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Chest ultrasound in the diagnosis of pulmonary embolism in a pregnant patient - a case report

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Address for correspondence:

Address for correspondence:

Address for correspondence:

Address for correspondence:

Address for correspondence: Grzegorz Małek, Department of Radiology, Institute of Tuberculosis and Lung Diseases, Płocka 26, 01–138 Warsaw, Poland tel.: (+48 22) 431 21 16, fax: (+48 22) 431 24 17, e-mail: malekg@wp.pl

Received: 3.03.2009 Copyright © 2009 Via Medica ISSN 0867–7077

Grzegorz Małek1, Alicja Drygalska1, Jarosław Kober2, Liliana Wawrzyńska2, Romuald Dębski3, Marek Dąbrowski4, Adam Torbicki2

1Department of Radiology, Institute of Tuberculosis and Lung Diseases in Warsaw, Poland Head: I. Bestry, MD

2Department of Internal Diseases of the Chest, Institute of Tuberculosis and Lung Diseases in Warsaw, Poland Head: Prof. A. Torbicki

3Department of Obstetrics and Gynaecology, Centre for Postgraduate Medical Training, Bielanski Hospital in Warsaw, Poland Head: Prof. R. Dębski

4Clinical Research Team for Cardiovascular Disease, Institute of Experimental and Clinical Medicine, Polish Academy of Sciences, Bielanski Hospital in Warsaw, Poland

Head: M. Dąbrowski, MD, PhD

Chest ultrasound in the diagnosis of pulmonary embolism in a pregnant patient — a case report

Abstract

Pregnancy is a risk factor for both pulmonary embolism (PE), and an incorrect diagnostic assessment in cases of suspected PE with potentially dangerous consequences for the mother and foetus. The major concern is ionising radiation utilized by diagnostic tests and its potential negative effect on foetal safety. This paper presents diagnostic difficulties encountered in a 31-year-old patient at 20 weeks of gestation who was admitted to hospital with non-specific chest pain and suspected PE as a complication of right lower limb venous thrombosis. The case study reminds of chest ultrasound as a useful tool in the diagnosis of PE. The official clinical practice guidelines do not recommend the use of chest ultrasound for diagnosing of PE due to lack of a sufficient number of published studies. This case report may encourage further, prospective studies in the hope to define whether and when chest ultrasound might find its place in the diagnostic strategy of PE, especially in pregnant women.

Key words: deep vein thrombosis, pulmonary embolism, ultrasound, chest, pregnancy, diagnosis

Pneumonol. Alergol. Pol. 2009; 77: 560–564

Introduction

The contemporary practice guidelines in pul- monary embolism (PE) recommend diagnostic al- gorithms, whose efficacy and safety have been ve- rified in prospective clinical studies [1]. The recom- mended diagnostic methods include: determina- tion of D-dimer, angio-CT, pulmonary scintigraphy, pulmonary arteriography, venous ultrasound and, in some cases, echocardiography. The selection of diagnostic methods depends, among other factors, on the clinical likelihood of PE, the actual availa- bility of a specific test and the clinical context.

Ultrasonographic assessment of the chest has been suggested as a potentially useful tool in the differential diagnosis of dyspnoea in patients with COPD [2] and heart failure [3]. In patients with COPD, the sensitivity of ultrasound in detecting pneumothorax is 100% with a specificity of 84%, although it does not replace other diagnostic me- thods. Pleural ultrasound is also used in evaluating the nature of pleural effusion [4, 5]. In the case of pleural effusion, the sensitivity of ultrasonography in detecting cancer is 73% with a specificity of 100%, positive predictive value (PPV) of 100% and negative predictive value (NPV) of 79%. Pleural

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2027 µg/l, APTT 31 s, INR 0.92, antithrombin III 86%, fibrinogen 6.47 g/l, TSH 0.005 µIU/ml, FT4 17.9 pmol/l. Blood gas analysis (arterialised blood) revealed PaO2 96 mm Hg, pH 7.45, pCO2 35 mm Hg.

ECG revealed no significant abnormalities. We continued treatment with subcutaneous low-mo- lecular-weight heparin at a weight-adjusted dose started upon the diagnosis made in the outpatient settings. We also contacted the patient’s endocri- nologist, who recommended no changes to her endocrine treatment regimen.

