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Histology of intraspinal tumors

Intramedullary tumors

Tumors emanating from the medulla spinalis make up around 20 % of intraspinal tumors in adults. Over 90 % of intramedullary tumors begin in glial cells, hence the term glioma. The majority of gliomas share a tendency for diffuse infiltration of the spinal cord. This limits the possibility for radical surgical treatment. It is extremely rare for these to metastasize to other organs. Ependymomas and astrocytomas are most common. Oligodendrogliomas are extremely rare in the spinal cord. Intramedullary gliomas are more common in patients with neurofibromatosis. Ependymomas are relatively common in patients with type 2 neurofibromatosis, whereas astrocytomas develop in those with type 1.

Ependymomas

The cells in the ependymomas resemble ependymal cells, and presumingly the ependymomas emanate from the ependymal cells in the central canal. These tumors make up around 60 % of intramedullary tumors, and are the most common type of intramedullary tumors in adults. The tumor is most common in the 20-30 year age group, but can occur at any age. Unlike astrocytomas, ependymomas in the spinal cord are relatively well-defined and are, therefore, more easily accessible for surgical resection.

Intramedullary ependymomas occur most often in the cervical region. 45 % affect this area only; whereas in 25 % of cases, the tumors are localized in both the cervical and upper part of the thoracic sections. In 25 % of the cases the tumor is localized in the thoracic and upper lumbar sections.

MRI of a patient with myxopapillary ependymoma. Click to enlarge the image. Optical light microscope image of a myxopapillary ependymoma. Click to enlarge the image.

In accordance with the WHO's classification, so-called myxopapillary ependymomas make up a separate entity. They differ in histological terms from ordinary ependymomas and are almost exclusively localized in the caudal cone/filum terminale region. Over 80 % of tumors in this region are myxopapillary ependymomas. These can often be radically operated.

Astrocytomas

The cells in the astrocytomas resemble astrocytes. These tumors make up around one third of all intramedullary gliomas.

Optical microscope image of pilocytic astrocytoma. Click to enlarge the image. MRI of patient with oligodendroglioma. Click to enlarge the image.

In accordance with the WHO, astrocytomas are graded from I-IV according to an increasing degree of malignancy. Grade I, so-called pilocytic astrocytomas, are often well-defined and the most low-grade variant. Grade II corresponds to low-grade astrocytomas of the fibrillary type. These two types make up around 75 % of intramedullary astrocytomas. Grade III, anaplastic astrocytomas, make up around 25 %. Only 0.2–1.5 % of astrocytomas of the spinal cord are classified as grade IV, i.e. glioblastomas. In the brain, glioblastomas make up half of all gliomas. Astrocytomas occur most often in the thoracic medulla.

Capillary hemangioblastomas

Capillary hemangioblastomas are the third most common type of intramedullary tumor.

MRI of patient with a capillary hemangioblastoma. Click to enlarge the image. Optical light microscope image of a capillary hemangioblastoma. Click to enlarge the image.

Even though such tumors are most often intramedullary (75 %), they can also be localized intradurally/extramedullarily and extradurally. The majority of capillary hemangioblastomas occur in persons under 40 years of age and are solitary.

In around 25 % of cases, this tumor is a stage of von Hippel-Lindau disease, an autosomal dominant hereditary disease. This condition should therefore be considered if the patient has multiple capillary hemangioblastomas or also has tumors in the retina, kidney, adrenal medulla, pancreas or in the inner ear.

Intradural/extramedullary tumors

Schwannomas 

Schwannomas are benign tumors that normally emanate from the sensory nerve roots. Schwannomas are the most common primary tumor in the spinal cord and make up 30 % of such cases. They can occur in all age groups, but are most common in the 30-50 year age group. Schwannomas occur equally often in men and women.

MRI of patient with Schwannoma.
Click to enlarge the image.
Optical microscope image of a Schwannoma. Click to enlarge the image.

Often the tumor emanates from parts of a sensory nerve root, and in some cases these tumors can be extirpated without destroying the entire root. Malignant transformation of Schwannomas is extremely rare. Schwannomas occur sporadically or as a stage of type 2 neurofibromatosis.

Meningiomas

11–12 % of all meningiomas occur in the spinal cord. Meningiomas are the second most common intraspinal tumor and make up 25 % of such cases. They occur in all age groups, but are most common in the 45-50 year age group. Meningiomas are more common in women than in men. This can partly be explained by the growth-stimulating effect of female hormones.

MRI of patient with meningioma.
Click to enlarge the image.
Optical microscope image of a meningioma. Click to enlarge the image.

Meningiomas emanate from arachnoidal cells. They are normally well-defined with regard to the spinal cord, surrounded by a capsule, and they push the spinal cord ahead of them during growth. The majority of meningiomas occur in the thoracic region and are found in a postereolateral location in the spinal canal. Meningiomas usually grow very slowly and 95 % of tumors are benign. Multiple mengingiomas can be a stage of type 2 neurofibromatosis. 

Neurofibromas

By definition, a neurofibroma is a benign tumor that emanates from nerves. As a rule the entire nerve root is diffusely affected and will be damaged in the event of an operation. Intraspinal neurofibromas are often a stage in type 1 neurofibromatosis (Von Recklinghausen disease). In contrast to Schwannomas, neurofibromas can undergo malignant transformation. 5–10 % of the neurofibromas that affect multiple nearby nerve roots, so-called plexiform neurofibromas, develop into a malignant peripheral nerve sheath tumor. Half of all malignant peripheral nerve sheath tumors are a stage in neurofibromatosis.

Extradural tumors

Metastases

5–15 % of all patients with cancer will experience symptom-producing spinal/epidural metastases. The primary tumor is generally localized in the chest, lungs, prostate or kidneys.

On the other hand, intradural metastases are extremely rare and make up just 1–4 % of all symptom-producing metastases in the spinal canal.

MRI of patient with a spinal/epidural metastasis. Click to enlarge the image.

Compression of the intraspinal area can occur in several ways:  intraspinal tumor growth, a compression fracture with pressure on the rear part of the vertebral body in the spinal canal, or luxation/subluxation secondary to tumor destruction. In very rare cases, intracranial tumors can metastasize into the spinal canal. In such cases the spreading has occurred through the flow of cerebrospinal fluid, and the secondary tumors are therefore located in the subarachnoidal space - so-called "drop metastases". Medullablastomas can metastasize in this manner, and one should therefore always examine the spinal canal in patients with an intracranial medullablastoma (posterior cranial fossa).

Multiple myeloma

Multiple myeloma is a malignant systemic disease that is generally localized in the bone marrow. The tumor consists of monoclonal myeloma cells that produce a pathological immunoglobulin. It is not unusual for this disease to present debut symptoms in the form of back pain and progressive neurological effects, secondary to compression of the spinal cord.

Lymphoma

The majority of spinal lymphomas affect the vertebrae or epidural space. However, intramedullary lymphomas do occur, and make up 3.3 % of all CNS lymphomas.

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