Ann Thorac Surg 2005;80:726-729
© 2005 The Society of Thoracic Surgeons
Case report
Mycotic Aneurysm of the Descending Thoracic Aorta in a 2-kg Neonate
Nathalie Roy, MD
a
,
Anthony Azakiea, MD
a
,
Anita J. Moon-Grady, MD
b
,
Dominic J. Blurton, MD
b
,
Tom R. Karl, MD
a
,
*
a Division of Pediatric Cardiothoracic Surgery, Children’s Hospital, University of California, San Francisco, California
b Division of Pediatric Cardiology, Children’s Hospital, University of California, San Francisco, California
Accepted for publication January 28, 2004.
* Address reprint requests to Dr Karl, Division of Pediatric Cardiothoracic Surgery, University of California, San Francisco, 505 Parnassus Ave, Room S-549, San Francisco, CA94143-0118 (Email: karlt{at}surgery.ucsf.edu).
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Abstract
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Umbilical artery catheterization is often performed in critically ill neonates. Infection and thromboembolic events are relatively frequent complications, but aneurysm formation is rare. We describe the case of a premature baby who developed a rapidly expanding aneurysm of the descending thoracic aorta, secondary to a highly placed infected umbilical catheter. The rapid progression under medical therapy prompted us to replace the thoracic aorta with an 8-mm polytetrafluoroethylene graft, using extracorporeal circulation and core cooling. The baby had an excellent recovery and was discharged home after a prolonged antibiotic course. He is being followed with repeated imaging studies for a small abdominal aneurysm. We describe a novel approach to this rare and complicated problem and provide a review of the literature on the subject.
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Introduction
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Low-birth-weight infants with respiratory failure at birth may need prolonged mechanical ventilation and intraarterial monitoring. Umbilical arterial catheters have been used for this purpose since 1962 [1]. Infection and thrombosis are frequent complications, and can lead to aneurysm formation. There is a high risk of lethal rupture of the aneurysm in this compromised population. Mycotic aneurysms also pose a serious therapeutic challenge in a small patient. We report the case of a low-birth-weight premature infant who developed a rapidly enlarging thoracic aneurysm, and we describe the novel surgical approach used to address the problem.
A 32-week premature male infant who weighed 1.97 kg at birth had respiratory distress and was intubated. As part of his neonatal critical care, the infant received an umbilical intraarterial catheter that was placed in a supradiaphragmatic position. He had a ductus arteriosus that was closed with indomethacin by day 5. The infant subsequently developed Staphylococcus aureus septicemia and was started on vancomycin and gentamicin. He remained febrile and developed septic arthritis of the left wrist and right knee. The umbilical arterial line was removed and the patient was transferred to the UCSF Medical Center for further investigation and treatment.
On arrival, the patient was febrile to 39.5°C and the physical exam revealed no new findings. A chest roentgenogram showed an abnormal aortic contour (Fig 1) and an echocardiogram suggested a saccular aneurysm of the descending aorta, with a maximum diameter of 10 mm (versus an aortic diameter of 5 mm). The aneurysm extended more than 20 mm, from a point distal to the left subclavian artery, and involved most of the descending thoracic aorta. No other intracardiac anomalies were found. He was initially treated with antibiotics and followed with serial echocardiograms.
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Fig 1. A preoperative chest roentgenogram showing a large aortic contour (arrow), which corresponds to the descending aortic aneurysm.
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The blood cultures became negative, but repeated echocardiography over a 2-week period showed that the thoracic aneurysm was progressing in size. A magnetic resonance angiogram (MRA) showed a large saccular dilatation of the descending thoracic aorta, measuring 22 mm x 23 mm in diameter and 25 mm in length (Fig 2). Also found just above the celiac vessels was a small aneurysm of the abdominal aorta that measured 8 mm x 4 mm in diameter and 8 mm in length. The rapid progression of the mycotic aneurysm prompted us to recommend an operation.