Due to the respiration-dependent chest pain and dyspnoea, in light of the preserved haemody- namic stability, normal systolic blood pressure and no manifestations of shock, a suspicion of non- -high-risk PE was raised. We considered indications for extending the diagnostic assessment to inclu- thickening of > 10 mm, its nodular outline and

diaphragmatic thickening of > 7 mm are all sug- gestive of cancer. Some authors reported useful- ness of this diagnostic method in the diagnostic as- sessment of PE [6] by visualising lesions consistent with distal postembolic foci in the pulmonary pa- renchyma [7–9]. The knowledge about the sensiti- vity and specificity of this method is scarce and mainly based on reports inspired by one team of researchers [8]. It is unclear whether this is due to the lack of other studies or to their discouraging results making publications difficult (the so-called publication bias).

We therefore decided to improve our own experience using chest ultrasound in the diagno- stic assessment of PE. In the case of favourable outcomes, the method might be particularly use- ful in pregnant women, expanding the panel of diagnostic tests based on the emission of ultraso- unds rather than ionising energy [10].

This paper presents the first case of a pregnant woman with a suspected PE, in which a compre- hensive ultrasound assessment of the chest was performed and the images were compared with those described in the available literature.

Case report

A 31-year-old woman at 20 weeks of gestation was admitted emergently with right lower limb venous thrombosis. The symptoms developed on 11 September 2008 in the form of lower leg pain accompanied by a slight oedema. The diagnosis was made in the outpatient setting by compression ultrasound of the veins (Fig. 1). Two weeks before these events the patient experienced “pain in her spine” and left-sided chest pain. The patient gave a history of deep vein thrombosis in the left lower limb seven years before, following the use of hor- monal contraceptives. She had been receiving an- ticoagulant treatment for a short period, but could not remember the names of the medications or the details of treatment. No diagnostic evaluation for thrombophilia had been performed at that time.

The patient also gave a history of recurrent lower limb venous thrombosis suffered by her father.

During pregnancy the patient was under con- stant care of an obstetrician and gynaecologist and had been taking intravaginal progesterone until she was hospitalised. She was also under constant care of an endocrinologist due to hyperthyreosis in the course of Graves disease diagnosed in 2004.

Laboratory tests following admission to the ward revealed, among others: HGB 10.72 g/dl, HCT 31.5%, RBC 3.64 ¥ 109/l, PLT 334 ¥ 106/l, D-dimer

Figure 1. Ultrasound of the veins. A. Compression ultrasound of the popliteal vein. The popliteal vein only slightly reduces its diameter on compression. Visible echoic reflexions in its lumen (arrow). The vein diameter is higher than that of the artery. These are sonogra- phic signs of thrombosis. B. The image was taken with a convex head to document the extent of the lesions in the popliteal vein (arrows) and the presence of signs of mobility of the head of the thrombus

A

B

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Table 1. Criteria recommended in the diagnostic evaluation of PE with the use of chest ultrasonography [8]

Confirmed PE ≥ 2 triangular/round lesions with the base on the pleura

Probable PE A single typical lesion in the presence of pleural effusion

Possible PE A small (< 5 mm) subpleural lesion or asymmetrical pleural effusion

de chest imaging. Due to the pregnancy, good over- all condition of the patient and the pleural natu- re of the pain we started the diagnostic investiga- tion with a chest ultrasound and a detailed asses- sment of the prognostic risk markers.

The ultrasound scan revealed no changes in the left pleura. In the right pleura a small amount of effusion was detected, over three intercostal spa- ces. Behind the effusion, we visualised a lung with poorer aeration and slightly reduced volume. In its lower portion, we observed at least three subpleu- ral hypoechoic areas in the shape of a triangle with the base facing the pleura. The largest of the three areas had a base of 37.5 mm and a height of 18 mm.

The dimensions of the smaller lesions were up to 22 mm in base and up to about 15 mm in height.

Between the lung and the chest, at the site of the greatest accumulation of effusion, the thickness of the layers was up to 22 mm. The parietal pleura was slightly thickened (Fig. 2).

