A concussion is a mild form of closed head trauma, so an injury that results in a skull fracture or subdural hematoma (bleeding between the brain and skull) can't be accurately described as a concussion. In other words, if bleeding is present in a computer topographic (CT) scan, then another type of brain injury is present [source: Cuhna]. Most mild brain injuries can't be detected by magnetic resonance imaging (MRI) or a computer topographic CT scan [sources: CINN, Yamamoto]. Even so, such procedures are often used to detect possible severe brain damage in patients who have experienced head trauma.
In addition to lasting cognitive and emotional effects, concussion victims typically exhibit several immediate signs and symptoms that can help you diagnose such an injury.
A few common characteristics of concussions include nausea, loss of coordination or balance, confusion, delayed reaction time, slurred speech and memory loss. Although it isn't necessarily required for diagnosis, loss of consciousness is among the most common signs that a concussion has occurred. However, some alteration of consciousness must take place in order to accurately classify an injury as a concussion [Source: Lew].
People commonly keep small alterations of consciousness to themselves, which can contribute to the underreporting of concussions. However, there are a few outward signs that a person typically displays after experiencing one. Among these symptoms are vacant facial expressions, delayed reaction times, loss of focus or inability to pay attention. Therefore, even if a victim adamantly denies having experienced a subtle change in consciousness, there are certain telltale signs that allow an experienced observer to detect when a concussion has occurred [source: Lew]. Later, we'll go into detail about the various tests you can administer someone that you suspect may have recently had a concussion.
Other common symptoms include headache, dizziness and visual disturbances. Examples of the kind of vision problems that concussions might cause include photophobia -- a strong aversion to bright lights -- as well as seeing stars or having double vision.
Auditory disturbance is another symptom of concussion. A victim may experience phonophobia -- an aversion to loud noises -- and ringing of the ears. Concussions can also be psychologically disruptive, and victims may exhibit irritability, anxiety and depression. They can also experience sleep disturbance and fatigue [source: Lew].
So far, we've mostly covered the physical effects of concussion, but concussions don't stop there -- they can also affect a person's ability to think, which can be especially debilitating. A person who has experienced a concussion can become confused and disorientated. He or she may also lack attentiveness or have difficulty concentrating. Concussions can impair memory and could even hamper a person's ability to learn. Post-traumatic or retrograde amnesia is not uncommon, and the centers of the brain that control planning, ability to follow instructions, verbal fluency and brain-eye coordination may all become discombobulated by concussion [source: Lew].