British Journal of Radiology (2007) 80, e125-e127
© 2007 British Institute of Radiology
doi: 10.1259/bjr/61486305
Pseudocalcification on chest CT scan
R Tiruvoipati, FRCSEd
1
S K Balasubramanian, MRCS
1
J J Entwisle, FRCR
2
R K Firmin, FRCS
1 and
G J Peek, MD, FRCS
1
1 Department of ECMO and Cardiac Surgery, 2 Department of Radiology, Glenfield Hospital, Groby Road, Leicester LE3 9QP, UK
Correspondence: Dr R Tiruvoipati, Department of ECMO, Glenfield Hospital, Groby Road, Leicester LE3 9QP, UK. E-mail: rtiruvoipati{at}yahoo.co.uk
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Abstract
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Liquid ventilation with perfluorocarbons is used in severe respiratory failure that cannot be managed by conventional methods. Very little is known about the use of liquid ventilation in paediatric patients with respiratory failure and there are no reports describing the distribution and excretion of perfluorocarbons in paediatric patients with severe respiratory failure. The aim of this report is to highlight the prolonged retention of perfluorocarbons in a paediatric patient, mimicking pulmonary calcification and misleading the interpretation of the chest CT scan. A 10-year-old girl was admitted to our intensive care unit with severe respiratory failure due to miliary tuberculosis. Extracorporeal membrane oxygenation (ECMO) was used to support gas exchange and partial liquid ventilation (PLV) with perfluorodecalin was used to aid in oxygenation, lavage the lungs and clear thick secretions. The patient developed a pneumothorax (fluorothorax) on the next day and PLV was discontinued. Multiple bronchoalveolar lavages were performed to clear thick secretions. With no improvement in lung function over the next month a CT scan of the chest was performed. This revealed extensive pulmonary fibrosis and multiple high attenuation lesions suggestive of pulmonary calcification. To exclude perfluorodecalin as the cause for high attenuation lesions, a sample of perfluorodecalin was scanned to estimate the Hounsfield unit density, which was similar to the density of high attenuation lesions on chest CT scan. High-density opacification should be interpreted with caution, especially following liquid ventilation.
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Introduction
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High-density opacification on chest radiography or a CT scan is frequently seen in various pathological and non-pathological conditions. Calcification, one of the causes of high density opacification in the chest, may affect the lung parenchyma, mediastinum, lymph nodes, pleura, chest wall or a combination of these structures and a previous infectious process is the usual cause for calcification. Less often calcification is due to neoplasm, metabolic disorders, occupational exposure or previous medical therapy [1]. Calcification may provide important information for establishing the diagnosis and evaluation of the progress of disease. Less often it may mislead, especially if interpreted without considering the clinical scenario. High-density material such as barium sulphate within the lung following aspiration after a barium meal and retained perfluorocarbons following liquid ventilation can mimic calcification. We report an interesting case of pseudocalcification on a chest CT scan, where perfluorocarbon was misinterpreted as intraparenchymal calcification in the lungs.
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Case report
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A 10-year-old girl was admitted to our intensive care unit with miliary tuberculosis associated with severe respiratory failure. She was managed initially with mechanical ventilation. Due to the progressive worsening of her respiratory status, other treatments such as inhalation of nitric oxide, surfactant and high frequency oscillatory ventilation (HFOV) were tried. The CT scan of the chest showed diffuse mixed alveolar and interstitial shadowing in both lungs with patchy honeycomb changes in left upper lobe, lingual and some segments of the left lower lobe. There was no mediastinal, hilar or axillary lymphadenopathy.
With further deterioration of her respiratory function and development of bilateral pneumothoraces requiring intercostal tube drainage, a decision was made to use extracorporeal membrane oxygenation (ECMO) to support gas exchange. She was cannulated for veno-venous ECMO via the right internal jugular (21 F Medtronic Biomedicus DLP; Medtronic BioMedicus Inc, Minneapolis MN) and right femoral veins (21 F Medtronic Biomedicus DLP). The initial ECMO flow and sweep were 2.18 l min–1 and 3.0 l min–1, respectively. Fibre optic bronchoscopy performed the next day showed thick secretions partially occluding the trachea and other major airways. Bronchoscopies with bronchoalveolar lavage (BAL) were repeated over 3 consecutive days with an aim to clear the secretions from the airways. These efforts were found to be futile and so partial liquid ventilation (PLV) with perfluorodecalin was used on the fourth day of ECMO support in an effort to lavage the lungs and clear the secretions. However, the next day she developed a fluorothorax, with the drainage of the perfluorodecalin from the intercostal drains. In view of this PLV was discontinued. Bronchoscopies were repeated daily for the next few days to perform BAL and clear secretions.
