About the brain and cranial surgery
What is the brain?
The brain is the seat of consciousness- it houses all of a person’s thoughts, memories, emotions, and is responsible for thoughts, sensations, movement, and behaviors. It resides within the skull and along with the spinal cord, makes up the central nervous system.
The brain is divided into several parts:
- The cerebrum - the cerebrum is the largest part of the brain. It is divided into left and right hemispheres and also into lobes. The largest is the frontal lobe which lies under the forehead and controls voluntary movement. The parietal lobe lies behind the frontal lobe and is the center for sensing touch. The temporal lobe lies tucked under the frontal lobe and is the site where memories are stored. The occipital lobe is the smallest and lies in the very back of the head and is where vision is housed.
The cerebrum functions at its surface, called the cerebral cortex. To increase surface area, the cortex folds creating the unique appearance of the brain’s surface. The folds create ridges, called gyri (singular= gyrus) and the crevasses between them called sulci (singular = sulcus).
- The cerebellum – the cerebellum resides in the back of the skull, underneath the cerebrum. It partially surrounds and is attached to the brain stem. The cerebellum also has a cortex which is folded into gyri and sulci. It is responsible for coordination of movements.
- The brain stem – the brain stem also resides in the back of the skull. It connects the cerebrum to the spinal cord and it controls a number of very important brain functions. First, it sends signals to the cerebrum, allowing it to maintain consciousness. It also controls basic and reflexive functions such as eye movement and the eyes adjusting to bright light; facial movement and sensation hearing; and balance; taste, gagging, swallowing and tongue movement.
- The brain is covered by three layers of proactive coverings, collectively called the meninges. The outer-most layer is the dura mater (“tough mother” in Latin); it is the leathery covering of the brain that adheres to the inside of the skull. The middle layer is the arachnoid (Greek for “spider”) membrane; it is very thin and web-like, and contains the cerebrospinal fluid (CSF). The innermost layer is the pia mater. It is a thin protective layer on the surface of the brain itself.
What is the cranium?
The cranium is more commonly called the skull. It is the bone encasing and protecting the brain. Along with the brain, the cranium also contains the nerves that connect directly to the brain (the cranial nerves), the vessels that delivery blood to & drain blood from the brain (arteries and veins, respectively), the salty water in which the brain floats (the cerebrospinal fluid), and the coverings of the brain (the meninges).
When is brain surgery indicated?
There are many reasons that brain surgery is needed. The most common indications for brain surgery are to remove tumors and treat brain injuries.
Brain Tumor SurgeryA tumor is a growth of abnormal tissue. Tumors are often classified as benign or malignant. There are many types of tumors that can arise within or adjacent to the brain for which surgery is needed. Surgery is typically recommended when a tumor is growing in such a way that it is damaging, or threatening to damage, the delicate brain tissue adjacent to it. Tumors may present with signs of injury to the brain such as weakness, loss of speech, loss of vision or with a seizure. Others may cause headache, nausea, or vomiting. Still others may be found fortuitously on medical imaging studies performed for an unrelated reason. Occasionally, the best strategy to treat a tumor is to watch it carefully with repeated brain imaging (like MRI). Once indicated, surgery is typically performed to resect as much of the tumor that can be removed safely in order to remove pressure and irritation on the surrounding brain. Click here for more information
Tumors arising from the brain
Just as there are many types of cells making up the brain, there are many types of tumors that can start within the brain itself. The most common are derived from the cells that support the nerve cells within the brain. These support cells are collectively called glia. The two most common are astrocytes and oligodendrocytes. A tumor that grows from one of these types of cells is called a glioma. Gliomas can display a variety of behavior, from benign and slow growing to malignant and life-threatening. They are divided into four grades:
- Grade 1 gliomas are specific tumors that are generally seen in children. When completely resected, they have only a small change of recurrence. These are called juvenile pilocytic astrocytomas, a slow growing tumor.
- Grade 2 gliomas are called diffuse astrocytoma or oligodendroglioma, depending on the cell of origin. They can act benignly and grow very slowly, but can change their behavior without warning. They are typically discovered after a seizure or incidentally, and surgical resection is typically recommended. Further treatment with chemotherapy and radiation therapy are often not needed.