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Fig 2. The preoperative magnetic resonance image demonstrates a large saccular aneurysm (arrow) of the thoracic descending aorta resulting from a highly placed infected umbilical artery catheter.
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The procedure was done using extracorporeal circulation and core cooling. With the patient supine, a 6F DLP arterial cannula (Medtronic Inc, Minneapolis, MN) and a 10F Bio-Medicus venous cannula (Medtronic, Inc) were used to cannulate the right common carotid artery and internal jugular vein after systemic heparinization. Cardiopulmonary bypass was begun at flows of 200 mL·kg–1
·min–1 using a blood-primed (280 mL) neonatal circuit with a Baby-RX oxygenator (Terumo, Tokyo, Japan), and the patient’s core temperature was reduced to 18°C.
The patient was placed in a right lateral position and a left thoracotomy in both third and sixth intercostal spaces was performed through a single skin incision. The cardiopulmonary bypass flow was reduced to 50 ml·kg–1
·min–1, and the aortic arch was clamped between the left carotid and the left subclavian artery. The proximal descending aorta was transected through healthy tissue, and an 8-mm thin-walled polytetrafluoroethylene (PTFE) graft was anastomosed to the undersurface of the aortic arch. The distal aorta was clamped at the level of the hiatus, the aneurysm was opened longitudinally, and three pairs of intercostal arteries were ligated. The circulation was arrested for 8 minutes at 18°C to allow accurate resection of the infected aneurysmal aortic tissue and to perform the distal anastomosis with an open vessel technique.
Cardiopulmonary bypass was resumed and the baby was warmed to 37°C. The patient was weaned from bypass and heparin was reversed. The chest was closed, leaving a suction drain in place, and the baby was returned to a supine position to decannulate the cervical vessels. The carotid artery and internal jugular vein were repaired primarily in a transverse fashion.
The patient did well postoperatively. He moved all extremities within 12 hours, and was extubated 4 days after surgery. He suffered a left vocal cord paralysis. The patient received an esmolol infusion to control his blood pressure, and heparin was started on the first postoperative day at an hourly rate of 10 U/kg, and then 1 week after the procedure was converted to daily aspirin (at 5 mg/kg). The antibiotic regimen consisting of nafcillingentamicin, and rifampin was continued intravenously for 6 weeks after surgery. All blood cultures remained negative and there was no significant febrile episode.
At 6 month follow-up, the infant is doing well but has a 15 mm Hg arm-leg gradient, probably because of the long segment of noncompliant graft. An echocardiogram shows unobstructed flow in the thoracic aorta, and the dimensions of the abdominal aneurysm have not changed (8 mm).
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Comment
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Since Wigger and colleagues first described a mycotic aneurysm of the aorta related to an umbilical artery catheter in 1970, approximately 50 cases have been reported in the literature [2–6]. Their pathogenesis involves intimal trauma, thrombus formation around the catheter, infection, and ischemia of the arterial wall. The intrathoracic position and the duration of intraarterial catheter monitoring also correlate with an increased risk of aneurysm formation [3]. It is conceivable that the presence of a ductus arteriosus in our patient may have been a contributory factor by causing turbulence in the thoracic aorta in proximity of an infected arterial catheter.
Mycotic aneurysms can present as incidental findings on chest roentgenograms, a mass palpated in the abdomen, new onset of hypertension, and septic embolism. They can also present dramatically with rupture and cardiovascular collapse. Once suspected, the diagnosis is made by ultrasound or contrast computed tomographic scan, but delineation of the anatomy is best obtained with an angiogram or MRI [4, 5]. In our patient an MRA precisely demonstrated the location and extent of the thoracic involvement and diagnosed a second aneurysm.
