Pulmonary hydatid disease

Hydatid cyst (echinococcosis) is caused by infestation by larval tapeworms of the genus Echinococcus. The disease is extensively distributed worldwide, and it has been rarely reported in Punjab, India. Although it is more commonly reported in liver, it is also seen in other organs as well. We describe the cyto morphological features in a case of pulmonary hydatid cyst in a 22 year female. Computed tomography revealed a solitary nodule in the lower lobe of left lung. The smears showed tegument, hooklets, and laminated membrane. © 2019 Published by Innovative Publication. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by/4.0/)


Introduction
Hydatid disease is caused by Echinococcus granulosus, which is endemic in the cattle and sheep raising regions of the underdeveloped and developed countries. 1,2 The prevalence of this disease is high in several countries of the Mediterranean region, mainly in the pastoral areas where the dog-sheep cycle of the parasite exists. 3 It continues to remain a health problem in India, mainly in the rural areas of the eastern part of the country. Liver and lungs are the preferred sites of infection, however the other relatively rare anatomic locations include the central nervous system, muscles, subcutaneous tissue, kidneys, bones, and body cavities. 1 Though clinical suspicion coupled with radiological and serological findings are good pointers towards diagnosis; pathological diagnosis remains the gold standard. Longstanding infection presents as an organized, solid, atypical pulmonary nodule which is a mimicker of bronchogenic carcinoma. 4 Image guided fine needle aspiration cytology (FNAC) is a useful tool for diagnosis. 5

Case Report
We report the case of a 22 year old immunocompetent nonsmoker female who presented with cough and with no other co-morbidity or past history of tuberculosis. The provisional clinical diagnosis was tuberculosis while the radiological diagnosis was suspicious of malignancy.
Computed tomography revealed a solitary nodule in the left lower lung lobe which was suspicious of malignancy ( Figure 1).
A CT guided FNAC was performed from the lung nodule under aseptic precautions. Direct air-dried smears from the aspirated clear fluid material were stained with May-Grünwald-Giemsa (MGG), and alcohol-fixed smears were stained with the Papanicolaou stain and hematoxylin and eosin.
The aspirate showed scolices with rendered laminated membrane fragments and plenty of pathogonomic hooklets in the backgound of the inflammatory cell reaction seen as neutrophils, eosinophils, lymphocytes, histiocytes, plasma cells, necrotic debris, erythrocytes, foamy macrophages, and reactive bronchiolar epithelial cells.  showed remarkable clinical and radiological improvement after three cycles of albendazole and did not require a surgical procedure.

Discussion
Hydatid disease is a chronic parasitic zoonotic infection in humans, which is transmitted between dogs and domestic livestock, particularly sheep. 2 It is an important health problem not only in developing and agricultural reliant countries, but also in industrialized countries due to influx of immigrants. 1 Most of the patients are asymptomatic, but it can produce non-specific symptoms, like, cough, chest pain, and hemoptysis depending on the localization and the size of the focus. 6 The complicated and ruptured cysts present with systemic manifestations like fever, fatigue, and weight loss.
The lungs are the second most common site of involvement next to liver. The diagnosis of pulmonary hydatid cyst is based on the clinical and radiological findings, as well as serological analysis (echinococcosis Eliza IgG test). FNAC is generally not preferred, and generally contraindicated due to fear of an untoward allergic reaction and dissemination following the procedure unless the presentation of the disease is atypical. [7][8][9][10] Longstanding pulmonary infection may present with a solid and solitary nodule, which may clinically and radiologically mimic malignancy like in our case. In this situation, FNAC can be considered to reach the diagnosis.
Diagnostic cyto-morphological features of hydatid cyst include presence of laminated cyst wall fragments (also called cuticula), scolices, and hooklets. Identification of hooklets is pathogonomonic, but observation of laminated membranes by itself is a presumptive finding in the cytodiagnosis of hydatid cyst. 11 A background of inflammatory cell reaction with necrotic debri, foreign body giant cells, hemosiderin-laden alveolar macrophages is also seen. But this infiltrate by itself is not diagnostic. 9 These findings were present in our case.
Hydatid disease is endemic mainly in the rural areas of the eastern part of India. In the western parts of the country, including Punjab, the disease is rare.
Fine needle aspiration cytology is a useful, rapid, and diagnostic technique for the diagnosis of an organized form of pulmonary hydatid cyst, which clinically mimicks a malignancy. No post aspiration adverse reactions were reported in the FNAC of such cases. [8][9][10][11][12] One should keep in mind the possibility that carcinoma may rarely have clinical, radiological, and serological features, similar to those of hydatid cyst. Singh N, et al. reported a case of a large cell type lung carcinoma mimicking pulmonary HD, with a positive serological test for Echinococcus granulosus. 13 FNAC was not done in this case, and the histopathological diagnosis of carcinoma was made on the surgical specimen. The possible antigenic similarity between lung carcinom a and hydatid cyst was also reported. 14 In conclusion, our primary aim is to emphasize the importance of considering hydatid disease of the lung in the definite diagnosis of atypical lung lesions such as bronchogenic carcinoma in endemic areas. A high index of suspicion and vigilant scrutiny of slides for parasitic components will allow for correct diagnosis and avert unnecessary surgery and related morbidity.

Source of Funding
None.

Conflict of Interest
None.