Isolated dilatation of cystic duct

A 90-year-old female patient presented to A&E with complaint of back pain after falling two times at home. The GP had prescribed Co-codamol after the first fall, 5 days before, but it did not relieve the pain sufficiently. After the second fall she became off legs which necessitated hospital admission.

On the initial x-ray examination of the thoracolumbar spine, no acute fractures were found. An abdominal ultrasound scan (US scan) was performed which reported extrahepatic biliary duct dilatation (Fig. 1) and cholecystitis. The report diverted the attention of clinicians towards a possible biliary pathology causing back pain. This was followed by several blood tests (as described later). However, on the follow-up MRCP (which was performed a few weeks after the US scan) there was no evidence of cholecystitis. Only, isolated cystic duct dilatation was seen (Fig. 2). The cystic duct diameter measured 10mm at the junction with the common hepatic duct (CHD). No evidence of stone or other obstructing lesion was seen in the distal cystic duct or Common Bile Duct (CBD). The CBD measured 8 mm in diameter and tapered down smoothly. There was no evidence of anomalous union of the pancreaticobiliary duct (AUPBD).

Isolated dilatation of the cystic duct is a rare finding. The hallmark Todani’s classification of bile duct dilatation does not include a description of an isolated cystic duct dilatation [1]. However, more recently this entity has been proposed as type-VI of the choledochal cyst classification. The case report is being presented to increase awareness of the occurrence of this rare entity which may help in avoiding unnecessary investigations and a delay in management. Review of the literature reveals that it is a rare finding with only about 20 cases having been described previously [2]. Most of the authors have regarded it as a congenital malformation [3], although acquired aetiology has also been proposed by some [4, 5]. In the case presented, an US scan report led to the assumption of obstructive biliary cholecystitis. The blood tests showed raised CRP and mildly deranged Liver Function Tests (LFTs). As the cause of back pain was not attributable to any acute fracture on the basis of x-rays, an alternative diagnosis of obstructive biliary disease was considered even though the initial clinical examination had not elicited symptoms relating to biliary colic. In fact, ALT and ALP were out of range but Bilirubin was within normal limits. A urine dip was also positive for leukocytes indicating a possible urinary tract. However, the focus remained on the biliary pathology. Surgical referral was made and an MRCP was requested. Meanwhile, a course of antibiotic was initiated. The MRCP did not demonstrate Common Bile Duct (CBD) dilatation or intrahepatic duct dilatation. Retrospectively, the initial deranged LFTs were attributed to the pre-existing CCF and the cystic duct dilatation was considered an isolated type VI choledochal cyst. The raised CRP was most likely due to urinary tract infection. After a further period of observation of one week, the patient was discharged and physiotherapy was continued on an outpatient basis to restore her mobility. Four months later during another hospital admission, for an unrelated presentation, an abdominal CT examination of the patient was performed in which the cystic duct appearances were found stable and without any biliary pathology (Fig. 3). This case shows how an incidental finding of variant anatomy can be misleading if not identified so. Recognition of isolated cystic duct dilatation is essential to avoid distraction from actual pathology and prevent unnecessary delay in the management of patients. Written informed patient consent for publication has been obtained.