VOLUME 10 | ISSUE 1 9 H R J Mega Cisterna Magna: A Case Series, p. 00-00 SUBMISSION: 17/04/2024 - ACCEPTANCE: 11/07/2024 Mega Cisterna Magna: A Case Series Abdulwahab F. Alahmari Radiology Department, Al-Namas General Hospital, Ministry of Health, Al-Namas City, Saudi Arabia. Abstract This paper presents nine cases of mega cisterna mag- na, which could be a normal anatomical variation, not a result of a pathological process in many cases. The cases in this paper show three patterns of mega cister- na magna: bilateral, unilateral, and contained. One of these types is more dangerous because it is more associ- ated with anatomical variations of falx cerebelli. All the patients in this case series were all male patients who were collected randomly, which contradicts the gender predilection in the literature. Corresponding Author, Guarantor Abdulwahab F. Alahmari Radiology Department, Al-Namas General Hospital, Ministry of Health, Al-Namas City, Saudi Arabia Email: afaa99@hotmail.co.uk Phone number: +966562428716 Original Article Neuro Imaging Key words Mega Cisterna Magna; Cisterna Magna; Computed Tomography; Brain Cisterns; Normal Variation; Neuroradiology. Introduction Mega Cisterna Magna (MCM) is a focal subarachnoid space filled with CSF in the reterocerebellar space in the posterior cranial fossa. MCM is found in 1% of post-natal brain scans and it makes up to 54% of the cystic malformation of the occipital fossa [1]. MCM is associated with infarctions, chromosomal malforma- tions (i.e. trisomy 18), and infections (i.e. cystomegalo- virus). The differntial diagnosis for MCM includes the following: posterior fossa cysts (i.e. both epidermoid and arachnoid), Dandy-Walker variant, persistent Blake’s pouch cyst, and posterior fossa neoplasia (i.e. pilocystic astrosytoma) [2]. MCM has been associat- ed with autism spectrum disorder [3, 4]. When MCM exists and there is no abnormility in the ventricles, it should be considered an anatomical variation with no prognostic significance [2]. There is no surgical inter- vention for MCM cases [2].