An 8-year-old intact male mixed-breed dog weighing 23 kg was referred to the author’s hospital with a 6-day history of persistent anorexia, lethargy, and vomiting. Antigen testing for D. immitis was positive, and a peripheral blood smear revealed circulating microfilariae. The thoracic radiographs revealed a normal cardiac silhouette and a generalized bronchial lung pattern. A mid-abdominal mass effect was also identified on the abdominal radiographs. Abdominal ultrasonography showed a thickened segment of the small intestine with disrupted wall layering, accompanied by enlarged mesenteric lymph nodes (Fig. 1). Echocardiography revealed heartworms within the main pulmonary artery and an approximately 1.7 cm echogenic structure on the right atrial free wall. Accurate cardiac and vascular anatomical structure was assessed using an 80-row multidetector CT (Aquilion Prime SP; Canon Medical Systems, Japan) under general anesthesia. The dog was premedicated with fentanyl (10 μg/kg/h, intravenous [IV], constant rate infusion injection; Myungmoon, Korea) and midazolam (0.2 mg/kg, IV, injection; Bukwang, Korea), induced with propofol (3 mg/kg, IV, Anepol; Hana, Korea) and maintained with isoflurane (Ifran; Hana) in oxygen (2.0 L/min) via endotracheal intubation. The dog was placed in a sternal recumbent position throughout the entire procedure. A helical scan was conducted in the cranial to caudal direction to determine the position of the test bolus site and perform electrocardiography-gated cardiac CT angiography (CTA). The scanning parameters of the pre-contrast and angiographic volume images were as follows: 100 kVp, 95 mAs, 0.35 seconds rotation time, and 0.5 mm thickness. A non-ionic iodinated contrast medium (iohexol, 300 mg/mL; Omnipaque 300; GE Healthcare, Norway) was administered at a dose of 2 mL/kg through an 18-gauge IV catheter, followed by saline at 1 mL/kg, using a dual-head power injector (Salient; Medrad Inc., USA). A test-bolus technique was used to determine the peak enhancement time of the ascending aorta. For the test bolus, 10 mL of contrast was injected at a rate of 2 mL/sec, followed by a diagnostic injection of 36 mL at 3.6 mL/sec and a saline chaser of 23 mL at 3 mL/sec. The post-contrast thoracic scans were obtained at 14 seconds (peak enhancement of the ascending aorta) and 60 seconds (delayed phase) after the contrast medium injection. CTA revealed an aneurysmal dilation of the left subclavian artery with a centrally located linear hypoattenuating structure consistent with an intimal flap, indicating arterial dissection (Fig. 2). Multiple linear filling defects were present in the main and lobar pulmonary arteries, consistent with heartworms. In addition, numerous punctuation and linear intraluminal filling defects throughout the pulmonary arterial tree were consistent with a pulmonary thromboembolism. A right atrial lesion previously detected by echocardiography was identified as a non-enhancing lesion on cardiac CTA, suggesting thrombus or granulomatous inflammation associated with D. immitis. The abdominal CT revealed multiple enlarged mesenteric lymph nodes, adjacent fat stranding, and segmental thickening of the small intestine (Fig. 1). Fine-needle aspiration of a mesenteric lymph node and cytology of peritoneal fluid confirmed the lymphoma. (Fig. 1). The patient received one session of chemotherapy (vincristine) and treatment for D. immitis (ivermectin), but the clinical condition did not improve. Treatment was terminated upon the owner’s decision, and the patient died thereafter.

Vascular dissection is rarely reported in veterinary medicine, with only a few cases described in dogs [2-6]. Vascular fragility associated with hypertension, infection, or iatrogenic catheter injury has been recognized as a potential predisposing factor [1,7]. In the present case, the blood pressure was 120 mmHg, and there was no history of catheterization or trauma. Therefore, the coexistence of a D. immitis infection and disseminated lymphoma may have contributed to the vascular compromise, culminating in a subclavian artery dissection. A chronic D. immitis infection has been reported to cause mechanical injury to the vascular intima and persistent inflammation of the vessel wall, resulting in weakening and a predisposition to arterial dissection [3]. Although the subclavian artery is not a common site of heartworm infections, ectopic migration of D. immitis into the systemic arteries, including the iliac, femoral, and abdominal arteries, has been documented. Moreover, such a mechanism was considered a possible contributor in the present case [10,11]. In addition, lymphoma-associated arterial dissections have been reported in humans, with the proposed mechanisms including direct lymphocytic infiltration of the vascular wall, cytokine-mediated vascular remodeling, and compression by proliferative lymphoid tissue, which may have contributed to the medial weakening in this case [8,9]. The diagnosis was established definitively through cardiac CTA, which showed a dissecting intimal flap with concurrent aneurysmal dilation in the left subclavian artery, and the lesion was more conspicuous on the cardiac CTA protocol than on conventional delayed-phase thoracic CT. According to previous studies, the cardiac CTA protocol includes the following factors that clarify the conspicuity and delineation of the vascular and cardiac walls [12]. First, operating multidetector CT at high spatial and temporal resolution sharpens the lumen-wall interface. Second, the injection duration, injection rate, and total iodine dose are adjusted according to patient factors (cardiac output and body weight), and biphasic or multiphasic contrast injection or saline flushing is used. Third, the scan timing and contrast distribution are optimized with a test bolus or bolus tracking to achieve homogeneous opacification across the target vascular territory, with dose and injection rate scaled to the body size and scan delay individualized.

Through these processes, mixing and streak artifacts are reduced; a prolonged enhancement plateau is maintained, and wall depiction is improved compared to conventional delayed-phase thoracic CT [12]. In the present case, an 80-row, 160-slice CT scanner was used, and the rotation time was set to 0.35 seconds to improve the spatial and temporal resolution. The contrast dose and injection duration were adjusted according to the patient factors, and a test bolus was used to individualize the scan timing. A dual-injection approach with a saline chaser was used. In the present case, the cardiac CTA protocol depicted the vascular wall more clearly than conventional thoracic delayed-phase CT. This improvement was attributed to the technical factors described above.

In conclusion, this case describes a rare presentation of left subclavian artery dissection associated with a concurrent D. immitis infection and lymphoma in a dog. To the authors’ knowledge, this is the first report to describe the CT features of a subclavian artery dissection in veterinary medicine, and it highlights the clinical value of using a cardiac CT protocol, as applied in the present case, for precise visualization of the cardiac and vascular walls [12].