As there was no improvement in the pulmonary function despite more than 1 month of ECMO support and anti-tuberculous therapy, a repeat CT scan of chest was performed to assess the pulmonary morphology; 28 days had elapsed since PLV was stopped. CT scan revealed extensive pulmonary fibrosis with traction bronchiectasis and multiple high attenuation lesions suggestive of calcification (Figure 1
). The CT scans were further reviewed in a multidisciplinary case conference and a possibility of perfluorodecalin accounting for the calcification-like appearance was suggested, in spite of the frequent BAL and suctioning of the airway and an interval of 4 weeks between the last use of liquid ventilation and the CT scan. The chest radiograph at this time was suggestive of consolidation of both lungs with no evidence of calcification. To confirm or refute perfluorodecalin as the cause for these findings, a sample of perfluorodecalin in a syringe was scanned to estimate the Hounsfield unit density. When this was compared with the Hounsfield density of the reported calcification on CT film, it was clear that both the densities were similar and the "calcification" reported before was residual perfluorodecalin. The patient later required thoracotomy for significant bleeding into the right hemi-thorax. This was due to autolysis of right middle lobe, which was floating freely in the right pleural cavity. There was no gross calcification in the lung. Lung biopsies were taken at this time from the upper and lower lobes (in an attempt to gain more prognostic information). The histology showed abnormal architecture with interstitial fibrosis and alveolar haemorrhage. There was no evidence of calcification. Unfortunately it did not prove possible to control the haemorrhage from the patient's lungs and she died after a total of 1011 h of ECMO support.
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Figure 1. Axial image of a contrast-enhanced CT through the level of the aortic root. The lungs show widespread consolidation with areas of diffuse high attenuation. There is a right pneumothorax which has been partially drained by the intercostal drain.
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Discussion
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Liquid ventilation using perfluorocarbons has been used for treating severe respiratory failure in neonatal [2], paediatric [3] and adult patients [4–6] when conventional ventilation alone is not successful. Perfluorocarbons are also used in non-respiratory pulmonary applications such as delivering drugs and radio imaging [7–10].
The distribution and rate of elimination of perfluorocarbons instilled intratracheally has been studied previously in patients with and without ECMO support for respiratory failure and in animal models [2, 4, 11, 12]. The usual distribution of perfluorocarbons is mainly gravity dependent [12]. Following intratracheal administration the lungs are rendered completely radiopaque, and non-opacification of a region of lung suggests bronchial occlusion. Elimination of perfluorocarbons is mainly by evaporation through the airways. In addition to the pulmonary elimination, small amounts of perfluorocarbons are cleared by transpiration and urinary excretion. Uptake of perfluorocarbons by lymphatics has been reported and the deposits of perfluorocarbons in lymph nodes may persist for months after the perfluorocarbons have been cleared from the lungs [13].
Clearance of perfluorocarbons occurs first from the non-dependent regions of lungs with dependent regions retaining them for a longer period [4]. Clearance is also related to time: the rate of elimination was reported to be high in the first 48 h after the last dose of perfluorocarbons, and the elimination after this slower [4]. Reickert et al [4] speculated that the elimination is very slow in patients with severe respiratory failure and will not be complete until sufficient recovery of pulmonary function has occurred. It may be further delayed in patients with endobronchial obstructions [12] and in patients requiring extracorporeal life support as the volume of minute ventilation is significantly reduced in such settings. Shaffer et al in their experiment with premature lambs found that the elimination is faster as soon as the lambs receiving liquid ventilation (with a liquid ventilator) were connected to a gas ventilator [11], suggesting that the main route of elimination is by evaporation from the airways.
Leach et al [2] reported that most of the radiographic clearance of perfluorocarbons occurred by 48 h after cessation of liquid ventilation when used in neonatal patients with severe respiratory failure on conventional ventilators. In adult patients with severe respiratory failure requiring ECMO support the rate of elimination appears to be different. Kazerooni et al [12] reported that two thirds of the instilled perfluorocarbon was eliminated by 7 days and only minimal amounts remain after 21 days in adult patients requiring ECMO support. There are no reports evaluating the distribution and elimination of perfluorocarbons in non-neonatal paediatric patients requiring ECMO support and HFOV for respiratory failure.
Although minimal amounts of perfluorocarbon are known to remain in the lungs and lymph nodes for prolonged periods of time, extensive retention of perfluorocarbons in both dependent and non-dependent regions of lungs, as seen in our patient after a period of 1 month from stopping PLV (and the frequent BAL), is unusual, making this an interesting finding. This may be due to the combined effects of severe respiratory failure, the presence of endobronchial obstructions due to thick secretions, and the use of ECMO with HFOV, all of which are known to reduce the elimination of perfluorocarbons. Interpretation of radiological investigations such as CT scans under these circumstances should be made with caution.
To conclude, high-density opacification should be interpreted with caution, especially following liquid ventilation.
Received for publication September 26, 2005.
Revision received April 3, 2006.
Accepted for publication April 7, 2006.
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References
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Abstract
Introduction
