Abstract
The Hepato-cystic duct of Luschka (HCDL), although a rare anomaly of the biliary tree, carries with it a potential risk of postoperative bile leak and added morbidity in patients undergoing cholecystectomies. Magnetic resonance cholangi-opancreatography (MRCP) is an excellent modality for the detection of HCDL. However care should be taken not to misinterpret signal from stationary fluid in the duodenum or peritoneum.

Introduction
Hepato-cystic duct or duct of Luschka, first reported by a German anatomist Hubert von Luschka, is a rare anomaly of the biliary tree in which small bile ducts arising from the hepatic bed drain directly into the gallbladder. Their importance lies in the fact that they can be severed accidentally if unrecognized during cholecystectomy and hence may be a source of post operative bile leak and morbidity.^5,10,12

We report a case in which a duct of Luschka was identified on a preoperative magnetic resonance cholangio-pancreatography (MRCP), confirmed during operation and successfully ligated.

Case Report
A 79 year old male patient with a history of chronic alcohol abuse presented with complaints of upper abdominal pain associated with vomiting of one days duration. The pain was diffuse and colicky in nature. Blood investigations done revealed leucocytosis, raised urea/sugar and markedly raised amylase and lipase. X-ray abdomen showed the ‘colon cut-off sign’ while a computed tomography of the abdomen with and without intravenous contrast showed a swollen and heterogeneously enhancing pancreas with calcification and peripancreatic fat stranding. Areas of necrosis of around 30%-40% of the gland were seen. There was trace pleural, peritoneal and retroperitoneal fluid. Based on CT findings a diagnosis of acute on chronic pancreatitis was made. The patient was managed medically and subsequently discharged.

However, the patient presented again after 1 month with a relapse of acute pancreatitis. Ultrasonography of the abdomen done this time showed three cystic areas in the head of pancreas (largest 4.2 x 2.3 cm) with distended gallbladder containing sludge. Tumour markers CA-19-9, CEA, CA-125 were negative. Cholecystectomy was planned but the patient wished to defer the same. Patient was again managed medically and discharged on clinical improvement.
Patient again presented 1 month later with pyrexia, shivering and pain in right hypochondrium. Ultrasonography showed a large cyst with internal echoes and pockets of air within, in the head of pancreas (size 7.5 x 7.7 x 7.6 cm). Repeat ultrasongoraphy five days later showed that the volume of cyst was increasing. It was decided to drain the cyst per cutaneously. The aspirated fluid was clear at first but later turbid and haemorrhagic. It was sent for biochemical and cytological analysis. However per cutaneous drainage was not found to be satisfactory as the cyst fluid was seen to be increasing on serial ultrasonography.

A Magnetic Resonance Cholangio-pancreatography (MRCP) done at this stage showed a large cyst in the head of pancreas indenting on the distal common bile duct and causing dilatation of its proximal portion. The pancreatic duct was irregular in its course. An interesting finding was the presence of a duct arising from the right hepatic duct and the liver bed, draining directly into the gallbladder near its neck (Fig. 1).

In view of the failure of per cutaneous drainage it was decided to perform a cysto-gastrostomy and choledocho-jejunostomy so as to facilitate the drainage of cyst fluid and also of the common bile duct. While dissecting the gallbladder bed the anomalous duct seen on MRCP was identified and ligated.

Fig. 1 : MRCP shows a small duct arising from the right hepatic duet and draining directly into the gall bladder near its neck; the duct of Luschka. Also seen are cyst in the pancreatic head causing distal CBD obstruction and irregular pancreatic duct.

Discussion
Anomalies of the biliary tree present a potential for surgical complication during cholecystectomy. Often small anomalous ducts are severed during surgery resulting in post surgical complications. A second procedure is often needed when an anomalous duct is injured, causing more risk and discomfort for the patient. MRCP is a non-invasive imaging technique, which can illuminate the biliary anatomy with comparable results to intravenous cholangiography and ERCP, allowing a pre operative evaluation of biliary tree anatomy.

One anomalous duct, the hepatocystic duct of Luschka (HCDL), cannot often be visualized by direct inspection until after it has been injured due to its location between the gallbladder and the liver bed. The first description of the HCDL is attributed to a German anatomist Hubert von Luschka (1820-1875). The HCDL is a source of post cholecystectomy bile leak in 0.15% to 0.5% of all patients.^5,10,12

Up to 15% of postoperative bile leaks are from an HCDL.3 However, the incidence of HCDL, which are either observed and ligated during surgery, or found during post mortem examination, is higher. One series found the total incidence during laparoscopic cholecystectomies to be 2.7%.11 In cadavers, 10% of the 277 examined were found to have either HCDL or hepatocystic ducts coursing along the gallbladder wall. The superficial hepatocystic ducts were more common in the cadavers of the elderly.2 When the gallbladder was examined microscopically, as many as 50% were found to have evidence of small HCDL.⁹

Leak of bile into peritoneum is a potential dangerous complication of an unnoticed HCDL cut during surgery.14 The danger can be minimized by limiting the use of electro cautery on liver bed. Electrocautery can damage an HCDL within the liver capsule and prevent its visualization during surgery. The dissection of the gallbladder from the liver bed should stay close to the gallbladder serosa preserving the areolar tissue of the bed because of the risk of HCDL coursing superficially along the gallbladder wall.⁴

This may specially be important in elderly patients, who as discussed above may have a higher incidence of superficial ducts.²

MRCP is a relatively new technique, which can be used to image the biliary anatomy pre-operatively.1 Introduced in 1991; it originally was performed with heavily T2 weighted pulse. This technique had the disadvantage of a low signal to noise ratio and motion artifact due to longer acquisition time. Newer methods such as rapid acquisition with relaxation enhancement and Fourier acquisition single shot Turbo spin - echo allow faster imaging with a breath hold of less than 20 seconds.

In MRCP, slow flowing fluid such as pancreatic juice and bile has a higher signal intensity compared to the surrounding tissue and fast moving blood has a very small signal. Therefore, the lumen of the biliary tree can be visualized without contrast and duct lumens can be differentiated from blood vessel lumens. The images are reconstructed from multiple angles allowing views similar to those possible with traditional cholangiography, while avoiding the risk associated with injection of contrast and endoscopy. MRCP also allows visualization of cystic tumours of pancreatic head and communication with the biliary tree with better results than ERCP.7 In one trial, MRCP was more informative for evaluation of the gallbladder, the cystic duct and the CBD than ERCP in 55%, 45% and 40% of patients respectively.¹⁵

MRCP has several disadvantages compared to other modalities. Endoscopic ultrasonography can detect smaller stones more reliably.8 ERCP allows therapeutic interventions such as stone extraction, stent placement, and biopsy without necessitating a second procedure. Stationary fluid in the duodenum and peritoneum can produce a bright signal similar to bile and pancreatic juice.6 Also, MRCP can have local signal dropout near metal clips from previous surgeries, and it would not be able to be used in case of implanted metal such as leads or fixation plates. MRCP was not useful for imaging thickened gallbladder walls and shrunken gallbladders.¹³

Conclusion
It therefore seems to be highly advisable to specifically look for them during the preoperative evaluation of such patients. It has the advantage of being non-invasive, not requiring intravenous contrast, multiplanar imaging and better delineation of the biliary tree and cystic lesions in pancreatic head.

References

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