Concussion or mild traumatic brain injury often goes undiagnosed at the emergency room. The reasons for this can be varied. In some cases, emergency room doctors and nurses are working very quickly and are focused on identifying serious and obvious injuries that can be life threatening. If a car accident patient is in acute pain because of a compound fracture to the femur, it is likely that emergency room staff will focus their attention on the most prevalent injury – the broken femur.  This means injuries that present with more subtle symptoms can be missed. Mild traumatic brain injury can often fall between the cracks because a car accident patient may also be focused on other physical pain. This is often referred to as a distracting injury. Moreover, sometimes patients don't realize they have suffered a concussion until days or even weeks later when they find they are more confused, forgetful and foggy than they were before the car accident. Sometimes, close family members are the first to notice these changes. The symptoms of a head injury may not immediately present, may not immediately be noticed, and might be confused with other types of injuries. For example, one of the most common symptoms of a mild traumatic brain injury is headache, but headaches can occur from non-concussion related neck strain due to whiplash. Sometimes patients don't become aware of a brain injury until they try to do something that requires complex executive functioning like multi-tasking at work.

The symptoms to watch out for include headache, brain fog, fatigue, light sensitivity, balance issues, forgetfulness, difficulty with multi-tasking, and irritability. If these symptoms present in the days and weeks after your car accident, you should talk with your doctor about having a concussion evaluation. Consider seeking a referral to a neurologist who will be able to diagnose and treat mild traumatic brain injury. You may be referred to physical therapists who focus on brain injury treatments such as vestibular therapy. You may be referred to treatment providers who focus on cognitive linguistics. There are  a number of different types of therapy that can be helpful during recovery from a concussion. In most cases, mild traumatic brain injury will resolve in three to six months. In some cases, a serious concussion can still be symptomatic after twelve months. A small number of cases will have ongoing symptoms that last for years. Even a one-time mild traumatic brain injury can increase a patient's risk of developing dementia later in life.

A 2008 article by Janet M. Powell and others titled Accuracy of Mild Traumatic Brain Injury Diagnosis appeared in the Archives of Physical Medicine and Rehabilitation. The study concluded that 56% of mild TBI cases did not have a documented diagnosis of concussion or mild TBI at the emergency room. The study suggests that the main reasons mild TBI appears to be under diagnosed at the emergency room is that technicians appear to be more focused on ruling out more serious brain injury. The study posits that negative CT scans appear to be given the greatest weight when ruling out TBI. The second most important factor appears to be whether the patient suffered a loss of consciousness.

Research on concussion has come a long way since 2008. Most neurologists now accept that loss of consciousness is not a requirement for a diagnosis of mild traumatic brain injury. A positive CT scan is also not required. While a CT scan can be effective for identifying a life-threatening brain bleed, it is not as effective in detecting the sometimes-subtle changes in the brain that correspond with mild TBI.