British Journal of Radiology 75 (2002),271-274 © 2002 The British Institute of Radiology
Intrabiliary rupture of hydatid cyst: diagnosis with MRI and hepatobiliary isotope study
R Kumar, DRM, DNB1,
S N Reddy, MS, FRCS Ed2 and
S Thulkar, MD3
Departments of 1 Nuclear Medicine, 2 Surgery and 3 Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India
Correspondence: Dr Rakesh Kumar, F-74, Ansari Nagar, AIIMS Campus, New Delhi 110 029, India
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Abstract
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Intrabiliary rupture is the most common complication of hepatic hydatid cyst yet it is unusual, occurring in only 3–17% of cases. The diagnosis is rarely difficult on ultrasound and CT when typical radiological features are present. In rare cases of complete evacuation, when characteristic findings of hydatid cyst are absent or when there is no evidence of the previous existence of liver hydatid cyst, the diagnosis may be difficult. In difficult cases, MRI, MRCP, ERCP and 99Tcm-mebrofenin hepatobiliary scintigraphy are employed. We present a rare case of surgical obstructive jaundice due to rupture of a liver hydatid cyst into the biliary tract and gall bladder, with complete evacuation of its contents leading to misdiagnosis on CT and ultrasound. MRCP and 99Tcm-mebrofenin hepatobiliary scintigraphy were able to establish a firm pre-operative diagnosis.
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Introduction
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Hepatic hydatid disease (HHD) is a major endemic problem in sheep-rearing regions of the world. The liver acts as a filter for hydatid larvae, making it the most commonly affected organ. Up to one-third of patients with HHD present with complications such as rupture (into the biliary tree, thorax or peritoneum), secondary infection, anaphylactic shock, sepsis and liver replacement.
The incidence of rupture into the biliary tree has been reported as 3–17% [1–4]. It presents clinically as pain, obstructive jaundice, cholangitis or sepsis, and can be fatal without intervention. Successful outcome depends on accurate pre-operative diagnosis. Diagnosis of this complication can usually be made using ultrasound and CT. Complete evacuation of the contents of a liver hydatid cyst is very rare and can present diagnostic problems. We present a case of complicated HHD with intrabiliary rupture, which on ultrasound and CT was misdiagnosed. MRI, magnetic resonance cholangiopancreatography (MRCP) and 99Tcm-mebrofenin hepatobiliary scintigraphy made a definite pre-operative diagnosis possible.
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Case report
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A 45-year-old farmer with a history of recurrent episodes of right upper abdominal pain was referred after a sudden episode of acute abdominal pain, low grade fever and icterus associated with clay coloured stools and itching. On abdominal examination there was tenderness in the epigastrium and right upper quadrant. Laboratory investigations revealed serum bilirubin 156.4 µmol l-1 (normal 1.7–17 µmol l-1), serum glutamic oxaloacetic transaminase 56 international units (IU), serum glutamic pyruvic transaminase 78 IU (normal up to 50 IU) and serum alkaline phosphatase 562 IU (normal 80–280 IU). Ultrasound of the abdomen showed an anechoic small cyst in the right lobe of the liver and a soft tissue mass in the gall bladder lumen with gall stones. Contrast enhanced CT revealed a hypodense lesion with enhancing walls in segment eight of the liver (Figure 1
). The lesion was communicating with the right hepatic duct. Intrahepatic biliary radicles and the common duct were dilated, with a few hypodense foci in their lumen. CT also showed focal thickening of the gall bladder wall in the region of the fundus, with an isodense mass in the lumen. An oval subcapsular fluid collection with enhancing walls, possibly a subcapsular extravasation of the contents of the cyst, was also seen in the vicinity. A differential diagnosis of inflammatory/malignant mass in the liver and gall bladder was made. MRI and MRCP (T2 weighted images) revealed a 4 cmx4 cm well defined heterogeneously hyperintense cystic lesion surrounded by a hypointense rim in segment eight of the liver. Thin detached infolded membranes within the cyst were seen as linear hypointense filling defects (Figure 2). The common bile duct (CBD) and gall bladder showed similar hypointense filling defects (Figure 3). 99Tcm-mebrofenin hepatobiliary scintigraphy showed a filling defect in the right lobe of the liver in the initial images, which was seen to fill up in delayed images, clearly delineating the cystobiliary fistula (Figures 4a,b). The patient underwent a surgical exploration, which confirmed the radiological findings. The small subcapsular collection along the right lobe of the liver was found to contain clear fluid.
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Figure 1. Contrast enhanced CT of the abdomen. A cystic lesion with enhancing walls is seen in the right lobe of the liver (arrow). An oval subcapsular fluid collection with enhancing walls is also seen in the vicinity. Intrahepatic biliary radicles are dilated.
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Figure 2. Magnetic resonance cholangiopancreatography. The cystic lesion in the right lobe of the liver is seen communicating with biliary radicles. Collapsed wall of the cyst is seen as multiple linear filling defects.
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Figure 3. Coronal T2 weighted MRI shows membrane in the gall bladder, seen as hypointense linear filling defects (arrows).
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Figure 4. 99Tcm-mebrofenin hepatobiliary study. (a) An early image (15 min) showing two photopenic areas in the right lobe of the liver (arrow). (b) The same area shows increased uptake on delayed imaging (120 min), suggesting biliary communication (arrow).
