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 Table of Contents  
Year : 2022  |  Volume : 9  |  Issue : 3  |  Page : 104-107

Computed tomography diagnosis of pulmonary hydatid disease

1 Department of Clinical Medicine, Dali University, Dali, China
2 Department of Medical Imaging, Calmette Hospital, The First Hospital of Kunming, Kunming, China
3 Department of Medical Imaging, Yunnan Cancer Hospital, Kunming, China
4 Department of Medical Imaging, The First Affiliated Hospital of Dali University, Dali, China

Date of Submission14-Apr-2022
Date of Acceptance26-Oct-2022
Date of Web Publication22-Dec-2022

Correspondence Address:
Bin Yang
Department of Medical Imaging, Calmette Hospital, The First Hospital of Kunming, Kunming 650000
Zhengyu Liu
Department of Medical Imaging, The First Affiliated Hospital of Dali University, Dali 671000
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/RID.RID_25_22

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Pulmonary hydatid disease is a helminthic zoonotic disease caused by Echinococcus infection. The symptoms may appear several years after infection. Chest computed tomography (CT) is the preferred examination method and plays an important role in early diagnosis, treatment, and prognosis evaluation. CT can be used to diagnose simple cystic lesions. However, when the cysts are infected or ruptured, atypical imaging findings such as increased cyst density, blurring of the cyst wall, and surrounding exudation may lead to misdiagnosis of lung infection or lung abscess, hindering the therapeutic effect. We analyzed and compared the atypical imaging manifestations of pulmonary simple hydatid disease and hydatid cyst rupture. The aims of this report are to improve clinicians' understanding of these diseases, promote early diagnosis and treatment, and reduce the occurrence of complications.

Keywords: Computed tomography, imaging diagnosis, pulmonary hydatid disease

How to cite this article:
He H, Chen X, Yang Q, Peng Z, Wang C, Ke T, Liu Z, Yang B. Computed tomography diagnosis of pulmonary hydatid disease. Radiol Infect Dis 2022;9:104-7

How to cite this URL:
He H, Chen X, Yang Q, Peng Z, Wang C, Ke T, Liu Z, Yang B. Computed tomography diagnosis of pulmonary hydatid disease. Radiol Infect Dis [serial online] 2022 [cited 2023 Jun 5];9:104-7. Available from: http://www.ridiseases.org/text.asp?2022/9/3/104/364771

  Introduction Top

Hydatid disease is a zoonotic disease caused by tapeworms of the genus Echinococcus.[1] The Echinococcus life cycle includes the ultimate carnivorous host (usually a dog or fox) and an intermediate host (human, ungulate, or rodent).[2] Hydatid disease is distributed worldwide and is more common in countries and regions with developed animal husbandry. China has one of the highest reported incidences of human echinococcosis, which is mainly found in Qinghai, Tibet, Inner Mongolia, Gansu, Ningxia, and other areas containing livestock.[3] Echinococcosis can affect all organs of the body. The liver (65%) and the lung (25%) are most commonly infected,[4] and these infections mainly include cystic echinococcosis caused by Echinococcus granulosus and alveolar echinococcosis caused by Echinococcus multilocularis. Of these, the former is more common[5] and its cysts are characterized by a fibrous envelope. After years of growth, the diameter may be as large as 50 cm. Alveolar echinococcosis is less common and does not feature a fibrous envelope around the periphery. Moreover, no large vesicles are formed. Instead, multiple small vesicles aggregate, resulting in a sponge-like sign. The clinical symptoms of the disease vary depending on the location and size of the cysts. The incubation period is long. Individuals can be asymptomatic for years after the initial infection. The incubation period of hydatid disease in the lungs is shorter than that in other organs. The clinical symptoms of pulmonary hydatid disease include cough, expectoration, chest pain, shortness of breath, and hemoptysis.[6] Empyema and anaphylactic shock occur when a cyst ruptures. Therefore, timely diagnosis and treatment are very important to prevent complications of hydatid disease. Hydatid disease can be diagnosed by imaging combined with serological testing. Typical imaging features usually accompany the disease. Atypical imaging findings are rare in the lungs. The presence of atypical imaging may lead to misdiagnosis.