- Grade 3 gliomas are called anaplastic astrocytomas (AA). They typically grow more rapidly and can present with signs of damage to the surrounding brain. When suspected, anaplastic astrocytomas are removed when possible. Chemotherapy and radiation therapy are typically recommended after surgery.
- Grade 4 glioma is called glioblastoma multeforme. These tumors are highly malignant; they grow rapidly and cause severe damage to surround brain. Like AA, they are removed whenever possible and typically require further treatment with chemotherapy and radiation therapy.
- A few other, less common, tumors arising from the brain include ependymoma, ganglioglioma, hemangioblastoma, and craniopharyngioma.
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Tumors that have spread from another part of the body.
The most common tumor to develop in the brain is a cancerous tumor that has originated in another organ (like the lung or breast) and then spread to the brain. This process of tumor spreading is call metastasis. These tumors can cause damage to the surrounding brain tissue leading to headache, loss of brain function, or seizure. Surgery is often recommended for a single, solitary, metastatic tumor. Surgical resection may also be indicated in patients with more than one metastatic tumor, and biopsy may be beneficial in determining the origin of the tumor.
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- Tumors arising from the coverings of the brain
Some tumors grow from the coverings of the brain. These covering are called the meninges and the tumors from which they derive are called meningiomas. These tumors are usually slow growing. They grow into the brain from the dura mater on inner surface of the skull exerting pressure on the underlying brain. They can also invade into the brain causing brain swelling and seizures. When meningiomas are discovered incidentally, are small, and have no aggressive features, surgery is not typically recommended. Rather they are observed. If however, a tumor is large or shows growth, or it is irritating the brain, surgical resection is indicated. Maximal safe resection is the goal of surgery. The vast majority of meningiomas are benign, but a small number can be more aggressive. Meningiomas have been divided into three grades:
- Grade 1 is a typical, benign meningioma.
Click here to see a surgical case involving a Grade 1 meningioma.
- Grade 2 tumors are called atypical meningioma and incomplete resection may indicate postoperative radiation therapy.
- Grade 3 meningiomas are called anaplastic. These are malignant and require postoperative radiation.
An alternative to surgical resection of small meningiomas is stereotactic radiosurgery (SRS), a type of focused radiation therapy.
- Grade 1 is a typical, benign meningioma.
- Tumors arising from the pituitary gland
The pituitary gland is the master endocrinological gland in the body, controlling many of the body’s hormonal processes. It is attached to the brain by a thin stalk, like a cherry on its stem. The pituitary gland, only about half an inch in diameter, resides in it’s own compartment in the skull, called the sella turcica (“Turkish saddle” in Latin). It is located in the midline behind the nasal sinuses.
Small abnormalities in the gland are not unusual and tumors can not uncommon. They are almost always benign, but can cause loss of vision when they grow into the nerves convey information for the eyes to the brain. They can also produce an excess of normal hormone that can lead to serious threats to health. There are other, more rare lesions that can arise in the pituitary gland. If a pituitary lesion is discovered, it can often be observed. However, if the tumor is threatening vision or secreting an excess of hormone it should be treated. Some can be treated with medication alone, but most should be resected with surgery.
- Tumors arising from the nerves of the brain (cranial nerves)
The brain gives rise to twelve sets of nerves that exit the skull to innervate structures in and around the head. These nerves are called cranial nerves. They carry the information allowing the special senses of smell, sight, hearing, and taste. They also carry motor and touch sensation to and from the face, and control swallowing and some other functions. Occasionally, a tumor can arise from one of these nerves. The most common is the vestibular schwannoma, a benign tumor arising from the balance nerve as it enters the inner ear. It typically causes hearing loss. Similar to other benign lesions, if it is small and causing minimal or no problems, it can be observed. However, if it is large, growing, or causing significant symptoms, it should be treated. Treatment can be surgical resection or with stereotactic radiosurgery (SRS), a type of focused radiation therapy.