Topographic classification
Dividing tumors into spaces (compartments) is a fundamental principle of spinal neuroimaging. Although a large mass may involve multiple zones at once, the primary site of origin is critically important.
- Extradural tumors (Extradural). Located outside the dura mater. This is the most common group (about 60%). Vertebral metastases are most frequently identified here. Primary bone neoplasms are much less common.
- Intradural extramedullary tumors (Intradural extramedullary). Grow beneath the dura mater but outside the spinal cord tissue (30% of cases). Typical representatives: meningiomas, nerve sheath neoplasms (schwannomas, neurofibromas), as well as metastases spreading along cerebrospinal fluid pathways.
- Intramedullary tumors (Intramedullary). Grow directly within the spinal cord parenchyma. The rarest group (only 10%), dominated by astrocytomas and ependymomas.
Intramedullary tumors: general characteristics
These lesions occur 10–15 times less frequently than primary brain tumors. The incidence is extremely low—about 1.1 cases per 100,000 population. Nearly 90% of them are of glial origin.
The histological picture strongly depends on the patient's age:
- In adults, ependymomas rank first (up to 60%), followed by astrocytomas and hemangioblastomas.
- In children, the absolute majority (60–90%) are astrocytomas, with gangliogliomas in second place. Ependymomas in childhood are rare and are usually associated with neurofibromatosis type 2 (NF-2).
Localization also has its patterns: astrocytomas prefer the thoracic region, ependymomas the cervical region, while myxopapillary variants of ependymomas affect the filum terminale and the conus medullaris.
Ependymoma
This is the most common intramedullary tumor in adulthood (peak incidence occurs at 40–50 years). The source of growth is the cells lining the central canal. The pathology develops slowly: sensory disturbances appear first (due to compression of the spinothalamic tracts), and motor deficits join in later stages.
Growth patterns and histology As a rule, these are benign lesions (WHO grade 2). Their key feature is compressive rather than infiltrative growth. The tumor displaces the spinal cord tissue while having clear boundaries, which makes its complete surgical removal possible.
MRI features:
- Signal on T1 is isointense or hypointense, on T2 isointense or hyperintense.
- Following gadolinium administration, bright homogeneous contrast enhancement is observed.
- A cleavage plane (cleavage plane) between the tumor and healthy tissue is clearly traceable.
- Tractography (DTI) demonstrates displacement of nerve fibers rather than their destruction.
- In a quarter of patients, the cap sign (Cap sign) is detected—areas of low signal on T2 along the edges of the mass. These are traces of hemosiderin deposition after microhemorrhages, which is a strict marker of ependymoma.
- Associated satellite cysts and syringomyelia are often discovered.
Myxopapillary ependymoma
A specific subtype (WHO grade 1) growing from the cells of the filum terminale. It affects the conus medullaris (conus medullaris) and cauda equina zone. More common in children, young adults, and males.
Clinical presentation and risks The classic symptom is chronic lower back pain that intensifies at night. Due to slow growth, by the time of detection the mass often reaches giant proportions. The tumor is highly prone to hemorrhages, which can provoke the sudden onset of leg weakness, pelvic organ dysfunction, and in severe cases, subarachnoid hemorrhage and superficial siderosis.
MRI picture: A heterogeneous mass with a hyperintense signal on T2 (due to the presence of mucin) is revealed. Enhancement is strong but heterogeneous due to multiple cysts and traces of old hemorrhages. CT and MRI may also show bone changes from prolonged compression: widening of the intervertebral foramina and vertebral scalloping.
Briefly: answers to topical questions
What is the classification of all intramedullary tumors by degree of malignancy (WHO grade)?
The following WHO grades of malignancy are indicated for the intramedullary tumors listed in the sources:
- Myxopapillary ependymoma (myxopapillary ependymoma) — WHO grade 1.
- Pilocytic astrocytoma (pilocytic astrocytoma) — WHO grade 1.
- Ependymoma (ependymoma) — predominantly WHO grade 2; anaplastic ependymoma — WHO grade 3.
- Fibrillary astrocytoma (fibrillary astrocytoma) — WHO grade 2.
- High-grade gliomas (high-grade gliomas) — WHO grades 3 and 4.
- Hemangioblastoma (haemangioblastoma) — a benign low-grade tumor (low grade).
Which genetic syndromes, besides neurofibromatosis type 2, are associated with primary spinal cord tumors?
In addition to neurofibromatosis type 2, von Hippel–Lindau syndrome and neurofibromatosis type 1 are linked to tumors of the spine and spinal canal in the sources.
- Von Hippel–Lindau syndrome (VHL syndrome) — associated with spinal hemangioblastomas; in this syndrome, lesions can be multiple and located at all levels of the spinal cord.
- Neurofibromatosis type 1 (NF-1) — associated with multiple neurofibromas, which belong to nerve sheath tumors of intradural extramedullary localization.
EAM: Ependymomas — cervical region (adults), Astrocytomas — thoracic (children), Myxopapillary — conus medullaris.
Class and exam questions
Why is it important to differentiate ependymoma from astrocytoma on MRI?
Ependymomas have clear borders (compressive growth) and can be completely removed by neurosurgeons. Astrocytomas, on the other hand, grow infiltratively, invading normal tissue, which makes radical surgery practically impossible.
What does the cap sign mean?
This is a zone of low MRI signal in T2 sequences at the superior and inferior poles of the tumor. It occurs due to hemosiderin accumulation resulting from chronic hemorrhages and is a specific sign of ependymoma.
How are ependymomas and neurofibromatosis type 2 related?
Patients with NF-2 often develop multiple small ependymomas that are asymptomatic. They are usually not operated on, but only regularly monitored using MRI.
Why might radiation therapy be prescribed after the removal of a benign myxopapillary ependymoma?
Despite the low grade of malignancy (WHO grade 1), these tumors can disseminate along the cerebrospinal fluid pathways (including due to manipulation during resection). Irradiation reduces the risk of such recurrences.
What else to study on this topic
- Nerve sheath tumors (schwannomas and neurofibromas)
- MRI semiotics of spinal cord astrocytomas
- Metastatic involvement of the extradural space
- Mechanism of syringomyelia development in tumors
- Superficial siderosis: pathogenesis and neuroimaging
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