Left Hemi-Diaphragmatic Hydatid Cyst-A Rare Presentation and Diagnostic Challenge

Echinococcosis or hydatid cyst disease is among the oldest diseases known to man. Common presentations include involvement of liver and lungs. Hydatid cyst in diaphragm without hepatic involvement is rare and less than 100 cases are reported in literature. We are describing a case of a young female who presented with cough anddyspnea secondary to large cysts that appeared to involve the right lung and spleen on initial imaging studies. Peroperatively, however, the presumed spleenic cystwas surprisingly found to be lying within left hemidiaphragm. Complete surgical resection of the cysts was performed with uneventful post-operative recovery.


Introduction
Hydatid Cyst (HCs) is a zoonosis caused by cestode Echinococcus granulosus and is endemic in many parts of the world.The most common organs that are affected by E. granulosus are liver and lungs (78%) [1].Diaphragmatic localization is very rare with the incidence of around 1%, and most of these are generally associated with hepatic hydatid cysts [2].According to Kjosseve all, less than 100 cases of diaphragmatic HCs have been reported in the international literature so far and most of them had concomitant involvement of right hemidiaphragm [1].Herein, the authors report a case of a young female who presented with cough and dyspnea.Initial imaging studies showed large hydatid cysts involving the right lung and spleen.Peroperatively , however, the presumed spleenic cyst was surprisingly found to be lying within left hemidiaphragm.

Case History
A 16 years old girl presented with cough, dyspnea and pain in left hypochondrium for 15 days.She denied history of fever, weight loss and hemoptysis.Her past and family history was negative for congenital or hereditary diseases.General physical examination was unremarkable.Her respiratory system examination revealed dull percussion note and absent breath sounds in right mid and lower chest.A mass was palpable in the left hypochondrium which was interpreted as splenomegaly.Her ultrasound abdomen revealed large cystic hypo echoic lesions in right lower lung and spleen suggestive asymptomatic until they are large enough to cause mass effect in an involved organ [3].As in our case, the common presenting symptoms are cough, chest pain, and breathlessness [3].
More than one pathway has been proposed to explain the development of intrathoracic HCs.It is thought that small sized embryos (< 0.3 mm) initially gain access to the systemic venous system, as they can't be filtered out from the portal blood by virtue of their small size, and thereafter get pumped to all parts of body.Another proposed mechanism presumes that embryos gain access into the systemic circulation via intestinal lymphatics.Some researchers have supported a third pathway that involves direct exposure to lungs through inhalation of contaminated air [4].After gaining access to the systemic circulation, further voyage to the diaphragm may involve pulmonary-bronchial anastomosis, arterial channels from the phrenic artery and branches from the intercostal arteries [1].Left hemidiaphragmatic cyst in our case can be explained with the embryos bypassing the two filters i.e. liver and lungs.
Serological tests for hydatid disease have low sensitivity (64-87%) and imaging modalities are the mainstay for diagnosis [5].Both sonography and CT scan have their pros in the form of cost and widespread availability but when it comes to cysts with atypical appearance on CT scan and peridiaphragmatic location, MRI is a better imaging modality due to its superiority in defining anatomical relationships and better chest wall and diaphragm delineation [1,6].MRI may have helped in making correct localization of the cyst within the left hemidiaphragm.Eren et al. and Mekki et al. have also proposed MRI as a superior imaging modality in comparison with CT scan for evaluation of complex giant hydatid cysts, their topographical relationships and suspected diaphragmatic and hepatic involvement [2,7].

Conclusion
Hydatid cysts of diaphragm should be considered in patients with preoperative imaging data indicating cystic lesions adjacent to the diaphragm.MRI should be done if the cyst is found to be in close proximity of diaphragm, or elsewhere if in doubt, to determine accurate soft tissue relationship preoperatively.
The symptoms of thoracic hydatidosis depend on the size and the site of the lesion.Thus, slowly growing HCs are generally

Figure 1 :
Figure 1: CT scan (coronal view) of bilateral hydatid cysts.One in right lung and the other 'reported' to be within spleen with floating membranes.

Figure 3 :
Figure 3: Histopathology section of HC showing thin germinal layer which gives rise to brood capsules.