correction of scoliosis. There she underwent anterior spondylosyndesis through placement of an inner vertebral fixator secured to vertebrae from the 5th thoracic.
Case
Reports
Josip Sokolic, MD, PhD Tomislav Sosa, MD Ranko Ugljen, MD Bojan Biocina, MD Slavko Simunic, MD Zoran Slobodnjak, MD
Extrinsic Erosion of the Descending Aorta by a Vertebral Fixator We report a rare case in which mechanical extrinsic erosion of the descending thoracic aorta resulted in perforation and periaortic hematoma formation in a 16-year-old girl. Five months before admission to our clinic, the patient had undergone surgical spondylosyndesis with inner vertebral fixation, for the correction of scoliosis. Subsequently, a screw on the fixatorbecame loose, erodingandeventuallyperforating the wallof the descending aorta. The resultant lesion was at first misdiagnosed as a paravertebral abscess; extrinsic perforation of the descending aorta was suspected prior to operation, but was confirmed only upon surgical exploration. After evacuation of the hematoma, the 1.5-cm aortic perforation was closed directly with continuous sutures. Seven months later, the patient continues to do well. (Texas Heart Institute Journal 1991;18:136-9)
W
e report a rare case of mechanical erosion of the descending thoracic aorta caused by a loose screw on an inner vertebral fixator implanted for the treatment of scoliosis. To our knowledge, this is the first case of
its kind to be reported in the literature.
Case Report In mid-June of 1989, a 16-year-old girl was admitted to an orthopedic clinic for the correction of scoliosis. There she underwent anterior spondylosyndesis through placement of an inner vertebral fixator secured to vertebrae from the 5th thoracic through the 1st lumbar with metal screws. The operation was performed through a left thoracotomy. The patient did well until the 4th postoperative month, when she began to experience pain in her left hemithorax, followed by dyspnea, hemoptysis, and anemia, accompanied by a low-grade fever. Because she continued to have dyspnea and dull thoracic pain for 2 weeks after first manifestation of symptoms, she
admitted to a pediatric clinic. Laboratory studies then revealed mild anemia, erythrocyte sedimentation rate of 65 to 86 mm/hr, and leukocytosis (13.3 x 109/ L). Computed tomography disclosed a rounded shadow in the posterior mediastinum, adjacent to the vertebrae, and 99mTc scintigraphic examination showed a zone of radiocolloid hypofixation in the posterior segments of the upper, apical, and lower left pulmonary lobe. On the basis of these findings, a provisional diagnosis of paravertebral abscess was made. Roentgenography appeared to indicate bronchopneumonic infiltration in the left supradiaphragmatic portion of the left lung. Within 7 days, the patient was transferred back to the orthopedic clinic and prepared for evacuation of a paravertebral abscess. To rule out a differential diagnosis of chest tumor and to confirm the presence of an abscess, the lesion was subjected to preoperative aspiration. Because this procedure yielded blood clots rather than pus, a vascular surgeon was consulted. The patient underwent repeat chest radiography, which showed a mediastinal prominence around the aortic knob (Fig. 1). Transesophageal ultrasonography, digital subtraction angiography (Figs. 2 and 3), and computed tomography (Fig. 4) were also performed. Two days later, in late November of 1989, the patient exhibited symptoms of hemorrhagic shock, with recurrent hemoptysis, and was transferred to our surgical clinic. Upon examination of the digital subtraction angiogram-which showed extravasation of contrast medium-we strongly suspected aortic puncture, but
was
an
Key words: Aorta, descending; aortic aneurysm/aneurysm,
dissecting; aortic erosion, extrinsic; scoliosis From: The Clinic for Surgery (Drs. Sokolic, Sosa, Ugljen, and Biocina), the Department of Radiology (Dr. SimuniO), and the Clinic of Thoracic Surgery (Dr. Slobodnjak), The Medical University of Zagreb, Zagreb, Yugoslavia
Address for reprints: Josip Sokolic, MD, PhD, The Clinic for Surgery, The Medical University of Zagreb, Ki.patideva ul. 12/Il, 41000 Zagreb, Yugoslavia
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Extrinsic Erosion of the Descending Aorta
Volu"ze 18, Number 2, 1991
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Fig. 3 Digital subtraction angiogram, showing how a loose screw from the inner vertebral fixator has penetrated the aortic wall, causing formation of a large hematoma. This interpretation was suspected preoperatively, but was confirmed only upon surgical exploration, when the hematoma and puncture wound became apparent.
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Fig. 1 Preoperative chest radiograph, showing widening of the mediastinum and blurring of the aortic knob.