We decided not to intervene on the abdominal aneurysm at the time of the thoracic repair because of its remote localization and small size. Subsequently, it did not progress in the follow-up, and no septic episodes have resulted from it. Small aneurysms in stable patients can be observed closely, but if there is rapid expansion or in the presence of continued sepsis, then surgical repair is warranted [4, 5]. Thoracic aneurysms have a higher propensity for rupture and that should be taken into consideration when a surgical decision is being made [4].
Cardiopulmonary bypass was useful in our 2-kg premature neonate who underwent surgical replacement of the thoracic aorta. In this case, the dissection and anastomosis could have been difficult, increasing the ischemic time as well as requiring the ligation of many arterial branches. Core cooling probably allowed better spinal protection, which was critical because the entire thoracic aorta was involved. Extremity weakness that results from mild spinal cord injury is a well-known complication of thoracoabdominal surgery in older patients. It has been reported in a 15-month-old patient following the repair of a very extensive thoracoabdominal aneurysm [4].
Cannulation of the cervical vessels allowed good bypass flows in this small neonate, and the proximal clamp could be placed in a way to allow flow in the left carotid artery. It was possible to repair the right carotid artery and jugular vein at the end of the procedure. In our experience with extracorporeal membrane oxygenation, this has usually been the case, and good Doppler patency has been documented [7].
The infant tripled his birth weight by 6 months of age, and the arm-leg gradient is currently 15 mm Hg. It is expected that the graft will need to be replaced, although the interval is uncertain. Follow-up of patients operated on as neonates for interruption of the aortic arch shows that PTFE grafts demonstrate patency and an acceptable arm-leg gradient up to 5 years postoperatively [8].
Regarding alternate surgical techniques for mycotic aneurysms in children, some authors have advocated a primary repair by using an end-to-end anastomosis or aneurysmorrhaphy [4]. In the case of our patient, the long segment of aorta involved and friable inflammatory tissue left us with the interposition graft as the sole option. Aortic and pulmonary artery homografts could offer the theoretical advantage of reduction of subsequent infectious risk in cases where the disease would be more circumscribed, but their propensity for early stenosis and calcification make them less desirable in infants. We would not recommend them in the presence of extensive involvement of the aorta in neonates. Close monitoring of the left ventricular dimensions, hypertrophy, and function will be important in view of the small caliber of the PTFE graft. Equally important is to continue appropriate anticoagulation and avoid dehydration as it may precipitate graft thrombosis.
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References
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- Warley MA, Gairdner D. Respiratory distress syndrome of the newborn-principles in treatment Arch Dis Child 1962;37:455-465.
- Wigger HJ, Bransilver BR, Blanc WA. Thromboses due to catheterization in infants and children J Pediatr 1970;76:1-11.[Medline]
- Drucker DE, Greenfield LJ, Ehrlich F, Salzberg AM. Aorto-iliac aneurysms following umbilical artery catheterization J Pediatr Surg 1986;21:725-730.[Medline]
- Cribari C, Meadors FA, Crawford ES, et al. Thoracoabdominal aortic aneurysm associated with umbilical artery catheterizationcase report and review of the literature. J Vasc Surg 1992;16:75-86.[Medline]
- Mendeloff J, Stallion A, Hutton M, Goldstone J. Aortic aneurysm resulting from umbilical artery catheterizationcase report, literature review, and management algorithm. J Vasc Surg 2001;33:419-424.[Medline]
- Lobe TE, Richardson CJ, Boulden TF, et al. Mycotic thromboaneurysmal disease of the abdominal aorta in preterm infantsits natural history and its management. J Pediatr Surg 1992;27:1054-1059.[Medline]
- Karl TR, Iyer KS, Mee RB. Infant ECMO canulation technique allowing preservation of carotid and jugular vessels Ann Thorac Surg 1990;50:488-489.[Abstract]
- Yasui H, Kado H, Yonenaga K, et al. Revised technique of cardiopulmonary bypass in one-stage repair of interrupted aortic arch complex Ann Thorac Surg 1993;55:1166-1171.[Abstract]
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Abstract
Introduction