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Discussion
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HHD disease is the commonest form of echinococcosis. The right lobe of the liver is affected in 80% of cases and the left lobe in 20%. Rupture into the biliary tree, although uncommon, is the most common complication of HHD. It occurs into the right duct in 55–60% of cases, into the left duct in 25–30% and rarely into the confluence or gall bladder [5, 6]. Intrabiliary rupture can lead to obstructive, septic or allergic manifestations. Patients commonly present with right upper abdominal pain (82%), obstructive jaundice (57–100%), fever (70–90%), acute cholangitis (20–37%), abdominal lump (22–39%), and rarely with acute pancreatitis, liver abscess or septicaemia, or it may be asymptomatic (5–6%) [3, 7].
Lewall and McCorkell [8] have classified rupture of echinococcal cysts into three types: contained, communicating and direct. Communicating rupture can be simple communication between small biliary radicles and the cyst, or frank rupture into the biliary tree (as in the present case). An accurate pre-operative diagnosis helps in planning the line of treatment and also helps during surgery. Ultrasound and CT are routinely used to confirm the diagnosis, but rupture of the cyst and evacuation of its contents may change the radiological appearance necessitating more sophisticated investigations such as MRI, MRCP, endoscopic retrograde cholangiopancreatography (ERCP) and hepatobiliary scintigraphy.
Ultrasound is the most commonly employed initial investigation. A complicated cyst has a multivesicular/multiseptate appearance with a heterogeneous echogenic interior [9]. A dilated CBD in a jaundiced patient with a hydatid-like cystic lesion in the liver should prompt a diagnosis of intrabiliary rupture. In frank communicating rupture, the cyst becomes smaller and undulating membranes may be seen within it. Extrahepatic biliary dilatation is a constant feature. Echogenic or non-echogenic material without posterior acoustic shadowing is seen in the biliary tree, suggestive of sludge and daughter cysts. A correct diagnosis of intrabiliary rupture using ultrasound was possible in 66.6–94% of cases, and the accuracy was increased when both CT and ultrasound were used [4, 7, 8]. Direct communication was visualized in only 20% of cases [9]. The other differential diagnoses considered are abscess, malignancy or metastatic lesion.
The features of a hydatid cyst on CT are enhancement of the cyst wall and the internal septae, visualization of detached undulating membranes and calcification of the cyst wall [10, 11]. A dilated CBD with low attenuation intraluminal material suggests the presence of hydatid sand and cysts in the CBD. An interrupted area of the cyst wall proximal to a dilated duct may be identified as representing the site of communication. Cyst wall discontinuity, a direct sign of rupture, was seen in only 75% of cases [4]. CT can demonstrate high attenuation material passing through the defect of the cystic wall and filling up the intrahepatic biliary radicles or CBD [12]. The accuracy of CT combined with ultrasound was near 100% in cases with uncomplicated intrabiliary rupture [3].
MRI is a useful tool in difficult cases such as intrabiliary rupture, where CT and ultrasound are not conclusive. The wall of the hydatid cyst is seen as a low intensity rim, a reliable sign to differentiate hydatid cyst from other simple cysts [11]. Daughter cysts have a lower signal intensity compared with the mother cyst. The MRI finding in ruptured hydatid cyst can be direct or indirect [13]. A breach in the low intensity rim of the cyst wall with extrusion of cyst contents is a direct sign, while increased echogenicity, fluid levels, presence of air and changes in signal intensity are indirect signs. Direct signs were seen in the present case.
ERCP is the gold standard in confirming biliary tract involvement and may be of therapeutic benefit in selected cases. On ERCP, a swollen ampulla of Vater may be seen, with hydatid material protruding out. Dilated ducts with debris and daughter cysts may appear as radiolucent filling defects. Irregular leaf-like material that changes shape with changes in pressure differentiates this condition from other causes of obstructive jaundice [14]. A small cystobiliary communication cannot always be excluded by ERCP and should be actively sought during surgery [14].
Hepatobiliary scintigraphy (HIDA) was routinely used in the diagnosis of HHD before the advent of ultrasound. There is only one case report of intrabiliary rupture seen on a HIDA scan, which was initially misinterpreted as a choledochal cyst [15]. The usual findings are a photopenic area in the liver in initial images, which gradually fills up in delayed images indicating bile leak into the cyst. Although it cannot document the exact nature of communication, HIDA can be helpful in doubtful cases with cystobiliary communication where ultrasound and CT are not conclusive.
We present our case because of the rarity of two findings. First, complete evacuation of the liver hydatid cyst following rupture into th ehepatic ducts and gall bladder. Second, the presence of collapsed folded membranes in the gall bladder mimicking a soft tissue mass. The correct diagnosis was not made on CT and ultrasound as the empty cyst was mistaken for a collection and the presence of soft tissue in the gall bladder led to an initial diagnosis of carcinoma of the gall bladder. The presence of a well defined low intensity rim with communication into the biliary duct, a characteristic MRI finding of ruptured HHD, clinched the diagnosis. Interruption of the cyst wall and communication with the bile duct were delineated on CT, MRI and scintigraphy.
Received for publication May 24, 2001.
Revision received November 12, 2001.
Accepted for publication November 21, 2001.
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Abstract
Introduction