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Fig. 4 Computed tomogram, in which the aortic defect is lateral (approximate location shown with arrow) because of
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Fig. 2 Digital subtraction angiogram, indicating leakage of contrast material from the descending aorta.
could not rule out puncture of paravertebral "abscess." After 4 hours of intensive care, she was taken to the operating room, where we performed a left thoracotomy through the 4th intercostal space and encountered a large, pulsating mass in the left portion of the mediastinum. Under controlled hypotension, we cross-clamped the proximal aorta between the origin of the left common carotid artery and the left subclavian artery. The thoracic aorta was clamped distally just above the diaphragm. Femorofemoral bypass was in use for partial cardiopulmonary support. After the aorta had been cross-clamped, the wall Texas Heail b-istituteJournal
of the hematoma was incised, and numerous clots were evacuated. For the first time, a rounded perforation measuring 1.5-cm in diameter was clearly observed in the posterolateral portion of the descending aorta, just above the loosened 1st screw of the inner vertebral fixator (Fig. 5). This defect was closed directly with continuous 3-0 sutures. When the cross-clamps were released after an ischemic time of 11 minutes, there was no bleeding from the suture site. Because the hematoma had compressed the left pulmonary lobe, partial pulmonary decortication had been performed during repair of the hematoma's outer wall. Despite this, the lower lobe had to be slightly reexpanded. The inner vertebral fixator was then removed. Histopathologic examination of the wall of the hematoma disclosed blood clots and lung Extrinsic Erosion of the Descending Aorta
137
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Fig. 6 Chest radiograph obtained 7 months after surgery.
Fig. 5 Sketch derived from Figure 3, showing more clearly the site of aortic erosion and puncture.
tissue fragments, including septa destroyed by lung infarction. Twenty-four hours after surgery, minor transudation was observed in the left side of the chest. By the 8th postoperative day, most of the transudate had been resorbed, so the patient was discharged from the hospital. Seven months later, chest radiography showed operative adhesions without pleural transudation (Fig. 6). The mediastinal outline was normal. Correction of the scoliosis has been postponed until such time as a posterior vertebral fixator can be
placed.
Discussion Although penetrating injuries of the abdominal aorta involve a wide range of mechanisms, no cases similar to ours could be found in the available literature.'1' The aortic wall perforation resulted from the chronic erosive action of an extrinsic mechanical device. Direct injuries of the vessel wall are usually related to penetrating or blunt trauma and are heralded by immediate vascular symptoms.2'3'6'7"2 In our patient, however, the implanted vertebral fixator had a loose screw above the 5th thoracic vertebra; during each diastole, this screw touched the descending aorta, thereby compressing and gradually eroding the aortic wall (Fig. 4). Four months after placement of the fixator, this pulsatile movement finally caused perfo138
Extrinsic Erosion of the Descending Aorta
ration of the outer arterial wall, initiating a complex series of events. A pulsatile periaortic hematoma expanded into the left pleural cavity, in an area of reduced tissue resistance. This hematoma subsequently became organized with the connective tissue investing the lower pulmonary lobe. Eventually, its wall comprised the mediastinal pleura, the visceral pleura, and the fibrous outer layer of the lung. Lung compression then ensued, inducing stasis in the fragile pulmonary veins. Increased pulmonary venous pressure caused small vessels to rupture, producing recurrent hemoptysis. In brief, high-pressure hemorrhage from the aorta resulted in low-pressure hemorrhage from the pulmonary circulation.13 The unrelenting pain in the thoracic vertebrae was caused by the posterior location of the hematoma. When the patient was first admitted for diagnostic workup, the abnormal radiographic density observed in her mid-chest was misinterpreted as an inflammatory process around the site of the spinal operation. On radiography, vascular abnormalities are often hard to distinguish from more common lesions such as neoplasms, cysts, and abscesses, especially in the absence of a corroborative clinical history or physical finding.'4 In our patient, back pain arising from the descending aortic perforation could easily be ascribed to scoliosis, or to the orthopedic procedure itself. Therefore, the most pertinent symptom was hemoptysis, which suggested a compressive hemothorax.'3 Although preoperative digital substraction angiography (Fig. 3) had revealed a large hematoma, it was only postoperatively and in retrospect that we were able to see clearly in the angiogram what we had observed during surgery-evidence of aortic puncture by a screw (Fig. 5). Volume 18, Number 2, 1991
Operative intervention was deemed necessary because of bleeding and persistent pain.'5 To prevent spinal cord injury,'2 femorofemoral bypass was used;4' 6 and the hematoma itself was repaired without disturbing the aortic anatomy.3 The unplanned 3-week delay before surgical repair was fortunate, insofar as the lesion's advanced state of organization enabled safer access to the pleural cavity (without bleeding) and safer proximal and distal aortic clamping before opening the wall of the hematoma.'7'8 Partial pulmonary decortication promoted lung reexpansion, which in turn stopped the bleeding from the pulmonary circulation.'3 Because the perforation was closed directly with continuous sutures, aortic crossclamp time was minimized.
Conclusion Extrinsic mechanical erosion of the aorta resulting in perforation is an extremely rare injury that necessitates prompt surgical intervention. Cross-clamp time should be kept short by direct closure of aortic perforations measuring 1.5 cm or less. If the lung is compressed, partial decortication is advisable to facilitate reexpansion. Despite the successful outcome in our patient after an unplanned 3-week delay, it should emphasized that in such cases early diagnosis and surgical intervention are advisable. Widening of the mediastinal silhouette should always suggest a potentially lethal descending thoracic aneurysm.
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