CT is widely used for the initial staging of CC, providing high-resolution images that help define the morphology and extent of the tumor. It is particularly useful for detecting vascular involvement, lymphadenopathy, and distant metastases. However, its sensitivity decreases when assessing small hepatic lesions and nodal metastases, potentially limiting its diagnostic accuracy. Contrast-enhanced CT with multiphase acquisitions remains essential in evaluating arterial, venous, and delayed-phase enhancement patterns, which are crucial for differentiating CC from other hepatic masses.

MRI, on the other hand, offers several advantages over CT, particularly in evaluating soft-tissue contrast and biliary involvement. The use of diffusion-weighted imaging (DWI) enhances the detection of tumor cellularity, helping to differentiate malignant from benign lesions. Magnetic resonance cholangiopancreatography (MRCP) provides a non-invasive visualization of the biliary tree, aiding in the identification of strictures, ductal dilatation, and tumor infiltration. The combination of DWI and MRCP significantly improves diagnostic accuracy, particularly in cases where CT findings are inconclusive.

Morphological Subtypes and Imaging FeaturesCholangiocarcinoma is classified into three morphological subtypes: mass-forming, periductal infiltrating, and intraductal (1). Each subtype presents distinct imaging characteristics that influence diagnostic and therapeutic approaches (2–4):

• Mass-forming CC is the most common subtype,  often seen in intra-hepatic CC, typically appearing as a non-encapsulated lesion with lobulated contours. On CT, rimlike enhancement is frequently seen around the periphery of the tumor on arterial phase images and it exhibits progressive centripetal and continuous enhancement in the delayed phase due to its desmoplastic stroma. MRI findings include hypointensity on T1-weighted images and heterogeneous signal on T2-weighted images depending on tumor composition, centrally hypointense area and peripherally hyperintense rim on DWI giving the target sign. The presence of this sign favors cholangiocarcinoma over hepatocellular carcinoma.  It is present in 57-83% of intrahepatic cholangiocarcinomas compared to 3-15% of hepatocellular carcinoma 
• As associated signs we can see capsular retraction, Segmental dilatation of intrahepatic bilary duct, lobar or segmental atrophy of the tumoral liver and hepatic hyperarterialization adjacent to the tumor. Multicentricity, particularly around the primary tumor, is frequently observed, likely due to the tumor's tendency to invade the peripheral branches of the portal vein. The imaging characteristics of mass-forming hilar cholangiocarcinomas closely resemble those of peripheral cholangiocarcinomas, with the key distinction being the presence of intrahepatic bile duct dilatation. Extrahepatic ductal cholangiocarcinoma may also present as a mass mimicking pancreatic adenocarcinoma. In such cases, evaluating the pancreatic duct on MRCP can aid in distinguishing between the two tumor entities (5–9).
• Periductal infiltrating CC is usally seen extra-hepatic CC and accounts for more than 70% of perihilar cholangiocarcinomas and is characterized by biliary stricture without mass formation. It spreads along the bile ducts without forming a distinct mass. CT and MRI often reveal diffuse bile duct wall thickening and dilatation. MRCP is particularly useful in identifying long-segment strictures and assessing the degree of ductal involvement. In favor of malignant stenosis we note irregular and asymmetrical parietal thickening > 3mm with extent > 20mm with an abrupt stop and enhancement >> healthy liver. infiltration of adjacent periductal fat may also be seen, and lymph node metastases are relatively frequent. Diffusion-weighted imaging may improve sensitivity in the detection of tumor extent along the bile duct and the detection of liver invasion (2,10).
• Intraductal CC presents as an exophytic mass within the bile ducts, often associated with (3,5)intraluminal filling defects. It may exhibit an enhancing polypoid appearance on contrast-enhanced studies, and MRCP provides detailed visualization of the intraductal component. typically, the tumor remains confined to the mucosa and only invades the wall and surrounding tissue in the very late stages (4,6,7).

Assessment of Resectability and Vascular InvolvementDetermining surgical resectability is a critical aspect of pre-treatment imaging. Both CT and MRI assess vascular invasion based on the extent of tumor-vessel contact (Misalignment > 180°), deformation of vascular contours, and the presence of vascular occlusion or thrombosis or perfusion disorders.  Although narrowing the portal veins, or less frequently hepatic veins, is seen, unlike hepatocellular carcinoma, cholangiocarcinoma only rarely forms a tumor thrombus

Suspicious lymph nodes are characterized by a short-axis diameter exceeding 1 cm, abnormal morphology, heterogeneous enhancement, or central necrosis.

Regional lymph nodes depend on tumor site for exemple in intra hepatic HCC,  regional nodes in sided lesions,  include inferior phrenic, hilar and gastrohepatic lymph nodes. However, for right sided lesions, regional nodes include hilar, periduodenal and peripancreatic lymph nodes.

Non resecability criteria include bilateral involvement of bilary ducts beyond 2nd-order ducts, portal vein thrombosis, lobe atrophy with contralateral biliary invasion, distant metastases and/or adenomegaly.

For perihilar cholangiocarcinoma, the evaluation of the future remnant liver volume is crucial, particularly in cases where extended hepatectomy is planned. The volume of the future remnant liver should be greater than 30% of the initial total liver volume (excluding the tumor) for resectable cases. Identifying vascular and biliary anatomical variations ensures optimal surgical planning and minimizes postoperative complications (3,5).

Metastatic disease :

The liver is a frequent site of metastasis, while other metastatic locations include the lungs, and less commonly, the bones, adrenal glands, and peritoneum.

Role of Advanced Imaging TechniquesRecent advancements in imaging have further improved the diagnostic accuracy of CC. The use of hepatocyte-specific contrast agents in MRI enhances the detection of small lesions, while functional imaging with DWI provides additional information on tumor aggressiveness and prognosis. Positron emission tomography (PET) combined with CT or MRI may offer complementary data in cases with suspected distant metastases.