Acute dissection of the aorta is a vascular surgical emergency. The majority of dissections originate in the thoracic aorta. Dissection originating in the infrarenal abdominal aorta is very rare and, given the vagueness of presenting symptoms of uncomplicated dissection, diagnosis is very difficult in the early stages. In the absence of a pulsatile abdominal mass, acute uncomplicated aortic dissection should be considered in the differential diagnosis of sudden onset of abdominal and back pain.^1,2 We report a case of spontaneous infrarenal abdominal aortic dissection occurring in an ostensibly normal aorta, and discuss the diagnostic dilemma and subsequent management of the patient.

A 53-year-old woman was admitted under the care of the urologists with a history of acute onset of sharp pain in the right loin lasting 45 minutes. This was followed three hours later by sharp pain in the left loin radiating to the left groin. This pain resolved within twenty minutes. She had no other symptoms. There was no significant past medical history. Clinical examination revealed mild tenderness in the left loin and left iliac fossa, pulse rate of 72/min and blood pressure of 140/85 mm of Hg. A provisional diagnosis of renal colic was made and intravenous urography was performed. No calculus, however, was demonstrated and the patient was discharged the next day, in the absence of symptoms, with a diagnosis of abdominal pain of unknown aetiology. No outpatient clinic follow up was arranged.

Five days later she was referred urgently by her general practitioner to a vascular surgeon because the patient was complaining of severe pain in her right loin, buttock, and calf on walking. On clinical examination she had a cold right foot with no pulses palpable in the right lower limb.

The patient was admitted to hospital and urgent arteriography performed via a left trans-femoral artery approach. This investigation demonstrated an aortic dissection (Figure 1a) arising immediately subjacent to the origin of the right renal artery. The true aortic lumen was grossly narrowed by the dissection, which spiraled inferiorly to include the right common, external and internal iliac arteries with the latter vessel almost completely occluded at its origin.

A dynamic enhanced computerised tomography (CT) scan demonstrated no evidence of a leak from the dissection. The true and false aortic lumens were seen separated by the dissection flap (Figure 1b). The immediate infrarenal origin of the dissection was also confirmed.

Figure 1: a) Digital subtraction angiography showing true aortic lumen compressed (arrow A) and dissection (arrow D).

b) Dynamic enhanced computerised tomography (CT) showing aortic lumen (arrow A) and dissection (arrow D)

Both the angiogram and the CT scan ruled out the origin of the dissection in the thoracic aorta.

The patient underwent urgent aortic grafting. During surgery, a large right-sided aortic dissection was noted. The true aortic lumen was compressed. Distally, the dissection involved the right external iliac artery but did not extend into the left common iliac artery.

The aorta was transected below the renal arteries. No dissection was noted in the proximal aorta and a woven bifurcated (16mm x 8mm) Dacron graft was sutured with an end-to-end anastomosis proximally; the false lumen below transection was obliterated by suturing to prevent bleeding from the lumbar arteries. In view of the extent of the findings described above, the distal anastomoses comprised a right end-to-side anastomosis to the common femoral artery and a left end-to-side anastomosis to the external iliac artery.

The patient made an uneventful postoperative recovery and was discharged home ten days later. At outpatient review two months after surgery, she was noted to be well with no history of claudication and she had a full complement of peripheral pulses in both lower limbs.

Aortic dissection is produced by entry of blood into the tunica media, where it separates the aortic wall into an inner layer comprising the intima and part of the media and an outer layer comprising part of the media and the adventitia, resulting in a double lumen aorta.

Systemic arterial hypertension is identified as the single most consistent factor predisposing to aortic dissection. Other causes include Marfan's syndrome, Ehlers Danlos' syndrome, aortic coarctation, bicuspid aortic valve, aortic hypoplasia, cystic medial necrosis, pregnancy, trauma and iatrogenic causes.

The overwhelming majority of dissections originate in the thoracic aorta and primary dissection of the abdominal aorta is rare. Hirst et al (1958) reported only 2.5% incidence of abdominal aortic dissection.² Crawford and Crawford (1984) found only one case out of 250 thoracoabdominal dissections.³

The presenting symptoms are vague and variable and include acute belt like abdominal pain, left upper quadrant pain, abdominal heaviness, shearing lower back pain and, in many cases, surprisingly, no symptoms at all. ^4,5 In this patient, the only symptom was two bouts of loin pain lasting 40 and 20 minutes; the second episode of pain radiated to the left groin, giving rise to the initial suspicion of renal colic. The only physical sign in this patient was mild left loin tenderness, however, the groin pulses were not examined at initial presentation. The role of contrast enhanced CT in the diagnosis of aortic dissection is well established and Carreno et al (1998) believe that no further investigation is required if there are normal peripheral pulses, no clinical evidence of intestinal involvement, normal renal function studies and the CT confirms non progression of dissection to the proximal suprarenal aorta and the presence of normal nephrograms.⁶ CT scanning, however, has been known to be inaccurate in ruling out the suprarenal origin of dissection.¹ Moreover, exact extent of dissection and the state of lower limb arteries can only be demonstrated by angiography. We believe that before embarking on a major surgical procedure, such as replacing the abdominal aorta, the best information can be gained by a combination of contrast enhanced CT and angiography, and some authors consider the combination mandatory.⁴

Spontaneous dissection of the infrarenal abdominal aorta is a rare but recognised entity. Symptoms are variable and may mimic renal colic or be notable by their absence. The condition should be considered in the differential diagnosis of acute abdominal pain. This case also illustrates the importance of routine palpation of pulses in patients presenting with an 'acute abdomen'.

Devolfe C. Chatelard P. Chovier M.N. Bruchet P. Nenet J. Loire R. Spontaneous and isolated dissection of the external iliac artery. Presentation of a case (French). Journal Des Maladies Vascularis 1990;15:144-7 Acute dissection of the infrarenal aorta and horseshoe kidney. A proposition of a case and review of literature. Journal De Cherurgie 1992; 129:330-4

Correspondence: Professor S. Homer-Vanniasinkam, Consultant Vascular Surgeon, Vascular Surgical Unit, The General Infirmary at Leeds, Great George Street, Leeds LS1 3EX, U.K.

The Royal College of Surgeons of Edinburgh
and
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invites applications for

THE LLOYDS TSB TRUST FELLOWSHIP

This Fellowship is being awarded initially for a one-year period with a possible extension for a further year. The recipient will be based at Queens University Hospital and the University of Nottingham, working with Professor O Eremin, Special Professor of Surgery. The research project will study inflammatory bowel disease.

Applicants must be Fellows of the Royal College of Surgeons of Edinburgh, in good standing, and under 40 years of age.

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Closing date for applications is: Friday 16 February 2001

Š2000 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb. 45, 6: 408-410

Spontaneous dissection of the abdominal aorta

THE LLOYDS TSB TRUST FELLOWSHIP