We gotta feel for Lexie, right? Like being a fourth year surgical resident isn't stressful enough -- managing your case load, putting up with the fifth years, dealing with the interns… And now, she's been assigned to the toughest attending at Seattle Grace Mercy West: Derek Shepherd. He may be McDreamy, but he's also an incredible surgeon who likes his operating room set up in a very particular way. Not only does Derek want his dissectors organized by size, but he also wants that sixteenth towel placed perfectly for his arm when using the microscope. 

It's pretty impressive that Lexie persuaded Derek to take on the butterfly tumor. Why is it nicknamed a "butterfly"? Well, when looking at a scan of the tumor in the brain, the image appears in the shape of a butterfly – it extends across both hemispheres of the brain. And when a tumor has become bilateral, many surgeons consider it inoperable because removal would encompass creating deficits on each side. Traditionally, a patient would struggle with coming back from that.

Mary suffered from a Grade IV "astrocytoma."

Astrocytomas are the most common type of gliomas – brain tumors that contain a variety of cell types. Astrocytoma cells are star-shaped (hence the name) and usually grow very slowly or even not at all for some periods of time. Experts measure the malignancy of astrocytomas on a grading scale devised by the World Health Organization. There are four grades (I, II, III, IV), and the differences in each level stem from the tumor's growth rate, blood supply, presence of a necrotic center, border distinctness, and similarity to normal cells.

Mary's tumor was the most malignant of the grades – Grade IV. Grade IV astrocytomas invade a vast amount of surrounding normal tissue, grow aggressively, and possess dead cells in their centers. They definitely have the worst prognosis. An example of a Grade IV astrocytoma is called a glioblastoma multiforme.

How do astrocytomas present themselves?

Well, symptoms of all brain tumors depend on their location and severity, but generally, astrocytomas start making themselves known with the increasing pressure inside the skull. Various symptoms include:

- Persistent headaches.
- Vomiting.
- Loss of appetite.
- Double or blurred vision.
- Mental status changes.
- Drowsiness/Lethargy.
- Seizures.
- Disordered conduct or personality changes.
- Impaired mental faculties.
- Speech difficulty of gradual onset.

In infants, another sign of an astrocytoma could be an enlarged head due to the swelling inside the skull, before the bones have completed fusing.

Diagnosis of an astrocytoma does not differ from other types of brain tumors. Usually the mass will be detected through sophisticated imaging techniques such as computed tomography (CT scan), magnetic resonance imaging (MRI), and positron emission tomography (PET scan).

Depending on the tumor's grade, treatment exists. Options include surgery, radiosurgery, radiation, and chemotherapy.

Surgeons strive to remove as much of the tumor as possible without damaging certain areas of the brain needed for vital functions (such as sight, the ability to speak, move, etc). But many high-grade tumors, like Mary's astrocytoma, have grown tentacle-like pieces that invade tissues extremely difficult to reach in the operating room. If the tumor's location prevents complete removal, then the surgeons will at least attempt to reduce the tumor's size by excising a piece of it.

With radiation therapy, the doctors plan the course of treatment to kill tumor cells without injuring too much leftover healthy tissue. Radiation usually entails multiple sessions, ranging from ten to thirty treatments. Radiosurgery uses computerized calculations to focus radiation exactly to the tumor to minimize the exposure to the rest of the unaffected brain.

Chemotherapy is another treatment method, but the overall survival rates for patients with advanced brain tumors do not increase drastically with this option. Doctors often give their pediatric patients chemotherapy instead of radiation to minimize any lasting effect on the developing brain. Also, not everyone can withstand chemotherapy's side effects, so the patient's team of doctors will need to conduct a thorough evaluation of the patient's overall health and strength.

Meanwhile, to improve survival rates, researchers have been continuing to experiment with gene therapy, highly focused radiation, immunotherapy, and adjusted doses of chemotherapy drugs.

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