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Cardiovascular Anesthesiology: Echo Rounds

Transesophageal Echocardiography: Identification and Management of a Misplaced Pedicle Screw in the Descending Thoracic Aorta After Posterior Spinal Fusion

Iyer, Manoj H. MD; Engoren, Milo MD; Martin, Matthew W. MD

Author Information
doi: 10.1213/ANE.0b013e318275341d
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A 50-year-old woman presented with low back pain 3 months after a T4–S1 posterior spinal fusion. A computed tomography (CT) scan showed malpositioning of 2 pedicle screws at the T8 and S1 levels. The S1 screw was encroaching on the spinal canal and was likely the source of her pain. Of higher concern was the misplaced screw at the T8 level, which was impinging on the descending thoracic aorta (Fig. 1). Based on the CT scan, the working preoperative diagnosis was that the screw was adjacent to, but not penetrating the thoracic aorta. After joint discussion between the surgical and anesthesiology teams, the patient was brought to the operating room for screw removal and hardware revision with possible thoracic aortic endograft placement.

Figure 1
Figure 1:
Three-dimensional computed tomography (CT) reconstruction of the spinal fusion hardware and the aorta. Of note is the location of the pedicle screw in relation to the descending aorta.

After induction of general anesthesia and placement of invasive monitors, a transesophageal echocardiography (TEE) probe was placed. This was used to diagnose the exact location of the screw and to monitor for bleeding during its removal. The patient was positioned prone to facilitate surgical access to the screw. TEE confirmed a screw posterolateral to the descending midthoracic aorta at the level of the main pulmonary artery (Video 1, see Supplemental Digital Content 1, http://links.lww.com/AA/A489, and Video 2, Supplemental Digital Content 2, http://links.lww.com/AA/A490; Fig. 2). The long and narrow band of echoes protruding from the posterolateral wall into the aortic lumen raised suspicion that the screw had penetrated all 3 layers of the aorta.

Video 1
Video 1:
Long-axis view of the descending aorta. Color flow Doppler demonstrates flow through the aorta. The narrow band of echos raised suspicion that the screw had penetrated all 3 layers of the aorta. There is also evidence of acoustic “shadowing,” an attenuation artifact caused by the echodense metallic screw. The apparent thickening between the intima and adventitia is due to imaging plane orientation, rather than intramural hematoma.
Video 2
Video 2:
Short-axis view of the descending aorta. The pedicle screw is located in a posterolateral position relative to the aorta. The metalic tip is easily visualized in this image. The image shows color Doppler flow through the descending aorta without evidence of flow extravasation through the aorta.
Figure 2
Figure 2:
Long-axis (A) and short-axis (B) views of the descending aorta at the level of the main pulmonary artery. Color flow Doppler demonstrates flow through the aorta. The pedicle screw is located in a posterolateral position relative to the aorta. The images show color Doppler flow through the descending aorta without evidence of flow extravasation outside of the aorta. The narrow band of echoes raised suspicion that the screw had penetrated through all 3 layers of the aorta. There is also evidence of acoustic “shadowing,” an attenuation artifact caused by the echodense metallic screw (indicated by unlabeled arrows). The apparent thickening between the intima and adventitia is caused by imaging plane orientation, rather than intramural hematoma.

Given the heightened concern for potential aortic intimal injury, we altered our management and used deliberate controlled hypotension to decrease shear stress. During screw removal, the surgeons reported aortic bleeding in the field. TEE showed simultaneous color Doppler flow extravasation traversing posterolaterally through the penetrated aorta in continuous flow with systolic augmentation (Video 3, see Supplemental Digital Content 3, http://links.lww.com/AA/A491; Fig. 3). This confirmed our echocardiographic finding of a small intimal penetration. The surgical field was packed, and direct pressure was applied. After 15 minutes of direct pressure, there was no longer evidence of bleeding (as measured by echocardiography and in the field). Given the TEE findings and initial brisk bleeding after screw removal, the patient was transported to angiography, which found no filling defect, no focal dissection flap, and no contrast extravasation. The patient’s trachea was extubated after the procedure without incident. CT angiogram, done the following day, showed no evidence of dissection or periaortic hematoma formation.

Video 3
Video 3:
Long-axis view of the descending aorta. The screw has now been removed by the surgeon. The arrow points to color flow Doppler demonstrating flow extravasation with systolic augmentation through the aortic wall in a posterolateral direction. The aortic blood flow was also confirmed in the field by the surgeons.
Figure 3
Figure 3:
Long-axis view of the descending aorta at the level of the main pulmonary artery. The screw has now been removed by the surgeon. The arrow points to color flow Doppler demonstrating flow extravasation through the aortic wall in a posterolateral direction.

DISCUSSION

TEE is a well-defined modality for assessing the descending thoracic aorta. No formal study has described the amount of descending aorta that can be visualized, but it is widely accepted that the entire descending thoracic aorta can be visualized given its proximity to the esophagus. Visualization is often lost at the level of the median arcuate ligament, which is typically located at the T12–L1 level. Coupled with color flow Doppler, TEE is excellent for evaluating small intimal tears that may not be visualized by CT angiogram or aortography.1 TEE also allows for rapid evaluation of the aorta in multiple planes with relatively high detail. The descending aorta can be found by rotating the probe posteriorly and to the left. Imaging is completed by slowly advancing or withdrawing the probe at angles of both 0 degrees (short-axis) and 90 degrees (long-axis) along the length of the descending aorta. This is extremely valuable as it permits an echocardiographer to diagnose dissection, aneurysm, or intramural hematoma across a wide area of the aorta.

