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Second Impact Syndrome

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Last Update: July 3, 2023.

Continuing Education Activity

Second impact syndrome is a condition in which an individual experiences a second head injury before completely recovering from a prior head injury. It is thought that athletes who sustain a concussion and return to their sport early are at exceptionally high risk. Though second impact syndrome is a relatively rare condition, individuals who have experienced or are at risk of experiencing a head injury should be educated about the risks associated with sustaining another head injury before recovering from a prior injury. This activity describes the pathophysiology, evaluation, and management of second impact syndrome and highlights the role of the interprofessional team in the management of affected patients.


  • Identify patients at risk for second impact syndrome based on their clinical history.
  • Evaluate patients for the signs and symptoms of second impact syndrome.
  • Assess and manage the complications of second impact syndrome.
  • Develop and implement effective interprofessional team strategies to improve outcomes for patients with head injuries.
Access free multiple choice questions on this topic.


Second impact syndrome (SIS) is a condition in which an individual experiences a second head injury before completely recovering from a prior head injury[1]. Second impact syndrome has recently gained increased attention as many cite athletes sustaining a concussion and returning to the sport early as being particularly at risk. Though it is a relatively rare condition, physicians should be aware of SIS and educate patients who have experienced or are at risk of experiencing a head injury, as the syndrome is often deadly. The term second impact syndrome entered the medical lexicon in 1984 when Saunders and Harbaugh wrote an article describing a case report of a football player who died four days after suffering a head injury after he returned to play on the day of his death. He collapsed and died after a presumed second head injury.[2]


There have been very few confirmed cases of SIS to date; therefore, the exact incidence, risk, and pathophysiology of the condition are unknown. According to the Centers for Disease Control and Prevention, an estimated 1.6 to 3.8 million sports-related concussions occur in the United States each year.[2]While the etiology of a concussion is generally understood, the etiology of a second impact syndrome is not well understood. The generally accepted cause relates to sustaining a second concussion before the brain has a chance to recover from the initial insult fully. The athlete will rapidly develop altered mental status and a loss of consciousness within seconds to minutes of the second hit, resulting in catastrophic neurological injury.[3] The devastating injury results from the dysfunctional cerebral blood flow autoregulation, leading to an increase in intracranial pressure. The pressure rapidly develops and eventually results in brain herniation. The herniation may occur either medially across the falx cerebri or inferiorly through the foramen magnum, resulting in brain stem injury and rapid deterioration and leading to death within 2 to 5 minutes. A recent case report sheds some light on the injury pattern[4]. An athlete returned to hitting drills five days after his initial concussion. He had a routine CT scan on day four but had a persistent severe headache. After getting hit at practice one day later, he collapsed several plays later after complaining of headaches and not being able to feel his legs. A second CT done in a local emergency room demonstrated bilateral but thin subdural hematomas. However, a subsequent MRI demonstrated caudal displacement of midline structures with injury to both thalami resulting in transtentorial herniation.[4]


A review article in 2016 completed a PubMed search and found only 36 cases reported in 15 publications, with 17 cases meeting the inclusion criteria.[3] The characteristics of an athlete susceptible to a second impact injury were male gender, aged 13 to 24 years, and contact sports like American football, boxing, and hockey. Only 7 of the 17 received a direct blow to the head; the others were thought to have received a blow to the body and the forces transmitted to the head. Computed tomography (CT) demonstrated diffuse cerebral edema with midline shift leading to herniation in 4 of the cases. Additionally, all of the cases had either thin or moderate subdural hematomas, 2 of the cases had a subarachnoid hemorrhage, and 3 suffered an ischemic stroke.