  Case Report Top

A 10-year-old girl presented for examination due to a cough, shortness of breath, and chest pain. Plain and enhanced chest computed tomography (CT) showed a low-density round cystic mass in the inferior lobe of the left lung, measuring approximately 6.1 cm × 5.0 cm. The mass exhibited uniform density and had a CT value of about 8–12 HU. The border was smooth. There was no exudation in the surrounding lung tissues. The adjacent pleura was slightly reactively thickened, and there was a small amount of effusion adjacent to the pleural cavity. After enhancement, only the cyst wall was slightly enhanced. Enhancement was not observed in the cystic part [Figure 1]a, [Figure 1]b, [Figure 1]c. The patient had a long history of living in other places but not in an epidemic area. Physical examination revealed a body temperature of 36.5°C, pulse rate of 83 beats/min, respiratory rate of 20 breaths/min, and blood pressure of 91/50 mmHg. The laboratory tests results were as follows: white blood cells, 5.88 × 109/L; hemoglobin, 158 g/L; eosinophils, 0.11 × 109/L; platelets, 403 × 109/L; carcinoembryonic antigen, 0.26 ng/mL; and alpha-fetoprotein, 2.55 ng/ml.
Figure 1: Computed tomography and histopathologic findings. (a and b) A plain chest CT revealed a round cystic low-density mass in the left lower lung, approximately 6.1 cm × 5.0 cm in size. The mass showed uniform density, a CT value of 8 to 12 HU, and a clear boundary. (c) Enhancement of cyst wall on enhanced CT examination. No obvious enhancement other than that of the cyst is seen. Mild reactive thickening of the adjacent pleura and a small amount of pleural effusion are present. (d) Postoperative frozen section (H and E, 10 × 40). The anatomical structure of Echinococcosis granulosus is shown, including the outer capsule (△), horny cortex (▴), germ layer (◐), and ascus (↑). The outer capsule is accompanied by granulomatous reflection and multinucleated giant cell aggregation. The horny cortex is parallel and arranged in a lamellar-like structure. There are multiple asci in the cavity, and small sacs (grand sacs) are also seen in the asci. CT: Computed tomography

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Exploratory surgery was performed. A left lateral posterolateral oblique incision was made to enter the chest. A cystic lesion measuring approximately 4.0 cm × 4.0 cm × 3.0 cm was found in the inferior lobe of the left lung. The cyst wall was thin, and yellow liquid tissue and a yellow oval jelly body were seen after the incision of the cyst wall. Histopathological examination revealed E. granulosus [Figure 1]d.

  Discussion Top

Pulmonary hydatid cysts are formed when E. granulosus larvae parasitize the peripheral blood vessels of the lungs through blood circulation. The lower lung has a high incidence of such cysts due to its abundant blood flow. The hydatid cyst wall is divided into two layers. The inner layer is the body of the worm, including its head segment and ascus. The outer layer is the host tissue, which is surrounded by a thin layer of fibrous connective tissue formed by the surrounding lung tissue. Most hydatid cysts grow slowly and cause no specific clinical symptoms. Lung tissues tend to be loosely structured and have low resistance. These characteristics together with abundant blood flow and negative pleural pressure can lead to a faster growth rate of cysts in the lung than of cysts in other organs. The average annual growth rate is twice the original volume. Early cysts are small, generally asymptomatic, and mostly found on physical examination. Clinical symptoms do not develop until the cyst enlarges and compresses the surrounding tissue years after infection. The clinical symptoms depend on the number and size of the cysts and the organs involved.[7] Cough, hemoptysis, and chest pain are the most common symptoms of cysts in the lungs before they rupture. As the cysts continue to grow, there is a risk of spontaneous or traumatic rupture, leading to serious complications such as fever, chills, and anaphylactic shock.[6] Approximately two-thirds of pulmonary hydatid cysts rupture and enter the surrounding lung tissues and bronchial tree, causing a secondary infection. A small number of ruptured cysts enter the pleural space and cause acute allergic reactions that may result in life-threatening hypotension.[8]

The simple cystic type is more common in patients with single or multiple pulmonary hydatid cysts. Cysts may be small in the early stages, and CT may show sheet-like shadows with indistinct borders. When the cysts enlarge, CT may show a well-defined round or oval cystic hypodense shadow in the lung. Giant cysts can also compress the lung markings and displace them. If the lesion is close to the pleura, reactive thickening or a small amount of pleural effusion may occur adjacent to the pleura. Ascus-bearing cysts are rare in the lungs but are very characteristic. They appear as honeycomb-like or petal-shaped ascocytes of varying sizes arranged along the wall of the mother sac with separation. Moreover, the density of the separation is greater than that of the fluid in the cyst. When a cyst ruptures and infects the surrounding tissue, the density of the fluid in the cyst increases in either a portion or a large area of the cyst, and the edges of the cyst wall become blurred and rough. When the internal capsules rupture, cystic fluid is discharged, and the collapsed internal capsule is observed in the capsule (serpent sign). When the cyst completely collapses, the collapsed internal capsule floats freely in the cystic fluid (water-lily sign).[9] When the outer capsule is ruptured and the inner capsule is intact, gas may enter between the inner and outer capsules to form a crescent-shaped translucent shadow referred to as the crescent sign. If the contents of the cyst break into the pleural cavity, they can cause different degrees of pleural effusion. On this basis, a combination of bronchopleural fistulas can lead to hydropneumothorax. Hydropneumothorax is prone to infection and empyema.