The lesions were compared with typical ima- ges characterising various pathologies and were found to meet criteria suggested for PE on chest ultrasonography [8] (Table 1).

In our case, three typical triangular lesions with bases on the pleura would allow us, accor- ding to the criteria reported in the literature, to make an unequivocal diagnosis of PE.

We also performed an assessment of risk as- sociated with the possibility of PE: the echocardio- gram did not show signs of right ventricular over- load, there was no elevation of NT-proBNP (84.3 pg/ml), and troponin T was also negative. There-

fore, in accordance with the European Society of Cardiology guidelines on the assessment of risk, we classified the patient as being at a low risk of early death related to PE. Because an unequivocal confirmation of PE in this risk group required tre- atment identical to the management of venous thrombosis (confirmed by compression ultraso- und), we decided not to perform any further ima- ging studies.

The further course of the treatment was con- founded by obstetric complications. On the third day of hospitalisation the patient reported that her water had broken. Following a telephone consul- tation with a gynaecologist, faced with the risk of premature labour, we decided to transfer the pa- tient to the gynaecology department.

Despite the efforts of the obstetric and gy- naecologic team aimed at maintaining the pre- gnancy in the situation of significant oligohy- dramnios, the patient eventually miscarried. In the post-procedural period, due to the non-spe- cific chest complaints, the patient underwent a contrast-enhanced CT scan, which finally con- firmed the presence of small distal embolic le- sions in the segmental arteries of the lower lobe of the right lung (Fig. 3). The patient was dischar- ged home in good overall condition and advised to continue secondary anticoagulant prophyla- xis for at least 6 months. Tests for thrombophi- lia were also ordered.

Discussion

Pregnancy, due to its adaptative physiological changes in hormone concentrations, the position of the enlarged uterus in the vicinity of large veins, as well as the physiological alterations in the coagulation system, is a risk factor for thromboem- bolism. At the same time, PE is the most common cause of death among women in puerperium in developed countries. Symptoms appearing during pregnancy, such as dyspnoea, asymmetric lower limb oedema, and even fainting or hypoxaemia, all resemble symptoms associated with PE [1, 10].

Figure 2. Ultrasound of the pleura. A large amount of effusion in the right pleural cavity. Two hypoechoic areas are visible that are con- sistent with subpleural foci of an early pulmonary parenchymal infarct. These areas are of a shape of the triangle whose base runs along the pleura. They are separated by a slightly uneven border from the remaining parenchyma. The lesions are localised in the right lower lobe, dorsally

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At the same time, pregnancy makes diagnostic testing difficult due to ionising radiation and its negative effect on foetal safety. In fact, depending on the timing of exposure during the prenatal pe- riod, irradiation may result in abnormal body ha- bitus, mental retardation or promote the develop- ment of malignancies in childhood. This is, how- ever, the case with doses exceeding 500 mSv. The acceptable safe dose for the foetus was defined as

< 50 mSv [1]. For comparison, the dose absorbed by the foetus during maternal chest X-ray is < 0.01 mSv, which is equivalent to the dose absorbed during an intercontinental flight. Ionising energy affecting the foetus during an angio-CT scan does not exceed 0.15 mSv being similar to the energy absorbed by the foetus during pulmonary perfusion scintigraphy.

Although the concerns about the adverse in- fluence of imaging studies that utilise ionising ra- diation are not objectively fully justified and should not significantly hinder diagnostic investi- gation [1, 10], they remain deeply rooted in the psy- chological sphere of the patients, their families, and many healthcare providers. At the same time, phy- siological pregnancy, particularly in the second and third trimesters, leads to non-specific eleva- tion in D-dimers, limiting the usefulness of this parameter in the attempts to rule out PE [11–13].

All those problems promote the use of inadequate diagnostic strategies in pregnant women with sus- pected PE, which in turn considerably increases the risk of venous thromboembolism and sudden death [14]. A wrong decision to refrain from treat- ment despite a clinical suspicion of PE may end tragically. On the other hand, a hasty decision to initiate treatment and, as a consequence, long-term

secondary anticoagulant prophylaxis may expose the mother and foetus to unnecessary risk of haemorrhagic complications.

For these reasons, confirmation of the reliabi- lity of chest ultrasound in the diagnosis of PE in pregnant women would be especially useful.

