Patient Care

Recognizing Arteriovenous Malformations in the Prehospital Setting

Issue 12 and Volume 41.

Arteriovenous Malformations

Intracranial arteriovenous malformations (AVMs) present a very unique challenge for emergency medicine. These congenital, vascular anomalies tend to cause illness within the first four decades of life and are the most common cause for spontaneous intracranial hemorrhages (ICH) in young adults.1 These rare and unique but potentially catastrophic vascular tangles are exactly what the old adage speaks of: Children and young adults don’t get critically ill—except for when they do.

AVMs are the most dangerous of all the congenital vascular malformations that occur within the central nervous system. As affected patients increase in age, so does the likelihood of complications such as ICH and/or epilepsy. Although AVMs can occur anywhere in the body, with common sites including lungs and kidneys, when referring to AVMs in this article it’s in reference to intracranial lesions.

Pathophysiology

AVMs are congenital lesions made of a tangle of arterial and venous vasculature. This tangle is often said to appear like a ball of spaghetti and is referred to as the AVM’s nidus. The actual disease process isn’t the jumbled mass itself, but rather the direct connection of the arteries to veins.

In normal vessels, arteries are exposed to a much higher blood pressure as a result of the left ventricle’s powerful ejection forces. The arteries are able to handle this pressure because of the amount of elastin in the vessel walls. However, veins almost completely lack the support that the elastin affords arteries which decreases the thickness of the veins’ walls. Upon gross examination, arteries look and feel like airline tubing, whereas veins are more like wet paper bags. This lack of tissue elasticity and girth make veins completely incapable of handling pressures even remotely close to that of their arterial counterparts.

Arteriovenous Malformations
An angiogram shows an arteriovenous malformation, depicted as a tangled ball on the left.
Photo courtesy Zach Roper

In normal circumstances, capillary beds buffer the veins from the ventricle’s constant pulsing. However, in AVMs, the nidus completely lacks the regulatory effect that the capillaries provide exposing the venous tissue to pressures much greater than they can handle. These flow and pressure anomalies create cellular changes within the AVM’s feeding and draining vessels.

One of the more concerning complications is the development of pedicle aneurysms (berry-like pouches on the vessel’s external wall) on both the efferent and afferent vessels.

The excessive pressure on the venous structures as well as the pedicle aneurysms are likely the mechanisms by which hemorrhage occurs as a result of the AVM and are associated with a worsened prognosis.2

Etiology & Epidemiology

The mechanism that causes AVMs to develop remains mostly shrouded in mystery. There are case reports of AVMs traveling down a familial lineage, but it’s uncertain if there’s a true genetic link there or if it’s just coincidence.3

There’s some interesting research exploring the possibility of a genetic predisposition to an angioarchitecture derangement suggesting that a series of genetic mutations may contribute to the development of an AVM.4

Brain AVMs occur in about 0.1% of the population,1 with a stable detection rate.5 In the U.S., roughly 300,000 people are thought to be housing an AVM. Of those affected, only 12% will transition to a symptomatic disease process; the rest will go undetected for the entirety of the patient’s life.6 Likely, as the threshold for neurological imaging continues to decrease around the world, the incidental discovery of these lesions will continue to rise.

Clinical Presentation

Of those who transition from occult to symptomatic disease, the two most frequent reasons for presentation are seizure and/or ICH.

A majority of AVM patients present with ICH as the inciting event, but AVM ruptures only account for 2% of hemorrhagic strokes.1 In AVM patients between the ages of 10 and 40, 41–79% present with ICH as the inciting event, and the percentage of children who present with ICH is significantly higher than that of the older patients.7

Since the vessels of an AVM are under an abnormal amount of pressure, the ICH is usually a result of a rupture resulting in a sudden onset of headache. This telltale symptom, often referred to as a “thunderclap” headache, is commonly described by patients as the “worst headache ever” with a completely unique quality compared to any previous headaches. Nearly 100% of patients with SAH and approximately 60% with IPH will present with headache subsequent to the bleeding.8

In particular, SAH will often present with the sudden onset of meningismus: the triad of nuchal rigidity, photophobia, and thunderclap headache. In both SAH and IPH, vomiting presents at the onset of rupture just over 50% of the time.8

Although much of the clinical presentation associated with the rupture of AVMs very much mirrors that of other spontaneous ICH, the degree of neurologic deficit is considerably less in severity and permanency. The ICH from AVMs tend not to cause the same neurologic deficits in both depth and breadth. In addition, the prognosis from these hemorrhages is also considerably better due to the low age of the affected population and the ability for the brain to reorganize around the AVM.6

Seizures/epilepsy are the initial presenting symptom in 11–33% of patients with symptomatic AVM, making seizures the second most common symptom initial symptom.9 With the variability in location, size and multiplicity of the AVM, the way in which the seizure can manifest itself is quite fickle. In general, most are focal seizures, either simple partial or complex partial. However, it’s common for many patients to suffer from focal seizures with secondary generalization. Of patients with asymptomatic AVMs, about 8% will develop epilepsy due to the AVM within 5 years of the AVM’s incidental discovery.9 Many will have the risk of seizure for the rest of their lives, but epilepsy as a result of an unruptured AVM is easily controlled with standard anticonvulsants in most cases.

