Spontaneous Regression of a Third Ventricle Colloid Cyst

Background Colloid cysts represent 0.5%–1% of intracranial tumors and most commonly occur in the third ventricle near the Monro foramen. Although benign, if the lesion obstructs the foramen abruptly, sudden death may ensue. Evolution of these cysts is poorly understood. Spontaneous regression has been reported in only 2 other cases. Management of such cysts depends on whether the cyst continues to grow, its location, and clinical presentation. Incidental asymptomatic colloid cysts are typically followed with neuroimaging surveillance. Case Description We present a case of an incidental third ventricle colloid cyst in a 46-year-old patient who was managed conservatively with neuroimaging surveillance. Thereafter, she started developing some working memory deficits and intermittent headaches, with the cyst volume increasing, leading to the decision to perform a resection. However, the cyst underwent spontaneous regression before the scheduled surgery date, 3 years after initial diagnosis. Conclusions This case confirms that some colloid cysts could regress spontaneously. Disappearance of the cyst is not necessarily accompanied by clinical worsening, as was reported by other investigators who noted deteriorating neurologic deficits as a result of worsening hydrocephalus. Assuming the cysts rupture, some patients tolerate the contents of the cyst leaking into the ventricular system, whereas others may mount an inflammatory reaction, causing a disruption in cerebrospinal fluid flow. In addition, it is still unclear what factors increase the likelihood of cysts to suddenly rupture.