CASE REPORT Traumatic Carotid Artery Dissection During Acrobatic Flight Associated with 2Gz Acceleration Alexandra Adler, Keith J. Ruskin, and David M. Greer ADLER A, RUSKIN KJ, GREER DM. Traumatic carotid artery dissectop of the loop, he was no longer able to control the tion during acrobatic flight associated with –Gz acceleration. Aviat airplane and could not respond to radio calls. He develSpace Environ Med 2013; 84:1201–4. oped right hemiparesis, expressive aphasia, and conBackground: A 38-yr-old man developed the acute onset of expressive fusion, during which time the airplane continued to roll. aphasia and right hemiparesis during the performance of an advanced aerobatic flight maneuver. Case Report: Magnetic resonance imaging The confusion resolved after 20 s and he was able to (MRI) demonstrated patchy infarction in the territory of the left middle land the airplane with some difficulty, using only his left cerebral artery. Magnetic resonance angiography (MRA) revealed a dishand. He remained conscious throughout the event. The section of the left internal carotid artery. He had flown an aerobatic rouhemiparesis and aphasia resolved after approximately tine with multiple abrupt transitions from 18 Gz to 26 Gz 4 d prior with no ill effects. He had no risk factors for dissection or stroke. The patient 120 min. He denied recent trauma to his head or neck, recovered full neurological function within several hours. Discussion: Delivered by Ingentaprevious to: Guestepisodes User of speech or language difficulties, We propose that the arterial dissection occurred during the patientOn: ’s preIP: 188.68.0.253 Sun, visual 26 Junchanges, 2016 02:56:39 facial drooping, lateralizing weakness, ceding aerobatic flight, leading to an embolic stroke 4 d later. The most Copyright: Aerospace Medical Association numbness, or impaired coordination. He denied any likely mechanism was sustained 2Gz acceleration combined with flexion and rotation of his neck during abrupt transition from 1Gz to 2Gz, personal or family history of connective tissue disorcausing stretching of the internal carotid artery at the point of entry to the ders, neurological disease, or early vascular events. skull base and development of an intimal tear. Upon evaluation, the patient had an unremarkable Keywords: dissection, stroke, aerobatic flight, negative Gz, internal carotid neurological examination with normal speech and gait, artery, acceleration. T HE EFFECTS OF 1GZ acceleration on the human body have been well characterized over several decades of research and operational experience, but little is known about the effects of 2Gz acceleration. This is largely because military flying does not routinely include maneuvers that produce high –Gz forces. Maneuvers associated with large, sustained –Gz (e.g., outside loops) are only performed by recreational and competition aerobatic pilots. We present an otherwise healthy, young male pilot who developed an internal carotid artery (ICA) dissection while performing aerobatic flight maneuvers. CASE REPORT A 38-yr-old, previously healthy man with no significant past medical or surgical history experienced sudden paralysis of his right arm and leg and expressive aphasia while performing in an air show. He had practiced a 25-min aerobatic routine four times in a Sukhoi SU-31 airplane 4 d prior to the event. This routine consisted of maneuvers that included vertical rolls, vertical snaps, and outside loops, and exposed him to acceleration between 18 Gz to 26 Gz. He did not have any unusual symptoms after practicing, and noted only conjunctival injection and a mild headache, which he typically developed after doing –Gz aerobatic maneuvers. At the air show, he performed a maneuver that he described as an “outside Immelman” (Fig. 1), with his neck flexed and rotated to the left. When he reached the and intact strength and cranial nerve function bilaterally. A computed tomography (CT) scan of the head did not reveal any abnormalities. Magnetic resonance imaging (MRI) showed patchy infarction in the distribution of the left middle cerebral artery (MCA) (Fig. 2). Magnetic resonance angiography (MRA) revealed a dissection beginning at the distal cervical portion of the ICA and extending to the petrous portion (Fig. 3A and B). Transesophageal echocardiograghy with agitated saline contrast was normal with no evidence of a patent foramen ovale. The patient was started on aspirin 325 mg daily. Upon follow-up 2 mo later, he had no neurological deficits and his aspirin dose was decreased to 81 mg daily. DISCUSSION Dissection of the internal carotid and vertebral arteries is an important cause of ischemic stroke in young people, and accounts for 10–25% of ischemic strokes in this population (13). The mechanism of stroke secondary to internal carotid artery dissection (ICAD) is primarily thromboembolic in nature, with the majority of From the Departments of Anesthesiology and Neurology, Yale University School of Medicine, New Haven, CT. This manuscript was received for review in June 2013. It was accepted for publication in July 2013. Address correspondence and reprint requests to: Keith J. Ruskin, M.D., Department of Anesthesiology, Yale University School of Medicine, 333 Cedar Street TMP3, New Haven, CT 06520; keith.ruskin@ yale.edu. