The spectrum of imaging findings in pulmonary hydatid disease and the additive value of T2-weighted magnetic resonance imaging in its diagnosis

Introduction
To describe the spectrum of imaging findings in pulmonary echinococcosis and to study the additive value of T2-weighted magnetic resonance imaging (MRI) in the characterisation of pulmonary hydatid disease.

Material and methods
This was a descriptive, prospective study conducted for a period of 3 years from December 2016 to November 2019. Patients suspected of having pulmonary echinococcosis (n = 110) on preliminary chest radiography were examined with chest computed tomography (CT). Among them 41 cases were additionally examined with T2-weighted MRI of thorax. Final diagnosis was based on surgery or histopathology.

Results
Of the 110 patients enrolled for the study 15 were lost to attrition, and among the final cohort of 95 patients CT correctly diagnosed 68/84 (80.9%) as hydatid cyst, whereas 16/84 (19.1%) received an erroneous alternate diagnosis on CT. Based on the classical findings of hyperintense pulmonary cystic lesion with T2-weighted hypointense rim or detached internal T2-weighted hypointense membrane, a correct diagnosis of hydatid cyst was possible in 30 patients whereas a correct alternate diagnosis was made in 8 cases. T2-weighted MRI was found to have sensitivity of 96.7%, specificity of 80%, positive predictive value (PPV) of 93.7% and negative predictive value (NPV) of 88.9% with an overall diagnostic accuracy of 92.6%. Using the McNemar test, MRI was found to be diagnostically superior to CT (p = 0.019).

Conclusions
Most of the pulmonary hydatid cysts can be diagnosed on CT; however, sometimes the findings may be indeterminate or atypical, leading to a diagnostic dilemma. MRI, owing to its ability to demonstrate hypointense endocyst, can act as a useful adjunct to correctly diagnose hydatid cyst or suggest an alternative diagnosis.