they are congenital benign tumor accounting for 15 - 20 % of intraventricular mass but only about 1% of intracranial ones ( 1 - 3 ) . they can be diagnosed at any age but usually become symptomatic in the third to sixth decades and more common in men than women . they usually found incidentally and are asymptomatic ; but in some instances may associate with rapid neurologic deterioration , herniation , and sudden death . so , recognition of this rare but important diagnosis may result in decreasing mortality ( 4 ) . in this report , we presented a 13-year - old boy with complaint of two times drop attack and final diagnosis of colloid cyst in the third brain ventricle . a 13-year - old boy was brought to the emergency department ( ed ) with complaint of two times drop attack . the patient mentioned that he felt sudden weakness in both lower limbs , which led to drop . these attacks were happened about 4 hours before admission and he did not have any same experience previously . he did not have complaint of nausea , vomiting , headache , vertigo , blurred vision , or palpitation . the subject did not have any known structural or congenital heart disease , but suffered from asthma and used salbutamol spray irregularly . the patient did not have trauma history and there was no positive history of any known medical illness in his parents or closed relatives . on arrival , he had 36.9c axillary temperature , 16/minute respiratory rate , 90/minute pulse rate , 120/80 mmhg blood pressure , and 96% oxygen saturation at room air .   on physical examination , he did not have focal neurologic findings or even paresthesia or paraplegia . general examination of head and neck , chest , abdomen , and limbs did not reveal any positive findings . following the evaluation process , a brain computed tomography ( ct ) was performed ( figure-1 ) . a hyperdense round lesion was seen in the third ventricle consequently caused that the corresponding physician requested a neurologic consultation in the ed . finally , the brain magnetic resonance imaging ( mri ) confirmed the diagnosis of third ventricle colloid cyst and the patient was underwent surgery and discharged without any problem ( figure 2 ) . the colloid cysts commonly settle near the foramen of monro in the anterior third ventricle and so may encounter with drainage of the cerebrospinal fluid ( csf ) ( 3 ) . since even a small lesion can block the mentioned foramen , these cysts may result in hydrocephalus and increase the intra cranial pressure ( 5 ) . increased intracranial pressure can be manifested with headache described as severe and intermittent , with short duration , usually located frontally . in contrast with usual headaches , secondary to intracranial tumors , the colloid cyst induced headache can be relieved by lying down ( 4 ) . other symptoms include drop attacks , gait abnormalities , progressive dementia , and transient loss of consciousness . in children , the most common symptoms are nausea , vomiting , headache , diplopia , and papilledema ( 6 ) . the classic clinical description of intermittent headaches and drop attacks occurs in only one - third of patients . sudden obstruction of the ventricular system and following rapid rising of intracranial pressure can lead to herniation and rarely sudden death ( 7 , 8) . colloid cysts size varies from 3 - 40 millimeters in diameter , but the size do not related to their symptoms or outcome , as even small ones may lead to sudden death ( 9 ) . colloid cyst is usually diagnosed by non - contrast computed tomography ( ct ) as an oval or rounded hyperdense mass on the anterior aspect of the third ventricle . they may occasionally be hypodense or isodense to the brain , or found in other areas of the brain . colloid cysts have different manifestation on mri . despite their variable signal characteristics , their location and shape help to the correct preoperative diagnosis in most patients ( 6 ) . half of the cases are hyperintense on t1-weighted mri images and hypointense on t2-weighted mri images respected to brain . isointense cysts are not easily identified on mri , and in such instances ct scan is more useful ( 9 , 10 ) . small asymptomatic colloid cyst can be considered for close follow up by serial examinations and neuroimaging ( 11 ) . there is also the rare report of spontaneous resolving of the third ventricle colloid cyst ( 12 , 13 ) . all authors passed four criteria for authorship contribution based on recommendations of the international committee of medical journal editors .
colloid cysts are mucous - filled masses with an outer fibrous layer . 
 these cysts are rare developmental malformation and not a true neoplasm . 
 they usually found incidentally and are asymptomatic ; but in some cases may associate with rapid neurologic deterioration , herniation , and sudden death . 
 recognition of this rare but important diagnosis may result in decreasing mortality . in this report 
 , we presented a 13-year - old boy with complaint of two times drop attack and final diagnosis of colloid cyst in the third brain ventricle .