This is a continuation of my earlier post on brain tumors where I went over the classification of brain tumors, their presentation (what signs and symptoms they present with) and briefly discussed about their management.
Primary brain tumors that is tumors which arise from the brain itself need to be differentiated from secondary brain tumors or metastatic spread of tumor to brain (this refers to a tumor which arise somewhere else as for example in the lung and then spreads to the brain. That is the primary site of the tumor is the lung and then it has metastasis to the brain). Various tumors can spread to the brain but the most common among them are:
1) Lung tumor–most common cause of lung tumor is smoking and it commonly spreads to the brain. Infact many times it is first detected only when it has spread to the brain. that is the time the patient either has a seizure or develops weakness on one side of the bogy. When a CT scan or MRI scan of the brain is done a tumor is found and when further investigations are done like Chest X-ray and CT scan of the chest the primary is found to be the lung. Lung tumor may produce multiple metastatic lesions to the brain (by that I mean there are commonly more than one lesion found when the brain is imaged). How does lung tumor spread to the brain you may ask. Well the most common route of spread is what is called the hematogenous route (meaning that some tumor cells from the lung enter the blood stream and are carried to the brain where they develop into secondary tumors).
2) Breast cancer: also commonly spreads to the brain and can present with multiple metastatic lesions. As you can imagine the prognosis is poor once there is evidence of metastatic disease. Thus oncologists (doctors who treat cancer) like to treat cancers aggressively so that they do not spread further and cause widespread disease).
3) Renal cell carcinoma: renal carcinoma may also spread to the brain.
4) Thyroid cancer
5) Colon cancer
6) Choriocarcinoma: choriocarcinoma is usually fulminant and has the potential for causing hemorrhagic brain lesions (meaning that the metastatic lesions in the brain are prone to bleeding).
7) Melanoma: malignant melanoma is frequently seen in the west. It too has the potential for causing hemorrhagic brain metastatic lesions. Hence it is imperative that you follow closely with your doctor if you are diagnosed with melanoma.
As you can imagine the treatment varies if you have a primary brain tumor versus if you have a secondary brain tumor. Treatment decisions also vary depending upon whether you have a solitary brain tumor versus if you have multiple metastatic lesions in the brain. The treatment also depends upon the site (location) of the tumor in the brain. Let me explain this a little further. If the tumor is in a part of the brain which can be easily accessed surgically, is small in size and does not involve any eloquent area of the brain then it more likely that it can be removed surgically. What do I mean by eloquent area of the brain. By eloquent I mean parts of the brain which perform vital functions. So if the tumor involves the speech center of the brain or lies very close to the area which controls the movement of the hand and leg or involves the area of the brain which controls vision, then you can understand that if the surgeon decides to remove it, more than likely the patient has awake from the surgery and be not able to speak or have weakness on one side of the body or may not be able to see. Thus surgical options are limited when tumors involve the eloquent cortex.
Primary brain tumors like glioblastoma multiforme (GBM) rarely ever metasize outside the brain. By this I mean it has been seen that primary brain tumors ususally remain confined to the brain itself and do not spread outside. That said and done, this is not a hard and fast rule and there are cases documented in which a primary brain tumor has spread outside the brain. Primary brain tumors though may spread via the white matter tracts to other parts of the brain and also spread via the cerebrospinal fluid (CSF). So sometimes one may have what we called a multi-centric primary brain tumor. As there are multiple lesions in the brain, this has to be differentiated from a secondary brain tumor (a tumor from outside that has spread to the brain).
Thus usually whenever someone is diagnosed with a brain tumor, multiple other tests are done apart from a MRI brain to rule out a secondary tumor. These include a CT scan of the chest (rule out lung cancer), CT scan of the abdomen and pelvis as well as a bone scan. These investigations also help in determining the spread of the disease and this information is vital in treatment decision making process.