A suprasellar mass is a tumor or abnormal growth situated just above the sella turcica, a saddle-shaped bony structure at the base of the skull. This small region is a highly complex crossroads of the brain, making any growth here capable of causing significant disruption. Analyzing a suprasellar mass involves determining its precise nature, assessing the extent of its growth, and formulating a plan to relieve the pressure it exerts on adjacent neural and hormonal pathways.
Anatomical Location and Significance
The suprasellar region refers to the area directly superior to the sella turcica, the bony depression that houses the pituitary gland. This location is functionally significant because it contains several structures responsible for vision and hormone control. The space itself is part of the suprasellar cistern, a fluid-filled cavity within the brain’s protective layers.
Within this cistern lies the optic chiasm, where nerve fibers from the inner half of each eye cross to the opposite side of the brain. The pituitary stalk, a thin connection carrying signals and hormones between the hypothalamus and the pituitary gland, also passes through this area. Just above the stalk and chiasm are the hypothalamus and the floor of the third ventricle, which regulate body temperature, hunger, and sleep.
A mass growing in this confined space inevitably presses upon these structures, leading to a predictable set of symptoms.
Primary Causes of Suprasellar Masses
The masses found in the suprasellar region are diverse, but a few types account for the majority of cases. Pituitary adenomas, which originate in the pituitary gland below, are the most common tumors to extend upward into the suprasellar space. When these growths exceed 10 millimeters, they are classified as macroadenomas and frequently push through the protective membrane above the gland.
Many large pituitary adenomas are non-functioning, meaning they do not secrete excess hormones, and grow silently until they cause compression symptoms. Craniopharyngiomas are another frequent cause, often presenting with a bimodal age distribution, affecting children and older adults. These growths arise from remnants of Rathke’s pouch, the embryonic tissue that forms the anterior pituitary gland.
Craniopharyngiomas are typically benign but are locally invasive, often presenting as a mixture of solid tissue and fluid-filled cysts, which may contain calcifications visible on imaging. Less common causes include meningiomas originating from the dural covering of the skull base, and large aneurysms of the internal carotid or anterior communicating arteries, which can mimic a solid tumor mass.
How Suprasellar Masses Affect the Body
The symptoms produced by a suprasellar mass are directly related to the specific structures being compressed. Visual impairment is one of the most common complaints, usually manifesting as bitemporal hemianopsia. This characteristic visual field defect involves a loss of peripheral vision on the outer (temporal) side of both eyes, creating a form of tunnel vision.
This loss occurs because the mass typically grows upward from below, placing pressure directly onto the center of the optic chiasm. This damages the crossing nerve fibers, which carry visual information from the peripheral fields. When these fibers are compressed, the temporal field of view is lost in both eyes.
The endocrine system is also affected due to pressure on the pituitary stalk and hypothalamus. This can lead to hypopituitarism, a condition where the pituitary gland stops producing sufficient amounts of one or more hormones, such as growth hormone, thyroid-stimulating hormone (TSH), or adrenocorticotropic hormone (ACTH). Damage to the hypothalamus or pituitary stalk can also cause central diabetes insipidus, a failure to produce or release antidiuretic hormone (ADH), resulting in the excessive excretion of dilute urine and intense thirst.
Neurological symptoms, such as persistent headaches, can occur because the mass may obstruct the flow of cerebrospinal fluid (CSF) in the third ventricle. This blockage causes CSF to accumulate, leading to obstructive hydrocephalus and a buildup of pressure within the skull. The mass can also lead to generalized symptoms, including fatigue, cognitive changes, or behavioral disturbances.
Identification and Treatment Strategies
The identification process for a suprasellar mass begins with magnetic resonance imaging (MRI) of the brain and sella, which is the preferred method for visualizing soft tissues and the relationship of the mass to the optic chiasm. A computed tomography (CT) scan may be used to identify any calcifications or bony erosion, which helps differentiate between tumor types. Visual field testing (perimetry) is performed to map the extent of bitemporal hemianopsia and monitor changes.
A comprehensive endocrine workup is also performed to identify any hormonal deficiencies or excesses. This involves blood tests to measure levels of key hormones, such as prolactin, TSH, and cortisol. Specialized dynamic tests, like the water deprivation test, are used if diabetes insipidus is suspected.
Surgical removal is often the first line of treatment, with the minimally invasive transsphenoidal endoscopic approach being favored when possible. This technique accesses the mass through the nasal cavity and sphenoid sinus, avoiding manipulation of brain tissue and offering better visual outcomes.
The transcranial approach, requiring an opening in the skull, is reserved for masses with significant lateral extension or those that are highly complex. Following surgery, radiation therapy may be used for tumor remnants, employing highly focused techniques to precisely target the tissue while sparing nearby structures like the optic chiasm.