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.3778.2013 Aviation, Space, and Environmental Medicine x Vol. 84, No. 11 x November 2013 1201 ARTERY DISSECTION FROM ACCELERATION—ADLER ET AL. Arterial dissection can be spontaneous or caused by trauma. An increased frequency of spontaneous dissection is seen in people with underlying connective tissue disorders such as Ehlers-Danlos type IV, Marfan’s disease, osteogenesis imperfecta type I, and autosomal dominant polycystic kidney disease. The trauma that precipitates dissection may be major, such as in motor vehicle accidents, but can also include seemingly minor events such as yoga, overhead painting, coughing, and chiropractic manipulations (13). The common theme between these activities is a forceful jerking motion of the head causing neck hyperflexion, hyperextension, or both. To our knowledge, this is the first report of ICAD and subsequent embolic stroke following exposure to high levels of 1Gz and –Gz acceleration. In this case, the ICAD began at the distal cervical segment of the ICA and continued distally into the petrous segment. PreFig. 1. Modified Immelmann turn. To perform this maneuver, the pivious case reports have proposed acceleration as a lot rotates the plane 180° to perform a half roll (A). He then pulls the mechanism of vascular injury. For example, renal artery aircraft into a vertical ascent (B) and completes a half loop (C). Once he has regained level flight (D), he performs another half roll (E). When our dissection has been attributed to the rapid onset of a patient reached D, he was unable to control his plane and continued to high 1Gz load in an aerobatic pilot who had been experform rolls until he was able to use his left hand to regain levelby flight. Delivered Ingentaposed to: Guest Userbetween 18 G and 26 G . The abrupt to forces z z Plane image adapted from Wikimedia Commons, last accessed June IP: 188.68.0.253 On:8,Sun, 26 Jun 2016 02:56:39 changesAssociation in acceleration theoretically caused the renal 2013 (http://en.wikipedia.org/wiki/File:Aerobatic_box.svg ). Aerospace Medical Copyright: artery to stretch and ultimately dissect (2). There have been numerous reports of extracranial infarcts affecting the MCA territory (1,7). Warning ICA and vertebral artery dissections in civilian patients symptoms associated with ICAD include ipsilateral face associated with the abrupt onset of Gz during roller or neck pain, ipsilateral frontotemporal headache, pulcoaster rides, bungee jumping, and, in one instance, tursatile tinnitus, and a partial Horner ’s syndrome (miosis bulence on a commercial airplane (6,12,14,15). All of and ptosis), although 20% of patients may have no these patients were young and had no significant medisymptoms (13). The period between dissection and the cal conditions. The postulated mechanism for these onset of stroke symptoms can range from hours to weeks events is sudden neck movement (hyperextension, (3). In this case, the patient was asymptomatic at the hyperflexion, flexion-hyperextension, or rotation) of a time he most likely had his dissection. restrained passenger during exposure to rapid acceleration (6,12,14,15). A roller coaster passenger, for example, can experience G forces in all three directions (Gx, Gy, and Gz). The bungee jumper who developed ICAD was exposed only to Gz acceleration and the authors concluded that the initial force and subsequent rebound could have: 1) stretched the ICA over the transverse process of the upper cervical vertebrae; 2) directly compressed the ICA between the angle of the mandible and the upper cervical vertebrae; or 3) caused impingement of the ICA by the styloid process. Stretching could result in an intimal tear (15). In three of these cases, embolic stroke occurred several days after the inciting event (6,12,14). Military pilots are exposed to sustained, predominantly 1Gz forces for which they receive regular physiologic training and wear protective equipment. During 1Gz acceleration, cardiac output is reduced and blood is forced toward the lower portions of the body (11). The pilot experiences loss of peripheral and color vision and eventual loss of consciousness due to stagnant hypoxia (1). Military pilots, therefore, wear anti-G suits that compress the lower body during extreme flight maneuvers and are taught physiologic techniques (i.e., Fig. 2. Diffusion-weighted imaging demonstrated multiple small ema Valsalva maneuver) to minimize the adverse effects of bolic infarcts in the left frontal and parietal cortices in the distribution of acceleration. the middle cerebral artery. 