Rare diseases · Sign or symptom
Arachnoid cyst
Fluid-filled sac located in membrane surrounding brain or spinal cord
HP:0100702
What it means
An extra-parenchymal and intra-arachnoidal collection of fluid with a composition similar to that of cerebrospinal fluid.
Arachnoid cysts can be found on the brain, or on the spine. Intracranial arachnoid cysts usually occur adjacent to the arachnoidal cistern. Spinal arachnoid cysts may be extradural, intradural, or perineural.
Rare diseases that can present with this21
Common30–79%
3Sometimes5–29%
13- Apert syndrome
- Autosomal dominant polycystic kidney disease
- Colobomatous microphthalmia-obesity-hypogenitalism-intellectual disability syndrome
- Facial dysmorphism-developmental delay-behavioral abnormalities syndrome due to WAC point mutation
- Houge-Janssens syndrome type 1
- Internal carotid absence
- Microcephalic cortical malformations-short stature due to RTTN deficiency
- Orofaciodigital syndrome type 2
and 5 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Arachnoid cysts
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.