Table 1.

Overview of various classifications [1–5]

	Classification	Current status
Farrar [1] (1951)	(i) Growth restricted to the cystic duct (ii) Absence of neoplastic process in the GB, hepatic, or CBD (iii) Histological evidence of carcinoma	-1st classification system but unsuitable in current scenario where advanced cases are being detected invading surrounding structures. -No mention about lymph node metastasis
Ozden et al. [2] (2003)	working definition of carcinoma of cystic duct is a GB tumor whose centre is located in the cystic duct (the geometric centre of the tumor)	-Practical to determine geometric centre during grossing however still may be difficult to label as cystic duct carcinoma if it had been unequal growth in different directions. -It was based on assumption that the tumor grows equally in all directions, which may not hold true for all cases.
Kim et al. [3] (2007)	(i) Type I-carcinoma confined within the cystic duct (ii) Type II-carcinoma extended to the GB neck and infundibulum or bile duct of cystic duct side without obstructive jaundice (iii) Type III-carcinoma extended up to the GB body or bile duct on the contralateral side of cystic duct opening which then causes obstructive jaundice [centre located in the cystic duct]	-Based on the extent of tumor infiltration and such classification defines treatment plan and improves resectability.
Yokoyama et al. [4] (2008)	A gallbladder tumor with centre of which is located in the cystic duct: (i) hepatic hilum type (HH)-tumor mainly invades the hepatic hilum (ii) cystic confluence type (CC)-tumor mainly involves the confluence of the cystic duct	-HH type presentation, behaviour and prognosis takes on the picture of gallbladder carcinoma, whereas CC type takes on the picture of bile duct carcinoma. -This classification may be helpful for making a diagnosis and planning the surgical procedure for individual cystic duct carcinoma patients.
Nakata et al. [5] (2009)	Based on extent of spread: Type I-the tumor was located wholly within the cystic duct Type II-the tumor extended to the gallbladder Type III-the tumor extended to the common hepatic duct or the common bile duct (including extension into the lumen and external invasion to the bile duct wall) Type IV-the tumor extended to both the gallbladder and the bile duct	-A high frequency of perineural infiltration and a low frequency of hepatic infiltration result in cystic duct carcinoma being a distinct entity from gallbladder carcinoma and better prognosis than gallbladder cancer and extra hepatic bile duct cancer.