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1
Department of Paediatric Radiology, Sophia Children's Hospital, University
Hospital Rotterdam, Ste. D-205, P. O. Box 2040, 3000 CA Rotterdam, The
Netherlands.
2
Present address: Department of Radiology, Academic Medical Center Amsterdam,
Meibergdreef 9, 1105 AZ Amsterdam Zuid-Oost, The Netherlands.
3
Department of Paediatric Cardiology, Sophia Children's Hospital, University
Hospital Rotterdam, 3000 CA Rotterdam, The Netherlands.
4Department of Radiology, University Hospital Maastricht, P.
O. Box 5800, 6202 AZ Maastricht, The Netherlands.
Received July 23, 2001;
accepted after revision September 12, 2001.
Address correspondence to R. R. van Rijn.
Abstract
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MATERIALS AND METHODS. Between January 1993 and December 1998, 96 children underwent 105 modified Blalock-Taussig shunt procedures. In eight children, 11 cases of perigraft seromas were identified. The mean age of these children at the time of operation was 3 years (range, 6 days to 5 years 8 months). Pre- and postoperative chest radiographs were routinely performed in the children in whom seromas had been found. Additional postoperative radiologic investigations consisted of thoracic sonography (in 11 cases), CT (in eight cases), and MR imaging (in two cases). In all cases of perigraft seroma, the modified Blalock-Taussig shunts were constructed through a posterolateral thoracotomy at the fourth intercostal space.
RESULTS. On average, the chest radiographs showed the first signs of the seroma on day 10 after the surgery (range, day 1-day 30). Using thoracic sonography, it was possible to visualize the perigraft seroma and the modified Blalock-Taussig shunt in eight (73%) of 11 cases. CT and MR imaging performed equally well in revealing perigraft seromas.
CONCLUSION. As was found in these critically ill children, sonography has an advantage over CT and MR imaging because of its portability and, therefore, capability for bedside use. We recommend the use of sonography as the initial imaging modality in suspected cases of perigraft seroma development.
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With the advent of artificial vessels made of materials such as Gore-Tex (W.L. Gore, Elkton, MD) or Dacron (DuPont, Wilmington, DE), a change in the procedure was introduced. In 1976, Gazzaniga et al. [3] were the first team to perform a modified Blalock-Taussig shunt, using a polytetrafluoroethylene graft (Gore-Tex; W.L. Gore) as an interposition between the subclavian and pulmonary arteries (Fig. 1).
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Several well-known complications of the modified Blalock-Taussig shunt, such as thrombosis, infection, hematoma, aneurysmal dilatation, mycotic pseudoaneurysm, and so-called perigraft seroma, have been described [4,5,6,7,8,9,10]. A perigraft seroma is defined as a sterile collection of fluid in a non-secretory wall surrounding a shunt. The cause of the formation of a perigraft seroma is still a matter of debate. One of the most widely accepted theories is that handling of the polytetrafluoroethylene graft causes leakage because of a change from a hydrophobic state into a hydophilic one. The fluid collection thus contains graft ultrafiltration (transudate). For a fuller discussion on this subject, we refer the reader to the article by Berger et al. [4].
In this article, we present the imaging features of a perigraft seroma correlated with surgical findings. Furthermore, we aim to define an optimal diagnostic strategy in patients with a suspected perigraft seroma.
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The mean age of the children at the time of operation was 3 years (age range, 6 days to 5 years, 8 months). The cardiac diagnosis in the eight children was pulmonary atresia with ventricular septum defect and systemic pulmonary collateral arteries (four patients), pulmonary atresia with intact ventricular septum (one patient), pulmonary atresia with ventricular septum defect (two patients), and pulmonary stenosis with monoventricle (one patient).
In all 11 cases of perigraft seroma, the modified Blalock-Taussig shunts were constructed through a posterolateral thoracotomy at the fourth intercostal space. Interposition of a poly-tetrafluoroethylene graft, with a diameter of 5 mm (n = 9) or 6 mm (n = 2), between systemic and pulmonary circulation, was performed using a 7-0 polyprolene continuous suture (Prolene; Ethicon, Sommersville, NJ) for both ends of the anastomosis. Three children required a second modified Blalock-Taussig shunt procedure on the contralateral side because of consecutive unifocalization procedures.
Imaging Modalities
In all eight children, pre- and postoperative chest radiography was
routinely performed. In addition, all children underwent sonography with
either a HDI 3000 (Advanced Technology Laboratories, Best, The Netherlands) or
a 128 XP10 (Accuson, Mountain View, CA) scanner. CT investigations were
performed in five children with either a Prospeed S (General Electric Medical
Systems, Milwaukee, WI) or a Somaton Plus (Siemens Medical Systems, Erlangen,
Germany). Helical CT was performed before and after the administration of an
IV contrast medium. Technical parameters were collimation, 3 mm; pitch, 1.5;
120 kV; 100 mAs, and rotation time, 2 sec.
For MR imaging (performed in two cases), a Gyroscan NT 1.0-T scanner (Philips Medical Systems, Best, The Netherlands) was used. In both cases, only unenhanced T1-weighted spin-echo and T2-weighted turbo spin-echo images were obtained in the axial, coronal, and sagittal planes.
The volume of the perigraft seroma was estimated by either sonography or CT
using the formula of an ellipsoid: length x width x depth x
(
/6).
Treatment of Perigraft Seromas
Six of the 11 cases of perigraft seroma were treated surgically because of
the clinical condition of the patient. In three of these cases, the perigraft
seroma was removed, and the modified Blalock-Taussig shunt was sealed. In
three other cases, the date for follow-up surgery was moved up, and during the
surgery, the modified Blalock-Taussig shunt was removed. The clinical
condition of the patients with the other five cases of perigraft seroma did
not warrant a second thoracotomy, and they were treated conservatively.
