Migration of VP Shunt Causing Pulmonary Infarction

2017-04-17 20:06:42

Category: Chest & Cardiac Imaging, Region: Thorax-Other and unknown, Plane: Axial

CASE: A three-year-old male presented with a one-week history of fussiness, lack of appetite, intermittent nausea and vomiting, and a one-day history of fever. Five weeks prior, he had a VP shunt placed for persistent hydrocephalus following resection of a cerebellar astrocytoma. To evaluate for shunt malfunction, shunt series radiographs were acquired. These demonstrated an abnormal location of the shunt tubing, which coursed over the heart with the catheter tip seen projecting over the right middle lobe (Fig. 1). A lateral chest radiograph confirmed the intracardiac course of the shunt tube (Fig. 2). Transthoracic echocardiography was subsequently performed, confirming multiple loops of the shunt tube in the right atrium and right ventricle and extending through the right ventricular outflow tract into the main pulmonary arteries. Next, a standard noncontrast chest CT was performed, which also demonstrated the coiled shunt catheter tubing within the right atrium, right ventricle, pulmonary artery and branch pulmonary arteries finally extending into a segmental branch of the middle lobe pulmonary artery. There was an associated wedge-shaped area of consolidation in the adjacent middle lobe consistent with infarction (Fig. 3). Because a thrombus along the course of the catheter in the cardiac chambers or pulmonary artery could not be excluded prior to operative intervention, an ECG-gated cardiac CT was then performed, which eliminated pulsation artifact and confirmed absence of thrombus (Fig. 4). Three-dimensional post processing was performed by the interpreting radiologist. The acquired images revealed entry of the VP shunt catheter into the venous system at the junction of the right subclavian and internal jugular veins (Fig. 5) with subsequent course through the superior vena cava, right atrium, right ventricle and main pulmonary artery and bilateral branch pulmonary arteries. Multiple coils along the course of the catheter were seen (Fig. 6) especially within the main pulmonary artery and bilateral branch pulmonary arteries. The tip of the catheter was identified extending into a segmental branch of the right middle lobe pulmonary artery causing occlusion and infarction in the lateral segment. No associated thrombus was identified along the course of the malpositioned shunt tube. Enlargement of the right atrium was noted with reflux of contrast into the inferior vena cava and hepatic veins, which could have been due to tricuspid regurgitation. Based on the information provided by the ECG-gated cardiac CT findings, the cardiothoracic surgery team felt that a simple retrieval by retraction of the shunt catheter via a neck incision might be difficult, with potential for injury to the tricuspid and pulmonary valves. Therefore, a more extensive surgical intervention was employed. Following removal of the shunt tube, a repeat TEE showed unchanged trivial tricuspid regurgitation with trivial pulmonary valve insufficiency. Right neck exploration with repair of the perforation at the junction of the right internal jugular and subclavian veins was also performed. Finally, the proximal portion of the VP shunt was externalized until postoperative day 6 when a formal shunt revision was completed. The patient did well in the postoperative period with an expedient recovery and subsequent discharge 8 days following surgery. Postsurgical echocardiogram revealed trivial tricuspid and pulmonary regurgitation as well as a small pericardial effusion, which improved over the hospital course. No vegetations were seen. DISCUSSION: Migration of a VP shunt catheter into the heart and pulmonary arteries is an uncommon complication. The exact mechanism by which this occurs is not fully understood, and there are multiple proposed mechanisms. One possibility is transvenous puncture during the initial tunneling procedure into the abdomen, resulting in central migration of the catheter secondary to venous flow and negative intrathoracic pressure. An alternative proposed mechanism is that the catheter could cause continuous mechanical erosion of an adjacent vein, resulting in eventual intravenous migration of the catheter. In our case, the most likely mechanism of shunt migration was intravenous placement of the shunt tube at the junction of the right subclavian and internal jugular vein, as shown in Figs. 5 and 6. In retrospect, the abdominal radiographs obtained in the immediate postoperative period for evaluation of abdominal distension following surgery of the cerebellar astrocytoma and VP shunt tube placement demonstrated an aberrant course of the catheter overlying the superior vena cava, right atrium, inferior vena cava, and hepatic veins with subsequent extension into the peritoneal cavity following perforation of the liver capsule (Figs. 7 and 8). Irrespective of the underlying mechanism, intracardiac migration of a VP shunt catheter is an extremely serious complication that may be life threatening. Meticulous attention during placement of the catheter is paramount, particularly while creating the subcutaneous tunnel within the neck and chest so as to avoid tunneling posterior to the clavicle, which increases the likelihood