In patients who suffered from a ruptured AVM, the five-year risk of developing a seizure disorder is nearly 3 times that of unruptured AVM patients.

On rare occasions, patients suffering from AVM may initially present with either primary headache or primary focal neuro deficit. Headaches (unrelated to ICH) as the single presenting complaint in patients with AVM is quite rare, with estimates being as low as 4%.6 Some experts even contend that headaches may be mere coincidence. Headaches alone in the absence of other neurologic symptoms should raise the suspicion of AVM. In patients who present with headache as their only complaint with a normal exam, only 0.2% were subsequently diagnosed with AVM.10

Prehospital Management

Management of AVMs in the prehospital setting focuses exclusively on symptom management and ruling out more common/treatable causes of the patient’s complaints. An unconscious patient with a Glasgow coma scale (GCS) score of < 8 should be intubated. If the patient is suffering from projectile vomiting from an SAH, administer ondansetron. If the patient is seizing, administer a benzodiazepine and load with an anticonvulsant.

Prehospital providers should especially be on the lookout for patients with known, but untreated AVMs that present with symptoms suspicious for ICH. Ruptured AVMs are neurosurgical emergencies and should be treated as such. In many instances, these patients will already have a tertiary care center that’s following them. Every reasonable effort should be made transport them to the most appropriate receiving facility first. Taking a patient with a very high suspicion of rupture to a community hospital without neurosurgical services available would be a great injustice. If the most appropriate center isn’t within a reasonable drive, certainly medical command should be contacted and air medical services considered.

Conclusion

AVMs are a diagnosis that will likely always elude prehospital medicine, but it’s one we can make a difference in. These young patients need our prompt attention and undivided care. Although their definitive treatment and cure will be at the hands of a neurosurgeon, the ability for the patients to make it into such expert hands depends on us. Being suspicious of the thunderclap headache and new-onset seizures in a young person will be of great benefit to these patients, and never ignore such symptoms when they’re confronted by the past medical history of an untreated AVM. Finally, we must partner with our physician colleagues and hospital partners to see that these patients are transported quickly to facilities that can care for them.

References

1. Mohr JP, Kejda-Scharler J, Pile-Spellman J. Diagnosis and treatment of arteriovenous malformations. Curr Neurol Neurosci Rep. 2013;13(2):324.

2. Perata HJ, Tomsick TA, Tew JM Jr. Feeding artery pedicle aneurysms: Association with parenchymal hemorrhage and arteriovenous malformation in the brain. J Neurosurg. 1994;80(4):631–634.

3. Singer R, Oglivy C, Rordorf G. (September 2016.) Brain arteriovenous malformations. UpToDate. Retrieved Oct. 25, 2016, from www.uptodate.com/contents/brain-arteriovenous-malformations.

4. Brouillard P, Vikkula M. Genetic causes of vascular malformations. Hum Mol Genet. 2007;16 Spec No. 2:R140–R149.

5. Stapf C, Mast H, Sciacca RR, et al. The New York Islands AVM Study: Design, study progress, and initial results. Stroke. 2003;34(5):e29–e33.

6. Sen S, Selph J, Webb S. (March 27, 2014.) Arteriovenous malformations. Medscape. Retrieved Oct. 14, 2016, from http://emedicine.medscape.com/article/1160167.

7. Fullerton HJ, Achrol AS, Johnston SC, et al. Long-term hemorrhage risk in children versus adults with brain arteriovenous malformations. Stroke. 2005;36(10):2099–2104.

8. Gorelick P, Hier D, Caplan L, et al. Headache in acute cerebrovascular disease. Nuerology. 1986;36(11):1445–1450.

9. Josephson CB, Leach JP, Duncan R, et al. Seizure risk from cavernous or arteriovenous malformations: prospective population-based study. Neurology. 2011;76(18):1548–1554.

10. Evans R. Diagnostic testing for the evaluation of headaches. Neurol Clin. 1996;14(1):1–26.


Learning Objectives

  • Define arteriovenous malformation.
  • Differentiate between normal vascular anatomy and that of an arteriovenous malformation.
  • Design a care plan that effectively treats the symptoms of arteriovenous malformation, while also recognizing its most common characteristics (age, ICH, & seizure).

