Arachnoid cyst: extremely large

Case contributed by Dr Yair Glick


Headache. Recurrent bouts of sinusitis. Suspected acute sinusitis.

Patient Data

Age: 16 years

Complete opacification of sphenoid sinus on left, mucosal thickening on right. Tiny focal polypoid muosal thickening in floor of left maxillary sinus.
Adenoidal hypertrophy with moderate narrowing of nasopharynx and pharyngeal tonsillar hypertrophy with severe narrowing of oropharynx (not shown in entirety).
Thickened nasal conchae, left concha bullosa.

Large fluid-density right frontotemporal structure, probably a huge arachnoid cyst.

NB: The study was uploaded with a higher contrast than the original "sinus" (i.e. "internal acoustic canal") window to better display the intracranial structure.


Huge right frontotemporal arachnoid cyst causing a mass effect very mild for its size, including narrowing of the right lateral ventricle and a relatively mild subfalcine herniation.

Case Discussion

Incidentally discovered arachnoid cyst on CT sinuses.

The window for CT sinuses is very wide, rendering brain parenchyma and fluid an almost identical medium gray but nevertheless, the radiologist noticed an ever so slightly hypodense intracranial area on the right. Owing to its sharp borders, arachnoid cyst was the most likely candidate, and this was indeed proved by MRI.

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Case information

rID: 68741
Published: 11th Jun 2019
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included
Institution: Laniado Hospital

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