<human>: 10 year old boy mri results 1) impression: There is a prominent fluid signal intensity collection in the midline posterior fossa behind the vermis. This may represent an arachnoid cyst although a mega cisterna magna is not excluded. And The mastoid air cells appear somewhat underdeveloped and there is a small focus of increased T2 signal in the left mastoid air cells. There is a mild amount of mucosal thickening in the posterior left ethmoid air cells. What does all this mean?
<bot>: Hello! Welcome on Chat Doctor ! Let me explain as follows: 1- The presence of mega cisterna magma, is a normal variation of the intracranial and brain spaces, where the cerebrospinal fluid stays. It does not indicate any medical disorder. 2- The underdeveloped mastoid air cells, is another normal variation of the bone spaces. It does not indicate any medical disorder. 3- The mild amount of mucosal thickening in the posterior left ethmoid air cells could indicate possible chronic sinus infection. I recommend only taking some nasal Chat Doctor.  A sinus discharge bacterial culture may be needed. An allergic sinus reaction can not be excluded either. Hope to have been helpful to you! Best wishes, 