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.
- Subarachnoid hemorrhage
A bleeding into the subarachnoid, the space between the arachnoid and the pia mater, the innermost membrane surrounding the central nervous system. Subarachnoid hemorrhage typically occurs when an artery breaks open in the brain, such as from a ruptured aneurysm. This can require emergency neurosurgical procedures.
Under the clavicle (the collar bone), as the subclavian artery or the subclavian vein.
- Subclavian steal
The symptoms of cerebral vascular insufficiency (not enough blood to the brain) when the patient exercises an arm, due to obstruction of the subclavian artery before the origin (the takeoff) of the vertebral artery. Exercising the arm causes the blood flow to reverse and the subclavian artery “steals” blood from the vertebral artery. The subclavian […]
- Subclinical disease
An illness that is staying below the surface of clinical detection. A subclinical disease has no recognizable clinical findings. It is distinct from a clinical disease, which has signs and symptoms that can be recognized. Many diseases, including diabetes, hypothyroidism, and rheumatoid arthritis, are frequently subclinical before they surface as clinical diseases.
- Subconjunctival hemorrhage
A very common cause of a painless bloody eye usually first noticed by somebody else or by the person with it when they look in the mirror. The bleeding results from a break in a small blood vessel in the sclera, the white of the eye. This releases a tiny amount (less than a drop) […]