Brain tumors: etiology and classification
Primary neoplasms develop from intrinsic structures: astrocytes, oligodendrocytes, ependymocytes, pinealocytes, and arachnoid fibroblasts. The overwhelming majority of glial tumors originate from immature (low-grade) cells.
Secondary lesions represent metastases from other organs (most commonly the lung and breast). In recent years, an increase in the number of primary CNS lymphomas has also been noted, which is closely linked to the spread of HIV infection.
Risk factors include exposure to high doses of radiation and genetic predisposition (for example, in phacomatoses such as neurofibromatosis or tuberous sclerosis).
Groups of primary tumors:
- Neuroepithelial tumors (astrocytomas, ependymomas, oligodendrogliomas).
- Meningeal tumors (meningiomas).
- Cranial nerve tumors.
- Embryonal tumors and pituitary neoplasms.
- Lymphomas.
Pathogenesis and symptoms of cerebral tumors
A growing tumor and its associated edema lead to increased intracranial pressure (ICP). This causes displacement (herniation) and compression of healthy structures.
The course of the disease is usually characterized by a gradual increase in neurological deficit. An apoplectic onset (due to hemorrhage into the tumor tissue) is less common.
Triad of main manifestations:
- Headache (may be accompanied by nausea or vomiting). It is a consequence of intracranial hypertension. This is the initial symptom in a third of patients.
- Epileptic seizures. Occur in ~30% of patients. They are especially typical for slow-growing, superficial neoplasms (such as meningiomas) and can remain the sole sign of the disease for years.
- Focal symptoms. Depend entirely on the localization of the lesion (paresis, sensory disturbances, psychiatric changes).
Spinal cord tumors
Topographic classification of spinal tumors is based on their relation to the spinal cord and its membranes:
- Intramedullary — grow directly inside the spinal cord (astrocytomas, hemangioblastomas).
- Extramedullary-intradural — grow beneath the dura mater, compressing the cord from the outside (meningiomas, neurofibromas).
- Extradural — located above the dura mater in the epidural space.
Clinical syndromes of spinal lesions
The symptom complex consists of three levels of disorders:
- Radicular syndrome: severe pain along the nerve root, accompanied by sensory disturbances (paresthesia, hyperalgesia). A specific sign is that pain worsens when lying down and coughing, and percussion of the spinous process in the projection of the tumor causes localized tenderness.
- Segmental disorders: peripheral paresis and autonomic dysfunction strictly at the level of the neoplasm's growth.
- Long-tract disorders: central paresis, sensory loss, and sphincter dysfunction below the level of the lesion.
Topography determines the scale of the long-tract deficit. A tumor in the cervical region causes disorders in both upper and upper/lower limbs, while in the thoracic region, it affects only the lower limbs. Lateral tumor location produces the classic Brown-Séquard syndrome. If the cauda equina is affected, severe radicular leg pain, peripheral foot paresis, and sphincter disorders dominate.
Diagnostic Principles
A neoplastic process should be suspected in any adult with a first-time seizure, as well as in progressive focal or generalized symptoms.
The gold standard of diagnosis is contrast-enhanced MRI. The method makes it possible to assess localization, differentiate intra-axial from extra-axial growth, and perform differential diagnosis of tumor types. Cerebrospinal fluid is additionally examined (to search for tumor cells in meningeal carcinomatosis). However, a definitive diagnosis always requires morphological verification via biopsy, which is most often obtained during surgery.
Briefly: answers to topical questions
Which malignant neoplasms most commonly metastasize to the brain?
- Malignant neoplasms of other sites (aliis localizationibus) — secondary brain tumors represent metastatic lesions from malignant neoplasms, most frequently of the lung and breast.
Brown-Séquard syndrome (in lateral spinal cord tumors): motor function and proprioception are "switched off" on the side of the lesion, while pain and temperature sensation are lost on the opposite side.
Class and exam questions
Which is more common: a primary tumor or brain metastases?
In clinical practice, secondary (metastatic) tumors are significantly more common than primary neoplasms. Their prognosis is generally extremely unfavorable.
Which tumors most frequently debut with epileptic seizures?
Epileptic seizures are particularly characteristic of slow-growing, superficially located tumors such as meningiomas.
How to suspect radicular syndrome of a spinal tumor based on complaints?
Pain worsens in the recumbent position and during coughing, and percussion of the vertebral spinous process over the tumor causes sharp local tenderness.
What else to study on this topic
- Mechanisms of intracranial hypertension development and types of brain herniation.
- Histological differentiation of glial tumors and their grades of malignancy.
- Features of cerebrospinal fluid examination in suspected carcinomatosis.
- Tactics for oncological screening of the primary site when CNS metastases are detected.
- Methods of intraoperative biopsy and principles of neurosurgical interventions.
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