of intravascular placement. It is recommended that a more superficial and lateral tunneling approach be performed using dull tunneling instruments. In our case, the catheter is seen posterior to the right clavicle, indicating that the tunnel was probably created posterior to the clavicle. While no single method has been established as the gold standard for evaluating the course of a malpositioned intracardiac VP shunt, ECG-gated cardiac CT provides an advantage over conventional chest CT when needing to confirm or refute any associated thrombi in the heart or pulmonary arteries because it eliminates cardiac pulsation artifact. Findings from this method can help determine the best possible management option when surgery is needed for retrieval of the migrated shunt catheter, as in our case. Also, the radiation dose-length product of the prospective ECG-gated cardiac CT for our case was 41 mGycm, which was 26 mGycm less than the dose-length product for the standard contrast enhanced CT. This is predominantly due to the difference in z-axis length of the region of the chest scanned with each imaging technique. Based on this case, we believe that ECG-gated cardiac CT could be more informative with less radiation dose compared to a routine chest CT for evaluation of intravascular foreign bodies in the heart and pulmonary arteries. FIGURE LEGENDS Figure 1: Frontal radiograph showing ventriculoperitoneal shunt catheter overlying the heart with multiple loops extending over the region of the right ventricular outflow and pulmonary artery (arrowheads) with the catheter tip over the right lower zone region (arrows). Ill-defined airspace opacities are also seen laterally adjacent to the horizontal fissure. Figure 2: Lateral chest radiograph confirming intracardiac location of the shunt tube (arrows) and extension of the catheter through the right ventricular outflow into the region of the pulmonary arteries. Figure 3: TOP = Routine non-contrast axial chest CT image showing shunt tube within the heart (arrows) in the right atrium and right ventricle not clearly delineated due to associated cardiac pulsation artifacts. MIDDLE = Routine noncontrast axial chest CT image showing shunt catheter within the main and bilateral branch pulmonary arteries (arrows) with minimal cardiac pulsation artifacts. Peripheral focal airspace opacity is seen in the region of the lateral segment of the right middle lobe due to pulmonary infarction (arrowheads). BOTTOM = Routine non-contrast axial chest CT image showing shunt catheter tip in the region of the right middle lobe (arrow) with associated wedge shaped airspace opacity in the region of lateral segment indicating pulmonary infarction (arrow heads). Figure 4: TOP = ECG-gated axial CT image showing shunt tube (arrows) in the right atrium and right ventricle without cardiac pulsation artifacts. MIDDLE = ECG-gated axial CT image showing the shunt tube extending through both branch pulmonary arteries without associated cardiac pulsation artifacts. BOTTOM = ECG-gated axial CT image showing shunt tube tip (arrow) in the region of right lower lobe with associated pulmonary infarction (arrow heads). Figure 5: Three dimensional (3D) volume rendering using gated CT images without associated bony structures or contrast in the cardiac chambers (Figure a) showing the shunt catheter entering the right subclavian vein-internal jugular vein junction (yellow arrow). The catheter makes several coils in its course through the right atrium, right ventricle main pulmonary artery and bilateral branch pulmonary arteries before terminating into the right pulmonary artery branch (white arrow). The catheter is clearly seen along its entire course due to removal of overlapping structures as compared to Figure 6. Figure 6: Three dimensional (3D) volume rendered ECG gated cardiac CT image with associated chest wall bony structures and contrast in the cardiac chambers showing the shunt catheter entering the right subclavian vein-internal jugular vein junction (yellow arrow). Portions of the catheter in the superior vena cava, right atrium and right ventricle are not seen due to contrast in these structures in this volume rendered post processed image. The catheter tip is seen terminating into the right pulmonary artery branch (white arrow) but better visualized in Figure 5. Figure 7: Left lateral decubitus abdomen radiograph obtained as part of acute abdomen series immediately after the shunt placement to evaluate for abdominal distension. Initially this was thought to be normal. In retrospect, the shunt catheter is seen to traverse over the course of the superior vena cava, right atrium, inferior vena cava and right hepatic vein (arrows) before having multiple coils over the peritoneal cavity terminating in the right lumbar region (arrow head). Figure 8: Frontal supine abdomen radiograph obtained as part of acute abdomen series immediately after the shunt placement to evaluate for abdominal distention. In retrospect, the shunt tube is seen traveling over the expected course of right hepatic vein (arrows) extending beyond the inferior margin of the liver over the peritoneal cavity with the catheter tip seen in the right lumbar region of the abdomen (arrow head). The shunt likely enters the peritoneal cavity after perforating the liver parenchyma and liver capsule.