Pulmonary cement embolism after pedicle screw vertebral stabilization.

Pulmonary arterial embolization of polymethylmethacrylate cement, most usually occurring after vertebroplasty or kyphoplasty, is very uncommon following vertebral stabilization procedures. Unenhanced CT scans viewed at lung window settings allow confident identification of cement emboli in the pulmonary circulation along with possible associate parenchymal changes, whereas hyperdense emboli may be less conspicuous on CT-angiographic studies with high-flow contrast medium injection. Although clinical manifestations are largely variable from asymptomatic cases to severe respiratory distress, most cases are treated with anticoagulation.

After a fall, a 75-years-old woman without significant past medical history was diagnosed to have amyelic L2 vertebral body fracture. Surgical stabilization was performed with posterior pedicle screw fixation and polymethylmethacrylate (PMMA) cement injection. Some left-sided paravertebral cement leakage was observed intraprocedurally [Figure 1a].

Figure 1

(a) Lateral CT scout-view shows pedicle screw fixation device positioned to stabilize L2 fracture. Epidural leakage of radio-opaque PMMA cement is seen (arrowhead). (b) Axial image from unenhanced CT acquisition viewed at bone window settings shows hyperdense linear structure consistent with cement embolus in a subsegmental arterial branch in the upper right lobe (arrowhead). (c) On axial image from contrast-enhanced CT angiographic acquisition, a larger cement embolus is seen distally in the ipsilateral pulmonary artery

After surgery, the patient complained of progressive dyspnoea with tachypnea and bilateral hypoventilation. Blood pressure, arterial gas and acid-base parameters remained stable within normal limits during oxygen administration through nasal mask. A frontal antero-posterior chest radiograph with the bed-ridden patient (not shown) showed reduced lung volumes without appreciable pleuro-pulmonary abnormalities. Chest computed tomography (CT)-angiography was requested by the anesthesiologist. Strongly hyperdense material consistent with cement embolism was seen on unenhanced images in the distal right pulmonary artery and in a segmental ipsilateral upper lobe branch [Figure 1b, c]. After initiation of anticoagulation with low-molecular heparin and warfarin, the patient recovered and was discharged.

Embolization of PMMA cement into the pulmonary arterial circulation represents the most frequent potential complication after vertebroplasty or kyphoplasty performed to treat painful vertebral compression fractures secondary to osteoporosis, trauma, hemangioma, or malignancies. Usually occurring following perivertebral or epidural cement leak, pulmonary cement embolism (PCE) may represent an incidental radiographic finding in asymptomatic patients, may be associated with variable-degree respiratory distress or may sometimes prove fatal when massive or in presence of severe comorbidities.[1-3]

Early studies underestimated the frequency of PCE in the range 3.5-6.8% after vertebroplasty or kyphoplasty procedures, whereas recently a much higher incidence (26%, 95% CI 16%-39%) has been reported with the routine use of postprocedural CT.[134] Conversely, PCE occurrence after pedicle screw augmentation surgery as in our case is very rare (0.8%).[5]

Opaque tubular or branching opacities, sporadically scattered or distributed diffusely throughout the lungs may be detected on postoperative chest radiographs. Unenhanced multidetector CT acquisition has a much higher sensitivity for detection of hyperdense emboli in the pulmonary vessels and their branches and may be warranted when intraprocedural cement leak is observed. Identification is easier on images viewed at bone settings, whereas high-attenuation cement emboli may be less conspicuous on mediastinal images or obscured during pulmonary CT angiographic studies with high-flow contrast injection. Differential diagnosis of hyperattenuating structures includes calcified granulomas or mucus plugs, surgical clips or endobronchial contrast material.[23]

Preventive strategies and optimal treatment are still controversial. Asymptomatic cases require no specific therapy, whereas central or symptomatic emboli should receive oxygen or mechanical ventilatory support as needed, plus anticoagulation starting with low-molecular-weight heparin and warfarin, the latter to be continued up to 6 months. Surgical embolectomy is reserved for exceptional cases of severe central embolism.[1]