A 35-year-old man presented with new onset headache and dizziness in our emergency service. An hyperdense lesion was determined near the third ventricle rostrum in the vicinity to the right of the Foramen of Monroe. The patient was immediately evaluated with MRI. MRI fi ndings were consistent with a colloid cyst. In addition, there was acute ischemia throughout the right anterior cerebral watershed area which was represented by edema and gyral thickening. The, patient was taken to the intensive care unit for follow up and for planning advanced evaluation. With symptomatic treatment, rapid improvement of the complaints was seen. Due to these follow up fi ndings, invasive procedures such as conventional angiography or operation was not applied. The cyst regressed and showed decreased density on the control CT scans taken the following day. Throughout the follow up periods, no signs of hydrocephalus, intracranial herniation or hemorrhage were determined. The fi rst distended cyst disappeared with complete resolution by spontaneous rupture. In the fi rst year control MRI, encephalomalacia had developed throughout the previous watershed area. A cystic lesion was no longer visible. Also, cranial MR angiography examination demonstrated occlusion of the right ACA. To the best of our knowledge, this is the fi rst case of a spontaneously ruptured colloid cyst that caused vascular compression which resulted in acute infarction of the ACA territory.

Keywords: Colloid cyst, spontaneous resolution, infarction