Key Terms

  • Arteriovenous malformations: Congenital anomalies by which arteries and veins form direct connections with one another in a tangled ball of vasculature.
  • Meningismus: A triad of symptoms (stiff neck, light sensitivity and headache) that are clinically indicative of meningeal irritation/inflammation.
  • Secondary generalization: A term used to describe a seizure that begins focally, but ultimately deteriorates to a generalized seizure, e.g., focal motor seizure with secondary generalization.

Zach’s Story

An internal look at a provider’s AVM experience

The fall of 2015 had been pretty amazing for Zach. After a decade-long career in EMS as a prehospital and critical care flight paramedic, he’d finally earned his nursing degree and license. Zach was only a few weeks into his dream job, a neuro-trauma ICU nurse at a large, academic medical center in the Philadelphia suburbs. The team of providers, nurses, therapists and technicians empowered Zach to care for critically ill patients in ways that were never afforded to him previously.

However, Zach’s love for prehospital medicine hadn’t fallen to the wayside, and he continued to moonlight as a paramedic between his nursing shifts.

The first Tuesday in December, only a few days after his last paramedic shift was spent studying in preparation for his next shift in the ICU. During study breaks, he would do little odds and ends around his house or sometimes stare outside the window at the towering ranges of the Pocono Mountains.

Arteriovenous Malformations
Zach’s CT rendering of his AVM, which presented at first with a thunderclap
headache. Photo courtesy Zach Roper

The weather that fall was miserable in the Philadelphia area. It had been extremely warm and wet. Much of the mid-Atlantic had struggled to achieve temperatures anywhere even close to normal and had been more or less below freezing. This weighed on Zach regularly. An active and fit 29-year-old, he was often outside, regardless of time of year, doing almost anything that got him moving and out of the house; and winter meant it was time for snowboarding! Living only a short drive from all of the Pocono Mountain ski resorts, the sight of the bare, snowless trails was only a constant reminder that he wouldn’t be breaking out his winter gear anytime soon. So he continued with his studying and to-do list.

Soon, Zach went upstairs to get ready for bed. He and his girlfriend talked about what the next day would bring. Despite the fact that Zach was knee-deep into his orientation, the palpable excitement he had for his new job made each day feel like the first day.

He walked into the bathroom to brush his teeth and finish his nightly routine, throwing his socks in the hamper as he told his girlfriend about the patients he would hope to take care of the next day. A little too excited and distracted by the conversation, one of the socks soared past the hamper and hit the floor.

Without even a moment’s pause, he steered toward the cheeky sock that seemed as though it had almost intentionally missed the hamper and bent over to pick it up. At that instant, he hears what he thinks is a balloon popping in the room. As the balloon explodes, it drowns out the sounds of his girlfriend talking, the rain hitting the window, the hum of his furnace, even the sounds of Zach’s own thoughts. The sound waves collide with the back of his head and are so forceful and electrifying that he’s positive the balloon’s demise had happened only inches from the back of his head.

Zach wonders why in the world his girlfriend would pull a stunt like this right before bed. She isn’t exactly a practical joker.

But Zach can still see her across the room. She has no balloon, and she’s still talking in midsentence. Zach can see her lips are moving, but there’s no sound. It’s as if the world is standing still. At the very instance that the balloon disintegrates, the sound and progression of time is sucked from the room.

Time and space come crashing back just as quickly as they’d stopped. Zach is immediately overtaken by a pain like nothing he’s ever experienced or even imagined was possible.

A clawing, molten pain envelopes his entire head. Failing to muster the slightest strength against the pain, Zach drops to his knees and hits the floor. The vice-like death-grip on his brain chases away any ability to comprehend what had just taken place.

Perched on all fours and staring into the floor, Zach feels his body lose the ability to regulate itself. Sweat rains from his pores, and his inner ear fails to calm the vertiginous spinning that had overtaken the room.

In an attempt to fend off unconsciousness, Zach rolls himself onto his back trying to stir up any semblance of a thought. But all he can think is, “Something is wrong!”

Over the next hour, Zach tried desperately to bargain with his body about what had just happened, but he’s soon interrupted by the siren-like urgency that’s accompanied with incessant, unrelenting projectile vomiting.

With each wrenching heave, the vice around his head only got tighter.

As his body continued to misfire its normal processes, Zach’s body becomes arctic-cold. Zach’s girlfriend loads him into her car and takes him to local community hospital’s ED.

Less than an hour later the ED physician puts his hand on Zach’s shoulder, and said the words that no 29-year-old ever plans to hear: “There’s an MICU on the way to pick you up. The radiologist called about your CT scan; you have an arteriovenous malformation in your brain that has burst. It’s pouring blood into your subarachnoid space. There’s a neurosurgeon waiting for you.”