Pituitary and Parasellar Tumors
The pituitary gland sits in a small bony pocket (called the sella turcica) at the base of the skull just behind the nose. The pituitary gland is known as the “master gland” because it helps control the secretion of hormones from a number of other endocrine glands in the body. The pituitary gland secretes growth hormone (GH), prolactin (PRL), and adrenocorticotropin hormone (ACTH), which serve a variety of essential hormonal and metabolic functions. The hypothalamus, a part of the brain near the pituitary, signals the pituitary gland to secrete more or less hormones depending on the needs of the body. A stem-like stalk connects the pituitary gland to the hypothalamus and it is through this stalk that the hypothalamus sends signals to control the activity of the pituitary gland.
Most pituitary gland tumors, called pituitary adenomas, are benign slow growing tumors that develop in the anterior part of the gland. Pituitary adenomas are relatively common and are very treatable. Some tumors can be treated with medications while others require surgery or radiation. Because the pituitary gland is important in the function of other glands in the body, treating a pituitary tumor requires an active coordinated multidisciplinary health care approach.
Other tumors that appear in this area, called the sellar/parasellar region, include craniopharyngiomas, germ cell tumors, and epidermoid cysts, which are tumors that arise from developmental cells; meningiomas, tumors of the protective covering of the brain; gliomas, tumors that arise from the supporting cells in the brain; and metastatic tumors that originate in another part of the body and spread to the brain.
Many pituitary adenomas are fairly small and do not lead to any symptoms. When symptoms do arise from a pituitary tumor they are caused by two mechanisms: hormonal changes caused by the tumor and the growth of the tumor. Excess hormone production can lead to the lack of a menstrual period (amenorrhea) and infertility, production of breast milk without pregnancy (galactorrhea), excess or abnormal growth (acromegaly), Cushing’s syndrome with high blood pressure and unusal changes in the skin and body, or a hyperactive thyroid. Tumors that produce hormones, known as functioning tumors, often cause symptoms when they are very small (microadenomas- less than 1 cm in diameter).
Once a pituitary tumor enlarges and it can also disrupt the remainder of the healthy pituitary gland, causing a lack of certain hormones leading to fatigue, weakness, growth problems and excessive thirst and urination. As a pituitary tumor or parasellar tumor enlarges it can lead to symptoms from direct pressure against the optic nerves. These larger pituitary tumors, known as macroadenomas (>1 cm), are usually not hormonally active and may grow outside of the sella turcica and compress the surrounding structures. These tumors can cause headaches, nausea, vomiting, and when they compress the optic chiasm can cause vision loss.
The diagnosis of pituitary and parasellar tumors is based on your symptoms, physical exam and specialized testing including an endocrine and ophthalmic assessment. For an endocrine assessment, special blood tests determine your hormone levels and whether the pituitary gland is the source of any excess hormone. Sometimes, a scan of the chest or abdomen is needed to verify that the hormone imbalances are caused by the pituitary gland. An ophthalmologist may examine your eyes and perform a visual field test to determine if the tumor is affecting your visual acuity or impairs your peripheral vision.
Imaging studies are also an important component of the diagnosis of pituitary and parasellar tumors. Magnetic resonance imaging (MRI) and Computed tomography (CT) scans are often used. The scan is usually performed with a contrast dye that makes the border and details of the tumor more visible in relation to the surrounding normal brain. The scan also provides detail information regarding the exact size, location and other structures involved by the tumor. In some cases, neurological surgeons may employ an MRI or CT scan with frameless stereotactic guidance for preoperative planning purposes. For this study, a high-resolution contrast MRI or CT is performed and then processed by a computer to create a three-dimensional model of the brain and skull base. This can be used in the operating room when performing endoscopic minimally invasive pituitary or parasellar tumor surgery.
Special tests such as MRA and angiography are sometimes used for parasellar tumors to help your medical team better see a growth or abnormality and identify its blood supply. Minimally invasive endoscopic surgery for pituitary tumors are usually performed through the sinuses with an endoscope together with an ENT surgeon that specializes in skull base surgery. The ENT specialist may evaluate your particular anatomy before surgery and perform endoscopy of the sinuses. Only examination of a patient’s tumor tissue under a microscope can confirm an exact diagnosis. This tissue is usually obtained with tumor resection.
Treatment for a pituitary or parasellar tumor depends on its hormonal activity, size and location of the tumor. The goals of treatment can vary from person to person depending on the age and overall health of the patient and their particular symptoms or hormone levels. Some small benign tumors without any symptoms or hormonal imbalances may be simply observed over time and only treated if the tumor grows over the period of observation. Certain tumors such as prolactin producing tumors could be treated with medications alone. In this situation, the drugs reduce the size of the tumor and are often prescribed long term with the help of your endocrinologist. Sometimes medications are used for hormone secreting tumors if hormone levels do not fully normalize after surgical resection.
Surgical removal of the pituitary or parasellar tumor may be recommended depending on its size, effect on surrounding structures such as the optic nerves, or its hormone secreting status. The goal is to remove as much tumor as safely possible and preferably minimally invasively. The development of endoscopic minimally-invasive skull base techniques has made surgical treatment of pituitary adenomas and parasellar tumors safer and more effective. This type of surgery avoids any skin incisions or openings of the outside of the skull. An ENT surgeon usually helps approach the tumor through the nose (endonasal) and natural sinuses and together with the neurosurgeon they remove the tumor through a thin tube with a light source at the end called an endoscope. Endoscopic techniques continue to evolve and requires careful analysis by your surgeon to determine if you are a candidate. While every effort is aimed at total removal, certain tumors present a formidable technical challenge because they adhere to vital neural and vascular structures at the base of the brain. After surgery, the tumor tissue is microscopically examined to establish an accurate diagnosis, assess the risk of recurrence and dictate the next step in treatment.
In addition to surgery, non-invasive, stereotactic radiosurgery (CyberKnife and Gamma Knife) may be used as either primary or adjunct treatment for small or residual tumors in difficult to reach locations or in patients that cannot undergo surgery. Stereotactic Radiosurgery uses numerous finely focused beams of radiation to accurately target the tumor and while minimizing the effects to any surrounding tissue. The target tumor is usually outlined on a 3-Dimensional model of the brain by the neurosurgeon and the radiation oncologist prior to the procedure.