Mathis et al. were the only researchers who conducted a prospective study in 352 patients to evaluate this method versus angio-CT [8]. In 144 cases the sonographic picture classified as “un- equivocal PE” or “probable PE” was subsequently confirmed by CT. In 150 cases PE was not detec- ted using either method. In 8 cases ultrasound de- tected PE unconfirmed by CT and in 50 cases failed to detect PE found on CT. In total, the sensi- tivity and specificity of chest ultrasound in diagno- sing PE was estimated at 74% and 95%, respecti- vely. The positive and negative predictive values were estimated at 95% and 75%, respectively.

In our case we found identical lesions on chest ultrasound as those presented previously in the literature in cases of PE documented by chest CT.

They correlated with the patient’s symptoms and were confirmed several days later by the presence of typical lesions on angio-CT.

We do not consider the reported case as a con- firmation of the reliability of the method, but as an incentive for further, prospective studies of its clinical usefulness. It seems that a highly sugge- stive sonographic picture of the chest, even in the face of a low clinical likelihood of PE, should prompt one to order angio-CT scans in all patient groups, even in pregnant women.

References

1. Torbicki A., Perrier A., Konstantinides S. et al. Guidelines on the diagnosis and management of acute pulmonary embolism:

the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC). Eur. Heart J. 2008; 29: 2276–2315.

2. Slater A., Goodwin M., Anderson K.E., Gleeson F.V. COPD can mimic the appearance of pneumothorax on thoracic ultrasound.

Chest 2006; 129: 545–550.

3. Liteplo A.S., Marill K.A., Villen T. et al. Emergency Thoracic Ultrasound in the Differentiation of the Etiology of Shortness of Breath (ETUDES): sonographic B-lines and N-terminal pro- brain-type natriuretic peptide in diagnosing congestive heart failure. Acad. Emerg. Med. 2009; 16: 201–210.

4. Qureshi N.R., Rahman N.M., Gleeson F.V. Thoracic ultrasound in the diagnosis of malignant pleural effusion. Thorax 2009; 64:

139–143.

5. Dulchavsky S.A., Schwarz K.L., Kirkpatrick A.W. et al. Pro- spective evaluation of thoracic ultrasound in the detection of pneumothorax. J. Trauma 2001; 50: 201–205.

6. Reissig A., Kroegel C. Transthoracic ultrasound of lung and pleura in the diagnosis of pulmonary embolism: a novel non- -invasive bedside approach. Respiration 2003; 70: 441–452.

7. Mastruzzo C., Perracchio G., Poidomani G., Romano M., Crimi N., Vancheri C. Subsegmental pulmonary embolism: value of thoracic ultrasound for diagnosis and follow-up. Intern. Med.

2008; 47: 1415–1417.

8. Mathis G., Blank W., Reissig A. et al. Thoracic ultrasound for diagnosing pulmonary embolism: a prospective multicenter study of 352 patients. Chest 2005; 128: 1531–1538.

Figure 3. Contrast-enhanced computed tomography. Free fluid in the pleural cavity. Thrombi in segmental arteries of the lower lobe of the right lung (arrow) (seg. 8, 9)

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9. Reissig A., Porner T., Hocke M., Kroegel C. Trans thoracic ul- trasound in the diagnosis of cough, dyspnea an chest pain.

Pneumologie 2007; 61: 20–36.

10. Marik P.E., Plante L.A. Venous thromboembolic disease and pregnancy. N. Engl. J. Med. 2008; 359: 2025–2033.

11. Lippi G., Montagnana M. D-dimer testing in pregnancy: clini- cally useful, but at what cost? Ann. Intern. Med. 2008; 148:

484–485.

12. Eichinger S. D-dimer testing in pregnancy. Semin. Vasc. Med.

2005; 5: 375–378.

13. Kline J.A., Williams G.W., Hernandez-Nino J. D-dimer concen- trations in normal pregnancy: new diagnostic thresholds are needed. Clin. Chem. 2005; 51: 825–829.

14. Roy P.M., Meyer G., Vielle B. et al. Appropriateness of diagnos- tic management and outcomes of suspected pulmonary embo- lism. Ann. Intern. Med. 2006; 144: 157–164.

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