AssessmentsBrain tumors: Clinical practice
USMLE® Step 2 style questions USMLE
A 43-year-old woman comes to the neurology clinic because of weakness in her right leg which she says began about three weeks ago. This has been associated with frequent headaches, especially in the mornings, in the bifrontal region. She has not had nausea, vomiting, or visual changes. When asked about personality changes, her partner says that she has noted increased aggression over the past two weeks. The patient appears comfortable and is in no distress. Neuromuscular examination shows no atrophy or fasciculations. There is focal weakness of the right leg with 4-/5 power. The remainder of the neurologic examination is unremarkable. A CT head with contrast is obtained, and the image is shown below:
Content Reviewers:Rishi Desai, MD, MPH
Brain tumors are broadly classified into primary tumors originating from cells within the central nervous system, and metastatic tumors originating from cells outside the central nervous system.
Primary brain tumors are the most common solid tumors in children, while metastatic tumors are more common in adults.
In adults, gliomas are followed by meningiomas, and in children, medulloblastomas and ependymomas are next on the list. These are followed by the less common schwannomas, oligodendrogliomas, craniopharyngioma, choroid plexus tumors, germinomas, hemangioblastomas, and primary central nervous system lymphoma.
Also, in children, most brain tumors are located below the cerebellar tentorium, or are infratentorial. Whereas in adults, most brain tumors are above it, or are supratentorial. Just remember that adults are taller than children.
The main environmental risk factor for brain tumors is exposure to ionizing radiation, which can come from therapeutic radiotherapy for cancer, or diagnostic imaging like CT scans.
Electromagnetic radiation from cell phones and microwaves is currently being researched as potential risk factors in humans.
A small proportion of brain tumors occur secondary to genetic syndromes.
Individuals with brain tumors typically have some combination of 4 symptoms: headache; focal neurological deficits like cranial nerve palsies or seizures; a neurocognitive disturbance, that often causes a decline in school or work performance; and psychiatric symptoms including depression.
The headache caused by a brain tumor is usually dull, slowly progressive, and poorly localized; usually involving the whole head. Often, the headache is worse in the morning, during a change in position such as bending, or when coughing, sneezing, or Valsalva maneuvering. That’s because during all these states, the intracranial pressure or ICP increases, worsening the headache. Additionally, the headaches may be accompanied by nausea and vomiting in the morning.
Now, pre-verbal children may not be able to communicate a headache. But, because brain tumors in children tend to be infratentorial, there’s a high risk of the tumor interrupting CSF flow and causing obstructive hydrocephalus. Because the skull sutures are still unfused in infants, this may lead to an enlarged head or macrocephaly. This is actually relatively fortunate, because it means the head can accommodate this mass without causing a rapid increase in ICP and deterioration of the child’s neurological status.
As for focal neurological deficits, brain tumors tend to cause gradually developing deficits, which differentiates them from the sudden-onset deficits seen in strokes. But sometimes, the blood vessels in a rapidly-growing tumor can rupture, causing acute bleeding within the tumor, and therefore the acute symptoms of intracranial hemorrhage.
The pattern of symptoms depends on the location of the tumor.
For example, involvement of the primary motor cortex would cause weakness, whereas involvement of the primary sensory cortex would cause sensory symptoms, like astereognosis, which is the inability to identify objects by touching them.
The complex, intertwining visual pathway runs through the brain from eyes to occipital lobe, so brain tumors can cause a variety of visual field disturbances, like bitemporal hemianopsia, which is blindness in the outer half of both the right and left visual fields. This classically occurs with pituitary tumors that compress the optic chiasm. Also, infratentorial tumors which can cause cranial nerve palsies or cerebellar symptoms like ataxia.
Craniopharyngiomas arise above the sella turcica where the pituitary gland sits. If they get big enough, they can compress the pituitary gland, causes disturbances in growth and pubertal development in children.
The classic triad includes paralysis of upward gaze, pupillary light-near dissociation; which means the pupils react to near objects, but not to light, and thirdly convergence-retraction nystagmus, which is oscillation of the eyes inwards, that is convergence, and backwards, that’s retraction.
Another focal neurologic finding is that brain tumors can cause focal seizures, and occasionally they can cause generalized seizures as well. It’s the location of the tumor rather than the size that predicts the seizure symptoms.
The location of the tumor also determines the pattern of focal seizure symptoms.
On exam, there may be signs of cranial nerve defects as well as signs of increased ICP.
Also, Cushing’s triad, which includes hypertension, bradycardia, and an irregular breathing pattern also strongly suggests an increased ICP.
If a brain tumor is suspected, the next step is a brain MRI with contrast, which is optimal for identifying soft tissue structures like tumors.
Sometimes a CT can be helpful as well, because it can more easily identify calcifications, which are seen in oligodendrogliomas and craniopharyngiomas.
Now, if an individual has sudden-onset neurological deficits that are suggestive of intracranial hemorrhage, then a non-contrast CT scan may be done first.
In the acute phase of intracranial hemorrhage, blood may obscure your view of the tumor on imaging. Therefore, a follow-up MRI is usually done about 7 to 10 days after the event, once the blood has been absorbed.
Normally contrast is unable to penetrate the blood-brain barrier, so if there’s contrast enhancement, that means that the tumor has broken down that barrier and leaked in. The MRI also shows the edema surrounding the tumor, or hemorrhage inside the tumor.
Also, large tumors can cause a mass effect, which manifests as a midline shift to the opposite side. If the tumor obstructs the flow of cerebrospinal fluid, then hydrocephalus becomes apparent above the level of obstruction.
Now, “grade” is a basic pathology term referring to the degree of tumor differentiation, or in other words; how closely does the tumor resemble normal tissue.
The higher the grade, the less it resembles normal tissue, and the more aggressive the tumor is.
Glioblastoma commonly shows a rim of enhancement along the margins of the tumor, also called a ring-enhancing lesion. The reason behind this appearance is that the center of the tumor does not enhance because it’s mostly made up of necrotic cells, whereas the peripheral rim is made of live tumor cells.
Cerebral metastasis and lymphoma can also give off this ring-enhancing appearance, so it’s not unique to glioblastoma.
Now, glioblastoma tends to be really aggressive, and in fact may cross from one cerebral hemisphere to the other across a white matter bridge called the corpus callosum, giving the tumor the appearance of a butterfly.