Epidermoid tumors (epidermoid cysts or epidermal cysts) are very rare (about 0.3% of all brain tumors). They are benign, congenital tumors that usually grow very slowly. They arise due to developmental disorders of embryonic cells that actually belong to the epithelium of the skin but were dispersed into the brain tissue during embryonic development. These cell clusters can increase in volume, usually over a period of years, and they produce horny scales that spread as a doughy mass surrounded by a thin capsule in the spaces between the brain and the base of the skull - the cerebro-spinal fluid spaces. The dermoid cysts, which are even rarer than epidermoid cysts, arise from multiple skin layers and may contain hair, glands and even embryonic teeth.
The most common location of epidermoid tumors is the posterior fossa, specifically the cerebellopontine angle and the space in front of the brainstem. Very rarely they are located in the spinal canal. Because of their slow growth, they usually do not become symptomatic until young to middle adulthood.
Epidermoids grow slowly and symptoms can be subtle and wide-ranging. When the tumors reach a certain size, symptoms result from pressure on the surrounding brain structures and cranial nerves. If the tumor is located at the brainstem and cerebellopontine angle, the irritated cranial nerves may cause hearing loss, facial pain, dizziness, difficulty swallowing or unsteady gait. Over time paralysis and disturbances of the cerebro-spinal fluid (CSF) circulation with loss of consciousness and respiratory disturbances may occur. Occasionally, spontaneous emptying of the encapsulated contents of the epidermoid cysts may occur, which may lead to irritation of the meninges and cranial nerves, culminating in aseptic meningitis with headache, fever and neck stiffness.
Magnetic resonance imaging (MRI / MRT) is the investigation of choice. In T1 and T2 sequences, epidermoid tumors appear similar to cerebrospinal fluid (CSF); in diffusion-weighted MRI sequences, they stand out with a bright signal compared to their surroundings. In high-resolution CISS sequences, the tumor tissue and the usually deformed cranial nerves can be visualized, which is very helpful for 3D surgical planning and intra-operative 3D navigation.
Complete microsurgical resection of an epidermoid or dermoid is the therapy of choice. Cure is possible with surgery. Occasionally, the tumor capsule is adherent to cranial nerves and vessels, and in these cases small portions of the capsule might be left behind in order to minimize the risk cranial nerve palsy or hemorrhage.
Because of the spatial growth and extent of epidermoid tumors between cranial nerves and blood vessels and into the smallest pockets of the subarachnoid space, the use of endoscopes is very advantageous for tumor removal. With this technique, parts of the tumor that are not visible in a straight line with the microscope can be reached and removed gently without having to move healthy tissue aside during the operation, thus exposing it to a risk of injury. In addition, during each operation, the functions of the cranial nerves and the brainstem are monitored by state-of-the-art intra-operativeneuro-monitoring. Combined, these technologies allow for maximum microsurgical precision and patient safety.
Patients can usually leave
the hospital 2-4 days after surgery. With complete resection, even if tiny
remnants of the capsule were left behind, recurrence, i.e., regrowth of the
epidermoid tumor, is highly unlikely.