Abstract
Background and Clinical Significance: Fourth-ventricular epidermoid cysts are rare intracranial lesions. They account for fewer than 1% of all primary brain tumors. Fourth-ventricular epidermoid cysts grow slowly because they are closely related to brainstem, cerebellum, and major blood vessels, so their treatment requires special caution. Because the cyst capsule attaches to functionally sensitive locations, complete removal is usually not possible without compromising some aspect of brain or spinal cord function. Surgical decision-making always involves weighing the need to remove the entire cyst against the potential loss of function of the affected area. The following case study describes how a patient was treated with a focus on the relationship between the cyst and surrounding anatomy, allowing for successful decompression with minimal risk to the patient's neurologic status. Case Presentation: A young adult female patient was hospitalized with progressive truncal ataxia, disequilibrium and occipital headache accompanied by papilledema. Her physical examination disclosed significant dysfunction of the midline cerebellar region (SARA score = 18/40, ICARS score = 42/100), gaze-evoked nystagmus and bilaterally elevated grade II papilledema. MRI and MRA demonstrated a large, lobulated, nonenhancing, avascular mass located within the fourth ventricle, encroaching upon the dorsal medulla and obstructing both the foramen of Magendie and foramina of Luschka-findings typical of an epidermoid cyst. Microsurgical resection was accomplished via a median suboccipital craniectomy using a telovelar approach along the embryonic cerebellomedullary fissure to protect the integrity of the vermis and brainstem. The cyst contained layers of keratin embedded in a thin, translucent capsule. The capsule was carefully dissected away from the floor of the fourth ventricle. A very narrow band of capsule attached to the rhomboid fossa was intentionally spared to avoid damaging the cranial nerves. The patient had normal cerebrospinal fluid circulation restored and normal ventricular pulsation observed during surgery. Histopathology confirmed a benign epidermoid cyst consisting of keratinizing stratified squamous epithelium containing cholesterol clefts and laminated keratin debris. After surgery, the patient exhibited continuous neurological improvement including restoration of balance, disappearance of her headaches, and normalization of ocular pursuit. Sequential imaging studies were conducted post-operatively at one week, one month, three months, five months, and seven months to document stable decompression of the fourth ventricle, re-expansion of the fourth ventricle, and no evidence of cyst recurrence. Post-operative course was uncomplicated and the patient has remained free of symptoms and fully independent functionally at most recent follow-up. Conclusions: This case illustrates that when anatomically oriented, "maximal safe resection" can result in long-lasting decompression and clinically meaningful improvement in neurological function in patients with fourth-ventricular epidermoid cysts. Restoration of the patient's natural cerebrospinal fluid pathway and preservation of neural interface relationships is more beneficial than pursuing aggressive removal of the cyst capsule. Although the risk of late recurrence is present even after nearly total removal, continuous radiologic monitoring is necessary to identify any recurrence. These experiences illustrate that with the principles of surgical restraint and anatomical guidance, there can be a balance between long-term stability and low operative risk.