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Using thoracic sonography, it was possible to visualize the perigraft seroma and the modified Blalock-Taussig shunt in eight (73%) of the 11 cases. In early stages of the development of a perigraft seroma, sonography showed heterogeneous tissue with mixed echogenicity, sometimes resembling atelectatic lung tissue. However, color-flow Doppler sonography showed a striking absence of flow, making the differentiation from atelectatic lung tissue possible (Fig. 3A,3B,3C,3D). The modified Blalock-Taussig shunt itself could also be seen in most cases and flow within the modified Blalock-Taussig shunt could be seen and quantified using Doppler sonography. Subsequently, liquefaction of the perigraft seroma began, and the enhanced gray-scale images then showed a central anechoic lesion directly surrounding the modified Blalock-Taussig shunt.
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In five children, thoracic CT showed eight perigraft seromas. In three cases, the seromas were bilateral, and one had not been noticed on several previous thoracic radiographs. CT examination showed a fluid collection of intermediate density surrounding or adjacent to the modified Blalock-Taussig shunt. After the administration of IV contrast medium, the capsule of the perigraft seroma showed slight enhancement, and the modified Blalock-Taussig shunt itself could be seen as a hyperdense structure that was adjacent to or transversing the perigraft seroma (Fig. 4A,4B).
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In two children, MR imaging was performed; T1-weighted spin-echo images revealed the seroma as a well-delineated isointense mass in the upper lobe of the ipsilateral thorax. The signal intensity of the perigraft seromas was comparable to that of the mediastinal structures. However, on T2-weighted turbo spin-echo images, the perigraft seromas showed high signal intensity with some septation in both children (Fig. 5A,5B). The high signal intensity of the seroma on T2-weighted turbo spin-echo images was somewhat lower than the signal of cerebrospinal fluid, a finding that fits with our theory of leakage through the modified Blalock-Taussig graft. The modified Blalock-Taussig shunts themselves showed a signal void, indicative of the patency of the shunts.
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The diagnosis of perigraft seroma was confirmed by surgical findings in seven cases (correlating with positive findings on six sonograms, five CT scans, and both MR exams). Histologic studies showed amorphous tissue in all seven cases, consistent with the diagnosis of perigraft seroma. In the four remaining cases, the definitive diagnosis was based on the results of CT investigation; all four cases were treated conservatively.
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The patients presented in the study by Berger et al. [4] form part of the patients described in our study. In their study, Berger et al. found the use of heparin to be an independent risk factor for the development of perigraft seromas.
With respect to imaging, we must state that this is a retrospective study with all drawbacks inherent in that. In the years since these cases occurred, the diagnostic modalities have improved tremendously, and thus, new imaging protocols have been adapted over the course of time. Also, with every perigraft seroma we encountered, we gained more experience in diagnosing this condition. In reviewing all 11 cases, we found several imaging patterns that are either suggestive of or conclusive for the diagnosis of perigraft seroma (Table 1). A radiograph of the thorax is not an adequate diagnostic tool with which to diagnose a perigraft seroma. In the early stages, one cannot discriminate among atelectasis, infiltration, lymphoma, or perigraft seroma using chest radiographs. A lesion that becomes more spherical over time is suggestive of perigraft seroma development.
On sonography, the diagnosis of perigraft seroma may initially be difficult. However, the use of color-flow Doppler sonography facilitates the diagnosis of perigraft seroma by showing an absence of flow. When liquefaction occurs, the anechoic zone that surrounds the modified Blalock-Taussig shunt is characteristic of a perigraft seroma. In our study, CT revealed three cases of perigraft seroma that we had missed on sonography. In these cases, the perigraft seroma was relatively small (in one case) or situated deep within the mediastinum (in two cases). We could find only one previous report in which sonography—in this case, echocardiography—was useful in identifying a perigraft seroma [11]. In that case report, liquefaction had already occurred, and the use of color-flow Doppler sonography was not described.
In CT examinations, the enhancement we saw after administering IV contrast material has previously been described by Fink and Ditchfield [7]. They also reported that the enhancement of the capsule persisted on delayed images. Because of the retrospective nature of our study, we cannot confirm this finding. In the differential diagnosis between abscess and perigraft seroma formation, the absence of any clinical markers of infection leads one to the diagnosis of perigraft seroma.
We found two case reports on the use of MR imaging in identifying perigraft seroma [12, 13]. In both cases, intermediate signal intensity on T1-weighted and high signal intensity on T2-weighted images were seen. Duerinckx et al. [12] also performed a breath-hold ECG-triggered gradient-echo sequence to visualize flow within the modified Blalock-Taussig shunt itself; they used this sequence to rule out leakage from the shunt as well. In contrast to the two cases in which we used MR imaging, neither of these two studies described the septation we found on T2-weighted images.
As a diagnostic strategy, we propose using sonography as the first diagnostic tool when children with modified Blalock-Taussig shunt present with a persisting opacification of the ipsilateral thorax or a widening of the superior mediastinum. However, a negative sonographic result does not exclude the presence of a perigraft seroma, as we have shown in our study. Therefore, a negative result on sonography should lead to further investigation with CT or MR imaging. The advantage of using MR imaging rather than CT is that MR imaging can show flow within the modified Blalock-Taussig shunt and does not involve ionizing radiation. A positive finding on sonography means that no further radiologic investigations are indicated.
Because of its portability and, thus, capability for bedside use, sonography has an advantage over CT and MR imaging for use in these critically ill children. Therefore, we promote the use of sonography as the initial diagnostic modality in patients with suspected perigraft seroma development.
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