Dissecting aortic aneurysm in a cat

A 2.5-year-old, mixed breed female cat was referred to the Veterinary Hospital, São Paulo State University, for an ovariosalpingectomy. On clinical examination, intense cardiac systolic murmurs (grade V/VI) were detected at several locations. However, there was no evidence of pleural effusion, tachycardia, blanched mucous membranes, cool extremities, or electrocardiographic abnormalities, and the heart rhythm was normal, so the cat was subjected to the surgery. Subsequently, the cat was returned to the hospital with signs of acute dyspnea, anorexia, and paralysis of the hind limbs.

On examination, the cat was weak and lethargic. It was 8% dehydrated and hypothermic (37°C), with an elevated heart rate (250 beats/min) and increased respiratory rate (50 breaths/min). The mucous membranes were pale and the capillary refill time was 3.5 s. There was no femoral pulse. Cardiac murmurs were still present, but the cardiac rhythm was regular and normal upon electrocardiographic examination. There were crackling sounds upon auscultation of the lungs. Radiographic examination of the thorax revealed that there was pulmonary edema. The extremities of the hind limbs were cold and there were no withdrawal reflexes. There was no evidence of vertebral lesions on radiographic examination of the spinal column. The cat was admitted to hospital for treatment.

Treatment consisted of furosemide (Lasix; Hoechst QuÍmica e Farmacêutica do Brasil, São Paulo, SP, Brazil), 1–2 mg/kg bodyweight (BW), IV, q4h; nitroglycerin topical ointment 2% in a lanolin-petroleum base (Nitradisc; Biolab Ind. Farmacêutica S.A., São Paulo, SP, Brazil), 0.6 cm topically, q8h; aminophylline (Aminofilina; Mesquita Ltda, São Paulo, SP, Brazil), 6 mg/kg BW, IV, q12h; acetylsalicylic acid (Aspirin; Bayer S.A., São Paulo, SP, Brazil), 17 mg/kg BW, PO, q72h; captopril (Capoten; Bristol-Myers Squibb S.A., São Paulo, SP, Brazil), 0.5 mg/kg BW, PO, q24h; oxygen, 6–10 L/min, 60% concentration (6).

After 12 h in hospital, the cat was stable and was discharged. It died 24 h later. On necropsy, bilateral dilatation of the heart and a semilunar aortic endocarditis (Figure 1), edema and hemorrhage in the lungs, ascites, edema of the intestines, congestion of the spleen, degeneration in the liver, and an infarct in the right kidney were noted. On longitudinal sectioning of the aorta, a dissecting aneurysm was seen extending from the site of the endocarditis to just cranial to the kidney (Figure 2). On microscopic examination of the aorta, the dilatation was observed to be in the tunica media (Figure 3).

Figure 1. Macroscopic appearance of the heart, showing semilunar aortic endocarditis.

Figure 2. Gross appearance of the dissecting aneurysm. Longitudinal (A) and transverse (B) sections of the thoracic aorta.

Figure 3. Histologic section of thoracic aorta, showing the dissection of the tunica media (arrow).

Aortic aneurysms are characterized by blood flow dissecting the tunica media and forming a distal channel from rupture of the wall (2,3,4). An aneurysm can be either true or false. A true aneurysm is bounded by generally complete, but often attenuated, arterial wall components (2), and the blood within it remains within the confines of the circulatory system. In contrast, a false aneurysm (pseudoaneurysm) is actually an extravascular hematoma that communicates with the intravascular space (producing a pulsating hematoma) (2). Aortic aneurysms have been described in horses (4,5), dogs (3), and primates (6).