Presentation
Headache.
Patient Data
MRI study demonstrates a large left frontotemporal extra-axial cystic lesion expanding the left middle cranial fossa and Sylvian fissure, measuring 9.5 x 10.5 x 5.1 cm. The lesion follows cerebrospinal fluid (CSF) signal intensity on all pulse sequences and does not show abnormal enhancement, consistent with a Type III Galassi arachnoid cyst. There is notable displacement of the adjacent frontal and temporal lobes with a 10 mm midline shift at the anterior aspect of the falx cerebri. No associated perilesional edema is observed.
Additionally, the MRI reveals a developmental venous anomaly (DVA) in the right occipital lobe, characterized by multiple small veins converging into a single large vein draining into a deep ependymal vein. This is associated with an area of hypersignal intensity on FLAIR, suggestive of gliosis or mild edema.
Case Discussion
Arachnoid cysts are benign lesions most commonly located within the intracranial compartment. In this case, the large left frontotemporal arachnoid cyst corresponds to a Type III Galassi cyst, which is the rarest subtype, accounting for only 3% of cases. Type III cysts are typically large, cause significant mass effect, and, as seen here, may result in a midline shift or compression of adjacent brain structures without evidence of perilesional edema. The midline shift and the displacement of the frontal and temporal lobes in this case underscore the impact of the cyst's size on intracranial dynamics. Arachnoid cysts are often asymptomatic but may lead to neurological dysfunction when large enough to exert mass effect.
The right occipital developmental venous anomaly (DVA) observed in this patient is a common cerebral vascular malformation, often incidentally discovered. DVAs are usually asymptomatic, but they can be associated with other vascular anomalies, such as cavernous malformations, or lead to complications like ischemic events or hemorrhage. The associated FLAIR hypersignal intensity in this case may reflect gliosis or subtle edema, which can occasionally be seen in the surrounding brain tissue of DVAs.
Although both lesions are considered benign, their size and location warrant clinical correlation, especially in the context of symptoms such as headaches or neurological deficits. Treatment options for the arachnoid cyst may include surgical intervention, especially if symptoms of mass effect worsen. DVAs, in contrast, generally do not require treatment unless associated with complications.
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