A 59-year-old man presented to the emergency department with complaints of sudden onset pain on the right side of the buttocks and the inability to move his right leg without great pain. He also described numbness in his right leg and foot. The symptoms had lasted approximately 30 minutes prior to arrival. Soon after presentation, the patient also developed mild midsternal chest pain with radiation to his back. The patient thought the pain in his buttocks was caused by sciatica, for which he had seen a chiropractor in the past. However, the patient described the pain as more intense than that associated with his prior sciatica-related back complaint. In addition to sciatica, the patient had a history of hypertension, migraines, and an enlarged prostate. Past surgical procedures included a cholecystectomy. The patient was taking metoprolol (25 mg daily) to control his blood pressure. 

Initial vital signs included the following: temperature, 97.4°F (36.3°C); pulse, 61 beats per minute; respiration, 16 breaths per minute; and blood pressure, 157/50 mm Hg. He rated the pain in his leg as 8 out of 10 on a visual analog scale, with 10 indicating extreme pain. Results from physical examination were notable for generalized diaphoresis. Findings from head, neck, cardiovascular, lung, and abdominal examinations were normal. Strength of pulses palpated on the left upper and left lower extremities were normal (2+). On the right upper extremity, strength of the radial pulse was decreased but present (1+). We were unable to palpate dorsalis pedis or popliteal pulses on the right (0). We were also unable to obtain a pulse in these regions using handheld Doppler ultrasonography. The patient had a greatly diminished right femoral pulse by palpation. Range of motion in all extremities was equal, but sensation in the right lower extremity was decreased. 

Laboratory test results were normal for complete blood cell count, comprehensive metabolic profile, international normalized ratio, and troponin I (0.02 ng/mL). Laboratory values were elevated for creatinine kinase (351 U/L) and creatinine kinase-MB fraction (8.7 ng/mL). Results of a portable chest radiograph were normal (Figure 1). 

Results of the electrocardiogram showed sinus bradycardia without ST-T segment abnormalities. The patient underwent a computed tomography angiogram of the thorax, abdomen, and pelvis. Results of the computed tomography angiogram of the chest showed a Stanford type A aortic dissection involving the left subclavian artery (Figure 2). In addition, the patient had a dissection flap extending into the aberrant right subclavian artery, which had a retroesophageal tract (Figure 2). He also had a common origin for the common carotid arteries (Figure 2). The dissection continued into the abdomen and extended into the left renal artery approximately 3 cm. The dissection continued into the bifurcation of the aorta and involved the left common iliac artery. Because of the patient's vascular anomalies, the cardiothoracic surgeon requested that the patient be transferred to a tertiary care center by helicopter. At the tertiary care center, the patient underwent surgery and the aortic arch was replaced. At 6-month follow-up, the patient was still receiving metoprolol (increased to 50 mg daily) for blood pressure control. He was active with minimal discomfort. 

Aberrant right subclavian artery (ARSCA) is the most common anomaly of the aortic arch.³ According to Edwards,³ the incidence rate for ARSCA is 0.48%, or about 1 in 200 individuals. A series of autopsies performed by Holzapfel⁴ found that, in patients with this anomaly, the ARSCA travels in a retroesophageal track 80% of the time, between the trachea and esophagus 15% of the time, and in front of the trachea 5% of the time. In 3 studies^5-7on dissection of the aorta involving the ARSCA, 12 of 28 patients had a Stanford type A aortic dissection, as our patient had. The acute angle of the ARSCA may cause a weakening of the aortic wall, which could increase the risk of dissection.⁵ 

In addition to the ARSCA, our patient had another vascular anomaly: a common trunk for the common carotid arteries. A search of the medical literature using the National Library of Medicine's PubMed database revealed a limited number of reported cases in which ARSCA occurs with a common trunk for the common carotid arteries and thoracic aortic dissection.^8-10 In one of these cases, the patient was reported to have an aneurysm of the ARSCA.⁹ Another case, discovered during a routine cadaver dissection, involved an ARSCA and common trunk for the common carotid arteries but not aortic dissection.¹¹ 

The embryologic variation of the aorta has been discussed in many articles. These articles have focused on 2 major theories in the development of the aortic anomalies. The first theory, which involves the Rathke diagram,¹² describes ventral and dorsal aortas with their 6 pairs of interconnecting branchial arches. In this theory, the right aortic arch 4 degenerates, which causes the right seventh cervical intersegmental artery and the right dorsal aorta that is caudal to it to fuse and become the ARSCA.^13,14 

The second theory, first described by Edwards,³ involves a “double arch system.” This hypothesis involves a double aortic arch with a ductus arteriosus on each side. Each arch produces a common carotid and subclavian artery. The malformation of the ARSCA is formed by an interruption in the connection of the right arch between the right common carotid artery and the origin of the right subclavian artery. This interruption, in turn, causes the subclavian artery to lose its connection with the ventral part of the aorta. The right subclavian artery then connects to what was the dorsal portion of the right aortic arch.^3,15,16 Poultsides et al¹⁴ describe how the third cervical aortic arches give rise to the carotid arteries. At 7 weeks gestation, the common carotid arteries have a common trunk and, if a failure of separation occurs at this stage, then a common carotid trunk will remain. 

These embryologic variations are important to be aware of when it comes to the repair of aortic dissection, because they could mandate a change in the surgical approach. For example, Kikuchi et al⁵ described a total arch replacement and additional “elephant trunk” procedure necessitated by the vascular anomalies. In this procedure, part of the prosthetic arch is left behind in the proximal descending aortic arch to help protect against a more severe dissection. 

High blood pressure is the largest risk factor for aortic dissection. During an acute dissection, the blood pressure and the contractility of the heart will propagate the dissection. Systolic blood pressure should be lowered to 100 mm Hg to 120 mm Hg, or the lowest tolerable blood pressure if this range is unreachable. In addition, the heart rate should be lowered to 60 beats per minute. Intravenous β-blockers such as labetalol hydrochloride and esmolol hydrochloride are the first line therapy. Other medication such calcium channel blockers maybe used only if β-blockers are contraindicated. Intravenous sodium nitroprusside may be used but only in conjunction with a β-blocker.² 

Because approximately half of patients with aortic dissection die within the first 48 hours of symptom onset, a quick diagnosis is essential. Physicians should be aware of the presenting symptoms of this disease as well as the potential vascular anomalies that can be associated with it. Embryologic variations can impact the surgical approach for aortic dissection repair.