The goal of this study was to evaluate the accuracy of CT-based computer-assisted pedicle screw insertion in the thoracic spine in patients with fractures, metastases, and spondylodiscitis compared to a conventional technique. A total of 324 pedicle screws were inserted in the thoracic spines of 85 patients: 211 screws were placed using a CT-based optoelectronic navigation system assisted by an image intensifier and 113 screws were placed with a conventional technique. Screw positions were evaluated with postoperative CT scans by an independent radiologist. In the computer-assisted group, 174 (82.5%) screws were found completely within their pedicles compared with 77 (68.1%) correctly placed screws in the conventional group ( p<0.003). Despite use of the navigation system, 1.9% of the computer-assisted screws perforated the pedicle wall by more than 4 mm. The additional use of the image intensifier helped to identify the correct vertebral body and avoided cranial or caudal pedicle wall perforations.
T HE image depicts an anterior mediastinal mass in a 4-yr-old who presented with numbness in the left arm. A large soft tissue mass can be seen in the anterior mediastinum. The mass extended into the neck and displaced the great vessels in the mediastinum and major vessels in the left neck. The airway and thyroid were deviated toward the right. The trachea was narrowed slightly at its midportion. The overall size of the mass was 12 ϫ 5 ϫ 5 cm. The patient presented for biopsy of the mass. Despite the impressive magnetic resonance imaging scan, the child preoperatively had no sign of airway obstruction. For the procedure, anesthesia was induced with propofol, and a laryngeal mask airway was inserted. Anesthesia maintenance was with a propofol infusion with fentanyl supplementation while the patient breathed spontaneously with the head elevated. The procedure was uneventful. The pathologic diagnosis was stage 3 T-cell lymphoplastic non-Hodgkin lymphoma with starry sky macrophages. Patients, particularly children, with anterior mediastinal masses can have pulmonary as well as cardiac collapse. 1,2 In a series of 98 adults who underwent 105 procedures, no patient during surgery had airway obstruction. 3 Infants and small children, though, have airways that are more compressible, and they may be more susceptible than adults to extrinsic airway obstruction. Preoperatively, patients should be evaluated for extension of the tumor to determine whether the tumor affects structures that can lead to respiratory and or hemodynamic instability. 4 Although there are risks in anesthetizing children with mediastinal masses, it is also important that an accurate tissue diagnosis can be obtained so appropriate therapy can be instituted. If airway obstruction preoperatively is not severe, anesthesia should generally be safe. 5 Spontaneous respiration is essential to maintain negative intrathoracic pressure and prevent compression of anterior mediastinal structures. 6 It is advisable, then, that paralysis should be avoided. Although the use of laryngeal mask airways has been described as part of the anesthetic management of patients with a mediastinal mass, an endotracheal tube can alleviate obstruction due to a mediastinal mass. 7
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