar coating) consider:

meningoradiculitis
- homogeneously enhancing CSF
- CSF correlation useful
arachnoiditis
- clumping of nerve roots
- "empty sac sign"
- often history of prior surgery
Guillain-Barre syndrome
- smooth pial enhancement of cauda equina and conus medullaris
- history of recent viral illness is typical

If nodular (mostly at cauda equina) consider:

spinal meningioma
- multiple meningiomas are most often associated with NF2
- dural tail sign
spinal neurilemmoma/schwannoma
- multiple schwannomas are often associated with NF2
- frequently associated with hemorrhage, intrinsic vascular changes, cyst formation and fatty degeneration
spinal neurofibroma
- multiple neurofibromes are often associated with NF1
leptomeningeal (pial) lipoma
- follows fat signal intensity
- no enhancement
post-arachnoiditic adhesions