Patients who have experienced a concussion show a poorly understood but complex array of neuronal, metabolic, and ionic changes. The mechanism of injury seems to be associated with axonal shearing. This causes rapid depolarization, neurotransmitter release, and ionic shifts where potassium ions leak extracellularly and are replaced with sodium and calcium intracellularly. This results in dysregulation of the cerebral blood flow leading to edema. Thus increased glucose utilization combined with the injury-related decrease in resting cerebral blood flow creates an energy mismatch. [5] All these changes require time and energy for a return to normal neurotransmitter physiology. Generally, this is thought to take about 7 to 10 days but may be longer in younger athletes. Metabolic abnormalities after an initial concussion may leave the brain more susceptible to further injury. [6]

History and Physical

Any athlete who has returned to play after a concussion should be watched carefully, even if they have had an appropriate recovery period and completed a return-to-play protocol. A concussed patient will report any combination of symptoms, including a headache, nausea, memory loss, dizziness, blurry vision, confusion, fatigue, photo- or phonophobia, motor or sensory loss, poor hand-eye coordination, or emotional irritability/lability. On physical examination, the patient may have an altered level of consciousness, retrograde, or post-traumatic amnesia, but generally, difficulty concentrating and balance seem to be consistently impaired. Additionally, there may be sensory or motor abnormalities or visual abnormalities. Unless the player has been knocked out, if they remain on the field of play, they may show signs of ataxia, running in the wrong direction, or slowed reaction time.

As concussions have been more widely recognized and the complications related to insufficient recovery have become better recognized, sideline evaluations have developed. Sideline evaluation of cognitive function is an essential component in assessing this injury. Brief neuropsychological (NP) test batteries that assess attention and memory function are practical and effective. Such tests include the SCAT5, which incorporates the Maddocks' questions, and the Standardised Assessment of Concussion (SAC).[7]

For an athlete who has collapsed with a suspected SIS, a Glasgow coma scale score, pupillary reactivity, deep tendon reflexes, upper/lower extremity clonus, and the presence or absence of a Babinski reflex can be done before transport or upon arrival at the emergency room.  

Due to the challenges of what constitutes a second impact syndrome, the lack of research, and the rapidly progressing nature of the condition, it is challenging to provide sound guidance on an appropriate history and physical exam. Perhaps clinicians should change their mindset and think every concussion they see, especially in male athletes aged 13 to 24, could be a second impact syndrome and observe the injured athlete closely for progressing signs or symptoms.  


Obtaining a thorough history is critical in evaluating a patient with a suspected brain injury. Though the patient will unlikely be able to provide a good history, one should gather as much information from those who may have witnessed the incident. It is essential to determine how the injury occurred, if there is any seizure or concussion history, if alcohol or illicit drug use was involved, whether or not there was any loss of consciousness, any resultant weakness or paresthesias, difficulty walking, or incontinence of the bladder or bowel.

Patients who have experienced significant injury or loss of consciousness, continued symptoms, deterioration in neurologic function, or neurologic deficits should be evaluated with imaging studies. Screening for alcohol or illicit drugs would be recommended. CT is the preferred imaging modality for acute head trauma. It is a more sensitive imaging modality for detecting acute hemorrhage than a nonenhanced CT, provides better delineation of bone, and is more sensitive in detecting acute hemorrhage and identifying any surgically reversible injuries. 

Current guidelines recommend a CT for a suspected skull fracture, intracranial bleeding, or other intracranial disorders based on physical exam findings.[8] Since second impact syndrome injuries generally cause loss of consciousness, it would seem prudent to start with a CT scan of the head. 

Treatment / Management

The management of second impact syndrome is limited due to the limited understanding of the condition, the lack of research, and the controversial nature of the condition. The management of SIS starts with prompt recognition of a sports-related concussion and protecting the athlete until they recover from the initial injury. The current treatment guidelines consist of relative rest, both cognitive and physical, and then a graded return to play. This should be supervised ideally by a team physician with experience in managing concussions and athletic training staff. The athlete should not be cleared to return to full participation until they have completed a return-to-play protocol and the medical staff gives clearance.[5]

Differential Diagnosis

The differential diagnosis of second impact syndrome includes:

  • Subarachnoid bleed
  • Ischemic stroke
  • Subdural hematoma
  • Basal skull fracture
  • Skull fracture.

