A carotid arteriovenous fistula refers to an abnormal connection between the carotid artery and jugular vein, where arterial blood flows directly into the vein without passing through capillaries. It can be congenital or acquired, with the majority being acquired due to trauma.
Etiology and Pathology
Congenital carotid arteriovenous fistulas are rare and result from abnormal connections between arteries and veins during embryonic development. Acquired cases are more common and are often caused by stab wounds, gunshot injuries, or iatrogenic factors such as intramuscular or intravenous injections, vascular imaging, or surgical trauma. When the walls of adjacent arteries and veins are damaged on the same plane by trauma, the significant pressure difference between the two vessels may cause them to adhere and form a direct fistula. In cases where the arterial and venous openings do not directly connect but form a hematoma between them, the hematoma may later organize into a fistula connecting the artery and vein, referred to as an indirect fistula.
Clinical Manifestations
Congenital cases are often accompanied by vascular birthmarks and typically present no symptoms during infancy or childhood. Over time, typically during adolescence, localized swelling or diffuse lesions develop, which may exhibit palpable vibrations and sometimes audible vascular bruits. The skin temperature over the affected area may also become elevated.
Acquired cases have distinctive symptoms, including pulsatile tinnitus, described as a buzzing, hissing, or high-pitched noise that may disrupt sleep. Compression of the common carotid artery can temporarily reduce or eliminate the tinnitus. Other symptoms may include headache, dizziness, hallucinations, delirium, visual and auditory disturbances, as well as recurrent oral or nasal bleeding. Cardiovascular symptoms vary depending on the size of the arteriovenous fistula and its proximity to the heart. Small fistulas located far from the heart often cause no significant cardiovascular symptoms. Larger fistulas closer to the heart may lead to significant morphological and functional changes in the arteries, veins, and heart, including the following:
- Unchanged arterial systolic pressure but reduced diastolic pressure, resulting in widened pulse pressure.
- Decreased arterial blood supply with increased heart rate, cardiac output, and blood volume.
- Elevated venous pressure at both ends of the fistula, increased skin temperature, and, over time, cardiac enlargement, which may eventually lead to heart failure.
Key local signs include bruits and palpable vibrations over the fistula site. A coarse roaring sound is often auscultated over the affected area, loudest during systole and progressively quieter during diastole, with the sound radiating along the involved vessels. Larger fistulas tend to produce more prominent bruits. Continuous coarse vibrations can typically be felt upon palpation of the affected area. When pressure is applied to the site, both the bruit and vibration generally disappear.
Diagnosis
The presence of a cervical mass with noticeable bruits and vibrations, combined with elevated venous pressure and increased venous oxygen partial pressure, following birth or trauma, is suggestive of a carotid arteriovenous fistula. Digital subtraction angiography (DSA) can reveal the location and size of the fistula, further confirming the diagnosis.
Treatment
Surgical resection is the primary treatment approach. The specific surgical technique varies depending on the condition of the lesion. The general principle involves excision of the fistula, ligation of all feeding vessels, and subsequent repair of the artery and vein.