A Heavily Giant Calcified Hydatid Cyst of the Liver with Thoracic Involvement Presenting as an Abdominal Mass (A Very Rare Case Report): The Role of Imaging

Hydatid disease is common in the tropics. It is caused by infection with the larval stage of Echinococcus tapeworm. Infestation of humans, who are accidentally the intermediate host, occurs from ingestion of water or food contaminated by fecal material of definitive host (dog, wolves, deer, sheeps). The most frequent organ of involvement is the liver in up to 70%, followed by the lung about 18% and with a lower reported incidence in other organs or tissues in the body. It primarily affects the liver and shows typical imaging findings. However clinical presentation varies widely and is non specific. Thus, imaging plays an important role in diagnosis of hydatid diseases. Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) can depict hydatid disease. The imaging methods used depend on involved organ and the radiological findings which range from purely cystic lesions to completely solid appearance. We report a very rare case of a calcified huge hydatid cyst in a 42 year old patient to buttress the role of imaging in management of such cases.


I. INTRODUCTION
Hydatid disease is common in the tropics. It is caused by infection with the larval stage of Echinococcus tapeworm [1]. Infestation of humans, who are accidentally the intermediate host, occurs from ingestion of water or food contaminated by fecal material of definitive host (dog, wolves, deer, sheep) [2].
Hydatid Hyadtid disease is common in the tropics. It is caused by infection with the larval stage of Echinococcus tapeworm [1]. Infestation of humans, who are accidentally the intermediate host, occurs from ingestion of water or food contaminated by fecal material of definitive host (dog, wolves, deer, sheep) [2].disease is a relevant health problem in underdeveloped areas where veterinary control does not exist. Hyadtid disease is common in the tropics. It is caused by infection with the larval stage of Echinococcus tapeworm [1]. Infestation of humans, who are accidentally the intermediate host, occurs from ingestion of water or food contaminated by fecal material of definitive host (dog, wolves, deer, sheep) [2]. The most frequent organ of involvement is the liver in up to 70%, followed by the lung about 18% and with a lower reported incidence in other organs or tissues in the body [3]. It primarily affects the liver and shows typical imaging findings. However clinical presentation varies widely and is non specific [4]. Thus, imaging plays an important role in diagnosis of hydatid diseases. Ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) can depict hydatid disease [5]. The imaging methods used depend on involved organ and the radiological findings which range from purely cystic lesions to completely solid appearance [6].
Ultrasound is the screening method of choice and is also used to monitor efficacy of medical therapy [5]. Computed tomography should be performed because of its high sensitivity of about 95% and as a diagnostic tool to determine vascular, biliary or extra hepatic extension, to recognized complication such as rupture and infection and also assess extend of resistibility [7]. Magnetic resonance is the best imaging procedure to determine a cystic component, to also help to determine vascular or biliary tree involvement as well as extra hepatic extension [8].
We reported a heavily calcified giant hydatid cyst with atypical imaging findings and also to analyze the challenges using various imaging modality.

II. CASE REPORT
A 42year old Nigerien man, who was referred from Niger Hospital to Usmanu Danfodiyo University Teaching Hospital (UDUTH) Sokoto, came to radiology department with a history of abdominal mass occupying his entire right upper abdominal quadrant with associated pain. No jaundice or body itching. A clinical diagnosis of hepatic mass to rule out renal involvement was made.
Ultrasound scan done in our department showed a huge hyperechogenic mass with extensive posterior acoustic shadow that prevented visualization of right hemi abdominal organs. An ultrasonographic impression of a huge calcified right hypochondrial mass was made, being non remarkable and inadequate, a complementary plain abdominal radiograph was done which show a huge somewhat elongated, multilobulated ground glass calcified mass extending to the lower abdomen with thoracic involvement and associated scoliosis with concavity to the right was demonstrated. Subsequently an abdominal CT was performed and shows a huge heavily calcified multi concentric mass lesion with a suggestion of a daughter component in the right lobe of the liver. A smaller but separate heavily calcified component is also seen rising out of the abdomen into the chest to involve the lung and pericardium with displacement of the heart. An impression of a giant heavily calcified hydatid cyst with thoracic involvement and features of chronic hepatic inflammation was made.
Patient was said to have had surgery at Niger hospital and lesions were removed. Histology confirmed hydatid disease of the liver.

III. DISCUSSION
Hepatic hydatid cyst is a helminthic arthropozoonosis with worldwide distribution due to close association with sheep and dogs. It can occur almost in any part of the body with a variety of imaging features which may changes according to the growth stages, associated complications and affected tissue [9]. The liver and lung are the common organs of involvement. In the liver the right lobe is most frequently involve portion because embryo from duodenum pass through the mucosa to reach the liver through portal venous system where the form cyst [10]. A definitive diagnosis of this disease required a combination of imaging, serologic and immunological studies [9]. Ultrasound, computed tomography, and magnetic imaging are highly accurate in detecting hydatid cyst [11].
Hepatic hydatic cyst of an unusual dimension with atypical imaging findings may complicate the differential diagnosis as seen in this patient [12]. Other differential of calcified hepatic lesions is hepatocellular carcinoma, calcified liver abscess or amebic cyst. Giant hepatic hydaid cyst has exophytic growth through the natural routes provided by the liver capsule and ligaments. It has been revealed that the largest giant hydatid cyst of the liver was 37x14.8x15 cm in size. However, in this patient it measured 19.5x15x14 cm in size [13].
Hepatic hydatid cyst usually show cystic wall calcifications and internal calcifications of the matrix and ultrasound will revealed hyperechoic or echogenic contour with cone shaped posterior acoustic shadow but when the cystic wall is heavily calcified only the anterior portion is visualized as a thick arc with posterior acoustic shadow [12]. In this case it shows a huge echogenic structure occupying the entire right hypochondrium with extensive posterior acoustic shadow preventing the visualization of the intra abdominal organs in the right hemi abdominal quadrant which make it difficult to ascertain the organ of involvement. Ultrasound is one of the best imaging modality of choice for the staging of evolution of the hepatic hydatid cyst [14]. Ultrasound in this case has been demonstrated to have limitation in a giant and heavily calcified hydatid cyst.
Plain radiograph of the abdomen may reveal a thin calcification in 20 to 30% of hepatic hydatid cyst, pattern which represent calcification of the pericyst [10]. During evolution toward healing dense calcification of all component of the cyst may take place. Densely calcified cyst may be assumed to be inactive just like in our case. But a partially/calcified cyst does not always indicate death of the parasite [1], [15]. It is worthy of note that plain radiographic features are nonspecific.
Computed tomography has a high sensitivity for hepatic hydatid cyst in both simple or complicated diseases and stages of evolution of the hydatid cyst [14]. Reasons why we finally used CT in this patient where it demonstrated the heavily calcified multi concentric intra hepatic mass lesion with a daughter components with the core of the mass having HU=37, mainly in the right lobe of the liver with thoracic involvement.

IV. CONCLUSION
The imaging has completely diagnosed the unsuspected huge calcified hydatid cystic mass with extension to the thoracic cavity, Hence its role has been demonstrated in the prompt diagnosis and management of such cases. Clinicians therefore should always consider imaging in the management of such patients.