LAUSR

A 45-year-old male visited the pulmonary medicine outpatient department with hoarseness of voice and left vocal cord palsy lasting 4 months. There was no other significant clinical history. On evaluation, the computed tomogram (CT) scan revealed an anterior mediastinal mass, measuring 5.2 9 5 9 4 cm. It was a well-defined, heterogeneously enhancing soft tissue mass located in the pre-vascular space with central cystic softening. No calcification or fatty component was noted. Vascular structures and bilateral lung fields were unremarkable. Based on the radiological findings, clinical possibilities of thymoma and lymphoma were entertained. The patient underwent CT-guided fine needle aspiration cytology (FNAC). In total, 10 mL of pale yellow coloured, semi-fluid granular material was yielded. Both air-dried and alcohol-fixed smears were prepared, which were stained with May-Gr€ unwald-Giemsa (MGG) and haematoxylin-eosin stain, respectively. Part of the sample was added to CytoRich Red preservative fluid and subjected to centrifugation for liquid-based cytology (LBC) preparation using the SurePath technique (BD India Pvt Ltd, Gurgaon, India). The rest of the sample was converted into a cell block. Smears showed many parasitic fragments of Echinococcus with scolices and rostella. The LBC sample showed many hooklets in a clear background which were seen singly scattered as well as within the scolex; however, the membranes of the hydatid cyst were not seen (Figure 1). The size of the hooklets was between 15 and 35 microns in length. Serologically the patient was found to be positive for hydatid serology (1:800) using the IgM ELISA method. Although rare, a small number of cases of mediastinal hydatid disease have been reported in the literature. FNAC of a hydatid cyst is contraindicated but, in this patient, FNA was attempted in view of suspected malignancy. There were no complications after FNAC. Currently, the patient is on albendazole treatment as per protocol and is planned for surgical removal. The incidence of mediastinal hydatidosis ranges from 0.5% to 2.6% of all chest locations. Hydatid disease is a parasitic infection caused by ingesting the eggs of Echinococcus tapeworms which are released in the stool of meat-eating animals, commonly dogs, infected by the parasite. The posterior mediastinum is the commonest site, and the anterior mediastinum is a rare primary location. Accurate clinical history, radiological findings and serology are useful tools for an early diagnosis. Thoracic ultrasound, CT and magnetic resonance imaging may not be able to diagnose mediastinal hydatidosis specifically. The commonest radiological differential diagnoses are carcinoma and lymphoma. Morphologically, hydatidosis can be confused with cysticercosis. Cysticercosis is caused by the young form of the pig tapeworm, which has a scolex bearing four suckers surrounding the rostellum. The short (130 lm) and long (180 lm) rostellar hooklets are of similar shape as that of hooklets of a hydatid cyst (1540 lm). The size of the daughter cyst (>2 cm), the presence of multiple scolices, laminated membrane, the number and size of hooklets can help in differentiating hydatidosis from cysticercosis. LBC preparation aids in proper interpretation and gives a clear background with better morphology in comparison to conventional smears. Although FNA is diagnostic, it is not an indicated diagnostic modality owing to its complications such as urticaria and anaphylactic reaction. F IGURE 1 (A) Computed tomogram (CT) scan showing a heterogeneously enhancing soft tissue mass with cystic softening; (B) a parasitic fragment comprising of hooklet-bearing rostellum (May-Gr€ unwald-Giemsa [MGG] 9 40X); (C) liquid-based cytology (LBC) sample showing granular acellular material comprising of fragments of proscolices (LBC Pap stain 9 109); (D) an LBC sample showing parasitic fragments comprising of hooklet-bearing rostellum of a proscolex with numerous free hooklets in a clear background (LBC Pap stain 9 409) Accepted: 9 May 2017