We believe that this is a novel use of TEE to diagnose and direct surgical management of iatrogenic penetrating aortic trauma. Although a misplaced pedicle screw in the descending aorta is a rare event, the usefulness of TEE to detect aortic pathology is important for all echocardiographers. Before high-resolution CT angiography, aortography was the “gold standard” for diagnosing aortic injury. TEE is now becoming a standard as well, as it can be done rapidly at the bedside, requires no nephrotoxic contrast, and emits no harmful radiation. TEE can be of particular use for unstable patients who cannot safely undergo a CT or aortography. TEE allows for high-resolution images of all 3 layers of the aorta: the intima, media, and adventitia.2 In a small case series, Taams et al.3 showed that TEE is as accurate as angiography in the detection of thoracic aortic pathology. TEE also has the ability to accurately diagnose intramural hematoma (sensitivity 90%; specificity 99%).4 In fact, 1 study described TEE to be more accurate than angiography in discerning minor aortic defects.1 Not only was the aortic pathology diagnosed accurately, but aortic bleeding after screw removal and its cessation with direct pressure was also diagnosed by TEE. The strong muscular tunica media combined with the initial direct manual pressure prevented any further bleeding, similar to the process of removing an angiogram sheath from the femoral artery. TEE findings were also instrumental in our plan for deliberate hypotension before screw removal. The TEE images and clips show some irregular thickening near the aortic wall, both before and after screw removal. Although there was some concern for intramural hematoma, this was likely artifact caused by imaging plane manipulation to allow optimal visualization of the screw. Furthermore, there was a significant “jet” of flow (Video 3, Fig. 3) after screw removal. Doppler flow from the aorta into atmospheric pressure (open wound) was easily visualized, even with high-aliasing velocities. This confirmed that the screw had penetrated all 3 layers of the aorta, because one would not expect high-velocity blood flow if this was an intramural hematoma. Lower-velocity blood flow, such as those into a tissue bed or venous bleeding can be visualized by reducing the aliasing velocity. Echocardiographers use this concept when diagnosing low-velocity intracardiac shunts such as a patent foramen ovale or atrial septal defects.

In summary, we have described a novel use for TEE in a combined orthopedic and vascular surgery. The TEE was instrumental in both the detection of an intraluminal pedicle screw and subsequent management during removal. Thoracic aorta visualization often provides valuable information via detection of atherosclerotic and aneurysmal disease, as well as identification of aortic injury.

ACKNOWLEDGMENTS

The authors acknowledge Kristen Kaufman, MD, Matthew Caldwell, MD, and Barbara Hammond for their assistance.

DISCLOSURES

Name: Manoj H. Iyer, MD.

Contribution: This author helped write and edit the manuscript and interpret the echo images.

Attestation: Manoj H. Iyer attests that the project described and data reported are the work of the authors. Manoj H. Iyer approved the final manuscript.

Name: Milo Engoren, MD.

Contribution: This author helped write and edit the manuscript.

Attestation: Milo Engoren attests that the project described and data reported are the work of the authors. Milo Engoren approved the final manuscript.

Name: Matthew W. Martin, MD.

Contribution: This author helped write and edit the manuscript and interpret the echo images.

Attestation: Matthew W. Martin attests that the project described and data reported are the work of the authors. Matthew W. Martin approved the final manuscript.

This manuscript was handled by: Martin J. London, MD.

REFERENCES

1. Goarin JP, Cluzel P, Gosgnach M, Lamine K, Coriat P, Riou B. Evaluation of transesophageal echocardiography for diagnosis of traumatic aortic injury. Anesthesiology. 2000;93:1373–7
2. Willens HJ, Kessler KM. Transesophageal echocardiography in the diagnosis of diseases of the thoracic aorta: part 1. Aortic dissection, aortic intramural hematoma, and penetrating atherosclerotic ulcer of the aorta. Chest. 1999;116:1772–9
3. Taams MA, Gussenhoven WJ, Schippers LA, Roelandt J, van Herwerden LA, Bos E, de Jong N, Bom N. The value of transoesophageal echocardiography for diagnosis of thoracic aorta pathology. Eur Heart J. 1988;9:1308–16
4. Keren A, Kim CB, Hu BS, Eyngorina I, Billingham ME, Mitchell RS, Miller DC, Popp RL, Schnittger I. Accuracy of biplane and multiplane transesophageal echocardiography in diagnosis of typical acute aortic dissection and intramural hematoma. J Am Coll Cardiol. 1996;28:627–36

Clinician’s Key Teaching Points

By Nikolaos J. Skubas, MD, Kent H. Rehfeldt, MD, and Martin J. London, MD

  • The descending thoracic aorta (DTA) can be easily imaged with transesophageal echocardiography (TEE) by rotating the probe posteriorly and to the left. With 2-dimensional or color flow Doppler, in either short-axis or long-axis view, the DTA from the distal arch to the T12–L1 level can be interrogated for dissection, aneurysm, ulcers, or intramural hematoma.
  • All 3 aortic wall layers can be imaged with TEE, However, off-axis imaging of the aortic wall, if the imaging place is transecting the DTA lumen obliquely, may be misdiagnosed as abnormal thickening or pathology.
  • In this case, intraoperative TEE in a patient with a previous thoracolumbar posterior spinal fusion verified the preoperative finding by computed tomography (CT) scan that a T8 pedicle crew was impinging on the DTA. After the removal of the screw under controlled hypotension, color flow Doppler showed blood extravasation consistent with a small intimal perforation. Direct manual pressure successfully stopped the bleeding. A subsequent angiogram demonstrated a normal aortic wall.
  • As a perioperative diagnostic technique, TEE is particularly suitable for the unstable patient. It can usually be done rapidly and does not involve nephrotoxic contrast agents or radiation exposure. It may be more sensitive than CT angiography or aortography in visualizing small aortic tears.
© 2013 International Anesthesia Research Society