Deterrence and Patient Education

Primary prevention seems to be the most logical answer for a second impact syndrome. Parents and athletes should be educated on the potential complications of a concussion, symptoms, and an expected time course for recovery. This would include discussing the potential problems related to returning to play too soon, including prolonged recovery, persistent symptoms, and a second impact syndrome. Encouragement from parents and coaches will help the athlete avoid minimizing symptoms and returning to play too soon. Most return-to-play protocols will take at least seven days before the athlete is cleared to participate.

Enhancing Healthcare Team Outcomes

The diagnosis of concussion remains a clinical one as it is based on a constellation of symptoms. Because of this, the team physician's experience in evaluating and managing concussions would be recommended. An interprofessional team with clear communication between the athlete, parents, coaches, athletic training staff (if available), and the physician or nurse practitioner would be essential. It appears at this time a second impact syndrome is a preventable injury. It is thought if an athlete is allowed to fully recover from an initial concussion and not be allowed to return too quickly, the second impact event will be unlikely to occur. School nurses should participate in the education of patients and their families.

If a player goes down on the field from a suspected head injury, the on-field medical staff, emergency personnel, and the emergency room should communicate clearly to optimize the care of the injured athlete. A standard communication tool like SBAR will allow for efficient and clear communication amongst the healthcare team. 

Review Questions


Halstead ME, Walter KD., Council on Sports Medicine and Fitness. American Academy of Pediatrics. Clinical report--sport-related concussion in children and adolescents. Pediatrics. 2010 Sep;126(3):597-615. [PubMed: 20805152]
Stovitz SD, Weseman JD, Hooks MC, Schmidt RJ, Koffel JB, Patricios JS. What Definition Is Used to Describe Second Impact Syndrome in Sports? A Systematic and Critical Review. Curr Sports Med Rep. 2017 Jan/Feb;16(1):50-55. [PubMed: 28067742]
McLendon LA, Kralik SF, Grayson PA, Golomb MR. The Controversial Second Impact Syndrome: A Review of the Literature. Pediatr Neurol. 2016 Sep;62:9-17. [PubMed: 27421756]
Weinstein E, Turner M, Kuzma BB, Feuer H. Second impact syndrome in football: new imaging and insights into a rare and devastating condition. J Neurosurg Pediatr. 2013 Mar;11(3):331-4. [PubMed: 23277914]
Harmon KG, Clugston JR, Dec K, Hainline B, Herring S, Kane SF, Kontos AP, Leddy JJ, McCrea M, Poddar SK, Putukian M, Wilson JC, Roberts WO. American Medical Society for Sports Medicine position statement on concussion in sport. Br J Sports Med. 2019 Feb;53(4):213-225. [PubMed: 30705232]
Stupecký J, Haisová L. [Evaluation of results of resection of the root apex with retrograd filling]. Cesk Stomatol. 1978 Jan;78(1):49-52. [PubMed: 274217]
McCrory P, Meeuwisse W, Dvořák J, Aubry M, Bailes J, Broglio S, Cantu RC, Cassidy D, Echemendia RJ, Castellani RJ, Davis GA, Ellenbogen R, Emery C, Engebretsen L, Feddermann-Demont N, Giza CC, Guskiewicz KM, Herring S, Iverson GL, Johnston KM, Kissick J, Kutcher J, Leddy JJ, Maddocks D, Makdissi M, Manley GT, McCrea M, Meehan WP, Nagahiro S, Patricios J, Putukian M, Schneider KJ, Sills A, Tator CH, Turner M, Vos PE. Consensus statement on concussion in sport-the 5th international conference on concussion in sport held in Berlin, October 2016. Br J Sports Med. 2017 Jun;51(11):838-847. [PubMed: 28446457]
Guenette JP, Shenton ME, Koerte IK. Imaging of Concussion in Young Athletes. Neuroimaging Clin N Am. 2018 Feb;28(1):43-53. [PMC free article: PMC5728158] [PubMed: 29157852]

Disclosure: Todd May declares no relevant financial relationships with ineligible companies.

Disclosure: Lisa Foris declares no relevant financial relationships with ineligible companies.

Disclosure: Chester Donnally III declares no relevant financial relationships with ineligible companies.

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Bookshelf ID: NBK448119PMID: 28846316


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