Definition of Subarachnoid
Subarachnoid: Literally, beneath the arachnoid, the middle of three membranes that cover the central nervous system. In practice, subarachnoid usually refers to the space between the arachnoid and the pia mater, the innermost membrane surrounding the central nervous system.
The subarachnoid space is a potential space. It normally contains cerebrospinal fluid. A subarachnoid hemorrhage is a bleed into this space.
The arachnoid is named for its delicate, spider-web-like filaments that extend from its undersurface through the cerebrospinal fluid in the subarachnoid space to the pia mater. "Arachnoid" comes from the Greek "arachne" meaning spider or cobweb + "eidos" meaning resemblance = spider-web-like.
Last Editorial Review: 8/28/2013
Back to MedTerms online medical dictionary A-Z List
Need help identifying pills and medications?
- Allergic Skin Disorders
- Bacterial Skin Diseases
- Bites and Infestations
- Diseases of Pigment
- Fungal Skin Diseases
- Medical Anatomy and Illustrations
- Noncancerous, Precancerous & Cancerous Tumors
- Oral Health Conditions
- Papules, Scales, Plaques and Eruptions
- Scalp, Hair and Nails
- Sexually Transmitted Diseases (STDs)
- Vascular, Lymphatic and Systemic Conditions
- Viral Skin Diseases
- Additional Skin Conditions