The sputum of infected patients living in pastoral areas has an odor or a powdery skin-like appearance. In the presence of this clinical sign combined with laboratory tests and typical imaging findings, it is not difficult to diagnose this disease. However, due to the duration between infection and consultation, cystic rupture of the internal and external sacs and discharge of the cystic contents may have occurred at consultation. In addition, depending on whether the condition is complicated by infection or whether it has broken into the thoracic cavity and other factors, the imaging signs of pulmonary hydatidosis are variable. All of these factors can lead to misdiagnosis. Therefore, pulmonary hydatid disease should be differentiated from intrapulmonary bronchial cysts, lung abscesses, pulmonary aspergillosis, and pulmonary Wegener's granulomatosis as follows.

  • The wall of an intrapulmonary bronchial cyst in the lung is uniform and thin, and the edge is smooth. Secondary infection can show signs of blurring, frizziness, and increased intracystic density. However, its direction is the same as that of the bronchi, and it can also be present in combination with intrapulmonary malformations such as pulmonary dysplasia, pulmonary sequestration, and thoracic collapse
  • When a hydatid cyst is infected, the fluid density in the cyst increases, the edge of the cyst wall becomes blurred, and the CT appearance of the cyst is similar to that of a lung abscess. However, an acute lung abscess has a rapid onset. The cavity wall is thick. The inner wall is mostly irregular, and there is a vague exudative shadow around the abscess
  • Pulmonary aspergillosis is common in patients with chronic obstructive pulmonary disease or low immunity. The cavity is a solid fungal ball that can move with changes in body position, and a half-moon-shaped space is formed between the upper edge and the wall (the “air half-moon” sign). The adjacent pleura is often markedly thickened
  • Pulmonary Wegener's granulomatosis is characterized by thick-walled cavities surrounded by ground-glass opacities. It is migratory, the cavity shape and size change rapidly, and it is easy to identify with dynamic follow-up.

  Conclusion Top

E. granulosus can parasitize the lungs for several years before symptoms appear. Before the cyst ruptures, it is easy to diagnose based on CT imaging combined with the patient's history of residence and laboratory test results. Imaging after the hydatid cyst ruptures is complicated. The ruptured cyst can cause serious complications, leading to misdiagnosis and inadequate or untimely treatment. Multislice spiral CT is the most effective examination method for differential diagnosis. It can accurately display the size and location of pulmonary hydatid cysts and provide a basis for surgery. Therefore, CT plays an important role in the early diagnosis and treatment of pulmonary hydatid disease, significantly improving the patient's prognosis.

Ethics statement

This retrospective study was approved by the Institutional Review Board of the First Affiliated Hospital of Dali University, which waived the need to obtain informed consent from the patient.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for the child's images and other clinical information to be reported in the journal. The guardian understands that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.


We thank Angela Morben, DVM, ELS, from Liwen Bianji (Edanz) (www.liwenbianji.cn), for editing the English text of a draft of this manuscript.

Financial support and sponsorship

This work was supported by the program for Cultivating Reserve Talents in Medical Disciplines from the Health Committee of Yunnan Province (H-2018008 to B.Y.) and the National Natural Science Foundation of China (NSFC) (82160348 to Y.B.).

Conflicts of interest

There are no conflicts of interest.

  References Top

Engström EL, Salih GN, Wiese L. Seronegative, complicated hydatid cyst of the lung: A case report. Respir Med Case Rep 2017;21:96-8.  Back to cited text no. 1
Zhang W, Ross AG, McManus DP. Mechanisms of immunity in hydatid disease: Implications for vaccine development. J Immunol 2008;181:6679-85.  Back to cited text no. 2
Mao T, Chungda D, Phuntsok L, Benjie T, Dondrup T, Dolma T, et al. Pulmonary echinococcosis in China. J Thorac Dis 2019;11:3146-55.  Back to cited text no. 3
Namn Y, Maldjian PD. Hydatid cyst embolization to the pulmonary artery: CT and MR features. Emerg Radiol 2013;20:565-8.  Back to cited text no. 4
McManus DP, Zhang W, Li J, Bartley PB. Echinococcosis. Lancet 2003;362:1295-304.  Back to cited text no. 5
Armoon A, Mehrian P, Soleimantabar H, Torabi S, Ghahderijani BH. Computer Tomography (CT) characteristics of pulmonary cystic echinococcosis. Med Arch 2019;73:338-43.  Back to cited text no. 6
Karimi M, Rostami A, Spotin A, Rouhani S. Ruptured pulmonary hydatid cyst: A case report. J Parasit Dis 2017;41:899-902.  Back to cited text no. 7
Sahoo S, Mitra S. An expectorated hydatid. Adv Respir Med 2019;87:307.  Back to cited text no. 8
Morar R, Feldman C. Pulmonary echinococcosis. Eur Respir J 2003;21:1069-77.  Back to cited text no. 9


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