By Darbi Invergo, Chief Neurosurgery Resident, Central Illinois Neuroscience Foundation, Central Illinois Neuro Health Sciences
Brain tumors are not uncommon and can arise from the brain substance itself (primary brain tumor) or travel there from a cancer in another region of the body (metastatic brain tumor). Just like tumors in other places of the body, some are benign (noncancerous), some are malignant (cancerous), while others are intermediate. Besides the degree of malignancy, many tumors respond to treatment regimens very differently. In fact, while some tumors need to be surgically removed others are to be treated without surgery. The most common type of primary brain tumor is a glioma, which comes in both low-grade and high-grade varieties. Gliomas need to be differentiated from metastatic brain tumors and lymphomas; some of which may be treated non-surgically with medication and radiation therapy.
Doctors use magnetic resonance imaging (MRI) to aid in diagnosing these tumors. Conventional MRI can show the number, size, and shape of tumors, as well as areas of intravenous (IV) contrast uptake (enhancement), swelling, and compression of normal areas of the brain. While this has been the standard of care for the diagnosis of brain tumors, recent advancements have been made in specialized MR imaging which can increase the diagnostic accuracy, expand or narrow the differential diagnosis, guide biopsy or resection, aid in planning radiation therapy (RT), and monitor treatment response. Two such advancements are magnetic resonance spectroscopy (MRS) and dynamic susceptibility contrast MRI (DSC-MRI).
MRI provides anatomic images of tumors, whereas MRS provides information on cellular functions and activities within the tumor and the surrounding brain. MRS is specifically useful to assist in identifying low- versus high-grade tumors; guide stereotactic biopsy and extent of tumor resection; and distinguish between tumor recurrence and radiation necrosis (a complication sometimes seen after radiation treatments due to swelling of the dying brain cells). MRS identifies the distribution of cellular metabolite levels. Many tumors have characteristic MRS profiles, which aid doctors in determining whether a particular lesion is high grade or low grade. Secondly, it can point to the area within a tumor where a biopsy with the highest likelihood of diagnosis should be taken, which decreases the likelihood of a sampling error. This is especially useful in mixed tumors or in tumors progressing from low-grade to high-grade, as the treatment of such lesions varies.
MRS patterns can also suggest the presence of malignant cells outside of the enhancing borders of the lesion and help determine the extent of surgery and potentially limit unnecessary resections at the tumor border, which is of paramount importance with tumors in or around areas of the brain that control speech, motor function, and the senses. Precise identification of tumor margins is also useful to more accurately determine the target volume for radiation therapy and thereby limit radiation exposure to healthy surrounding brain. Radiation therapy is an important therapeutic adjunct to surgical resection in many patients with newly diagnosed brain tumors. High doses of radiation kill tumor cells within a target region; however, this therapy can also lead to delayed radiation necrosis (pseudoprogression of tumor) in 20–30 percent of patients, which is typically indistinguishable from recurrent tumor on conventional MRI. Finally, MRS can also be used to discriminate radiation necrosis from tumor progression, which has implications for patient management and may prevent premature discontinuation of effective therapies.
Dynamic susceptibility contrast MRI (DSC-MRI) allows measurement of relative cerebral blood volume (rCBV) that correlates with the vascularity of a tumor with its grade. Low-grade glioma rCBV measurements also correlate well to the progression to high-grade glioma, raising the possibility that DSC-MRI can predict the risk of transformation.
Both imaging modalities are available in the Bloomington/ Normal area.
For more information, contact Central Illinois Neuroscience Foundation at 309-663-1522 or 309-663-7500. They are located at 1015 S. Mercer Avenue, Bloomington, IL 61701. The Central Illinois Neuroscience Foundation (CINF) is a nonprofit organization dedicated to the advancement of neurological health care through education and research.