A brain epidermoid cyst is a benign growth that originates from trapped skin cells during the earliest stages of fetal development. These are sacs lined with cells similar to skin, not tumors in the traditional sense. They grow extremely slowly, often taking many years or decades to manifest.
Causes and Formation of Brain Epidermoid Cysts
Brain epidermoid cysts are congenital. Their formation stems from a developmental anomaly during the third to fifth week of embryonic development. During this period, ectodermal cells, which form skin and its appendages, become trapped within the neural tube during brain and spinal cord formation.
These trapped ectodermal cells form a cyst with an outer capsule resembling the epidermis. The cyst expands as its lining cells continuously shed keratin flakes and cholesterol crystals into its central cavity. This accumulation of cellular debris causes the cyst to grow slowly, exerting pressure on surrounding brain structures.
Recognizing the Symptoms
Because epidermoid cysts grow at an exceptionally slow rate, symptoms often do not become apparent until adulthood, typically between the ages of 20 and 50. The specific symptoms experienced by an individual depend entirely on the cyst’s location within the brain and its size, as the cyst exerts pressure on adjacent neural tissues.
When an epidermoid cyst is located in the cerebellopontine angle, a common site, individuals may experience progressive hearing loss, tinnitus, or problems with balance and coordination. Pressure on cranial nerves in this region can also lead to facial numbness, weakness, or spasms. Cysts near the pituitary gland, which regulates hormones, can cause vision problems, such as double vision or partial blindness, or hormonal imbalances. Headaches are common, varying in intensity and frequency, and some individuals may experience seizures if the cyst irritates the brain’s outer layers. In rare instances, a cyst rupture can release its contents into the cerebrospinal fluid, leading to aseptic meningitis.
The Diagnostic Process
Identifying a brain epidermoid cyst primarily relies on advanced medical imaging techniques. When a patient presents with symptoms that suggest a brain abnormality, doctors will typically order imaging tests to visualize the brain’s internal structures. Magnetic Resonance Imaging (MRI) is the preferred and most effective diagnostic method.
MRI scans provide detailed images that allow clinicians to differentiate epidermoid cysts from other types of brain lesions, such as arachnoid cysts or dermoid cysts. On T1-weighted MRI sequences, epidermoid cysts usually appear dark, similar to cerebrospinal fluid, but they appear bright on T2-weighted sequences. A distinguishing feature is their bright signal on diffusion-weighted imaging (DWI) sequences, which helps confirm the diagnosis and distinguish them from other fluid-filled cysts. Computed Tomography (CT) scans can also be used, where epidermoid cysts appear as low-density lesions, but MRI offers superior soft tissue contrast and more definitive diagnostic information.
Treatment and Management
The primary treatment for symptomatic brain epidermoid cysts is surgical removal, also known as resection. The objective of surgery is to achieve the most complete removal of the cyst and its outer capsule. Removing the entire capsule is important because remaining cells can shed debris, leading to cyst recurrence.
However, complete removal is not always feasible, especially when the cyst capsule adheres tightly to delicate structures like cranial nerves, blood vessels, or the brainstem. In such cases, surgeons may perform a subtotal resection, leaving a portion of the capsule to avoid neurological damage. Patients undergoing subtotal resection require ongoing follow-up with regular MRI scans to monitor for regrowth or expansion of the residual cyst. The prognosis following surgical removal is generally favorable, particularly when total resection is achieved.