1202 Aviation, Space, and Environmental Medicine x Vol. 84, No. 11 x November 2013 ARTERY DISSECTION FROM ACCELERATION—ADLER ET AL. Delivered by Ingenta to: Guest User IP: 188.68.0.253 On: Sun, 26 Jun 2016 02:56:39 Aerospace Medical Association Fig. 3. A) Magnetic resonance angiography Copyright: of the head showed dissection of the left internal carotid artery (white arrow). B) Contrast-enhanced magnetic resonance angiography (3D-TOF) of the extra- and intracranial left internal carotid artery showed a small filling defect (white arrow), consistent with dissection below the skull base. Recreational and competitive aerobatic pilots are exposed to the abrupt onset of large 1Gz and –Gz forces and do not wear protective equipment. Although anti-G suits protect against 1Gz, there is currently nothing that can protect a pilot from experiencing symptoms of –Gz. There is also comparatively little research on –Gz acceleration, which is notoriously unpleasant and experienced almost exclusively by aerobatic pilots. During 2Gz maneuvers, pilots develop cranial venous congestion and often have petechial conjunctival hemorrhages following flight (9). Pilots may also develop G-induced vestibular dysfunction (the “wobblies”) after exposure to high 1Gz and –Gz loads during aerobatic competitions (10). Although spontaneous dissection remains a possibility in this patient, dissection secondary to extreme G forces is the most likely explanation for this patient’s symptoms. The dissection probably occurred while he was practicing his routine 4 d prior to the onset of his symptoms, specifically while he was performing what he described as an “outside Immelman” (Fig. 1). This exposed him to a maximum force of 26 Gz with his neck hyperflexed and rotated to the left. High performance aerobatic pilots who are routinely exposed to –Gz acceleration place their heads in this position because it allows them to view the horizon and minimizes neck stretching during the maneuver. It is reasonable that his neck position in the setting of 26 Gz was sufficient to cause stretching and an intimal tear of the ICA, especially since young, healthy people have developed ICAD during only brief exposures to high G forces (6,14,15). The increase in cerebral blood flow during high 2Gz could also have been a contributory factor. This patient had no personal or family history of connective tissue or vascular disorders and was otherwise in excellent health, so it seems unlikely that previously undiscovered pathology could have contributed to this event. Dissection of the extracranial segments of the ICA is far more common than dissection of the intracranial segments because of the greater mobility of the extracranial segments and their anatomic relationship to bony structures (13). In most cases, extracranial ICAD occurs 1-2 cm past the carotid bifurcation. However, in this case, it occurred in the distal extracranial segment of the ICA at the point where it enters the skull base and continued into the petrous segment intracranially. Dissection of the intracranial ICA has been seen in association with both minor trauma and blunt head trauma (5). A small case series of spontaneous intracranial dissections reported that the most common site for intracranial ICAD is the supraclinoid segment (4), although it has also been observed in the petrous segment (5,8). We suspect that the combination of our patient’s neck position and high G forces caused stretch of the distal cervical portion of the ICA as it entered the skull base, a position of relative mobility. This likely caused an intimal tear, similar to the mechanism proposed by Zhou et al. (15). The period between the patient’s intensive practice session and ischemic event would have allowed time for thrombus formation and eventual artery-to-artery embolism. Exposure to high 2Gz during the patient’s initial flight could also have contributed by increasing blood flow through the ICA, further stressing the arterial wall, perhaps similar to the mechanism of conjunctival vessel damage (9). Aviation, Space, and Environmental Medicine x Vol. 84, No. 11 x November 2013 1203 ARTERY DISSECTION FROM ACCELERATION—ADLER ET AL. REFERENCES After this event, the patient decided to discontinue 1. Benni PBP, Li JKJ, Chen BB, Cammarota JJ, Amory DWD. NIRS flying. According to the U.S. Federal Aviation Adminismonitoring of pilots subjected to 1Gz acceleration and tration (FAA), cerebrovascular events (embolic stroke G-induced loss of consciousness (G-LOC). Adv Exp Med Biol 2003; 530:371–9. and transient ischemic attack) are generally disqualify2. Beyer RW, Daily PO. Renal artery dissection associated with Gz ing. Special issuance of a medical certificate for any acceleration. 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